DRY FREIGHT TANK WITH COMPARTMENTS AND AN AIR PIPING SYSTEM TO EQUALIZE AIR PRESSURE IN THE COMPARTMENTS.

Abstract

A dry bulk cargo tank and a method for loading and unloading cargo therefrom. The dry bulk cargo tank includes a tank assembly having a first wall surrounding and defining a first compartment for carrying cargo therein and a second wall spaced outward from at least a portion of the first wall, wherein a second compartment is defined between the first and second walls. The tank assembly includes an air piping system selectively activated to place the first and second compartments under substantially similar or equal air pressure. In one example, the air piping system pumps air into the first and second compartments. In another example, the air piping system evacuates air from the first and second compartments.

Description

DRY FREIGHT TANK WITH COMPARTMENTS AND AN AIR PIPING SYSTEM TO EQUALIZE AIR PRESSURE IN THE COMPARTMENTS ANTECEDENT TECHNICAL FIELD In general, the technical field refers to cargo tanks or reservoirs or pneumatic tanks / trailers having a plurality of hoppers. More specifically, the technical field refers to such a tank or trailer having a first compartment for carrying a load, a second compartment located in contiguous contact with the first compartment, and a system for placing the first and second compartments under substantially similar or substantially the same pressure. BACKGROUND Cargo tanks and cargo tank trailers, or pneumatic tank trailers, are among many types of vehicles used to transport materials over roads and similar routes. These tanks or tank trailers are used to transport bulk materials, particularly dry, particulate bulk materials, from one location to another. The types of materials transported in these vehicles may include food products, such as sugar and flour, chemicals, silica, plastic pellets, and construction materials, such as sand or dry cement. The term “trailer” will be used throughout the rest of this specification to identify a bulk cargo tank trailer used to transport materials. However, it should be understood that the terms “trailer,” “cargo tank trailer,” “tanker,” “tank,” and “truck” may be used interchangeably in this description. Tanker trucks or tank trailers typically include several hoppers or cones that facilitate the discharge of bulk material from inside the tank into a discharge pipe. Pressurized air is then pumped through the pipe to discharge the material at the rear of the trailer. Valve assemblies are usually located at the bottom of the hoppers, allowing them to be opened or closed to permit the flow of bulk material from the hoppers into the discharge pipe, or to stop this flow. The tank itself is a sealable container with several access ports along its upper surface. Each access port is covered. These covers are removed when the material is to be placed in a designated storage compartment within the tank. The tanker truck or tank trailer is moved into a loading bay and positioned so that one or more access ports align with overhead pipes or hoses connected to a source of the dry materials to be transferred. Once the storage compartment is filled to the desired level, the covers are replaced, and the tanker truck or tank trailer proceeds to its destination. As previously mentioned, the lower region of the tanker truck or tank trailer consists of several hoppers, each terminating in an elongated discharge pipe that extends from the first hopper through the rear of the tank. Each hopper is connected to the discharge pipe via a T-fitting. A butterfly valve and an aeration device are typically located near the T-fitting between the hopper and the discharge pipe. The aeration devices keep the dry materials aerated and help ensure that the materials are fluidized, meaning they will flow in a liquid-like manner. The butterfly valves control the flow between the hopper and the discharge pipe. When the tanker truck reaches its destination, the operator connects the end of the discharge pipe to an inlet for a storage tank for the transported dry materials.The operator will go through a series of steps: pressurizing the discharge pipe, aerating the load, sequentially opening the butterfly valves, and emptying the transported material from the tank through the discharge pipe. The pressure inside the tank and the discharge pipe must be maintained within a certain range to ensure that all the material is evacuated from the storage compartment defined by the tanker body. Once virtually all the material has been removed from the storage compartment, the operator will use pressurized air supplied from an upper region of the tank to blow out the storage compartment and clear it. The operator will then sequentially close the hoppers, shut off the aeration devices, and stop pressurizing the discharge pipe in a predetermined sequence that ensures operator safety and tank integrity.In other examples, instead of pressurizing the tank to remove dry materials from it, a vacuum source can be connected to the end of the discharge tube, and a vacuum will be applied to the discharge tube to suction the dry materials out of the hoppers. These tanks or trailers typically include a relatively substantial or long frame on which the tank / hoppers are mounted. These frames are relatively heavy, which can, for example, decrease fuel consumption or reduce the amount of cargo that can be carried in the tank while remaining within government weight regulations. SUMMARY In one aspect, the present disclosure may provide a dry bulk cargo tank for carrying a load; said dry bulk cargo tank comprises a tank assembly; a first wall provided in the tank assembly; said first wall joining and defining a first compartment adapted to carry a load therein; a second wall spaced outward from at least a portion of the first wall; wherein a second compartment is defined between the first wall and the second wall; and an air piping system coupled with the tank assembly; wherein the air piping system is selectively activated to place the first compartment and the second compartment under substantially similar or substantially equal air pressure. In one example, the tank assembly comprises a vessel that is circular in lateral cross-section. In another example, the tank assembly includes a front end housing and a central section extending to the rear of the front end housing; and wherein each of the front end housings and the central section is circular in lateral cross-section. The first compartment is defined in the central section, and the second compartment is partially defined in the front end housing. In other embodiments, the second compartment is also partially defined in the central section. In other embodiments, the tank assembly further includes a rear end housing extending towards the rear of the central section; and wherein the rear end housing is circular in lateral cross-section, and wherein the second compartment is further defined, at least partially, within the rear end housing. The second compartment is sealed from contact with air located outside the tank assembly. The air piping system places the first and second compartments in fluid communication with each other. In one embodiment, the air piping system is actuatable to pressurize the first and second compartments and can simultaneously pressurize them to substantially similar or substantially equal pressures.In another embodiment, the air piping system is activated to place the first and second compartments under vacuum. The air piping system can be activated to simultaneously place the first and second compartments under substantially similar or substantially identical vacuums. When the air piping system is activated, the air pressure on one side of a portion of the first wall in the first compartment is substantially similar or substantially equal to the air pressure on the other side of a portion of the first wall in the second compartment. In one embodiment, the dry bulk cargo tank has a central section that includes at least one hopper extending downwards from a lower portion of the central section; and wherein an inner portion of at least one hopper forms a portion of the first compartment; and wherein a lower region of at least one hopper extends a distance below the second compartment. In another aspect, the present disclosure may provide a method of transporting and unloading dry bulk materials comprising providing a dry bulk cargo tank trailer including a first compartment and a second compartment; wherein the first and second compartments are located on opposite sides of a portion of a wall joining and defining the first compartment; loading a quantity of dry bulk materials into the first compartment; substantially equalizing the air pressure in the first compartment and in the second compartment; and unloading the dry bulk materials from the first compartment while the first and second compartments are under substantially similar or substantially equal air pressure. In one embodiment, substantially equalizing the air pressure in the first and second compartments involves pumping air into both compartments through the air piping system. This pumping occurs substantially simultaneously and continues until the air pressure in each compartment is approximately 10 psi to approximately 15 psi. In another embodiment, substantially equalizing the air pressure in the first and second compartments involves drawing air in from the first compartment and drawing air in from the second compartment until the air pressure is substantially similar or substantially equal in both compartments. Substantially equalizing the air pressure also involves drawing air in simultaneously from the first and second compartments. In one example, the method further comprises forming a dry bulk cargo tank trailer as a vessel that is generally circular in cross-section when viewed from a front or rear end. In another example, forming the dry bulk cargo tank includes providing a center section; providing a rear end housing longitudinally behind the center section; forming the first compartment within the center section; and forming the second compartment partially within the front end housing. The method may further include forming the second compartment partially within the center section beneath the first compartment.The method, in one example, may further comprise forming one or more hoppers in the central section and forming the first compartment at least partially within each of the hoppers; extending a portion of each of the hoppers downward above the portion of the second compartment located below the first compartment. The method may further comprise placing each of the hoppers in fluid communication with a discharge pipe. In one example, the discharge from the first compartment includes opening a valve assembly in each of one or more hoppers and allowing the material in the first compartment to flow from the first compartment into the discharge pipe under pressure. The method may further comprise maintaining substantially similar or substantially equal pressure in the first and second compartments during discharge and releasing the pressure in the first and second compartments after discharge is complete. In another aspect, the present disclosure may provide a dry bulk cargo tank for transporting a load, said tank comprising a tank assembly having a front end and a rear end, with a longitudinal axis defined between them; a plurality of ground contact wheels provided in the tank assembly; more than one sealable area provided in the tank assembly; and a system for changing the air pressure, wherein the system is in fluid communication with each of the more than one sealable area; and wherein the system is selectively actuated to substantially equalize the air pressure in the more than one sealable area. A first of the more than one pressurized area comprises a first compartment adapted to carry a load thereon. A second of the more than one pressurized area is located in contiguous contact with the first compartment.In one example, the second of more than one pressurized area is located in front of the first compartment. In another example, the second of more than one pressurized area is located below the first compartment. In another example, the second of more than one pressurized area is located behind the first compartment. In yet another example, the second of more than one pressurized area is located partially in front of the first compartment, partially below the first compartment, and partially behind the first compartment. In one embodiment, the tank assembly further comprises at least one hopper, wherein an inner compartment is defined within the at least one hopper and the inner compartment forms a part of the first compartment. For example, the at least one hopper may include a first hopper and a second hopper located adjacent to each other, wherein the upper region of the first hopper is joined to an upper region of the second hopper; and wherein a portion of an outer wall of the tank assembly extends between an outer surface of the first hopper and an outer surface of the second hopper. In one example, the dry bulk cargo tank further comprises a rib provided within the tank assembly; said rib is joined to the upper regions of each of the first and second hoppers. In one example, the tank assembly is a vessel that is circular in lateral cross-section; and an outer curved surface of the rib, generally U-shaped, is welded to a complementary inner curved surface of the vessel. The rib defines at least one opening therein, extending between a front and a rear surface of the rib; and wherein a portion of the rib that includes the opening is located within one of the more than one sealable areas in the tank assembly. In one example, the more than one sealable area that includes a portion of the rib is located between an outer surface of the first hopper and an outer surface of the second hopper. In one embodiment, the system pumps air into one of the sealable areas. In another embodiment, the system pumps air out of the sealable areas. The system includes piping extending from an air inlet tube to each of the sealable areas. A first section of piping terminates in an upper region of one of the sealable areas, where one of the sealable areas contains a first compartment adapted to carry cargo; and wherein air pressure is applied to the first compartment through the first section of piping and from above the cargo carried in the storage container.The tank assembly may include at least one hopper extending downwards from a lower region of the tank assembly that forms part of the first compartment; wherein at least one hopper defines an outlet opening therein through which the load is removable from the first compartment; and wherein the more than one sealable area includes a second sealed chamber that at least partially surrounds part of an outer surface of at least one hopper; and wherein a second section of piping terminates in the second sealed chamber and wherein air pressure is supplied to the second sealed chamber through the second section of piping and pushes upwards against the air pressure in the at least one hopper. In one example, the system comprises an air inlet tube adapted to be operatively coupled to a pump; an upper air tube operatively coupled to the air inlet tube; a first valve operatively coupled to the air inlet tube, the first valve being selectively movable between an open position and a closed position; and wherein the upper air tube can selectively place into fluid communication each of more than one sealable area when the first valve is in the open position. In another aspect, the disclosure may provide a dry bulk cargo tank for transporting a load, said tank comprising a tank assembly having a front end and a rear end, with a longitudinal axis defined between them; a plurality of ground contact wheels provided on the tank assembly; more than one sealable area defined on the tank assembly; and a system for placing all of the more than one sealable area under substantially similar or substantially equal air pressure; wherein one of the more than one sealable area shares a common wall with the one of the more than one area that carries the load. In one example, the system pumps air into the more than one sealable area. In another example, the system evacuates air from the more than one sealable area. In another aspect, the disclosure may provide a method for reducing stress and deformation in a bulk cargo tank trailer comprising forming an outer wall of the cargo tank trailer into a cylinder; providing one or more hoppers, each individually extending through a region of a lower end of the outer wall; defining a first compartment within an inner portion of the cylinder in at least one or more hoppers; defining a sealed compartment in contiguous contact with the first compartment; and applying air pressure substantially similar or substantially equal to the first compartment and the sealed compartment. The provision of the one or more hoppers comprises the provision of a first hopper and a second hopper; and the method further comprises extending a section of the outer wall of the cylinder between an outer surface of the first hopper and an outer surface of the second hopper.In one example, applying substantially similar or substantially equal air pressure involves pumping air into each of the first compartment and the sealed compartment. In another example, applying substantially similar or substantially equal air pressure involves drawing air from each of the first compartment and the sealed compartment. In another aspect, the present invention can provide a method of minimizing relative movement between parts of a tank trailer component comprising providing a first compartment defined by a first outer wall, said first compartment being adapted to retain a load therein; providing a second compartment defined by a second outer wall; positioning the first compartment adjacent to the second compartment so that a section of the first outer wall and a section of the second outer wall form a common wall separating the first and second compartments; moving an air pressure in the first compartment and an air pressure in the second compartment in the same direction; and reducing the movement in the common wall as the air pressure in the first compartment and the air pressure in the second compartment move towards a similar final air pressure.The method may further include reducing tension on the common wall as the air pressure in the first compartment and the air pressure in the second compartment move toward the final air pressure. The movement of air pressure in the first compartment and the movement of air pressure in the second compartment in the same direction involves increasing the air pressure in the first compartment and increasing the air pressure in the second compartment. The movement of air pressure in the first compartment and the movement of air pressure in the second compartment in the same direction involves decreasing the air pressure in the first compartment and decreasing the air pressure in the second compartment. The method may further include creating a vacuum condition in the first compartment and creating a vacuum condition in the second compartment. The method may further comprise substantially equalizing the air pressure in the first and second compartments. The movement of the air pressure in the first and second compartments in the same direction occurs during the loading or unloading of the first compartment. The method may further comprise applying a first force to the wall common to the air pressure in the first compartment and applying a second force to the wall common to the air pressure in the second compartment prior to the movement of the air pressure in the same direction; wherein the first and second forces are of unequal magnitude.The first force and the second force move toward a substantially similar or substantially equal magnitude as the air pressure in the first compartment and the air pressure in the second compartment move in the same direction. The method may further comprise moving a portion of the common wall out of the first compartment or moving a portion of the common wall into the first compartment prior to the movement of the air pressure in the first compartment and the air pressure in the second compartment in the same direction. The method may further include reducing the degree of movement of the portion of the common wall as the air pressure in the first compartment and the air pressure in the second compartment move in the same direction.The movement of air pressure in the first compartment and air pressure in the second compartment in the same direction involves placing the first and second compartments in fluid communication. Placing the first and second compartments in fluid communication includes providing a tube having one end in the first compartment and one end in the second compartment. The method may include establishing atmospheric pressure in the first and second compartments or evacuating the air from the first and second compartments. In another aspect, the invention may provide a method for loading and unloading a dry bulk cargo tank comprising a tank assembly that defines a first compartment for carrying a load and a second compartment located vertically below at least a portion of the first compartment and in contiguous contact with it; placing the first and second compartments in fluid communication with a device for pressurizing air in the first and second compartments or with a device for creating a vacuum in the first and second compartments. The method may further comprise placing the first compartment in fluid communication with the second compartment using an air piping system.The method may further comprise operationally coupling at least one valve to the air piping system; moving the at least one valve from a first position to a second position to evacuate the first and second compartments; and moving the at least one valve from the second position to the first position to pressurize the first and second compartments. The method may further comprise automatically moving the at least one valve between the first and second positions. Moving the at least one valve between the first and second positions includes using an operator located on the ground with the tank assembly. The method may also include creating a vacuum in the first and second compartments without an operator moving hoses between a front and a rear end of the tank assembly. BRIEF DESCRIPTION OF VARIOUS VIEWS OF THE DRAWINGS The patent or application file contains at least one color drawing. