VACUUM PUMP

Description

"VACUUM PUMP" On behalf of GREENBERG,. Dan 27206 ISRAEL EL / 109 ****** SECTOR OF INVENTION This invention relates to vacuum pumps. More particularly, the invention relates to a hybrid ejector vacuum pump containing multiple nozzles arranged to achieve high evacuation rates and to operate at high efficiency. '' . W99 4qo BACKGROUND OF THE INVENTION r * 0 Vacuum pumps are widely used in industry, for material processing and transportation, research, medical, and even agricultural purposes. The required vacuum level determines the type of pump that is best suited. Conventional vacuum pumps are typically driven by an electric motor or an internal combustion engine. The three most common types are the centrifugal compressor, the vane pump, and the plunger pump. Ejector type pumps are used to produce single-stage absolute air pressures of 60 mm Hg and a double-stage of 10 mm. Multiple stages can be combined, but for the very high vacuum required for applications such as vacuum-coated optical parts or vacuum-deposited thin films for microminiaturization, other types of pumps, such as rotary oil-sealed pumps or fusion pumps, are more suitable. A commercially available hybrid combination, for example a vapor / liquid circuit pump, may prove to be the best choice for some applications. Vacuum pumps are the most effective when They are positioned as close as possible to their intended use to avoid long connecting hoses that need to be evacuated each time the vacuum is used. For example, when vacuum is used with a robot for material processing tasks, the pump is preferably positioned on the robot's arm. However, the robot's arm movements are slowed, or even hindered, if a heavy load is attached to that arm. Consequently, it is advantageous for vacuum pumps for this purpose to be compact and lightweight. Many conventional vacuum pumps, which have metal bodies and connected electric motors, are poorly suited for this purpose. Ejector pumps, formerly known as jet pumps, operate on Bernoulli's principle, using a nozzle that discharges a high-velocity gas flow through a suction chamber connected to the device to be evacuated. The gas to be evacuated is entrained by a high-pressure gas and transported to a Venturi diffuser, which converts the velocity energy of the high-pressure gas into pressure energy. Any available pressurized gas can be used as a power source, but in practice gas Both steam and air are used. Ejector pumps have attractive advantages over other types in that they have no moving parts, and have low investment and maintenance costs. The disadvantages are higher energy costs; and although air is free, compressed air can be expensive in terms of electricity. Noise can also be a problem, although a suitably sized silencer mounted on the exhaust opening can reduce this to an acceptable level. Vacuum pumps of any type, including The ejector type can be connected in series to obtain a higher vacuum or in parallel to reach the required vacuum more quickly. The two connection types can be combined to produce a series-parallel pump configuration. Multi-stage ejectors have advantages in terms of efficiency and lower noise levels. Multi-stage ejectors produce a higher vacuum flow rate relative to the compressed air consumption, as opposed to single-stage pumps, which consume more compressed air than is extracted in the vacuum evacuation achieved. The noise levels of multi-stage ejectors ' i ! | Multi-stage units are in the 55 to 75 dBA range, usually not requiring a muffler, when compared to the typical 90 dBA expected for single-stage ejectors which require a muffler to be fitted. U.S. Patent No. 4,696,624, the present inventor, discloses a method of manufacturing an ejector apparatus in which a plurality of ejector units, each arranged in a common housing, has an inlet chamber. The apparatus is of the series-parallel type and has flap valves that allow air to pass from one chamber to the next. Such an apparatus is described and claimed by Basto in a previous U.S. Patent No. 4,880,358. The optimal nozzle geometry is primarily a function of the nozzle air, the engine gas pressure, and the Venturi throat; additional factors of secondary importance also impact the result. It is clear that the optimal desired nozzle geometry will vary as the pump progresses in evacuating a chamber. When starting the ejector pump, it is expected to rapidly remove large quantities of gas against a small resistance. ' j While toward the end of its operation, the pump must remove small amounts of gas against a much higher resistance. Optimizing the ejector nozzle for any given situation requires energy in the form of compressed motive gas, which is consumed both at the beginning of pumping and toward the end, since the nozzle shape and dimensions cannot adapt to the varying operating conditions. This problem was highlighted by Teli, who proposed in U.S. Patent No. 5,205,717 a method for achieving a desired underpressure in the shortest possible time and with the least energy use, using at least two ejectors operating with compressed air. Ejectors are connected to operate one at a time depending on which of them is supplied with compressed air. The compressed air supply is controlled by the vacuum in a collection chamber common to all ejectors. An ejector arrangement for the method includes at