LIQUID DISPENSING SYSTEM WITH LIQUID CONTROL PISTONS OPERATED BY PRESSURIZED AIR.

Abstract

A modular liquid dispensing system in which each module has a module body, a spray nozzle, and a piston to control the dispensing of liquid from the nozzle. Each module has a pneumatically operated system to move the piston to an open position while also facilitating a faster return movement to a closed position, allowing for the precise dispensing of small quantities of highly viscous liquids.

Description

LIQUID DISPENSING SYSTEM WITH AIR-OPERATED LIQUID CONTROL PISTONS CROSS REFERENCE TO RELATED APPLICATIONS This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 076.001, filed September 9, 2020, which is incorporated by reference. FIELD OF INVENTION The present invention relates to liquid dispensing systems and, more particularly, to liquid dispensing systems having nozzles for dispensing small, controlled quantities of highly viscous liquids. BACKGROUND OF THE INVENTION In many industries, there is a need to dispense small, controlled quantities of highly viscous liquids. In the food industry, for example, in commercial pizza production, it is necessary to dispense small droplet-sized amounts of sauce onto the pizza dough. Due to the thick nature of the sauce, it is difficult to quickly dispense the tightly controlled small droplets of liquid as desired. Furthermore, if the sauce contains solids that can clog the nozzle passages, the flow passages must be larger, which further complicates the control of the small droplet dispensing and often results in undesirable splashing of the dispensed sauce. Additionally, when the dispensing device uses an air-driven liquid control piston, the piston's rapid operation is limited by the compressibility of the control air.Furthermore, when air-operated devices are spring-returned, the return force of the springs can be limited to approximately half the air pressure force used to open the device, which resists the rapid closing of the piston. OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION It is an object of the invention to provide a liquid dispensing system having effective spray nozzles for accurately dispensing controlled small droplet-size quantities of highly viscous liquid. Another objective is to provide a liquid dispensing system as characterized above that is effective in rapidly and accurately depositing controlled pixel-sized droplets without undesirable splashing of the liquid. Another objective is to provide a liquid dispensing system of the above type in which the spray nozzles can operate with larger inlet conduits, less susceptible to clogging by solids content in the liquid. Another objective is to provide a liquid dispensing system of this type that can selectively dispense precisely controlled small drops of different sizes. Another objective is to provide a liquid dispensing system of this type that can operate more quickly. Another objective is to provide a liquid dispensing system of such a type as having air-driven pistons with return springs whose function is less resistant to the air pressures used in the operation of the system. Yet another objective is to provide a liquid dispensing system of the above type that is of relatively simple design and lends itself to economical manufacturing and efficient use. Other objects and advantages of the invention will become apparent from reading the following detailed description and from referring to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a fragmentary perspective of an illustrative modular liquid dispensing system according to the invention; FIGURE 2 is a perspective view of the fully assembled liquid dispensing system; FIGURE 3 is a vertical section of one of the liquid dispensing modules of the illustrated liquid dispensing system; FIGURE 4 is an enlarged vertical section of the central liquid control piston assembly of the liquid dispensing modules shown in FIG. 3; FIGURE 5 is an enlarged, vertical section perspective of the spray nozzle assembly of one of the liquid dispensing modules of the illustrated system; FIGURE 6 is a vertical section of the spray nozzle assembly shown in FIGURE 5; FIGURE 7 is an exploded view of the spray nozzle assembly shown in FIGURES 5 and 6; and FIGURE 8 is a schematic representation of a solenoid control valve associated with each respective liquid dispensing module. While the invention is susceptible to various modifications and alternative constructions, a certain illustrative embodiment thereof has been shown in the drawings and will be described in detail below. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but rather, the intention is to cover all modifications, alternative constructions, and equivalents that fall within the spirit and scope of the invention. ΙνΙΛ / c / zuzó / uóo zoz DETAILED DESCRIPTION OF THE PREFERRED MODALITY Referring now more specifically to FIGURES 1 to 3 of the drawings, an illustrative liquid dispensing system 10 according to the invention is shown. The illustrated liquid dispensing system 10 has the form of a modular valve manifold 11 comprising a plurality of individual liquid dispensing modules 12 supported and retained in a sealed side-by-side stacking relationship between end blocks 13 and 14 at opposite ends secured together by tie rods / connecting bars 15 and nuts 16.Each module 12 includes a module 20 nozzle support body formed with a liquid supply port 21 arranged in aligned relation to the liquid supply ports 21 of adjacent modules 12 to define a common liquid supply conduit 22 that communicates between a liquid inlet port 23 in the upstream end block 13 and a liquid outlet port 24 in the downstream end block 14. Thus, the liquid directed to the inlet 23 communicates through each of the stacked modules 12. Each illustrated module 12 has a respective spray nozzle 30 mounted in dependent relation to a lower side of the module nozzle support body 20, which has an upstream liquid inlet 31 on an upper side communicating with the liquid supply conduit 22. To control the liquid from the common liquid supply conduit 22 to the spray nozzle inlet 31 of module 12, a piston 32 is supported in each module body 20 above the spray nozzle inlet 31 for reciprocating movement between an open, raised inlet position and a closed, lowered inlet position. Each piston 32 in this case is supported for selective relative motion in a carrier 33 mounted in a sealed relationship within a vertical opening 34 of the respective module body 20 with a downstream end of the piston 32 extending through the liquid supply conduit 22 for coupling with the spray nozzle inlet 31. To deflect the piston 32 into a lowered position by closing the spray nozzle inlet 31, a return spring 35 is disposed within a spring chamber 36 of the module body 20 in an interposed relationship between a piston head 32a of the piston 32 and a retaining sleeve 37 secured within an upper end of the body opening 34 and retained by a retaining cap 38 threaded within an upper end of the body opening 34.The retaining sleeve 37 in this case extends downward around the return spring 35 and the piston head 32a, as best represented in FIGURES 3 and 4. The spring retaining sleeve 37 and the module 20 body opening 34 in this case define an annular airflow duct 40 (FIGURE 3) around the retaining sleeve 37 that communicates with and through the spring chamber 36 by means of circumferentially offset holes 41 in the spring retaining sleeve 37. A sealed piston chamber 42 is defined between the opposite ends of the piston head shaft 32a and the carrier 42 (FIGURE 4). According to an important feature of this embodiment, each module body has a pressurized air duct system controlled by a respective valve, such that the pressurized air that moves the piston to an open position also accelerates the piston's movement to closure. In the illustrated embodiment, the operation of the piston 32 of each module 12 between the open and closed positions is controlled by a respective solenoid valve 43, as best represented in FIGURES 3 and 8. Each module solenoid valve 43 is attached to its respective module body 20 with a solenoid mounting block 44, which is mounted in a sealed relationship with its respective module body 20 by screws 45.Each module 20 body has an air supply port 50 aligned with the air supply port 50 of each adjacent module body to define a common air inlet duct that communicates with a system air inlet port 51 in the end block 14. The module 20 bodies also each have an air outlet port 52 aligned to define a common outlet air duct that communicates with a system exhaust outlet port 53 at the end 14. The air supply port 50 of the module 20 body communicates via inlet air ducts 63, 63a in the module 20 body and solenoid mounting block 44 to an air inlet port 55a of the solenoid valve 43.The air outlet port 52 of the module body 20 communicates via outlet conduit 60 with the return spring chamber 36 through holes 41 in the retaining sleeve 37 and the annular conduit 40 around the sleeve 37, and outlet conduits 61, 61a in the module body 20 and solenoid mounting block 44 with an exhaust port 55b of the solenoid valve 43. The piston chamber 42 communicates via working conduits 62, 62a in the module body 20 and solenoid mounting block 44 with a working port 55c of the solenoid control valve 43. When solenoid valve 43 is in its neutral or unenergized state, the inlet pressure at the air inlet port of solenoid valve 55a is blocked by a stem-shaped mechanism 43 of solenoid valve 43 (FIGURE 8), preventing pressurized air at the air supply port 50 of module body 20 from communicating with the piston chamber 42 through conduits 62a and 62 in the solenoid mounting block 44 and module body 20. Additional conduit routing when solenoid valve 43 is in its neutral or unenergized state connects ports 55c and 55b of solenoid valve 43, allowing air communication between the piston chamber 42 and the outlet port 52 in module body 20 through conduits. 