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the required fee. A sample embodiment of the disclosure is set forth in the following description, shown in the drawings, and specifically and clearly indicated and set forth in the appended claims. The accompanying drawings, which are fully incorporated herein and form part of the specification, illustrate various examples, methods, and other exemplary embodiments of various aspects of the disclosure. It will be appreciated that the boundaries of the illustrated elements (e.g., boxes, groups of boxes, or other shapes) in the figures represent an example of the boundaries. A person skilled in the art will appreciate that in some examples, one element may be designed as multiple elements, or multiple elements may be designed as one element. In some examples, an element shown as an internal component of another element may be implemented as an external component, and vice versa. Furthermore, the elements may not be drawn to scale. Figure 1 is a side elevation view of a state-of-the-art cargo tank. Fig. 2 is a cross-sectional view of the state-of-the-art dry bulk cargo tank taken along line 2-2 of Fig. 1 and with various components omitted for clarity of illustration Fig. 2A is a longitudinal cross-sectional view of the STATE OF THE ART dry bulk cargo tank taken along line 2-2 of Fig. 1 and with various components omitted for clarity of illustration; and shows the bulk material being carried in the tank trailer region; Fig. 3 is a cross-section of the state-of-the-art dry bulk cargo tank taken along line 3-3 of Fig. 1 with various components omitted for clarity of illustration; and Fig. 4 is a side cross-sectional view of the STATE OF THE ART dry bulk cargo tank taken along line 4-4 of Fig. 1 with various components omitted for clarity of illustration; Fig. 5 is a side elevation view of a dry bulk cargo tank in accordance with this disclosure; Fig. 6 is a longitudinal cross-sectional view taken along line 6-6 of Fig. 5 and showing the openings for the piping used to pressurize the front end housing and the bulk material carried in the region; Fig. 6A is a longitudinal cross-sectional view of the dry bulk cargo tank showing the pressurization of the front end housing and the bulk material being carried in the region and the airflow from the pressurized front end housing through the chamber to the rear end housing; Fig. 7 is a side cross-sectional view of the dry cargo tank taken along line 7-7 of Fig. 6; Fig. 7A is an enlarged view of the highlighted region of Fig. 7; Fig. 8 is a cross-sectional view of the dry bulk cargo tank taken along line 8-8 of Fig. 6; Fig. 9 is a front elevation view of the dry bulk cargo tank of Fig. 5; Fig. 10 is run in color and shows an ANSYS® Deformation Analysis of a State of the Art dry bulk cargo tank (ANSYS® is a registered trademark of Ansys, Inc. of Canonsburg, Pennsylvania, USA); Fig. 11 is a color-rendered view and shows an ANYS® Deformation Analysis of the dry bulk cargo tank in accordance with this disclosure; Fig. 12 is a color rendering showing an ANSYS® Stress Analysis of a State of the Art dry bulk cargo tank; Fig. 13 is a color rendering showing an ANSYS® Stress Analysis of the dry loading tank in accordance with this disclosure; Fig. 14 is a side elevation view of a dry bulk cargo tank according to this disclosure and having an air piping system that includes a system for pressurizing the tank and a system for generating a vacuum inside the tank; Fig. 15 is a longitudinal cross-sectional view of the dry bulk cargo tank of Fig. 14 with the reinforcing hoops above the two wheel assemblies removed so that the ends of the exhaust pipe and the intake pipe can be seen; Fig. 16A is an elongated side elevation view of the front end of the dry bulk cargo tank of Fig. 14 showing the airflow through the air piping system when the tank is placed under vacuum; Fig. 16B is an elongated side elevation view of the rear end of the bulk dry cargo tank of Fig. 14 showing the airflow through the rear end of the bulk dry cargo tank when the tank is placed under vacuum. Fig. 17A is an elongated side elevation view of the front end of the dry bulk cargo tank of Fig. 14 showing the airflow through the front end of the dry bulk cargo tank when the tank is pressurized; Fig. 17B is an elongated front elevation view of the dry bulk cargo tank of Fig. 14 showing the airflow through the front end of the dry bulk cargo tank when the tank is pressurized; Fig. 17C is an elongated rear elevation view of the dry cargo tank of Fig. 14; and Fig. 18 is an elongated side elevation view of the front end of the dry bulk cargo tank of Fig. 14 showing the airflow through the front end of the dry bulk cargo tank when the tank is pressurized. Similar numbers refer to similar parts across all drawings. DETAILED DESCRIPTION Figures 1-4 show a bulk cargo tank trailer, and Figures 5-9 show a first embodiment of a bulk cargo tank trailer according to this disclosure. Figures 10 and 11 show a second embodiment of a bulk cargo tank trailer according to this disclosure. The term “trailer” will be used throughout the rest of this specification to refer either to the prior art bulk tank trailer or the bulk tank trailer as defined in this disclosure. However, it is understood that the terms “trailer,” “bulk tank trailer,” “tanker,” “tank,” “truck,” or “vehicle” may be used interchangeably herein. With reference to Figures 1-4, the prior art bulk tank trailer will be described in greater detail and is generally indicated in these figures by reference number 10. Bulk tank trailer 10 can be configured similarly to a bulk tank trailer described in U.S. Patent Application Serial No. 15 / 056,496 filed on February 29, 2016, and assigned to the same applicant as this disclosure. U.S. Patent Application Serial No. 15 / 056,496 is entitled “Pneumatic Tank with Tension Bar,” and the disclosure of this application is incorporated herein by reference. The trailer 10 may be a towed vehicle being towed by a towing vehicle, for example, a road tug (not shown), whereby the trailer 10 and the tug can form a towing platform in the form of a dry bulk tanker for transporting dry particulate or granular materials. The trailer 10 may have a front end 10a and a rear end 10b, defining a longitudinal direction between them. The front end may be coupled to a rear end of the tug by means of a coupling member 12. The coupling member 12 may be of any suitable type of coupling, such as a fifth-wheel coupling. The trailer 10 further includes a top portion 10c, a bottom portion 10d, a left side portion 10e, and a right side portion 10f (Fig. 3).The top part 10c and the bottom part 10d define a vertical direction between them, and the right and left sides 10e, 10f define a lateral direction between them. For clarity, an explanation of some terms used herein is provided. Trailer 10 may have an imaginary axial central plane CP (Figs. 3 and 4), which may have a plane extending longitudinally vertically, cutting through the center of trailer 10 midway between its right and left sides 10e and 10f. As is readily apparent from the Figures, various components may be axially displaced or separated from the central plane CP. The description of trailer 10 may refer to certain components, sides, surfaces, points, and the like as being inward or outward from one another, or this may be readily apparent from the Figure, even without the specific description. Such terms usually refer to the left or right halves of trailer 10, whereby, for example, with respect to the left half (right of the central plane CP), a first point that is outward from a second point is further to the left of the second point, or further outward from the second point in a first direction, or outward to the left, and thus the second point is inward from, or to the right of, the first point. Thus, within the left half, the first point is further outward from, or further from, the central plane CP than the second point.Similarly, with respect to the right half (right of the central plane CP), a third point that is outside a fourth point is further to the right than the fourth point, or further out than the fourth point in a second direction, or further out to the right, and thus the fourth point is inside or to the left of the third point. Thus, within the right half, the third point is further out or further from the central plane CP than the fourth point. It can be said that various surfaces face axially inwards or axially outwards, which can signify, respectively, the general orientation towards or away from the imaginary central plane CP. Therefore, in the left half of trailer 10, a surface facing axially inwards can be said to generally face to the left, and a surface facing axially outwards can be said to generally face to the right. Similarly, various components, surfaces, etc., can be said to extend axially inward or axially outward, which can respectively mean that they generally extend toward or away from the central plane CP. Thus, in the left half of trailer 10, a component that extends axially inward can be said to generally extend to the right, and a component that extends axially outward can be said to generally extend to the left. In the right half of trailer 10, a component that extends axially inward can be said to generally extend to the left, and a component, etc., that extends axially outward can be said to generally extend to the right. Furthermore, an explanation is provided regarding references to the longitudinal direction of trailer 10. Certain components of trailer 10 are forward or rearward of other components, or they may be in the same location along a longitudinal axis (where the longitudinal axis extends between the front end 10a and the rear end 10b). Thus, for example, a reference to two points, surfaces, components, or the like, being “in the same longitudinal position,” or “in the same longitudinal location,” means that the two points, surfaces, components, or the like are in the same position along the longitudinal axis, while they may be in different axial positions, i.e., spaced to the left or right of each other, or spaced above or below each other.Similarly, a reference to two points, surfaces, components, or the like that are “longitudinally adjacent” to each other means that the two points, surfaces, components, or the like are at or adjacent to the same position along the longitudinal axis, while they may be at different axial positions or spaced above or below each other. It is also noted that the term U-shaped or U-shaped configuration may be used herein to mean vertical U-shaped or U-shaped configuration, and the term inverted U-shaped configuration may be used herein to indicate an inverted U-shaped configuration. With primary reference to Figs. 1 and 2, the trailer 10 comprises a rigid tank assembly 14 including a front end housing 16, a center section 18, and a rear end housing 20. The front end housing 16 extends forward from the center position 18, and the rear end housing 20 extends to the rear of the center section 18. The front end housing 16, the center section 18, and the rear end housing 20 are formed from a plurality of differently shaped sheet metal sections that are welded together to form the illustrated outer shape of the tank assembly 14. The front end housing 16 forms a nose cone over the tank assembly 14. The housing 16 includes an outer wall 16a that joins and defines an inner front chamber 16b. The wall 16a defines one or more openings 16c that place the inner front chamber 16b in fluid communication with the surrounding air in the tank assembly 14. The front end housing 16 also includes one or more support walls 16d that provide strength and rigidity to the front end housing 16. The support wall 16d, as illustrated in Fig. 2, may also define an opening 16e that allows air to flow between the different inner sections of the front end housing 16 that are divided by the support wall 16d. Air from the outer tank assembly 14 can therefore circulate freely in, around, and out of the inner front chamber 16b.The outer wall 16a defines an entrance 16f in it, the purpose of which will be described later in this document. The central section 18 includes an external wall in the shape of a generally inverted U 18a. The upper wall in the shape of a generally inverted U 18a gives the tank assembly 14 a generally ovoid or elliptical shape when viewed in cross-section, as in Figs. 3 and 4. The upper wall 18a joins and defines an interior space, generally U-shaped 18b (when viewed transversely from the front or rear end of the trailer 10). An inlet 18c is defined in the upper wall 18a in an upper region near the top 10c of the trailer 10. The upper region of the upper wall 18a also defines one or more access openings 18d. The inlet 18c and the access openings 18d are in fluid communication with the interior space 18b. The access openings 18e extend upwards and outwards from the upper region of the upper wall 18a and the cover 18f selectively engages with the access ports 18e. When the covers 18f are removed, the access port openings 18d, and through them the interior space 18b, are in fluid communication with the surrounding air 10. When the covers 18f engage with the access ports 18e, the interior space 18b is no longer in fluid communication with the surrounding air 10. In the figures, the inlet 18c is shown located forward of the forwardmost access ports 18e, but it is understood that the inlet 18c can be provided at any suitable location on the upper wall 18a. The purpose of the inlet 18c will be described later. The rear end housing 20 extends longitudinally to the rear of the center section 18. The rear end housing 20 has an outer wall 20a that joins and defines an interior space 20b. One or more openings 20c may be defined in the outer wall 20a, and as a result, the air within the interior space 20b is in fluid communication with the surrounding air 14 of the tank assembly. One or more vertical support walls 20d extend from an upper region of the rear end housing 20 to a lower region thereof. The support wall 20d may define one or more openings 20e therein so that the air in the first section of the interior space 20b and a second section of the interior space 20b can mix with the outside air of the tank assembly 14. One or more hoppers are welded and extend downward from a lower end of the upper wall 18a of the center section 18. The trailer 10 can be configured with one, two, three, or more than three hoppers. As illustrated in Figs. 1-4, the trailer 10 includes a first hopper 22, a second hopper 24, and a third hopper 26. The center plane CP can be cut through the axial center of each of the hoppers midway between the left and right sides of the trailer 10. The first hopper 22 can be located closer to the front end housing 16, the second hopper 24 can be located longitudinally toward the rear of the first hopper 22 and generally centrally relative to the center section 18, and the third hopper 26 can be located longitudinally toward the rear of the second hopper 24 and closer to the rear end housing 20.First, the second and third hoppers 22, 24, and 26 can generally be aligned along the longitudinal axis of the tank assembly 14, where the longitudinal axis is aligned along the central plane “CP” and extends from the front end 10a to the rear end 10b of the trailer 10. Each hopper 22, 24, and 26 can be formed with a generally truncated conical outer wall that tapers in width from the lower end of the upper wall 18a to a lower portion 10d of the trailer 10. The term “conical,” as used herein, shall be understood to describe a hopper having a circumferential surface that is curved or partially comprised of flat surfaces, or that is entirely comprised of flat surfaces oriented at angles to each other. Hoppers 22, 24, and 26 will be described later herein. As best seen in Figs. 2 and 2A, the tapered outer wall of the first hopper includes a front region 22a and an opposing rear region 22b. An opening 22c is defined at a lower end of the tapered outer wall. The tapered outer wall of the first hopper 22 joins and defines an interior space 22d, and the opening 22c is in fluid communication with the interior space 22d. As illustrated in Figs. 2 and 2A, the opening 22c is also in fluid communication with the surrounding air 10, although the valve assembly 34 (Fig. 1) is usually provided at the lower end of the first hopper 22 to close off access to the interior space 22d. The front region 22a of the tapered outer wall of the first hopper 22 slopes forward and upward and is welded at its uppermost end to an inner upper region of the upper wall 18a. The front region 22a forms a more posterior wall of the front end housing 16. With reference still to Figs. 2 and 2A, the conical outer wall of the second hopper 24 includes a front region 24a and a rear region 24b, and an opening 24c is defined at the lower end of the conical wall. The conical outer wall of the second hopper 24 joins and defines an interior space 24d, and the opening 24c is in fluid communication with the trailer and surrounding air 10, although a valve assembly 34 (Fig. 1) is usually provided at the lower end of the second hopper 24 to close off access to the interior space 24d. An upper end of region 22b of the first hopper 22 and an