least two nozzles, each with optimal efficiency at a different compressed air supply level. A sensor measures the underpressure in the common chamber and directs compressed air to one ejector at a time in response to the measured underpressure. During operation, the ejector that performs best when evacuating large volumes receives compressed air first, and the nozzle that performs best when evacuation pressure is low receives compressed air last. A commercially available range of ejector-type vacuum pumps is marketed by PIAB. The lowest claimed vacuum that can be achieved is between 5 and 100 millibars, depending on the model chosen. The disadvantages of prior art ejector pumps is that the efficiency is deteriorated by the transfer of air into the intermediate chambers, i.e. gradually, between the two parallel air flows, one One is optimized for low-resistance, high-volume pumping, while the other is designed for high-resistance, low-volume pumping. This unwanted air transfer is made possible by using a common intermediate chamber for the two air flows. It is therefore one of the objects of the present invention to overcome the disadvantages of prior art ejector pumps and to provide a pump that operates more effectively both at the beginning and towards the end of vacuum exhaustion. SUMMARY OF THE INVENTION THE The present invention achieves the above-mentioned objects by providing a vacuum pump operating with compressed air of the ejector type, comprising a housing having an inlet for the compressed air, a second inlet connectable to the device to be evacuated, and an exhaust outlet, said incoming compressed air being divided into at least two parallel flows by means of a multiple-exit chamber, each flow of compressed air passing through at least two nozzles arranged in series, the intermediate chambers between the successive nozzles of each parallel flow being provided separately for each flow, the valves operating at pressure being provided to automatically prevent the flow of gas to be evacuated in any of said nozzles as progress is made in producing the desired vacuum, and thereby increasing the flow of air in the remaining nozzles to obtain a high vacuum, the pump being characterized by the use of a single-body structure which is used to support multiple nozzles having different shapes. In a preferred embodiment of the present invention, a vacuum pump of sandwich construction is provided which comprises at least a rigid body supporting the nozzles, a flexible gasket, and a rigid body containing a gas port, said gasket being compressed between the two rigid bodies. In an even more preferred embodiment of the present invention, a vacuum pump is provided in which said pressure-operated valves are integral with the flexible gasket. It will be noted that due to its modular nature, the apparatus of the present invention can be used to provide many different combinations. Each stream can be directed through multiple parallel nozzles to increase the exhaustion rate. Several flows can be provided. parallel, each optimized for a different stage of the vacuum exhaustion process. Only a few examples of the many possible combinations will be described below. Pressure sensors, such as those described by Teli, are not required, since the flexible flap valves automatically direct the incoming air from the area to be evacuated to the intermediate chamber operating at a sub-pressure appropriate to the current exhaustion stage. The invention will now be further described with reference to the accompanying drawings, which represent, for example, preferred embodiments of the invention. Structural details are shown only to the extent necessary for a fundamental understanding thereof. The examples described, together with the drawings, will make it clear to those skilled in the art how further embodiments can be realized. of the invention. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a top view of a preferred embodiment of the pump according to the invention; FIG. 2 is a side sectional view showing the sandwich construction of the pump; FIG. 3 is a top view of a gasket with integral valves; FIG. 4 is a top view of an intermediate plate with four gas openings; FIG. 5 is a top view of a sealed pump gasket; FIG. 6 is a top view of a body containing the pump; FIG. 7 is a top view of a pump system having multiple parallel nozzles; FIG. 8 is an end section view of a plate equipped with mushroom-type valves; * 1 FIG. 9 is a top view of the same implementation; and FIGS. 10 is like FIG. 9 but has a one-way valve; DESCRIPTION OF PREFERRED ACTUATIONS In FIG. 1 you can see a vacuum pump 10 that works with compressed air, ejector type. The pump case has two main components 12,. and 14 seen in FIG. 2. Both are advantageously made of plastic to produce a "light weight" pump. The pump has two inputs, a first input 16 for the compressed air seen in the upper part of the figure, and a second input 18 connectable to the appliance that needs to be evacuated, see in FIG. 2. A single screw drain outlet 20 self-threaded, also seen in FIG. 2, serves to exhaust all incoming gases; a silencer can be fitted if required. The incoming compressed air is divided into two parallel flows by a multiple-exit chamber 22. Each compressed air flow then passes through three nozzles 24 - 34 arranged in series, each air jet passing