62, 62a in the module body 20 and the solenoid mounting block 44, the outlet conduits 61a, 61 in the solenoid mounting block 44 and the module body 20, the annular conduit 40 around through the spring 35 through the holes 41, and the outlet conduit 60 When solenoid valve 43 is energized, the solenoid switches the actuating mechanism 43a to close the exhaust port 55b, disconnecting port 55c from the atmosphere and connecting solenoid valve ports 55 and 55c. Pressurized air in the air supply port 50 of module body 20 then communicates with pressure chamber 42 through conduits 63 and 63a in module body 20 and solenoid mounting block 44, solenoid valve ports 55a and 55c, and conduits 62 and 62, causing piston 32 to move upward, opening nozzle inlet 31 and compressing return spring 35. The upward stroke of piston head 32a imparts a positive air displacement within spring chamber 36, resulting in a slight pressure increase.36 drains through holes 41 in the spring retaining sleeve 37, the annular conduit 40, the outlet conduit 60, and the air outlet port 52 to atmospheric pressure (FIGURES 3 and 4). The nozzle inlet 31 remains open, allowing fluid to flow from the common fluid supply conduit 22 through the spray nozzle 30 to the atmosphere while the solenoid is energized. When de-energized, solenoid valve 43 returns to its natural state. The inlet air pressure at solenoid port 55a is again blocked, preventing pressurized air from entering the device. The rapid decompression of pressurized air in piston chamber 42 causes a high pressure migration within passages 62 and 62a in module body 20 and solenoid mounting block 44, ports 55c and 55b of solenoid valve 43, outlet passages 61a and 61 in solenoid mounting block 44 and module body 20, spring chamber 36, outlet passage 60, and outlet port 52 as the system pressure in piston chamber 42 is released and equalizes with the atmosphere.The migrating pressure in the annular conduit 40 communicates through the holes 41 in the spring retaining sleeve 37, causing elevated pressure within the spring chamber 36 and acting on the surface area of ​​the piston head 32a within the spring chamber 36, resulting in a momentary downward force that complements the constant downward force of the return spring 35, opposing the decompression pressure in the piston chamber 42, returning the return piston 32 to its natural state, closing the conduit 31 and stopping the flow of liquid through the spray nozzle 30, from the common liquid supply conduit 22. An appreciable decrease in the time required to return the piston 32 to its natural state is attributed to the momentary increase in pressure. IVIA / c / zuzó / uóo zoz inside the spring chamber 36. All ducts and cavities downstream of the solenoid valve 43 including the spring chamber 36 intrinsically return to atmospheric pressure through an outlet port 52 effectively eliminating the complementary force to the transient pressure applied to the piston head 32a. The further operation of the liquid dispensing module 12 by re-energizing solenoid 43 is unaffected by the previous pressure increase cycles in the spring chamber 36, since the pressure increase is transient and quickly returns to atmospheric pressure. This allows the pressure increase to have the desired effect on the opening stroke of piston 32 without affecting the closing stroke of piston 32. As will become apparent, the solenoid valve 43 can be cycled at predetermined speeds for the particular dispensing operation, with the variable opening time of piston 32 providing a variable pixel volume. According to another aspect of the present embodiment, each spray nozzle module 12 is operative for dispensing small, controlled, round pixel-sized droplets of highly viscous liquid as an incidental to the piston cycle 32, even when the liquid has an appreciable solids content. Each spray nozzle 30, with particular reference to FIGURES 5, 6, and 7, in this instance comprises a nozzle body 70, a