upper end of the front region 24a of the second hopper 24 may be welded together to a first plate 28. The first plate 28 extends transversely through the interior of the tank assembly 14. The ends of the first plate 28 are welded to opposite regions of the inner surface of the upper wall 18a. The first plate 28 may be of substantially constant height from an upper end 28a thereof to a lower end 28b thereof. The first plate 28 may comprise a substantially solid and substantially uninterrupted piece of metal (i.e., substantially without holes, openings, or slots defined therein). The outer conical wall of the third hopper 26 includes a front region 26a and a rear region 26b. An opening 26c is defined at the lower end of the conical wall. The outer conical wall of the third hopper 26 joins and defines an interior space 26d, and an opening 26c is in fluid communication with the interior space 26d. As illustrated in Figs. 2 and 2A, the opening 26c is also in fluid communication with the surrounding air 10, although the valve assembly 34 (Fig. 1) is usually provided at the lower end of the third hopper 26 to close off access to the interior space 26d. An upper end of the rear region 24b of the second hopper 24 and an upper end of the front region 26a of the third hopper 26 can be welded together to a second plate 30. The second plate 30 can be of a substantially identical configuration to the first plate 28, and the second plate 30 extends transversely through the interior of the tank assembly 14, with the ends of the second plate 30 welded to opposite regions of the inner surface of the upper wall 18a. The second plate 30 can be of substantially constant height from an upper end 30a thereof to a lower end 30b thereof. The second plate 30 can comprise a substantially solid and substantially uninterrupted piece of metal (i.e., substantially without holes, openings, or slots defined therein).The first plate 28 and the second plate 30 may be substantially parallel to each other and at right angles to the longitudinal axis of the trailer 10. The first plate 28 and the second plate 30 are also spaced longitudinally at a distance apart from each other. Most of the first plate 28 and most of the second plate 30 are located inside the interior of the tank assembly 14. However, a portion of the first plate 28 projects below the junction between the rear region 22b of the first hopper 22 and the front region 24a of the second hopper 24, and a portion of the second plate 30 projects below the junction between the rear region 24b of the second hopper 24 and the front region 26a of the third hopper 26. This can be seen in Figs. 1 and 2A. The rear region 26b of the third hopper 26 extends upward and rearward from the lower part 10d of the trailer 10 to the inner surface of an upper region of the upper wall 18. The rear region 26b is welded to the inner surface of the upper wall 18 and forms a rear wall of the center section 18 and a front wall of the rear end housing 20. The interior space 18b defined by the top wall 18a, the interior space 22d defined by the first hopper 22, the interior space 24d defined by the second hopper 24, and the interior space 26d defined by the third hopper 26 form a storage compartment 32 for the assembly of tank 14. The storage compartment 32 is suitable for carrying dry bulk materials. One or more access ports 18e provide a means for loading dry bulk materials into the storage compartment 32, and openings 22c, 24c, and 24d provide a means for removing dry bulk materials from the storage compartment 32. As is evident from Fig. 2A, chamber 16b of the front-end housing 16 is completely separate from the storage compartment 32. Similarly, chamber 20b of the rear-end housing 16 is completely separate from the storage compartment 32. Both chamber 16b and chamber 20b open for the assembly of the surrounding air tank 14. The storage compartment 32, on the other hand, can be sealed from contact with the surrounding air tank 14 by means of covers 18f that engage with access ports 18e and by means of valve assemblies 34 (Fig. 1) that are coupled with hoppers 22, 24, and 26. Each valve assembly 34 is individually movable between an open and a closed position.For example, with respect to the first hopper 22, when the associated valve assembly 34 is moved to the open position, bulk material from the interior space 22d of the first hopper 22 can flow through the opening 22c. When the associated valve assembly 34 is closed, bulk material can no longer flow out of the opening 22c. An aeration device 36 can also be coupled to each of the lower ends of each hopper 22, 24, and 26. The aeration devices 36 are provided to selectively agitate the bulk materials stored in the associated hopper. The aeration device 36 in a particular hopper, such as the first hopper 22, will be activated prior to the opening of the associated valve assembly 34.The aeration device will agitate the particulate materials within the first hopper 22 and effectively fluidize them, thereby making it easier for the particulate materials to flow through the opening 22c when the associated valve assembly 34 is moved to the open position. As shown in Figs. 1 and 3, a reinforcement assembly 38 is welded to the outer surface of the center section 18. The assembly 38 includes a plurality of inverted U-shaped ribs 38a, 38b, 38c, and 38d; a pair of horizontally oriented bars 38e and 38f (Fig. 3); and a plurality of reinforcement plates 38g. Typically, four triangular reinforcement plates 38g are provided as part of the reinforcement assembly 38, with each reinforcement plate 38g positioned where two adjacent hoppers are connected. The reinforcement plates 38g also reinforce the area on the outside of the tank assembly 14 where the first and second plates 28, 30 are welded to the top wall 18a and the front and rear regions of the adjacent hoppers 22, 24, or 26. Ribs 38a, 38b, 38c, and 38d are welded to the outer surface of the top wall 18a and are spaced longitudinally at intervals. Ribs 38a–38d can be oriented at right angles to the longitudinal axis. Bars 38e and 38f are located on opposite sides 10e and 10f of the trailer 10 and are welded to the top wall 18a, ribs 38a–38d, and the reinforcing plates. 38g. As stated above, each reinforcement plate 38g is located at the intersection of two adjacent hoppers, such as the first hopper 22 and the second hopper 24, or the second hopper 24 and the third hopper 26. The reinforcement plates 38 are welded to the top wall 18a, to one of the ribs 38b or 38c, and to portions of the tapered outer walls of the adjacent hoppers. Each reinforcement plate 38g can be positioned externally from the location where one end of the first plate 28 or the second plate 30 is welded to the top wall 18a and the tapered outer walls of the associated hopper. The reinforcement assembly 38 is provided to help the outer wall of the tank assembly 14 resist the stresses and strains placed upon it during the transportation of a load and during the loading and unloading of the storage compartment 32. The front end housing 16, the center section 18, the rear end housing 20, the hoppers 22, 24, 26, the reinforcement assembly 38, among other components in the tank assembly 14, can be formed mainly from metal, for example, aluminum alloy or any other suitable metal. The left and right ground contact wheel assemblies 40 can be rotatably mounted on the tank assembly 14 about their respective axles extending axially horizontally and by means of a suitable suspension assembly 42 that can be secured to the rear end housing 20 and extends downwards from it adjacent to the front end 10a. The landing gear 44 can be of any suitable type known in the art and can be configured to move between a lowered position (Fig. 1) in contact with the ground “G” to support the front end 10a of the trailer 10 when it is disconnected from the tug or other towing vehicle; and a raised position (not shown) out of contact with the ground “G” when the trailer 10 is coupled to the tug / towing vehicle for road travel. The tank assembly 14 may include a front frame 46, which may be referred to as a hitch mounting frame (for mounting the hitch member 12 thereon), a landing gear mounting frame (for mounting the landing gear 44 thereon), or a hitch and landing gear mounting frame (for mounting the hitch member 12 and the landing gear 44 thereon). The front frame 46 may be of a rigid structure and may be made primarily of an aluminum alloy or other suitable material. The front frame 46 may be rigidly secured and extend downward from a lower portion of the front end housing 16 and the front region 22a of the first hopper 22. The tank assembly 14 and the suspension assembly 42 may include a rear / suspension frame 48, which may be referred to as a wheel mounting frame, on which the wheels 40 are rotatably mounted.The upper suspension frame 48 may be of a rigid structure and may be formed primarily from an aluminum alloy or other suitable metal. The suspension frame 48 may be rigidly secured and extend downwards from a lower portion of the rear end housing 20 and a lower rear portion 26b of the third hopper 26. An air piping system 50 is provided on trailer 10. This system is intended to assist in the removal of the bulk cargo carried within storage compartment 32 of tank assembly 14. The air piping system 50 includes a variety of different tubes, hoses, lines, and valves (as discussed later). Assembly 50 can be connected to an air / pneumatic pump or compressor (not shown), which can be mounted on the towing vehicle, tractor, or any other suitable vehicle. The pump is typically located above the piping system 50 and storage compartment 32. The piping system 50 includes an air inlet tube 52 that can be selectively positioned in fluid communication with the upstream pump. A hose (not shown) can be coupled to the pump at one end and to a first end 52a of an inlet tube 52 at the other end. An upper air tube 54 diverts the air inlet tube 52, and a first valve 56 is coupled with the upper air tube 54. The upper air tube 54 terminates in and is in fluid communication with a purge tube 58. A first branch 58a of the purge tube 58 extends upward from the upper air tube 54 and terminates inside the storage compartment 32. The first branch 58a of the purge tube 58 enters the tank assembly 14 through an inlet 18c (Fig. 2) defined in the center section 18.A second branch 58b of the bleed tube 58 enters the front end housing 16 through inlet 16f and subsequently exits the front end housing 16 through one of the openings 16c in a lower wall of the front end housing 16. The second branch 58b terminates in an open end 58c (Fig. 2). A second valve 60 is coupled to the second branch 58b of the bleed tube 58. Each of the first and second valves 56 and 60 can be selectively and individually moved between an open and a closed position. When the first valve 56 is in the open position and the second valve 60 is in the closed position, air can flow from the air inlet pipe 52, through the upper air pipe 54, through the first branch 58a of the purge pipe 58, and into the storage compartment 32. The pump can be activated to pressurize the storage compartment 32 by pumping air through the upper air pipe 54 and the first branch 58a of the purge pipe 58 and into the storage compartment 32. The storage compartment 32 is pressurized from the top to push particulate material out of the openings at the lower end of the hoppers, as will be discussed later.Air is pumped into storage compartment 32 until the pressure is in the range of approximately 10–15 psi. The hatch pattern used in Fig. 2A indicates the parts of the tank assembly 14 that are pressurized in this way. As is evident from Fig. 2, only storage compartment 32 is pressurized. The front end housing 16 and the rear end housing 20 are open to the atmosphere due to openings 16c and 20c, respectively. Both the front end housing 16 and the rear end housing 20 are therefore under atmospheric pressure. Consequently, a pressure differential exists across all the walls that define and connect storage compartment 32. This pressure differential is the difference between the atmospheric pressure outside storage compartment 32 and the increased pressure inside storage compartment 32. When the first valve 56 is moved to the closed position, air can no longer flow through the upper air tube 54, through the first branch 58a of the bleed tube 58, and into the storage compartment 32. When the first valve 56 is in the closed position and the second valve 60 is also in the closed position, the air pressure inside the storage compartment 32 remains substantially constant. If it is desired to depressurize the storage compartment 32, the first valve 56 is held in the closed position and the second valve 60 is moved to the open position. This allows air to flow out of the storage compartment 32, through the first branch 58a of the bleed tube 58, through the second branch 58b of the bleed tube 58, and out of the open end 58c of the same, and into the air below the tank assembly 14. With reference still to Fig. 1, the piping system 50 further includes a supply pipe for the aeration device 62, which originates at 62a in the air inlet pipe 52 and connects to the aeration device 36 coupled to the lower ends of each of the first, second, and third hoppers 22, 24, and 26, terminating at an end 62b. When one of the aeration devices 36 is activated, air will flow through the supply pipe of the aeration device 32 and into the chamber of the associated hopper 22, 24, or 26 to agitate the bulk material in the chamber. This helps to fluidize the bulk material so that it is more easily able to flow out of an opening at the bottom of the associated hopper 22, 24, or 26. The piping system 50 also includes a discharge pipe 64 originating from the air inlet pipe 52. A discharge valve 66 is coupled to the inlet pipe 52 near a first end 64a thereof, and the discharge valve 66 is movable between an open and a closed position. The discharge pipe 64 is also coupled to the valve assembly 34 located at the lower end of each of the first, second, and third hoppers 22, 24, and 26. Each valve assembly 34 is selectively movable between an open and a closed position. The discharge tube 64 terminates in an open end 64b located at a rear end 10b of the trailer 10. When one of the valve assemblies 34 is moved to the storage position, the associated hopper chamber 22, 24 or 26, and therefore the storage compartment 32, is placed in fluid communication with the discharge tube 64.When the valve assembly 34 is moved to the closed position, then the fluid communication between the discharge tube 64 and the associated hopper chamber 22, 24 or 26 and thus with the storage compartment 32 is broken. When the discharge valve 66 is in the open position, the discharge tube 64 is in fluid communication with the air inlet tube 52, and air can flow from the pump through the inlet tube 54 and through the discharge tube 64 under pressure. If the valve assembly 34 associated with the first hopper 22, for example, is moved to the closed position, the bulk material will flow out of the storage compartment 32 through the valve assembly 34 of the first hopper 22 and into the discharge tube 64. The pressurized air flowing through the discharge tube 64 will entrain some of the bulk material, causing it to flow through the discharge tube 64 and out of the open end 64b. The state-of-the-art trailer is used as follows. When trailer 10 arrives at a facility to be loaded with particulate bulk material, trailer 10 is positioned so that at least one of the access ports 18e is located directly under a loading hose or pipe opening. The cover 18f of at least one access port 18e is removed, and the dry, particulate bulk material is loaded into storage compartment 32 through at least one access port 18e. The cover 18f is subsequently replaced on each access port 18e to seal storage compartment 32. Trailer 10 is then driven along roads to a second facility where the particulate bulk material will be delivered. The operator will connect a hose from a storage area at the second facility to end 64b of the discharge pipe 64. The discharge valve 66 is moved to the closed position if it is not already in that position. The first and second valves 56 and 60 are also placed in the closed position if they are not already in that position. A hose is connected from a pump to the first end 52a of the inlet pipe 52, and the pump is activated. Air flows through air inlet pipe 52, and because the discharge valve 66 closes, air will flow through the supply pipe of the aeration device 62. In one example method, a primer of the aeration devices 36 is activated to agitate the particulate material within the associated hopper 22, 24, or 26. Air will therefore flow from the inlet pipe 52 through the activated aeration device 36 and into the chamber of the associated hopper 22, 24, or 26.When the aeration device 36 has been operating for a few minutes, the discharge valve 66 is moved to the open position, and the valve assembly 34 in the aerated hopper 22, 24, or 26 is also moved to the open position. (The aeration device 36 is deactivated before or after the valve assembly 34 in the hopper is moved to the open position.) The first valve 56 can also be moved to the open position to allow air to flow to the lower end of the storage compartment 32 to pressurize it. The bulk material in the open hopper 22, 24, or 26 flows out through the open valve assembly 34 and into the discharge pipe 64.The air flowing through discharge tube 64 collects the bulk material from the hopper and carries it through discharge tube 64, out of the open end 64b, and into and through the hose connected to the storage tank at the second installation. When substantially all the loose material in the open hopper has flowed into the discharge pipe 64, the valve assembly 34 associated with that open hopper will close according to the discharge valve 66. The aeration device 36 coupled with another of the hoppers will be activated, and the process will be repeated until the hopper is substantially empty. The steps will be repeated once more for the final hopper. When substantially all the bulk material has been removed from the storage compartment 32, the purge pipe 58 will help dislodge any material remaining in any of the hoppers 22, 24, and 26. This dislodged material will flow into the discharge pipe 64, through its open end 64b, and into the hose connected to end 64b. The first valve 56 will then close, and the second valve 60 will open to depressurize storage compartment 32. The pump will shut off, all valves 56, 60, and 66 will close, and the hoses connected to the first end 52a of the air inlet tube 52 and to the end 64b of the discharge tube 64 will be disconnected. Trailer 10 is now free to travel back to the loading facility to take up its next load. It is understood that in other example methods of emptying a load from trailer 10, more than one of the aeration devices and more than one of the hoppers may be opened simultaneously instead of opening the aeration devices and hoppers sequentially, one at a time. In some example methods, the rearmost hopper (i.e., hopper 26 in the prior art figures) may be opened first, followed by the middle hopper (second hopper 24), and then the first hopper 22. In other example methods, the hoppers may be opened in the opposite sequence, starting with the first hopper 22, then the second hopper 24, and finally the third hopper 26. One of the problems with state-of-the-art tank trailers, for example, the bulk cargo tank trailer 10, is that the regions of the trailer where the hoppers 22, 24, and 26 meet the top wall 18, and where adjacent hoppers join together, tend to experience high stress when the storage compartment 32 is pressurized. This is particularly true because the trailer 10 is generally elliptical in shape (or usually ovoid), as can be seen in Figures 3 and 4. The stresses are particularly high where the tapered