through successively larger nozzles. The intermediate chambers 36, 38, 40, 42 between the successive nozzles of each parallel flow are provided separately for each. f flow, drawing the gas to be evacuated from each chamber. The separating walls 44, 46 between the adjacent vacuum chambers prevent the flow of gas between the intermediate chambers. The pressure-operated flap valves 48, 50 seen in FIG. 2 are designed to automatically prevent the flow of gas to be evacuated at some nozzles as the desired vacuum is achieved. This results in a stronger flow of air at the remaining nozzles to achieve a high vacuum. The pump is characterized by the use of a single body structure 12 which is used to support the Multiple nozzles 24-34 with different shapes. The same pump body can be used to support nozzles with different geometries. With reference to the remaining part of the figures, similar reference numbers have been used to identify similar parts. Referring again to FIG. 2, a vacuum pump of sandwich construction is shown. A rigid body 12 supports all nozzles 24 - 34, as well as the compressed air inlet 16. A first flexible seal 52, a rigid body 54 containing gas openings 56, and a second seal 58 the ( flexible are compressed between two rigid bodies 12, 14 comprising the mass of the pump. It can be seen in the figure that the nozzles 24 - 34 are supported in the rigid body 12, while the collector hole 60 appears in the second rigid body 14. This separation of functions contributes to the flexibility of the design configuration, so that different nozzle arrangements can be used without the need to change the collector. The second rigid body 14 comprises the inlet 18 from the chamber to be evacuated, and in this embodiment also the air outlet 20. FIG. 3 illustrates a flexible pump seal for vacuum described with reference to FIG. 2. Three valves operating at pressure 48, t50 are integral with the flexible gasket, the opening 62 allows the gas to be vented. The opening 64 allows free entry of gas from the chamber to be evacuated. The holes 66 in the four corners allow passage for the fastening devices 68 shown in FIG. 2 which pass through the entire pump. In FIG. 4 is seen an intermediate plate 54 which when assembled is adjacent to the gasket shown in FIG. 3. The plate carries four gas openings 56, some of which are * i J sealed with valves 48, 50 until the pressure in the intermediate chambers 36 - 42 seen in FIG. 1 drops below predetermined levels towards the end of the evacuation process. Referring now to FIG. 5, where a sealing gasket 52 is drawn which when assembled with FIG. 2, is arranged between the container 14 which contains the inlet 18 from the chamber to be evacuated and the plate 54 shown in FIG. 4. Where large quantities of pumps are to be produced in a single configuration, the intermediate plate shown in FIG. 4 is combined with the rigid body with the vacuum inlet and sealing gasket 52 of the present invention. figure is then eliminated. FIG. 6 shows a second rigid housing body 70 that includes the inlet 18 from the chamber to be evacuated. However, the body 70 does not have an air exhaust. Contrary to the object of FIG. 2, the present embodiment is used in conjunction with a first rigid housing body that contains the valves and has an air exhaust outlet. FIG. 7 illustrates an arrangement 72 for the exemplary pump that uses multiple parallel nozzles 74, 76, 78 to increase the rate of vacuum attainment. The intermediate chambers 80, 82 < using three nozzles are each served by a single valve 48 of the type shown in FIG. 3. An additional line of nozzles 84, 86, 88 are configured for the final stage of achieving vacuum when small amounts of gas are withdrawn against high resistance. Thus it is seen that the capacity can be increased without increasing the number of valves. If it is desired to increase the number of parallel nozzles even later, the rigid housing 90 can either be thickened, or an additional body added, to accommodate additional nozzle lines without any increase in the number of valves. In FIGS. 8 and 9, flexible inlet valves 92 are provided which operate at a pressure of a type different from that previously described, and which may be used in place of the valves 48, 50 shown in FIG. 3. The flexible inlet valves 92 are poppet-type valves added to the rigid base plate 94. When the valve 92 opens, gas passes through the openings 96. The valves 92 may be made of different sizes from each other or of different materials, such that one valve will open at a higher pressure than a second valve attached to the same plate. The opening 64 permits free entry of gas from the chamber to be evacuated. FIG. 10 shows a detail of a vacuum pump 98 similar to that of FIG. 9 but additionally including a one-way valve 100 in fluid communication with the second inlet 18. The one-way valve 100 prevents re-entry of gas from the evacuated chamber when pumping is stopped. The scope of the invention described is to encompass all objects that fall within the meaning of the following claims. The following examples illustrate useful forms of the invention, but are not to be considered as limiting its scope. since those skilled in the art will immediately realize that additional variations and modifications of the invention can be formulated without departing from the meaning of the following claims.