nozzle seat 71, and an internal nozzle core 72. The nozzle seat 71 in this instance has an externally threaded, cylindrical downstream end 73 that is threaded into an upstream cylindrical end 74 of the nozzle body 70 to secure the nozzle core 92 within the nozzle body 70. An upstream end 75 of the nozzle seat 71 defines the predetermined liquid inlet size 31, which is at the upstream end of the assembly.The nozzle core 72 in this case has an upstream cylindrical mounting flange 78 positioned on an annular projection 79 within the nozzle body 70 and held in place by the nozzle seat 71, although it will be appreciated that other methods can be used to secure the nozzle core 72 within the nozzle body 70. The cylindrical mounting flange 78 of the core 12 has a downstream end wall of concave configuration (relative to the fluid flow direction) 80 formed with a plurality of axially oriented, circumferentially spaced fluid orifices 81. These fluid orifices communicate between an expansion cavity 82 of the nozzle seat 71 and an annular fluid discharge conduit defined between the nozzle core 72 and the nozzle body 70 to direct the fluid in a controlled manner for optimal dispensing in the form of small droplets, as will become apparent. It is understood that while the polished nozzle 30 comprises a multi-part assembly, it could alternatively have a one-piece construction or fewer or more assembled parts. In carrying out this aspect of the present embodiment, the nozzle core 72 has a teardrop-shaped pivot 83 which, together with the inner circumferential surface of the surrounding nozzle body 70, defines an expanding discharge conduit 85 that reduces the exit velocity of the dispensed liquid to maintain a desired flow rate and a constant droplet size of the highly viscous discharge liquid. To this end, the polished pivot 83 (see FIGURES 5, 6, and 7) has a relatively small-diameter upstream end section 86 extending centrally from the mounting flange 78, a curved section extending radially outward 87 adjacent to the upstream end, and a relatively long, inwardly tapered terminal end section 90.As can be seen, the nozzle body 70 has a generally hollow cylindrical configuration, with the inner circumferential surface of the nozzle body 70 defining the outer wall of the annular discharge conduit 85 around the core section 72. The inner wall of the discharge conduit 85 is defined by the outer surface of the pivot 83. In this case, the inner circumferential surface of the nozzle body 70 includes an outwardly directed radial section 91 that extends in relation to the outwardly curved section 87 of the nozzle core 72 and a uniform diameter section 84 that then extends downstream substantially the remaining length of the pivot 83. The design is unique in that the flow through the annular discharge conduit causes the viscous fluid to expand inward as it passes through the nozzle body.The pivot geometry defines the inner diametral wall of the annular flow path while providing a structure against which a vacuum can form due to flow expansion. The deceleration of the fluid within the expanding annular discharge passage is a function of surface tension and the ability of capillary forces to generate a vacuum and resist flow. In operation, continuing with reference to FIGURE 3, when the piston 32 is in a raised open inlet position, fluid is allowed to pass in a controlled manner through the nozzle inlet 31 into the expansion cavity 82 defined within the downstream cylindrical end of the nozzle seat 71. The fluid passing through the nozzle inlet 31 is directed against an impact surface defined by the downstream concave end wall 80 of the expansion cavity 82. This causes the fluid to fill the expansion cavity 82 and then be subsequently extruded from the expansion cavity through the series of circumferentially spaced holes 81 in the discharge conduit 85. Furthermore, the size of each of the holes 81 is at least as large as the nozzle inlet 31 to allow solid particles in the fluid to flow from the expansion cavity 82 to the fluid discharge conduit 85 without obstruction.The collective area of ​​the circumferentially spaced holes 81 is greater than the area of ​​the nozzle inlet 31 such that the velocity of the liquid passing through the holes 81 is inversely proportional to the ratio of the size of the holes 81 to the size of the nozzle inlet 31. More specifically, the circumferential holes 81 at the downstream end of the expansion cavity 82 communicate with an inlet section 92 of the discharge conduit 85 that is defined between the outward-facing wall section 91 of the nozzle body 70 and the pivot 83 of the nozzle core 72. The