wall of each hopper 22, 24, and 26 meets the top wall 18. The regions where the tapered wall of each hopper 22, 24, and 26 meets the top wall 18 can experience stresses in the range of approximately 15 psi due to the internal pressure in the storage compartment 32.Furthermore, there can be considerable relative movement between the generally elliptical top wall 18 and the hoppers 22, 24, 26 and the ribs 38. In order to help the tank assembly 14 withstand these stresses due to pressure and to stabilize the trailer component parts against excessive relative movement, the bracing assembly 38 is provided. The ribs 38a-38d, the bars 38e, 38f, the plates 38g, and the first and second plates 28, 30 and the relatively thick outer wall provided to ensure that the tank assembly 14 can withstand the pressurization of the storage compartment 32. Figures 5-9 illustrate a tank trailer according to the present invention, generally indicated by 100. Trailer 100 is similar to the trailer of the State of the Art 10 in some aspects, but also very different in others. The differences between the State of the Art 10 trailer and the State of the Art 100 trailer will be described below. Trailer 100 has a front end 100a, a rear end 100b, a top end 100c, a bottom end 10Od, a left side 100e (Fig. 7), and a right side 10Of. Trailer 100, similar to trailer 10 of the PRIOR ART, comprises a tank assembly 102 that includes a front end housing 104, a center section 106, and a rear end housing 108. However, as is more evident when compared with Figs. 3 and 7, trailer 100 is generally circular in side cross-section, whereas trailer 10 of the PRIOR ART is generally elliptical or ovoid in cross-section. As illustrated in Fig. 5, trailer 100 can be mounted on a frame that includes left and right sets of ground-hugging wheels similar to wheels 40. The wheels are mounted to a frame of the tank assembly 102 and are rotatable about their respective horizontally extending axles.The wheels are attached to the frame by means of a suitable suspension assembly (similar to suspension 42) that can be secured to the rear end housing 108 and extends downwards adjacent to the rear end 100b of the trailer 100. The trailer 100 may include landing gear (similar to landing gear 44) generally adjacent to the front end 100a. The landing gear can be of any type suitable in the art and can be configured to move between a lowered position (Fig. 5) in contact with the ground to support the front end 100a of the trailer 100 when it is disconnected from the tug or other towing vehicle; and a raised position (not shown) out of contact with the ground when the trailer 100 is coupled to the tug / towing vehicle for road travel. The front end housing 104 is located close to the front end 100a of the trailer. The center section 106 extends longitudinally to the rear of the front end housing 104, and the rear end housing 108 extends longitudinally to the rear of the center section 106. The front end housing 104, the center section 106, and the rear end housing 108 are aligned along a longitudinal axis of the trailer 100. A rib assembly is welded to an outer surface of the center section 106. The rib assembly 107 includes a plurality of ribs 107a, 107b, 107c, and 107d that are spaced longitudinally at intervals along the center section 106. The ribs 107a, 107b, 107c, and 107d may be substantially parallel to each other.Some or all of the ribs 107a-107d may be circumferential and may substantially encircle the entire circumference of the center section 106. Other ribs 107a-107d may not extend the entire way around the circumference of the center section. The ribs 107a-107d are oriented at right angles to the longitudinal axis of the tank assembly 102 (where the longitudinal axis extends between the front end 100a and the rear end 100b). The ribs 107a-107d are provided to strengthen the center section 106. Trailer 100 may have an imaginary axial central plane CP (Figs. 7 and 8), which may be a plane extending longitudinally and vertically, cutting through the center of the trailer's midway between its left and right sides 10Oe and 10Of. The circumferential ribs of rib assembly 107 are oriented at right angles to this longitudinal plane. As is readily apparent from the figures, various components may be axially offset or spaced from the central plane CP. The description of trailer 100 may refer to certain components, sides, surfaces, points, and the like as being inside or outside each other, or this may be readily apparent from the figures even without a specific description.These terms usually refer to the right or left halves of the trailer 100, whereby, for example, with respect to the left half (right of the central plane CP), a first point that is outside a second point is further to the left than the second point, or further outside than the second point in a first or left-outer direction, and thus the second point is inside or to the right of the first point. Thus, within the left half, the first point is further outside or from the central plane CP than the second point. Similarly, with respect to the right half (right of the central plane CP), a third point that is outside a fourth point is further to the right than the fourth point, or further outside than the fourth point in a second or outsider direction, and thus the fourth point is inside or to the left of the third point.From this point, within the right half, the third point is also further out or further from the central plane CP than the fourth point. It can be said that various surfaces face axially inwards or axially outwards, which can significantly mean that, in general, they face towards or away from the imaginary central plane CP. Thus, the left half of trailer 10, a surface facing axially inwards, can be said to generally face to the right, and a surface facing outwards can be said to generally face to the left. Similarly, various components, surfaces, etc., can be said to extend axially inward or axially outward, which can respectively mean that they generally extend toward or away from the central plane CP. Thus, in the left half of trailer 100, a component that extends axially inward can be said to generally extend to the right, and a component that extends axially outward can be said to generally extend to the left. In the right half of trailer 10, a component that extends axially inward can be said to generally extend to the left, and a component, etc., that extends axially outward can be said to generally extend to the right. Furthermore, the explanation is provided with regard to references to the longitudinal direction of trailer 100. Certain components of trailer 100 are additionally forward or backward of other components, or may be in the same location along a longitudinal axis (where the longitudinal axis extends between the front end 100A and the rear end 100b). Thus, for example, a reference to two points, surfaces, components, or the like being “in the same longitudinal position,” or “in the same longitudinal location,” means that the two points, surfaces, components, or the like are in the same position along the longitudinal axis, while they may be in different axial positions, i.e., spaced to the left or right of each other, or spaced above or below each other.Similarly, a reference to two points, surfaces, components, or the like that are “longitudinally adjacent” to each other means that the two points, surfaces, components, or the like are at or adjacent to the same position along the longitudinal axis, while they may be in axial positions or spaced above or below each other. It is also noted that the term U-shaped or U-shaped configuration may be used herein to mean a U-shape or a U-shaped configuration, and the term inverted U-shaped configuration may be used herein to mean an inverted U-shaped configuration. With reference to Figs. 6 and 7, the front end housing 104 includes an outer wall 104a that joins and defines a front chamber 104b. However, unlike the front end housing of the PRIOR ART, the front end housing 104 of the trailer 100 does not include any opening in the outer wall 104a that would allow air to flow directly between the front chamber 104b and the trailer 100 with surrounding air (i.e., in contrast to the front end housing of the PRIOR ART 16 which has a plurality of openings 16c that allow fluid communication between the trailer 10 with surrounding air and the chamber 16b). Because the front end housing 104 lacks openings similar to the openings 16c, the front end housing 104 is sealed from the atmosphere surrounding the tank assembly 102. An inlet 104c (Figs.5, 6, 7 and 9) is defined on the outer wall 104a and the purpose of this entry 104c will be discussed in more detail later in this document. It will be understood that, in some examples, the front camera 104b may be comprised of two or more cameras that are in fluid communication with each other but are sealed from fluid communication with the trailer by surrounding air 100. The front camera 104b is illustrated as a single camera for clarity of illustration only. The central section 106 includes a circular outer wall 106a. As previously stated herein, the outer wall 106a gives the tank assembly 102 a circular lateral cross-sectional shape when the tank assembly 102 is viewed from either end 100a or 100b. The outer wall 106a joins and defines a circular interior space 106b. An inlet 106c is defined in an upper region of the outer wall 106a adjacent to the top 100c of the trailer 100. The inlet 106c may enter an upper region of the outer wall 106a in the central section 106, as shown in the illustrated embodiment, in which case the inlet 106c is in fluid communication with the first compartment 124. In other embodiments, the inlet may be defined in an upper region of the front end housing 104. As is evident from Fig.6 An inner wall separates the first compartment 124 from the front chamber 104b defined by the front end housing 104. In this example, the inlet 106c may be in fluid communication with the first compartment 124 even though it appears from the outside of the tank assembly 102 that the inlet 106c enters the front end housing 104. The upper region of the outer wall 106a also defines one or more access openings 106d. The entrance 106c and the access openings 106d are in fluid communication with the interior space 106b. The access openings 106e extend above and below the upper region of the outer wall 106a, and the covers 106f selectively engage with the access openings 106e. When the covers 106f are removed, the access openings 106d, and therefore the interior space 106b, are in fluid communication with the trailer 100 and the surrounding air.When the covers 106f are coupled to the access openings 106e, then the interior space 106b is no longer in fluid communication with the surrounding air 100. In the figures, the inlet 106c is shown located forward of the more forward access opening 1006e, but it is understood that the inlet 106c can be provided at any suitable location in the. As can be seen more clearly in Figs. 2 and 2A, the tapered outer wall of the first hopper 110 includes a front region 110a and an opposing rear region 110b. An opening 110c is defined at a lower end of the tapered outer wall. The tapered outer wall of the first hopper 110 joins and defines an interior space 110d, and an opening 110c is in fluid communication with the interior space 110d. A valve assembly 116 (Fig. 5) is provided at a lower end of the first hopper 110, and the valve assembly 116 is movable between an open position and a closed position. The valve assembly 116 (Fig. 5) is moved to the closed position to retain materials within the first hopper 110 and to the open position to allow materials to flow through the opening 110c and out of the first hopper 110.The front region 110a of the tapered outer wall of the first hopper 110 slopes forward and upward and is welded at its uppermost end to an inner surface of the upper region of the outer wall 106a. The front region 110a forms a rearmost wall of the front end housing 104. With reference still to Figs. 6 and 6A, the conical outer wall of the second hopper 112 includes a front region 112a and a rear region 112b, and an opening 112c is defined at the lower end of the conical wall. The conical outer wall of the second hopper 112 also includes side regions 112e (Figs. 7 and 7A) and 112f, which extends between the front region 112a and the rear region 112b. The conical outer wall 112 joins and defines an interior space 112d, and an opening 112c is in fluid communication with the interior space 112d. A valve assembly 116 (Fig. 5) is provided at the lower end of the second hopper 112, and the valve assembly 116 is movable between an open and a closed position. The valve assembly 116 (Fig. 5) is moved to the closed position to retain materials within the second hopper 112 and is moved to the open position to allow materials to flow through the opening 112c and out of the second hopper 112. The tapered outer wall of the third hopper 114 includes a front region 114a and a rear region 114b. An opening 114c is defined at the lower end of the tapered wall. The tapered outer wall of the third hopper 114 joins and defines an interior space 114d and an opening 114c in fluid communication with the interior space 114d. A valve assembly 116 (Fig. 5) is provided at a lower end of the third hopper 114 and is movable between an open and a closed position. The valve assembly 116 (Fig. 5) is moved to the closed position to retain materials within the hopper 114 and to the open position to allow materials to flow through the opening 114c and out of the third hopper 114.The rear region 114b of the third hopper 114 extends upward and rearward from the lower part 100d of the trailer 100 to the inner surface of an upper region of the outer wall 106a. The rear region 114b is welded to the inner surface of the outer wall 106a and forms a rear wall of the center section 106 and a front wall of the rear end housing 108. Referring to Figs. 6-8, an upper end of the rear region 110b of the first hopper 110 and an upper end of the front region 112a of the second hopper 112 can be welded together to a first rib 118. As shown in Fig. 8, the first inner rib 118 extends transversely through the interior of the tank assembly 14 and is oriented at right angles to the longitudinal axis of the tank assembly 102. The first inner rib 118 includes a first wing 118a and a second wing 118b that are connected together by a concavely curved bar 118c. The first and second wings 118a, 118b taper in width from the wider region near the bar 118c to a terminal end 118a' or 118b, respectively.It should be noted that a portion of each of the first wing 118a and second wing 118b extends upwards a distance beyond a central point “A” of the circular outer wall 106a of the central section 106. A space 118d is defined between the bar 118c and the lower inner surface of the central section 106. In this way, air can flow through the space 118d from a region on a front-facing side of the inner rib 118 to a region on a rear-facing side of the inner rib 118. A welding pad 2 can be interposed between each of the first and second wings 118a, 118b and the inner surface of the outer wall 106a of the central section 106. A second inner rib 120, which is substantially identical to the first inner rib 118, is located between the second hopper 112 and the third hopper 116. The second inner rib 120 serves the same purpose as the first inner rib 118, namely, to reinforce the outer wall while allowing air to continue flowing from the front end housing 104 to the rear end housing 108 and under the center section 106. It should be noted that where the first hopper 110 and the second hopper 112 are joined together, one of the ribs, namely rib 107b, is welded to the outer surface of the outer wall 106a of the center section 106, and the first inner rib 118 is welded to the inner surface of the outer wall 106a. In this way, a portion of the outer wall 106a is sandwiched between rib 107b and the first inner rib 118. Similarly, where the second hopper 112 joins the third hopper 114, one of the ribs, namely rib 107c, is welded to the outer surface of the outer wall 106a, and the second inner rib 120 is welded to the inner surface of the outer wall 106a. This coupling ensures a structurally sound connection between adjacent hoppers 110, 112, 114. A comparison between Fig. 1 showing trailer 10 of the PRIOR ART and Fig. 5 showing trailer 100 according to the present disclosure reveals a number of issues. First, trailer 100 includes a rib assembly 107 comprising a plurality of circumferential ribs (i.e., circular ribs), namely ribs 107a-107d, instead of the inverted U-shaped ribs 38a-38d and horizontal bars 38e of the bracing assembly 38 provided in trailer 10 of the PRIOR ART. Secondly, the first and second inner ribs 118 and 120 are located entirely within the interior of the tank assembly 102. No part of the inner rib 118 or the second inner rib 120 extends outward beyond the lower region of the outer “skin” of the trailer 100. This differs from the trailer 10 of the PRIOR ART where a portion of each of the first plate 28 and the second plate 30 extends downward to a distance below the lower region of the outer “skin” of the trailer 10. Third, most of each of the first, second, and third hoppers 110, 112, 114 of trailer 100 are located within the outer wall 106a of trailer 100. Consequently, only small portions of the tapered walls of the first, second, and third hoppers 110, 112, 114 form part of the outer “skin” of trailer 100. In contrast, in trailer 10 of the PRIOR ART, most of each of the first, second, and third hoppers 22, 24, 26 extend from the upper wall 18a, and the tapered hopper walls form part of the outer “skin” of trailer 10. Fourth, a portion 106a' (Figs. 5-8) of the outer wall 106a of section 106 extends around the outside of the tapered walls of each of the first, second, and third hoppers 110, 112, 114. For example, as can be seen in Figs. 7 and 7A, the portion of the outer wall 106a' is spaced a distance outward from the side regions 112e and 112f of the second hopper 112 as a gap 112a is defined between these. Another portion of the outer wall 106a' extends between adjacent hoppers (for example, between the first hopper 110 and the second hopper 112; and between the second hopper 112 and the third hopper 114). The lower parts of each hopper 110, 112, 114 thus extend outwards from part 106a' of the outer wall 106a. Therefore, an intermediate chamber 122 (Figs. 6 and 7) is defined between the conical walls of the first, second, and third hopper 110, 112, 114 and part 106a' of the outer wall 106a.Gap 112a forms part of this intermediate chamber 122. Thus, intermediate chamber 122 not only surrounds part of the outer surface of the tapered wall of each hopper, but also extends between the front end housing 104 and the rear end housing 108. In this way, the front chamber 104b of the front end housing 104 and the rear chamber 108b of the rear end housing 108 are placed in fluid communication with each other by means of intermediate chamber 122 (including gaps 122a). Front chamber 104b, intermediate chamber 122, and rear chamber 108 together form a second compartment 125, which is a single sealed chamber that is not in fluid communication with the air outside the trailer 100.Conversely, in trailer 10 of the state of the art, there is no component similar to the intermediate chamber 122 of trailer 100. In trailer 10, chambers 16b and 20b are discrete and separate and are not in fluid communication with each other. Furthermore, neither chamber 16b nor chamber 20b is sealed; instead, both are open to the outside atmosphere. Because the front chamber 104b, the middle chamber 122, and the rear chamber 108 are in fluid communication with each other, when the front chamber 104b is pressurized (as shown in Fig. 6 and described later herein), air flows from the front chamber 104b through the middle chamber 122 and