Claims

CLAIMS 1. In a compressed air-operated vacuum pump of the ejector type, comprising a housing having a compressed air inlet, a second inlet connectable to the vessel to be evacuated, and a discharge outlet, said compressed air output being divided into at least two parallel flows by means of a multiple outlet chamber, each flow of compressed air passing through at least two nozzles arranged in series, the intermediate chambers between the successive nozzles of each parallel flow being provided separately for each flow, pressure-operated valves being provided to automatically prevent the flow of gas from being evacuated to some of said nozzles as progress is made in producing the desired vacuum, and thus increase the air flow of the remaining nozzles to obtain a high vacuum, the pump being characterized by the use of a single-body structure which is used to support multiple nozzles having different shapes.

2. The vacuum pump as claimed in claim 1, wherein said pump is of the multi-ejector type.

3. The vacuum pump as claimed in the Claim 1, wherein said pump is of sandwich construction comprising at least one rigid body containing said nozzles, and a flexible gasket, and a rigid body containing a gas opening, said gasket being compressed between the two said rigid bodies.

4. The vacuum pump as claimed in claims 1 to 3, wherein said pressure-operated valves are integral with said flexible gasket.

5. The vacuum pump as claimed in claims 1 to 4, wherein the inlet opening and the outlet opening are on the same side.

6. The vacuum pump as claimed in claims 1 to 5, further comprising a single outlet valve in fluid communication with said second inlet.

7. The vacuum pump as claimed in claims 1 to 6, wherein said rigid bodies are made of a plastic to produce a low weight pump.

8. The vacuum pump as claimed in claims 1 to 7, wherein each row of chambers may be of one or more flows.

9. Vacuum pump as claimed in the claims 1 to 8, wherein all the nozzles are the same as or different from the nozzles in the other row of chambers.

10. The vacuum pump as claimed in claims 1 to 9, wherein said rigid bodies are made of plastic integral with one or more nozzles to produce a low weight pump.

11. The vacuum pump as claimed in claims 1 to 11, wherein the outlet opening is integral with the nozzle container. • 12. The vacuum pump as claimed in claims 1 to 11, wherein said pressure-operated valves are separated by the gasket.

13. The vacuum pump as claimed in claims 1 to 12, wherein said vacuum pump body and said vacuum chamber are in one piece.

14. A vacuum pump, substantially as described above and with reference to the accompanying drawings. With Lor spa