cross-sectional area of ​​the annular inlet section 92 can increase as the section extends in the downstream direction such that the fluid velocity in this region continues to decrease as the cross-sectional area of ​​the discharge conduit expands.A slight reduction in the cross-sectional area of ​​the discharge conduit 85 in a downstream stabilizing section 93 of the discharge conduit 85 (again defined by the outer surface of the pivot 83 and the inner circumferential surface of the nozzle body 70) immediately downstream of the inlet section 92 can provide a slight pressure increase. This pressure increase stabilizes and balances the flow by eliminating individual jet streams caused by the fluid entering the inlet section 92 of the discharge conduit 85 through the series of orifices 81 and allows uniform flow along the inner wall surface of the nozzle body 70. The cross-sectional area of ​​the stabilizing section 93 remains constant across this region as the fluid gains stability. Downstream of the stabilization section 93, the fluid enters a final expansion section 95 defined by the inwardly tapered end section 90 of the nozzle core 72, which extends downstream to a nozzle mouth 94 defined at the downstream end of the nozzle body 70. The progressively increasing cross-sectional area of ​​the final expansion section 95 is achieved by reducing the tapered diameter of the pivot 83 at the end section 90, while the inner circumferential surface of the nozzle body 70 is maintained at a constant diameter. The pivot 83 helps stabilize the fluid and allows for greater fluid expansion than could be achieved with a nozzle core having a single, uniform diameter. The sustained contact of the fluid with the inner and outer wall surfaces of the discharge conduit is a function of the fluid's surface tension. The cross-sectional area of ​​the end expansion section 95 at the nozzle mouth 94 defines the liquid exit velocity, which is inversely proportional to the cross-sectional area at the nozzle mouth 94 relative to the nozzle inlet area 31. The end section 90 of the nozzle core 72 preferably extends slightly beyond the nozzle mouth 94 to help break the surface tension of the liquid with the inner circumferential surface of the nozzle body 70 without impacting the outer diameter of the discharge liquid stream. Having the inner circumferential surface of the nozzle body 70 with a constant diameter helps establish a constant boundary layer diameter of the liquid as it exits the nozzle, which helps maintain the desired droplet diameter regardless of the distance from the nozzle to the target. It has been found that a drastic reduction in liquid velocity can be achieved by progressively increasing the cross-sectional area of ​​the discharge conduit 85. The inward expansion of the discharge conduit 85 is achieved by progressively reducing the diameter of the pivot 83 while maintaining the internal circumferential surface area of ​​the nozzle body 70. This helps produce discharge liquid with a constant jet diameter. The reduced liquid velocity allows for splash-free dispensing. This also allows the use of larger nozzle inlet orifices 31 to accommodate the dispensing of liquids with higher solids content.Once the nozzle discharge conduit is initially filled with viscous fluid, the surface tension of the liquid will keep nozzle 30 primed with liquid ready for dispensing when the nozzle inlet 31 opens. Because the liquid can be substantially incompressible, an exact ratio can be maintained between the volume of liquid entering nozzle 30 through inlet 31 and the liquid exiting nozzle 94. Cycling the piston 32 to open and close the inlet orifice 31 at a rapid rate, such as 50 milliseconds, produces small, consistent liquid droplets that are discharged at a reduced exit velocity. This allows the discharge droplets to deposit on a target, such as a target about 5 cm (2 inches) from the nozzle, without splashing. From the above, it can be seen that a liquid dispensing system is provided that can be selectively operated to dispense precisely controlled drops without unwanted splashing of the dispensed liquid. The system also includes spray nozzles that are less susceptible to clogging by solids in the liquid. However, the liquid dispensing system and its spray nozzles are of a relatively simple design, making them economical to manufacture and efficient to use. Although the spray nozzles have been shown and described in conjunction with an illustrative liquid distribution system, it is understood that the spray nozzles could be used in other applications to distribute relatively small, controlled quantities of liquid.