into the rear chamber 108b. This airflow is indicated by arrows showing the airflow from the front of the trailer 100 to the rear of the trailer. With reference to Figs. 6 and 6a, the interior space 106b is defined by the outer wall 106a, the interior space 110d is defined by the first hopper 110, the interior space 112d is defined by the second hopper 112, and the interior space 114d is defined by the third hopper 114 from a first compartment 124 for the assembly of tank 102. The first compartment 124 is suitable for carrying bulk materials. One or more access openings 106e provide a means for bulk materials to be loaded into the first compartment 124, and openings 110c, 112c, and 112d provide a means for bulk materials to be removed from the first compartment 124. An air piping system 126 is provided in trailer 100. The air piping system 126 is provided to assist in removing the bulk cargo carried within the first compartment 124 of the tank assembly 14. The air piping system 126 is also used to pressurize the first compartment 124 and the second compartment 125 (comprising the front chamber 104b, the intermediate chamber 122, and a rear chamber 108b), as will be described later herein. The second compartment 125 is effectively part of the air piping system 126, in that the second compartment 125 acts as a conduit that allows the movement of air between the front end housing 104 and the rear end housing 108 through the intermediate chamber 122.Therefore, the second compartment 125 assists in the circulation of air between the tank assembly 102, particularly by providing a duct that is located, at least partially, below the first compartment 124. As discussed herein, the first and second compartments 124, 125 share a common wall, and an air piping system 126 is provided to pressurize the air on both sides of that common wall. The air piping system 126 aerates the bulk material within the first compartment 124 and discharges that bulk material out of hoppers 110, 112, and 114 when the tank assembly 102 is unloaded. The air piping system 126 can also be used to pressurize the first compartment 124 to apply downward pressure to the dry bulk material held within it, thus aiding in its removal. Simultaneously, the air piping system 126 pressurizes the second compartment 125 for several purposes. First, the substantial equalization of air pressure in the first and second compartments 124 and 125 helps reduce some of the stresses and strains at the joints between the various sections of material forming the tank assembly 102.This can tend to increase the service life of the tank assembly 102. Secondly, substantial pressure equalization helps reduce relative movement between the various sections of the tank assembly 102. Substantial pressure equalization between the first and second compartments 124, 125 can particularly help reduce relative movement between adjacent sections of the tank assembly 102, which are joined together by a joint. In prior art trailers, there could be relative movement between adjacent sections of the tank assembly 102 of approximately one-quarter of an inch.With the introduction of substantial pressure equalization in the first and second compartments 124, 125, as discussed herein, the relative movement between adjacent sections of the tank assembly 102 (and the tank assembly 202, as described later herein) has been reduced to a few thousandths of an inch; for example, a movement of about fifteen thousandths of an inch would be characteristic. Because of the reduction in possible relative movement in the tank assembly 102 during loading and unloading due to the substantial pressure equalization in the first and second compartments 124, 125, the aluminum commonly used to manufacture this type of tank assembly has been thinner than that required in prior art tank assemblies.The reduction in the thickness of the aluminum (or other metals used during manufacturing) results in a tank 102 and trailer 100 assembly that weighs less than the prior art tank or trailer assembly. The reduction in relative motion also means that the material used to produce the tank 102 trailer does not need to be as strong as that required in prior art trailers or tank assemblies. It should be noted that trailer 100 is not driven on roads in a pressurized condition. The air piping system 126 is only activated during the unloading of a load from the first compartment 124 and is depressurized once the unloading is complete. The air piping system 126 includes a plurality of different tubes, hoses, lines, and valves (as discussed later). With reference to Figs. 5 and 9 in particular, an air piping system 126 includes, among other components, an air inlet pipe 128. The air piping system 126 can be selectively connected to a pressurized air source. A suitable pressurized air source could be an air / tire pump or compressor. By way of example only, Fig. 5 shows a pump “P” provided for operational coupling with the air piping system 126 on the trailer 100. The pump “P” can be operationally coupled to a power take-off (PTO) on the trailer or towing vehicle. (It should be understood that this pump “P” is representative of any suitable air source that can be coupled with the air piping system 126.)The pump “P” can be mounted on the towing vehicle or a tug, or on the tank assembly 102, or it can be a self-contained unit located on the ground adjacent to the trailer 100. For this reason, Fig. 5 (and Fig. 14) show a pump “P” spaced a short distance away from the trailer 100 (or trailer 200 in Fig. 14). The pump “P” will usually be located upstream of the air piping system 126 and a first compartment 124. The pump “P” is illustrated as having an air intake “P1” and an exhaust outlet “P2”. An operator can connect the pump “P” via a hose (not shown) to the first end 128a of the air inlet pipe 128. In particular, the hose will connect the first end 128a of the air inlet pipe 128 to the exhaust outlet “P2” of the pump “P”.The air expelled by pump “P” will be pumped into and flow through the hose and into the air piping system 126 by means of the air inlet pipe 128. This air, supplied under pressure by pump “P”, will be used to pressurize the first and second compartments 124, 125 as described herein. An air tube 130 extends from the air inlet tube 128, and a first check valve 129 is coupled to the air inlet tube 128 at a location between the first end 128a and an upper air tube 130. The air tube 130 extends between the air inlet tube 128 and the inlet 104c in the front end housing 104. A side branch 133 extends from the upper air tube 130 and terminates in a bleed tube 134. A first valve 132 is coupled to the upper air tube 130 at a location between the air inlet tube 128 and the side branch 133. A second check valve 135 is coupled to the side branch 133 at a location between the upper air tube 130 and the bleed tube 134.The bleed tube 134 extends from the side branch 133, over the top 100a of the trailer 100, and enters the first compartment 124 through the inlet 106c defined in the outer wall 106a. This is shown in Figs. 6 and 6A. A terminal end 134a of the bleed tube 134 is located inside the first inner compartment 124. The terminal end 134a defines an opening in the compartment, allowing the bleed tube 134 and the first compartment 124 to be in fluid communication. An emergency release valve 136 is provided in the fluid communication of the bleed tube. An emergency release valve 136 is provided in the bleed tube 134 and is located between the side branch 133 and the inlet 106c. A portion of the purge tube 134 extends down the side branch 133 and this portion forms a purge tube 138 that terminates in an inlet 138a (Fig. 9) that opens to the atmosphere.A second valve 140 is coupled to outlet tube 138 at a location between side branch 133 and outlet 138a. The first and second check valves 129, 135 allow air to flow in only one direction through the pipe to which the check valve is connected. The first check valve 129 allows air to flow from the first end 128a of the air inlet pipe 128 in one direction toward the upper air pipe 130 and beyond, but prevents air from flowing from the upper air pipe 130 in the reverse direction toward the first end 128a. The second check valve 135 allows air to flow from the upper air pipe 130 toward the purge pipe 134 but does not allow it to flow in the reverse direction.The second check valve 135 helps to ensure that bulk material in the first compartment 124 does not accidentally flow through the purge tube 134 and into the second compartment 125 where it would accumulate and reduce or eliminate the possibility of providing substantially similar or substantially the air pressure in the first compartment 124 and the second compartment 125. The first valve 132 and the second valve 140 are each independently movable between an open and a closed position. When the first valve 132 is in the open position, air can flow from the air inlet pipe 128 into and through the upper air tube 130 and subsequently through the inlet 104c and into the front chamber 104b of the front end housing 104. Air will also flow from the upper air tube 130 through the side branch 133 and into the bleed tube 134. When the second valve 140 is closed, air will flow upward through the bleed tube 134, through the inlet 106c, and into the first compartment 124. If air is supplied under pressure through the air inlet pipe 128, then the pressurized air will flow into the front chamber 104b and the first compartment 124.The front chamber 104b and the first compartment 124 will be pressurized to the same extent; that is, the air pressure in the front chamber 104b and in the first compartment 124 will be the same. When the first valve 132 is in the closed position, air is not suitable to flow from the air inlet tube 128 into and through the upper air tube 130 or into and through the side branch 133 or the purge tube 134. If the second valve 140 is moved to the open position, then air is able to flow out of the first compartment 124 through the purge tube 134, through the exhaust tube 138 and out of outlet 138a and into the atmosphere. The second valve 140 can therefore be opened to depressurize the first compartment 124. Because the second check valve 135 is provided in the side fork 133, when the second valve 140 is moved to the open position, air will also flow out of the front chamber 104b and back through the upper air tube 130. If the first valve 132 is closed, then the air flowing out of the front chamber 104b will flow through the side fork 133 and be carried along with the airflow into the exhaust tube 138. Thus, opening the second valve 140 depressurizes the first compartment 124 of the chamber 104b in the front end housing 104.The second check valve 135 prevents air flow from the purge tube 134 through the side branch 133 through the upper air tube 130. As discussed earlier in this document, the front chamber 140b is in fluid communication with the intermediate chamber 122 and the rear chamber 108b of the rear end housing 108, forming the second sealed chamber 125. Consequently, when air flows into the front chamber 104b under pressure, that air subsequently flows into the intermediate chamber 122 and the rear chamber 108b. Pressurization of the first compartment 124 and the front chamber 104b also results in pressurization of the intermediate chamber 122 and the rear chamber 108b. Depressurization of the first compartment 124 and the front chamber 104b also results in the simultaneous depressurization of the intermediate chamber 122 and the rear chamber 108b. When pressurized air flows into the first compartment 124 and the second compartment 125 (i.e., the front chamber 104b / intermediate chamber 122 / rear chamber 108b), the air pressure moves in the same direction, so the air pressure on both sides of the conical walls of the hoppers 110, 112, and 114 tends to be substantially similar or substantially equal. Because this pressure is substantially similar or substantially equalized, the walls that join and define the first compartment 124 and the hoppers 110, 112, and 114 are under substantially less stress and pressure than would be the case if only the first compartment 124 were pressurized and if they were less inclined to move relative to one another.Prior to movement, the air pressure in the first and second compartments is in the same direction. A force exerted by the air pressure in the first compartment could tend to cause a common section of wall between the two compartments to move. If the air pressure in the first compartment is greater, then the common wall section could tend to move outward into the second compartment. If the air pressure in the second compartment is greater, then the common wall section could tend to move inward into the first compartment. As the air pressure in the first and second compartments move to a condition where they tend to be substantially similar or substantially equal, then the force on either side of the common wall section tends to equalize, and therefore the movement of the common wall section tends to decrease in magnitude. When it is desired to depressurize the first compartment 124, pump “P” is switched off, and the first valve 132 is moved to the closed position and the second valve 140 to the open position. Air then flows into the opening at the end 134a of the bleed tube 134, through the bleed tube 134, and out of the exhaust tube 138 to the external trailer. If, during operation of the first compartment 124 and the front chamber 104b, the intermediate chamber 122 and the rear chamber 108b reach a predetermined critical threshold, the emergency safety valve 136 will automatically activate and move to an open position so that air can escape from the upper air tube 130 and the purge tube 134. The emergency safety valve 136 can also be operationally linked to pump “P” to shut it off if valve 136 activates. Still referring to Fig. 5, the air piping system 126 further includes an aeration device supply pipe 142 that originates at 142a in the inlet pipe 128 and terminates at 142b near the rear end 100b of the trailer 100. The aeration device supply pipe 142 connects to an aeration device (not shown) that is coupled to each of the first, second, and third hoppers 110, 112, and 114. The aeration device can be any type of device that fluidizes the bulk material retained within the first, second, or third associated hopper 110, 112, and 114. For example, the aeration device could be a rubber fluidizing disc or an air sweeper. Aeration device hoses 144 extend between the aeration device supply pipe 142 and each aeration device.When activated, air flows from the air inlet tube 128, through the aeration device supply tube 142, through the associated aeration device hoses 144, and the aeration device itself, into the associated hopper chamber 110, 112, or 114. This airflow in the hopper chamber agitates the bulk material. The airflow helps to fluidize the bulk material, making it easier to allow it to flow out of the opening at the bottom of the associated hopper 110, 112, or 114. The air piping system 126 further includes a discharge tube 146 originating from an air inlet tube 128. A discharge valve 148 is coupled to the air inlet tube 128 near a first end 146a of the discharge tube 146, and the discharge valve 148 is movable between an open and a closed position. The discharge tube 146 also couples to valve assemblies 116 located at the lower end of each of the first, second, and third hoppers 110, 112, and 114. Each valve assembly 116 is selectively movable between an open and a closed position. The discharge tube 146 terminates in an open end 146b located at a rear end 100b of the trailer 100. When one of the valve assemblies 116 is moved to the open position, the associated hopper chamber 110, 112 or 114, and thus the first compartment 124, is placed in fluid communication with the discharge tube 146.When the valve assembly 116 is moved to the closed position, then the fluid communication between the discharge tube 146 and the associated hopper chamber 110, 112 or 114 and thus with the first compartment 124 is broken. When the discharge valve 148 is in the open position, the discharge pipe 146 is in fluid communication with the air inlet pipe 128, and air can flow from pump “P” through the air inlet pipe 128 and through the discharge pipe 146 under pressure. If the valve assembly 116 associated with the first hopper 110, for example, is moved to the open position, the bulk material will flow out of the first compartment 124 through the valve assembly 116 of the first hopper 110 and into the discharge pipe 146. The pressurized air flowing through the discharge pipe 146 will carry some of the bulk material, causing it to flow through the discharge pipe 146 and out of the open end of the discharge pipe 146, through the hose attached to it, and into a storage compartment in the facility where the material is being discharged. The trailer 100 according to the present invention is used as follows. When the trailer 100 arrives at a facility to be loaded with the particulate bulk material, the trailer 100 is positioned so that at least one of the access ports 106e is located directly under an opening of the loading hose or pipe. The cover 106f of the at least one access port 106e is removed, and the dry, particulate bulk material is loaded into the first compartment 124 through the at least one access port 106e to seal the first compartment 124. The trailer 100 is then driven along the roads to a second facility where the particulate bulk material will be delivered. The operator connects a hose from a storage tank at the second installation to end 146b of the discharge tube 146 at the rear end 100b of the trailer 100. The discharge valve 148 is moved to the closed position if it is not already in that position. The first and second valves 132 and 140 are also placed in the closed position if they are not already in that position. A hose (not shown) is connected between pump “P” (Fig. 5) and the first end 128a of the inlet tube 128, and pump “P” is activated. Air flows through the air inlet tube 128 under pressure, and, because the discharge valve 148 is closed, air will flow into the supply tube of the aeration device 128.A first stage of one of the aeration devices can be activated to allow air to flow from the supply tube of the aeration device 128, through the hoses of the aeration device 144, and through the associated aeration device to agitate the particulate material within the associated hopper 110, 112, or 114. Therefore, air will flow from an air inlet tube 128, through the hoses of the aeration device 144, through the activated aeration device, and into the chamber of the associated hopper 110, 112, or 114. While the aeration device is activated, the discharge valve 148 moves to the open position, and the valve assembly 116 in the aerated hopper 110, 112, or 114 will also move to the open position. (The aeration device can be activated before or after the valve assembly 116 in which the hopper has been moved to the open position.)The first valve 132 can also be moved to the open position so that air flows from the air inlet tube 128, through the upper air tube 130, through the side branch 133 and the purge tube 134, and into the upper end of the first compartment 124, thereby pressurizing the first compartment 124. At the same time, as the first compartment 124 is being pressurized, air flows through the upper air tube 130 and into the front chamber 104b of the front-end housing 104, and thus into the intermediate chamber 122 and the rear chamber 108b. Therefore, the front chamber 104b, the intermediate chamber 122, and the rear chamber 108b are pressurized to the same extent as the first compartment 124.When the valve assembly 116 is moved to the open position, the pressurized bulk material held in the open hopper 110, 112, or 114 flows through the open valve assembly 116 and into the discharge pipe 146. The air flowing through the discharge pipe 146 picks up the bulk material from the open hopper and carries it through the discharge pipe 146, out of the open end 146b, and into and through the hose connected to the storage tank at the second installation. When substantially all of the loose material in the first hopper has flowed into the discharge pipe 146, the valve assembly 116 associated with that hopper will close as valve 148 discharges. The aeration device associated with the next hopper will be activated, and the process will be repeated until the next hopper is substantially empty. The steps will be repeated once more for the final hopper. It is understood that it is possible on trailer 100 to activate more than one aeration device and open more than one hopper at a time. When substantially all the bulk material has been removed from the first compartment 124 through the three hoppers 110, 112, and 114, the discharge valve 148 will remain in the open position to allow air to continue flowing through the discharge pipe 146. The first valve 132 will remain open to allow air to be moved from the air inlet pipe 128 through the upper air pipe 130 into the front chamber 104b / intermediate chamber 122 / rear chamber 108b, and through the side branch 133 and purge pipe 134 into the first compartment 124. The air flowing into the first compartment 124 through the purge pipe 134 will help to dislodge any material remaining in any of the hoppers 110, 112, and 114. This dislodged material will flow into the discharge pipe 146. and through the open end of it and in the hose connected to it. Pump “P” will shut off, and the first valve 132 will close and the second valve 140 will open to depressurize the first compartment 124 and the front chamber 104b / the middle chamber 122 and the rear chamber 108b. Subsequently, all valves 132, 140, and 148 will close, and the hoses connected to the first end 128a of the air inlet pipe 128 and to the open end of the discharge pipe 146 will be disconnected. The trailer 100 is then free to travel back to the loading facility to take up its next load. In summary, the 100 trailer differs from the 10 trailer in several aspects that allow the 100 trailer to be structurally stronger, lighter in weight (and therefore capable of carrying a heavier load), and more efficient. The 100 trailer has a true cylindrical shape compared to the generally oval or elliptical shape of the prior art 10 trailer. This true cylindrical shape (i.e., one that has a cross-section when viewed from the front or rear) is much stronger than an oval or elliptical shape because a cylinder has fewer stress points than an ellipse or oval. State Art Trailer 10 and Trailer 100, as described herein, were tested for deformation and stress using a computerized engineering analysis software known as ANSYS® (ANSYS® is a registered trademark of Ansys, Inc. of Canonsburg, Pennsylvania, USA). Figures 10 and 11 (both rendered in color) show an ANSYS® Deformation Comparison, and Figures 12 and 13 (both rendered in color) show an ANSYS® Stress Comparison between State Art Trailer 10 and Trailer 100, as described herein. In the Deformation Comparison of Figs. 10 and 11, the areas of highest deformation or movement are shown by the presence of the color red and are identified by the number 150. The high deformation areas 150 identify the region of high movement even though trailer 10 includes a reinforcement assembly 38 and the first and second plates 28, 30. The areas of progressively lower deformation or movement are colored orange, then yellow, subsequently green, then blue. The areas of least deformation are dark blue and are identified by the number 152. Fig. 10 shows very clearly in trailer 10 of the STATE OF THE ART, despite the presence of the reinforcement assembly 38 and plates 28, 30, the regions of the highest deformation 150 are located in the front and rear regions of each conical wall of the hoppers, for example, the front and rear regions 22a,22b of the first hopper 22.In particular, the high deformation regions 150 are located a short distance below the joints where the tapered walls of the hopper join the upper wall 18a and a first and second plate 285, 30. The area of ​​least deformation 152 in the trailer 10 is the upper wall 18a. In contrast, Fig. 11 shows that trailer 100 has non-obvious regions of high deformation in the cylindrical wall 106 of the tank assembly or any of the hoppers 110, 112, 114, or adjacent to any of the joints between wall 106 and hoppers 110, 112, 114. In other words, there are no regions colored red or orange. Therefore, there is less movement between the parts of the trailer 100 component than is the case with trailer 10 of the prior art. Figure 11 shows that there are regions of less deformation in trailer 100, namely yellow and green areas identified by the number 154. The regions of less deformation 154 are located towards the lower part of the tank assembly 102 where the hoppers 110, 112, 114 come out of the tank wall 106 and in the regions located between the first and second inner rib 118 and 120.Therefore, trailer 100 is subject to less deformation than the prior art trailer 10. In real-world terms, this means trailer 100 is stronger than the prior art trailer 10 and, therefore, better able to withstand the rigors of hauling loads. Furthermore, by substantially equalizing the pressure, thinner material can be used to manufacture trailer 100, thus substantially reducing its weight and allowing it to carry more payload while still complying with mandatory motor vehicle regulations. Furthermore, the front chamber 104b, the middle chamber 122, and the rear chamber 108b are provided in regions of the trailer 100 that could experience the least deformation 154. The stresses that could be experienced in these lower regions of the tank assembly 102 when the first compartment 124 is pressurized tend to be displaced by simultaneously pressurizing the front chamber 104b, the middle chamber 122, and the rear chamber 108b. The cylindrical shape of the outer wall 106 and the pressurization of the areas below, at the front of, and behind the first compartment 124 also allow the manufacturer to use thinner sheet metal in the manufacture of trailer 100 than in the production of the prior art ovoid trailer 10. The thinner metal can be used for trailer 100 because the metal and the joints between the various components do not have to withstand the same amount of relative movement as was the case with the prior art trailer 10. By way of example, trailer 100 is now about 600 pounds lighter than the prior art trailer 10 due to the thinning of the outer “skin” and the elimination of several components of the reinforcement assembly 38.The front end housing 104 on trailer 100 is also configured slightly differently from the front end housing 16 of trailer 10 of the STATE OF THE ART 10. The front end housing 104 is more symmetrical than the front end housing 16, and the pressurized area in and behind the front end housing 104 will also substantially reduce the weight and stress on the front end housing 104. Figures 12 and 13 show an ANSYS® Stress Analysis of a State-of-the-Art Trailer 10 and an ANSYS® Stress Analysis of a Trailer 100, respectively. Again, the regions of highest stress in these two analyses are identified by the color red, and progressively lower stresses by the colors orange, then yellow, then green, and finally blue. In both trailer 10 of the STATE ART and trailer 100 according to this disclosure, the maximum stresses are located where the hoppers join the wall that forms the rest of the tank body, i.e., the upper wall 18a in trailer 10 of the STATE ART and wall 106 in trailer 100. In trailer 10 of the STATE ART, the regions of maximum stress are identified by the number 156 and are clearly where the metal forming the upper wall 18a is welded to the metal forming the hoppers 22, 24, 26.The maximum stress measured in one of these regions 156 is shown on the left side of Fig. 12 which is 56, 522. Figure 13 shows that the regions of maximum stress in trailer 100 are at the joints where hoppers 110, 112, 114 are welded to wall 106. These regions are identified by the number 158. However, the maximum stress measured in one of these regions 158 is 30,454; therefore, the maximum stress measured in trailer 100 is approximately half of the maximum stress measured in trailer 10 of the PRIOR ART. Fig. 14-18 shows a second embodiment of a dry bulk cargo trailer, according to the present invention, with the trailer generally indicated as 200. Trailer 200 is substantially identical to trailer 100 in structure and function with some exceptions / additions that will be discussed later in more detail. The trailer 200 comprises a tank assembly having a front end housing 104, a center section 106, and a rear end housing 108 that are substantially identical to the front end housing 104, center section 106, and rear end housing 108 of the trailer 100. The center section 106 defines a first compartment 124 for carrying a load. The trailer 200 further includes a second compartment 125 consisting of a front chamber 104b defined by the front end housing 104, an intermediate chamber 122 defined around the outer surface regions of the first, second, and third hoppers 110, 112, 114, and a rear chamber 108b defined by the rear end housing 108.The front camera 104b, the middle camera 122 and the rear camera 108b of trailer 200 are in fluid communication with each other in the same way as the front camera 104b, the middle camera 122 and the rear camera 108b of trailer 100 and thus a second compartment 125 is formed which is sealed from the atmosphere surrounding trailer 200. The trailer 200 includes a rib assembly 207 that is welded to an outer surface of the center section 106. The rib assembly 207 is similar to the rib assembly 107 in that it comprises a number of ribs that are spaced a longitudinal distance apart. The rib assembly 207 for this trailer includes a first rib 207a located adjacent to the front end of the first hopper 110, a second rib 207c located where the first hopper 110 joins the second hopper 112, a third rib 207a located where the second hopper 112 joins the third hopper 114, and a fourth rib 207g located at a rear end of the third hopper. These ribs 207a, 207c, 207d and 207g are substantially identical to ribs 107a, 107b, 107c, and 107d, respectively, and are circumferential in nature.In other words, each of the first, second, third, and fourth ribs 207a, 207c, 207e, and 207g is welded to the outer surface of wall 106a and circumscribes the circumference of the center section 106. The rib assembly 207, unlike the rib assembly 107, also includes a fifth rib 207b, a sixth rib 207d, and a seventh rib 207e, all of which are welded to the outer surface of wall 106a. The fifth rib 207b is generally located midway between the first and second ribs 207a and 207c; the sixth rib 207d is generally located midway between the second and third ribs 207c and 207e; and the seventh rib 207f is generally located halfway between the third and fourth ribs 207e and 207g. The fifth, sixth and seventh ribs 207b, 207d, and 207f are not circumferential ribs that circumscribe the circumference of the central section 106 but instead are generally C-shaped ribs.The fifth, sixth, and seventh ribs 207b, 207d, 207f help to provide additional reinforcement to the center section 106 of the trailer 200 so that the center section 106 can better support the trailer 200 that is placed under vacuum conditions, as will be described later herein. Trailer 200 also differs from trailer 100 in that the air piping system 226 provided therein is not only useful for pressurizing the first and second compartments 124, 125 of the tank assembly 102 in a manner similar to air piping system 226, but can also be used to place the first and second compartments 124, 125 of the tank assembly 102 under a vacuum. Specifically, air piping system 226 can be used to pressurize the first compartment 124 and chambers 104b, 122, and 108b, or it can be used to place the first compartment 124 and chambers 104b, 122, and 108b under a vacuum. When a vacuum is applied to the tank assembly 102, dry bulk material can be loaded into the first compartment 124. When the tank assembly 102 is unloaded, pressure can be applied to help remove a load of dry bulk material from the first compartment 124.Simultaneously placing chambers 104b, 122, and 108b and the first compartment 124 under vacuum helps reduce some of the stress and deformation at the joints between the various sections of the tank assembly 202, thereby increasing the service life of the tank assembly 202. As with the air piping system 126, activating the air piping system 226 (by pressurizing the first and second compartments 124 and 125 or creating a vacuum in them) tends to reduce relative movement between the component parts of the tank assembly 202 (or trailer 200). This also helps extend the service life of the tank 202. The air piping system 226 includes a plurality of different tubes, hoses, lines, and valves (as discussed later). As discussed with reference to trailer 100, the second compartment 125 is also part of the air piping system 226. The air piping system 226 can be selectively connected to a pressurized air source or to a system capable of creating a vacuum. The device to which the air piping system 226 is operationally coupled can be one and the same device used in two different ways. A suitable device is the air / pneumatic pump or compressor represented by pump “P” in Fig. 14. Pump “P” can include an air inlet port “P1” and an exhaust outlet “P”.(It is understood that any source of pressurized air or vacuum may be used to cause air to flow through the air piping system 226 or to extract air from it.) Pump “P” may be mounted on the towing vehicle or tow vehicle, on the tank assembly 202, or elsewhere, for example, the floor adjacent to the trailer 200. Pump “P” will normally be located upstream of the piping system 226 and the first compartment 124. The air / pneumatic pump or compressor “P” may be used in a first state to pressurize at least a portion of the air piping system 226. In addition, pump “P” may be used in a second state to remove air from within the trailer 200. In particular, the air piping system 226 may be coupled with the exhaust “P2” or pump “P” to provide a source of pressurized air through the air piping system 226.The air piping system 226 can, alternatively, be selectively connected to either the air inlet “P1” or the pump “P,” and when activated, the pump “P” will draw air from the trailer 200 through the air piping system 226. Any type of vacuum system can be used in place of the pump “P.” The pump “P” in Fig. 14 is to be understood as representative of any suitable system that can be used to adjust (particularly to substantially equalize) the air pressure within the first and second compartments 124, 125. The specifications of the 202 air piping system and its use will be described in more detail below. With reference to Figs. 14 to 17, the piping system 226 includes a cooling assembly 227 located near a front end 200a of the trailer 200. The cooling assembly 227 is mounted to the front end housing 104 by one or more mounting brackets 227a and may include a radiator-type member with a plurality of fins and one or more cooling fans mounted between the front end 200a and the radiator-type member. The cooling assembly 227 is particularly useful for cooling the air that will be injected into the first compartment 124 during unloading. The air flowing from pump “P” used to pressurize the first compartment 124 tends to be very hot. If the bulk material carried in the first compartment could be damaged by being hot (as would be the case if the bulk material load consists of small plastic pellets, for example), then the cooling assembly 227 ensures that at least some of the heat from the “P” pump is, at least some, extracted before coming into contact with the bulk material. An air inlet pipe 228 is operatively coupled with the cooling assembly, and a number of pipes branch off to the air inlet pipe 228 downstream of the cooling assembly 227. In particular, an upper air pipe 230, an aeration device supply pipe 242, and a discharge pipe 246 are connected to an air inlet pipe 228. A discharge valve 248 is provided on an air inlet pipe 228 at a location between where the aeration device supply pipe 242 and the discharge pipe 248 connect to the air inlet pipe 228. The aeration device hoses 244 extend between the aeration device supply pipe 242 and the aeration devices in the first, second, and third hoppers 110, 112, and 114. The aeration device supply tube 242 terminates at an end 242a close to a rear end 200b of the trailer.The discharge pipe 248 similarly terminates at an end 246a close to the rear end 200b of the trailer 200. With reference to Figs. 16A, 17A, and 17B, the portions of the air piping system 226 near the front end 200a of the trailer 200 are shown in greater detail. The upper air pipe 230 includes an upper air valve 231 located between the air inlet pipe 228 and a branch pipe 233 into which the upper air pipe 230 terminates. The branch pipe 233 is generally oriented horizontally, and the upper air pipe 230 is generally oriented vertically. The branch pipe 233 terminates in a connector pipe 232 at one end and a purge pipe 234 at the other. One end of the connector pipe 232 enters the front end housing 104 through the inlet 104c and is thus in fluid communication with the front chamber 104b. The connector tube 232 extends down from the inlet 104c and then forward to the front end 200a of the trailer 200 and finally connects to a filter 235.Filter 235 is mounted to the front end housing 104 by means of a mounting bracket 235a and can be any suitable type of filter, such as a rotary flow filter. It should be noted that filter 235 is used during the pressurization of the first compartment 124 and the second compartment during the discharge of bulk material from the first compartment 124, but is bypassed when the first compartment 124 and the second compartment are placed under vacuum during loading. The connecting tube 232 includes a valve 237 and a check valve 239. The check valve 239 is positioned in a section of the connecting tube 232 located between the valve 237 and the filter 235. An inlet tube 241 connects the connecting tube 232 at a location between the valve 237 and the check valve 239. The inlet tube 241 terminates at an end 241a. (A cap or cover may be selectively placed on end 241a when not in use.) As shown in Figs. 16A and 17B, the tube 243 extends between the filter 235 and the cooling assembly 227. As previously stated, the branch tube 233 connects to the bleed tube 234. A check valve 245 (Fig. 16A) is located in the branch tube 233 between the upper air tube 230 and the bleed tube 234. The bleed tube 234 includes a first section 234a (Fig. 16A) that extends upward from the branch tube 233 and passes through the inlet 104d defined in an upper wall of the front end housing 104 but enters the first compartment 124 (Fig. 15) of the trailer 200. Therefore, the bleed tube 234 is placed in fluid communication with the first compartment 124. A second section 234b of the bleed tube 234 extends downward from the branch tube 233 and terminates in an outlet 234c located a distance below an outer surface of the housing. front end 104 (Fig. 15). A valve 247 is located in the purge tube 234 in a position between the branched tube and the outlet 234c. An air piping system 216 further comprises a plurality of tubes, valves, check valves, etc., which are primarily used by the vacuum assembly provided in the trailer 200. The vacuum assembly includes a filter assembly 249 which is mounted by mounting brackets 249a in a rear-end housing 108 adjacent to the rear end 200b of the trailer 200. An outlet tube 251 connecting to the filter assembly 249 has a first end 251a (Fig. 15) extending through the port 108d defined in the top of the outer wall 108a of the trailer 200. The