Claims

1. A spray nozzle assembly, characterized in that it comprises: a nozzle support body (20) having a liquid supply port (22) for coupling to a liquid supply, said nozzle support body (20) further having an air supply port (50) for coupling to a pressurized air supply and an air outlet port (52); a spray nozzle (30) supported by said nozzle support body (20); a piston (32), said piston having a head (32a) supported for movement in an opening (34) of said nozzle support body (20) with a downstream end of the piston (32) selectively coupling to a spray nozzle liquid supply inlet (31) to control the flow of liquid to and discharge from said spray nozzle (30); a return spring (35) supported within a spring chamber (36) in said nozzle support body opening(34) on an upstream side of said piston head (32a) to deflect said piston (32) to a spray nozzle liquid supply inlet closing position; said nozzle body opening (34) defines a piston chamber (42) on a downstream side of said piston head (32a) opposite said spring chamber (36); said nozzle support body has (20) an air duct system communicating with a control valve (43), said control valve (43) being selectively operable (1) to permit communication of pressurized air from said nozzle support body air supply port (50) to said piston chamber (42) to move said piston (32) to an open spray nozzle liquid supply inlet position against the deflecting force of said return spring (35) to permit flow of liquid to and discharge from said spray nozzle (30) and (2) to preventthe flow of pressurized air through said air duct system from said nozzle support body air supply port (50) to said piston chamber (42) while allowing communication of pressurized air from said piston chamber (42) to and through said spring chamber (36) to said nozzle support body air outlet port (52) to facilitate the return movement of said piston (32) under the deflection force of said return spring (35) to said spray nozzle liquid supply inlet closing position.

2. The spray nozzle assembly according to claim 1, characterized in that said control valve (43) has an air inlet port (55a), a working port (55C), and an exhaust port (55b) and an actuating mechanism (43a) movable between (1) a first position that opens said valve inlet port (55a) to allow communication of pressurized air from said nozzle support body air supply port (50) through said valve inlet port (55a) and the working port (55c) to said piston chamber (42) to move said piston (32) to said open position and (2) a second position that closes said valve inlet port (55a), blocking communication of pressurized air from said nozzle support body air supply port (50) through said control valve inlet port (55a) while opening said exhaust port (55b) to allow communication ofpressurized air from said piston chamber 42 through said valve working port (55C) and exhaust port (55b) to and through said spring chamber (36) to the nozzle support body air outlet port (52).

3. The spray nozzle assembly according to claim 1, characterized in that said nozzle body air duct system includes a first air duct (63) for communicating pressurized air from said nozzle support body air supply port (50) to said control valve (43), a working duct (62) for communicating pressurized air from said control valve (43) to said piston chamber (42), and the outlet air duct (61) for communicating pressurized air from said control valve (43) to and through said piston chamber (42) to the nozzle support body air outlet port (52).

4. The spray nozzle assembly according to claim 3, characterized in that said control valve (43) has a valve mechanism (43a); and said control valve (43) is operable to move said valve actuating mechanism (43a) between (1) a first position that permits communication of pressurized air from said air supply port (50) through said first nozzle support body air duct (63) and the working duct (62) to said piston chamber (42) to move said piston (32) against the force of said return spring (35) to said open position while blocking communication of pressurized air to said nozzle support body air outlet duct (61),the spring chamber (36) and the nozzle support body air outlet port (52) and (2) a second position that blocks the communication of pressurized air from said first air conduit (63) to said working conduit (62) while allowing the communication of pressurized air from said piston chamber (42) through said working conduit (62), the outlet air conduit (61) to and through said spring chamber (36) and to said nozzle support body air outlet port (52).