outlet tube 251 is therefore placed in fluid communication with the first compartment 124. A second end 251a of the outlet tube 251 connects to the filter assembly 249 and is therefore placed in fluid communication with it. As can be seen more clearly in Fig.16b, the second end 251a of the outlet tube 251 is connected to a lower region of the filter assembly 249. A valve is provided in the outlet tube 251 at a location adjacent to the filter assembly 249 and therefore closer to the second end 251b than the first end 251a of the outlet tube 251. A connecting tube (Fig. 16B) has a first end 255a that connects to an upper region of the filter assembly 249, subsequently extending forward and then rearward so that the connecting tube portion 255 is substantially vertically oriented. A first branched tube 257 extends outward from the connecting tube 255 and enters the rear end housing 108 of the trailer 200 through an inlet port 108c (Fig. 15). A lower region of the connecting tube 255 turns through a right angle to form a second branch tube 259 that is located a vertical distance below the first branch tube 257. The second branch tube 259 has an outlet port 255b that is located below a lower surface of the trailer rear end housing 108, as shown in Fig. 15. An emergency safety valve 261 is located between the first and second branch tubes 257, 259.If during operation the first compartment 124 and the front chamber 104b, the middle chamber 122 and the rear chamber 108b reach a predetermined critical limit, the emergency safety valve 261 will be automatically activated and moved to an open position so that air can flow into the storage chamber, the front chamber 104b, the middle chamber 122 and the rear chamber 108b through the connecting tube 255. The emergency safety valve 261 can also be operationally linked to pump “P” to shut off if valve 261 is activated. A first valve 263 is located in the connecting tube 255 between the check valve 261 and a second branch tube 259. A second valve 265 is located in the connecting tube between the first branch tube 257 and the first end 255a. A filter tube 269 extends downward from a lower portion of the filter 249. Bulk material may be drawn into the outlet tube 251 during loading and thus flow into the filter 249. This bulk material may clog the filter 249. The filter tube 269 can be used to inject air or any accumulated dust or particulate matter out of the filter 249. It should be noted that the filter 249 is only used when a vacuum is applied to the trailer 200 during a loading operation. The filter is diverted when the first compartment 124 and the second compartment (front compartment 104b, lower compartment 122 and rear compartment 108b) are pressurized. A filling tube 271 extends through the first inlet 108e in the rear end housing 108 and through the second inlet 106h defined in the rear region 114b. Consequently, a first part of the filling tube 271 is located within the first compartment 124, a second part of the filling tube 271 is located within the rear chamber 108b, and a third part of the filling tube 271 is located outside the outer surface of the trailer 200. The filling tube 271 has a first end 271a (Fig. 15) located in the first compartment 124 and a second end 271b that is located outside the outer surface of the trailer 200 (Fig. 16B). An air piping system 226 is used in the trailer 200 as follows. When it is desired to load bulk material into the first compartment 124, the vacuum assembly is used. A hose (not shown) will be connected to the second end 271b of the filling tube 271 and will also be connected to a storage container holding a quantity of bulk material to be loaded into the trailer 200. The storage container, for example, could be a vehicle. With reference to Figs. 15 and 16A, the various valves and check valves near the front end 200 and rear end 200b of trailer 200 need to be set to positions appropriate for the vacuum conditions that will be applied to trailer 200. Check valves 239 and 245 (Fig. 16A) are moved to a closed position. The closed position is indicated in Fig. 16A by an “x” placed on check valve 245. The “x” on check valve 239 is not visible in Fig. 16A due to the valve's orientation in the figure. Check valve 245 closes when trailer 200 is placed under vacuum so that bulk material cannot flow into the purge tube and the front chamber 104b and therefore accumulates in the second compartment 125.The check valve 239 also closes when the trailer 200 is placed under vacuum to ensure that bulk material cannot flow into the filter 235 or the cooling assembly 227. When the trailer 200 is also placed under vacuum, the upper air valve 231 and valve 247 also move to a closed position (indicated by the “x” on each valve). Valve 237 moves to an open position (indicated by the fact that the “x” on the valve is not shown in Fig. 16A). With reference to Fig. 16B, the first valve 263 moves to the closed position (indicated by the “x”), and the second valve 265 and valve 253 move to the open position (indicated by the absence of an “x”). As previously indicated herein, the pump “P” (Figs. 5 and 14) may be provided in the trailer 200 tank of the towing vehicle, mounted on the trailer 200 itself, or placed on the ground adjacent to the trailer 200. The pump “P” may include an air inlet “P1” and an exhaust outlet “P2”. An operator may connect the pump “P” by means of a hose (not shown) to the first end 241 of an inlet tube 241. The operator will connect the hose to an air inlet “P1” if he or she wishes to create a vacuum in the first and second compartments 124, 125, or will connect the exhaust “P2” to the pump “P” to pressurize the first and second compartments 124, 125. It should be noted that in trailer 200, the single inlet pipe 241 is used to connect the air piping system 226 to pump “P”. In state-of-the-art trailers that include an air system for pressurizing a trailer storage compartment and / or providing a vacuum therein, a pressurized air source would have to be connected to a first inlet on the trailer, and the vacuum source would have to be connected to a second inlet on the trailer. Typically, in these state-of-the-art trailers In the present invention, the first inlet would be located near one end of the trailer, and the second inlet would be located near the other end. The operator would therefore have to drag a long, heavy hose to connect it to the first inlet when the trailer needed to be pressurized and would have to remove the hose and move it to the other end of the trailer if the trailer needed to be vacuumed. In the trailer 200 according to the present disclosure, the hose can remain attached to the same single-inlet hose 241, and it is simply the valves in the trailer 200 that are changed (manually and / or automatically) to change the air piping system 226 from one that creates a vacuum in the trailer 200 to one that pressurizes the trailer 200. This greatly reduces the effort and time involved in loading and unloading a trailer 200 according to the present invention compared to prior art trailers. Referring to Figs. 16A and 16B, in trailer 200, the air piping system 226 can be activated to create a vacuum in the first compartment 124 for loading bulk material into it. Pump “P” is activated and begins drawing air through the inlet tube 241 and out of its first end 241a. The movement of air in the direction of arrow “B” through the inlet tube 241 causes air to be drawn through the connecting tube 232, thus drawing air out of the front chamber 104b of trailer 200. As the air flows out of the front chamber 104b through the connecting tube 232, it is drawn through the second compartment 125 created by the front chamber 104b, the intermediate chamber 122, and the rear chamber 108b. This air flowing through the second compartment 125 is indicated by the arrows “C” in Figs. 16A and 16B and in Fig. 15. Referring to Fig. 16B, as air flows out of the rear chamber 108b and into the intermediate chamber 122 into the front chamber 104b, air is drawn through the first branched tube 257 and a connecting tube 255 downwards in the direction of arrow “D”. This air flows through the connecting tube 255, drawing air through the filter 249 in the direction of arrow “D”, which draws air into the lower region of the filter 249 from the outlet pipe 251. The air is drawn through the outlet pipe 251 in the direction of arrow “I” and causes air to be drawn out of the first compartment 124 through the first end 251a in the direction of arrow “F” (Fig. 15). Continued operation of pump “P” will begin to evacuate all the air from the first compartment 124, establishing a vacuum condition within it.It should be noted that at the point of a vacuum condition existing in the first compartment 124, a substantially similar vacuum condition is also created simultaneously in the second compartment 125. Thus, the air pressure on the side of the common wall separating the first compartment 124 from the second compartment 125 is substantially the same. Because of this, there is relatively little movement between the various components that make up the trailer 200 and very little stress or strain placed on these components during the bulk material loading operation described below. Furthermore, due to the reduction in stress, strain, and movement, the thickness of the walls that will join and define the first compartment 124 and the second compartment 125 can be made from a thinner metal than would be required if the second compartment 125 were not to be vacuum-sealed along with the first compartment 124. Furthermore, it should be noted that the movement of valves 253 and 263 between the closed and open positions is preferably automated. Operation of valves 253 and 263 may be desirable due to the height at which these two valves are positioned on trailer 200. It is understood that valves 253 and 263 may, however, be manually controlled by the operator. The operator does not need to climb onto the trailer to switch these valves between the open and closed positions. A handheld controller may be provided to the operator when they can electrically operate valves 253 and 263, and one or more of the other valves on trailer 200. If valves 253 and 263 open automatically, when pump “P” is activated to create a vacuum condition within the first compartment 124, and as air is drawn through connecting tube 255 in the direction of arrow “D” and contacts valve 265, valve 265 will automatically move to the open position. This movement of valve 265 may automatically activate the opening of valve 253. Alternatively, the movement of air as it is drawn out of outlet tube 251 and into filter 249 may cause valve 253 to automatically move to the open position. (Similarly, when trailer 200 is pressurized during unloading as described later, as air flows in the opposite direction to arrow “D” and contacts valve 265, valve 265 may move to the closed position, and valve 253 may then be automatically activated to move to the closed position.)The vacuum condition in the first compartment 124 will cause air to be drawn into the first compartment 124 through the filling tube 271 in the direction of arrow “G” (Fig. 15). As previously stated, the second end 271b of the filling tube 271 is connected by a hose to a storage container holding a quantity of bulk material. As air flows through the filling tube 271 in the direction of arrow “G” to treat and neutralize the vacuum condition in the first compartment 124, the bulk material is entrained in the air flowing through the hose connected to the second end 271b and drawn into the filling tube 271. The bulk material flows through the filling tube 271 and is deposited into the first compartment 124.As the first compartment 124 fills with bulk material, the vacuum pressure in the fill tube 271 drops to the point where no more bulk material is drawn into the fill tube 271. Because the trailer 200 is not traveling under vacuum, the first valve 263 moves to the open position. This allows air to flow back to the connecting tube 255 and, consequently, into the first compartment 124 and the second compartment (i.e., the rear chamber 108b, the middle chamber 122, and the front chamber 104b). Pump “P” will also shut off, and all the various valves and check valves will move to a position that prevents bulk material from escaping the first compartment 124 or contaminants from entering the second compartment. In some embodiments, such as those illustrated in Fig. 17C, the trailer 200 can be provided with more than one filling tube 271. Fig. 17C shows two filling tubes 271 extending into the first compartment 124, each having a first end 271a located within the first compartment 124. Each of the two filling tubes has a second end 271b that can be selectively connected by means of a hose to a storage basket containing a quantity of bulk material. The difference between the two filling tubes 271 is that one of the filling tubes is larger than the other. The difference between the two lengths is related to how far each of the filling tubes 271,271 is located within the first compartment 124. Fig. 15 shows one of the tubes 271 where the first end 271a of it is located closer to the front end 200a of the trailer 200 than to the rear end 200b of it.It is understood that the second filling tube 271 may have its first end 271a located closer to the rear end 200b of the trailer 200 than to its front end 200a. This difference in the location of the first end 271a within the first compartment 124 helps ensure faster and easier loading of the first compartment 124. The longer filling tube 271 has its first end 271a closer to the front end 200a of the first compartment 124. The operator will then move the hose connecting the trailer 200 to the storage basket to the second, shorter filling tube 271 and subsequently load the rear region of the first compartment 124. This method helps to progressively fill the first compartment 124 in a way that tends to reduce the likelihood of a drop in vacuum pressure during loading.If the vacuum pressure falls below a certain level, the airflow through the filling tube(s) 271 may be insufficient to draw the bulk material from the storage basket or to move the bulk material through the filling tube(s) 271. It should be noted that if the filter 249 becomes clogged, the vacuum pressure may drop to a point where loading through the filling tube 271 slows or stops. The filter 249 must be cleaned regularly to ensure that sufficient vacuum pressure is available to load the first compartment 124 with bulk material. When trailer 200 reaches its destination and it is time to unload the bulk material from trailer 200, both the first compartment 124 and the second compartment are pressurized in a similar manner to what has been described with respect to trailer 100. With reference to Fig. 16B, valves 253 and 263 are moved to the closed position to allow pressurization of the first compartment 124, front chamber 104b, middle chamber 122, and rear chamber 108b. Referring to Fig. 17A, check valves 239 and 245 are moved to the open position. The upper air valve is moved to the open position, and valves 237 and 247 are moved to the closed position (as indicated by the “x”). Note that check valve 245 opens when the upper air valve 231 opens to allow air to flow into purge tube 234 but bulk material cannot move in the opposite direction. A pump is connected to the first end 241a of the inlet tube 241. Air flows from the pump “P” in the inlet tube 241 in the direction of arrow “Ή”. From the inlet tube 241, the air flows through the check valve 239, through the filter 235, through the tube 243, through the cooling assembly 227, and into the discharge tube 228. The air flows through the discharge tube 228, and when the air reaches the upper air tube, some of the air flows into the upper air tube 230 and some flows through the discharge tube 228. The airflow in the upper air tube 230 is indicated by arrow “I”. The airflow “Ί” splits where the upper air tube 230 connects to the branch tube 233, and some air flows through the branch tube 233 and into the connecting tube 232.Since valve 237 closes, air flows upwards through connecting tube 232 and into the front chamber 104b and subsequently into the middle chamber 122 and the rear chamber 108b. Air flows through branched tube 233, through check valve 245 and into purge tube 234a. The air flowing into the first compartment 124 of purge tube 234 applies pressure to the dry bulk material carried in the first compartment 124, forcing the material down into the first, second, and third hoppers 110, 112, 114. The valve 248 (Fig. 14) in the discharge pipe 228 can initially be placed in a closed position so that air flowing through the discharge pipe 228, past the upper air pipe 230, will be diverted into the supply pipe of the aeration device 242, through the aeration device hoses 244, and into the aeration device in the first, second, or third hopper 110, 112, 114 as described with respect to the trailer 100. When the valve 248 is moved to the open position, air will also flow through the discharge pipe 246, and as each valve assembly in the associated hopper 110, 112, 114 opens, bulk material will flow into the discharge pipe 246 and be entrained in the air flowing through and into a hose connected to the end 246a of the discharge pipe. 246.Once all the bulk material has been unloaded from the first pressurized compartment 124, valve 247 is opened so that the first compartment 124 and the second compartment will be depressurized and return to atmospheric pressure. It has been disclosed herein that the second compartment comprises front chamber 104b of the front end housing 104; intermediate chamber 122 (and 122a) and rear chamber 108b of the rear end housing 108, which are in fluid communication with each other and all are pressurized or evacuated when the first cargo compartment is pressurized or evacuated. However, in other embodiments, a partition wall is provided between front chamber 104b and intermediate chamber 122 and / or between rear chamber 108b and intermediate chamber 122, and only one or two of chambers 104b, intermediate chamber 122 (with 122a), or rear chamber 108b can be pressurized or evacuated with the first compartment. Furthermore, it is contemplated that in other embodiments, additional chambers or compartments may be provided on the outside of the first compartment, and these additional chambers or compartments may be pressurized in one embodiment or vacuum-sealed in another. It is further contemplated that, in other examples, the second, first compartment may comprise a layer of sheet material applied substantially around the entire outer surface of the wall defining the first compartment, so that a gap is formed between the sheet material layer and the wall defining the first compartment. Pressurized air may be pumped into the gap in one embodiment, and a vacuum may be applied to the gap in other embodiments.In this example, the wall surrounding the entire first compartment (except for the access openings and inlets) may have substantially similar or substantially equal pressure or substantially similar or substantially equal vacuum applied to both sides of the wall, and the wall will therefore be under substantially constant pressure. It shall be understood that the terms “substantially similar” and “substantially equal” are used herein as representing a state where the air being pressurized in the first and second compartments tends to move as close as physically possible to the same pressure or vacuum state. In the preceding description, certain terms have been used for brevity, clarity, and understanding. Unnecessary limitations should not be inferred from prior art requirements because these terms are used for descriptive purposes and are intended to be interpreted generally. Furthermore, the description and illustration of the preferred embodiment of the disclosure are an example and the disclosure is not limited to the exact details shown or described.

Claims

1. A dry bulk cargo tank for carrying a load; said dry bulk cargo tank comprises: a tank assembly; a first compartment defined in the tank assembly, said first compartment being adapted to carry a load of bulk material therein; a discharge system selectively placed in communication with the first compartment for conveying the load of bulk material out of the first compartment; and an air piping system provided in the tank assembly;characterized in that the air piping system includes a duct extending from a near front end of the tank assembly to a near rear end of the tank assembly, wherein the duct is located immediately below the first compartment, and is sealed from the air surrounding the tank assembly, and wherein the duct is selectively placed in fluid communication with the first compartment during loading of bulk material into the first compartment and during unloading of bulk material from the first compartment.

2. The dry bulk cargo tank as defined in claim 1, characterized in that the conduit and the first compartment are adjacent to each other.

3. The dry bulk cargo tank as defined in claim 1, characterized in that the conduit and the first compartment share at least one common wall.

4. The dry bulk cargo tank as defined in claim 1, characterized in that the first compartment and conduit are in fluid communication with each other.

5. The dry bulk cargo tank as defined in claim 1, characterized in that the conduit is separated from the first compartment so that none of the bulk materials are received into the conduit at any time.

6. The dry bulk cargo tank as defined in claim 1, characterized in that the duct selectively permits air to flow through it when the bulk material is loaded into the first compartment; and the duct permits air to flow through it in a second direction when the bulk material is removed from the first compartment.

7. The dry bulk cargo tank as defined in claim 1 further comprises a device for pressurizing the air in the first compartment; and when the first compartment is pressurized by the device, the duct is simultaneously placed under the same air pressure as the first compartment by the device.

8. The dry bulk cargo tank as defined in claim 1 further comprises a device for creating a vacuum in the first compartment; and when the first compartment is placed under vacuum by the device, the conduit is also simultaneously placed under vacuum by the device.

9. A dry bulk cargo tank for carrying a load; said dry bulk cargo tank comprises: a tank assembly; a first compartment defined in the tank assembly, said first compartment being adapted to carry a load of bulk material therein; an air piping system provided in the tank assembly; characterized in that the air piping system includes a duct extending from a near front end of the tank assembly to a near rear end of the tank assembly immediately below the first compartment; said duct being sealed from the air surrounding the tank assembly; and wherein the duct selectively permits air to flow through it when bulk material is loaded into the first compartment; and the duct permits air to flow through it in a second direction when the bulk material is removed from the first compartment. 100 10. The dry bulk cargo tank as defined in claim 9, characterized in that the air piping system includes a first filter that is used when the air piping system pressurizes each of the first compartment and the duct; and wherein the first filter is bypassed when the air piping system creates a vacuum in each of the first compartments and the duct.

11. The dry bulk cargo tank as defined in claim 10, characterized in that the air piping system further includes a second filter and the second filter is used when the air piping system creates a vacuum in each of the first compartment and the duct; and wherein the second filter is bypassed when the air piping system pressurizes each of the first compartment and the duct.

12. The dry bulk cargo tank as defined in claim 9 further comprises a cooling system that is used when the air piping system pressurizes each of the first compartment and the duct.

13. A dry bulk cargo tank for carrying a load; said dry bulk cargo tank comprises: a tank assembly; a first compartment defined in the tank assembly, said first compartment being adapted to carry a load of bulk material therein; an air piping system provided in the tank assembly; characterized in that the air piping system includes a duct extending from a near front end of the tank assembly to a near rear end of the tank assembly immediately below the first compartment; said duct being sealed from the air surrounding the tank assembly; and a device for pressurizing the air in the first compartment; and when the first compartment is pressurized by the device, the duct is simultaneously brought under the same air pressure as the first compartment by the device.

14. The dry bulk cargo tank as defined in claim 13, characterized in that the air piping system includes a first filter that is used when the air piping system pressurizes each of the first compartment and the duct; and wherein the first filter is bypassed when the air piping system creates a vacuum in each of the first compartment and the duct.

15. The dry bulk cargo tank as defined in claim 14 further comprises a cooling system employed when the air piping system pressurizes each of the first compartment and the conduit. 102 16. A dry bulk cargo tank for carrying a load; said dry bulk cargo tank comprises: a tank assembly; a first compartment defined in the tank assembly, said first compartment being adapted to carry a load of bulk material therein; an air piping system provided in the tank assembly; characterized in that the air piping system includes a duct extending from a near front end of the tank assembly to a near rear end of the tank assembly immediately below the first compartment; said duct being sealed from the air surrounding the tank assembly; and a device for creating a vacuum in the first compartment; and when the first compartment is placed under a vacuum by the device, the duct is also simultaneously placed under a vacuum by the device.

17. The dry bulk cargo tank as defined in claim 16, characterized in that the air piping system includes a second filter that is used when the air piping system creates a vacuum in each of the first compartment and the duct; and wherein the second filter is bypassed when the air piping system pressurizes each of the first compartment and the duct.

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