5. The spray nozzle assembly according to claim 1, characterized in that said control valve is a solenoid valve.

6. The spray nozzle assembly according to claim 1, characterized in that said piston (32) is supported within a piston carrier (33) mounted in a sealed relationship within said nozzle support body opening (34); and said piston carrier (33) and piston head (32a) define the limits of said piston chamber (42) within said nozzle body opening (34).

7. The spray nozzle assembly according to claim 4, characterized in that said return spring (35) is disposed within a retaining sleeve (37), and when said valve actuating mechanism (43) is in said second position, pressurized air is communicated from said piston chamber (42) around and through said retaining sleeve (40) to said nozzle body air outlet port (52).

8. The spray nozzle assembly according to claim 1, characterized in that said spray nozzle liquid supply inlet is an inlet (31) at an upstream end of said spray nozzle (30).

9. The spray nozzle assembly according to claim 1, characterized in that it includes a plurality of said nozzle support bodies, each of which has a respective of said control valves (43) and spray nozzles (30).

10. The spray nozzle assembly according to claim 9, characterized in that said plurality of said nozzle support bodies (20) are arranged side by side with the liquid supply port (22), the air supply port (50) and the air outlet port (52) of each nozzle support body (20) being in fluid communication with the respective liquid supply port (22), air supply port (50) and air outlet port (52) of the other of the plurality of nozzle support bodies.

11. The spray nozzle assembly according to claim 1, characterized in that said spray nozzle includes a nozzle body having a generally hollow cylindrical configuration defining an internal circumferential surface; and an internal nozzle core disposed within the nozzle body and including a teardrop-shaped pivot having an upstream end section adjacent to the upstream end wall of the expansion cavity, a radially outwardly curved section adjacent to the upstream end section, and a radially inwardly tapered terminal end section, an annular discharge conduit being defined between an outer surface of the pivot and the internal circumferential surface of the nozzle body that is in fluid communication with the expansion cavity of the nozzle seat.

12. The spray nozzle assembly according to claim 11, characterized in that said spray nozzle includes a nozzle seat having said liquid supply inlet and a downstream expansion cavity in fluid communication with the liquid inlet, the expansion cavity terminating in a downstream end wall, and said annular discharge conduit being in fluid communication with said expansion cavity.

13. A liquid dispensing system, characterized in that it comprises: a modular manifold having a plurality of individual liquid dispensing modules (12) supported in a sealed stacking relationship side by side; said modules (12) each including a nozzle support body (20) formed with a liquid supply port (21) arranged in alignment with the liquid supply ports (21) in adjacent modules (12) to define a common liquid conduit (12) communicating between the modules; said nozzle support body (20) of each module including an air supply port (50) and an air outlet port (52) communicating with a respective air supply port (50) and air outlet port (52) of adjacent modules; said modules (12) each including: a spray nozzle (30) supported by the nozzle support body (20); a piston (32), said piston having a head(32aj supported for movement in an opening (34) of said nozzle support body (20) with a downstream end of the piston (32) that can be selectively coupled with a spray nozzle liquid supply inlet (31) to control the flow of liquid to and discharge from said spray nozzle (30); a return spring (35) supported within a spring chamber (36) in said nozzle support body opening (34) on an upstream side of said piston head (32a) to deflect said piston (32) to a spray nozzle liquid supply inlet closing position; said nozzle body opening (34) defines a piston chamber (42) on a downstream side of said piston head (32a) opposite said spring chamber (36); said nozzle support body has (20) an air duct system communicating with a control valve (43), said control valve (43) canto be selectively operated (1) to allow communication of pressurized air from said nozzle support body air supply port (50) to said piston chamber (42) to move said piston (32) to an open spray nozzle liquid supply inlet position against the deflecting force of said return spring (35) to allow flow of liquid to and discharge from said spray nozzle (30), and (2) to prevent the flow of pressurized air through said air duct system from said nozzle support body air supply port (50) to said piston chamber (42) while allowing communication of pressurized air from said piston chamber (42) to and through said spring chamber (36) to said nozzle support body air outlet port (52) to facilitate the return movement of said piston (32) under the deflecting force of said return spring(35) to the spray nozzle inlet closing position.

14. The liquid dispensing system according to claim 13, characterized in that said nozzle body air duct system includes a first air duct (63) for communicating pressurized air from said nozzle support body air supply port (50) to said control valve (43), a working duct (62) for communicating pressurized air from said control valve (43) to said piston chamber (42), and the outlet air duct (61) for communicating pressurized air from said control valve (43) to and through said piston chamber (42) to the nozzle support body air outlet port (52).

15. The liquid dispensing system according to claim 14, characterized in that said control valve (43) has a valve mechanism (43a); and said control valve (43) is operable to move said valve actuating mechanism (43a) between (1) a first position that permits communication of pressurized air from said air supply port (50) through said first nozzle support body air duct (63) and working duct (62) to said piston chamber (42) to move said piston (32) against the force of said return spring (35) to said open position while blocking communication of pressurized air to said nozzle support body air outlet duct (61),the spring chamber (36) and the nozzle support body air outlet port (60) and (2) a second position that blocks the communication of pressurized air from said first air conduit (63) to said working conduit (62) while allowing the communication of pressurized air from said piston chamber (42) through said working conduit (62), the outlet air conduit (61) to and through said spring chamber (36) and to said nozzle support body air outlet port (52).

16. The liquid dispensing system according to claim 13, characterized in that said return spring (35) is arranged within a retaining sleeve (37), and when said valve actuating mechanism (43a) is said second position pressurized air, it communicates from said piston chamber (42) around and through said retaining sleeve (40) to said nozzle body air outlet port (52).

17. The liquid dispensing system according to claim 13, characterized in that said spray nozzle includes a nozzle body having a generally hollow cylindrical configuration defining an internal circumferential surface; and an internal nozzle core disposed within the nozzle body and including a teardrop-shaped pivot having an upstream end section adjacent to the upstream end wall of the expansion cavity, a radially outwardly curved section adjacent to the upstream end section, and a radially inwardly tapered terminal end section, an annular discharge conduit being defined between an outer surface of the pivot and the internal circumferential surface of the nozzle body that is in fluid communication with the expansion cavity of the nozzle seat.

18. A liquid dispensing system, characterized in that it comprises: a modular manifold having a plurality of individual liquid dispensing modules supported in a sealed, side-by-side stacking relationship with each other; said modules (12) each including a nozzle support body (20) formed with a liquid supply port (21) arranged in alignment with the liquid supply ports (21) in adjacent modules (12) to define a common liquid conduit (12) communicating between the modules; said nozzle support body (20) of each module including an air supply port (50) and an air outlet port (52) communicating with a respective air supply port (50) and air outlet port (52) of adjacent modules; said modules each including: a control valve (43) and a nozzle body conduit system including a first air conduit (63) for communicating airpressurized air from said air supply port of the nozzle support body (50) to said control valve (43), a working conduit (62) for communicating pressurized air from said control valve (43) to said piston chamber (42), and an outlet air conduit (61) for communicating pressurized air from said control valve (43) through said spring chamber (36) to the air outlet port (52) of the nozzle support body; said control valve (43) has a valve mechanism (43a); and said control valve (43) is operable to move said valve actuating mechanism (43a) between (1) a first position that permits communication of pressurized air from said air supply port (50) through said first air conduit of the nozzle support body (63) and the working conduit (62) to said piston chamber (42) to move said piston (32) against the force of said return spring (35) to said positionopen while blocking the communication of pressurized air to said nozzle support body air outlet duct (61), the spring chamber (36) and the nozzle support body air outlet port (52) and (2) a second position that blocks the communication of pressurized air from said first air duct (63) to said working duct (62) while allowing the communication of pressurized air from said piston chamber (42) through said working duct (62), the outlet air duct (61) to and through said spring chamber (36) and to said nozzle support body air outlet port (52).

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