DB VALVE HEIGHT CONTROL WITH DISCHARGE VALVE
Background of the Invention Field of the Invention This invention relates to a height control valve in a vehicle suspension and, more particularly, to a height control valve with a novel valve of # '% ak discharge. In another of its aspects, the invention relates to a discharge valve for a height control valve. State of the Prior Art Air suspension systems have become increasingly popular for use in vehicle suspensions, seats and cabins on semi-trailer truck platforms and other vehicles. Most air suspensions typically employ a height control valve that maintains the design height of the suspension. In a semi-trailer suspension, for example, the design height is the spacing between the frame and the axle. The height control valve detects when the spacing is greater or less than its design value and, consequently, adjusts the pressure in the air springs disposed between the frame and the axle, which expands or contracts the air spring to alter the spacing between the suspension and the frame. The air suspension system with a height control valve maintains a uniform spacing of the air spring and the frame under a range of vehicle loading conditions. The height control valve adjusts the spacing by selectively admitting fluid to or discharging fluid from a height control member, which is typically an air spring. On a rear arm suspension, the air spring is positioned between the vehicle frame and the rear arm. The rear arm carries the axle so that adjusting the air spring pressure also adjusts the distance between the vehicle's frame and the axle. The height control valve is typically mounted on the vehicle frame and has a control arm that is connected to the rear arm through a linkage. By varying the distance between the vehicle frame and the rear arm, the linkage causes the control arm to rotate a control arrow that extends to the height control valve, which, in turn, selectively allows it to be admitted. air is discharged from the air spring, depending on the direction of rotation of the control arm. Typically, the height control valve has three gates: an air spring gate connected to the air spring, an inlet gate connected to a source of pressurized air, and a discharge hatch open to the atmosphere. To increase the height of the air spring, the height control valve opens the fluid communication between the air spring gate and the intake gate, allowing the flow of air from the source of air under pressure, through of the height control valve and to the air spring. To reduce the height of the air spring, the height control valve opens the fluid communication between the air spring gate and the discharge gate, allowing air flow out of the air spring through the air valve. height control, to the atmosphere through the discharge gate. When the air spring is at the proper height, the valve is in a neutral position, where neither the inlet gate nor the discharge gate communicate with the air spring. There are generally two types of height control valves: an instantaneous response height control valve and a time delay height control valve. An instantaneous response height control valve is directly connected to a sensor, such as a mechanical link, which detects the position of the frame relative to the rear arm. The instantaneous response height control valve will respond immediately to any change in the position of the frame relative to the rear arm to add or discharge pressurized air from the air springs without delay. Therefore, such height control valves are driven by discontinuities in the road surface, such as potholes or repairs and changes in the plane of the vehicle relative to the road surface during turns.
In many applications it is undesirable that the height control valve responds immediately to road surface discontinuities or other rapid fluctuations in the height of the vehicle relative to the suspension. In such applications, a time delay height control valve is preferred. The time delay height control valve is linked to the frame in such a way that there is a delay in the response of the height control valve to a variation in the height of the frame. Such a height control valve is described in U.S. Patent Nos. 4,726,571, issued February 23, 1988; 3,858,903, issued January 7, 1975; and 3,884,454, issued May 20, 1975. The height control valve described in this background comprises a mechanical link, spring-biased, which is damped so that when the height of the vehicle is altered, the height control valve does not Operate until the link moves a predetermined distance for a predetermined time controlled by the physical structure of the link, the spring polarization and the damping element. Frequently, discharge valves are added to vehicles equipped with air suspensions to selectively "dump" air from the air springs and lower the height of the vehicle's chassis. A common application for tractor unloading valves allows air to be selectively discharged from the tractor suspension so that the tractor can be connected to a trailer disconnected. In disconnection, for example, the operator typically lowers the front carrier legs on the trailer until they touch the ground. The gear mechanism on the carrier legs is operated manually and thus is easier to turn without load on the legs. Instead of manually working the gear mechanism under additional load to lift the trailer, air is discharged or emptied from the tractor air springs, thereby lowering the tractor frame and moving the weight of the trailer to the carrier legs. The tractor is then free to separate from the trailer. Another application for dump valves is to adjust the height of the vehicle frame on trailers during loading conditions. Occasionally a condition known as trailer towing occurs when a trailer is loaded adjacent to a loading platform. If the height of the trailer is not controlled during the loading maneuver, the load that increases in the trailer will sometimes cause the trailer tires to rotate around the point of contact on the ground and will force the trailer forward away from the platform. In other words, the trailer tends to "move away" from the loading platform. This tendency presents obvious problems with levels of effort on the carrier legs of the trailer and access to the trailer from the platform. In this way, it is desirable to discharge (flush) all of the pressurized air out of the air springs before loading the trailer.
Typically, the prior art discharge valves used to discharge air from air springs were separate mechanisms that must be placed and mounted on the vehicle and connected separately to the air lines. The additional costs of labor and equipment often exceed the cost of the discharge valve and increase the time of assembly of the vehicle. Another problem associated with dump valves used especially in conjunction with certain types of time delay height control valves is that during the actuation of the dump valve, the height control valve may not completely seal the intake gate to the outlet valve. Same time. In this way, the pressurized air can be discharged unnecessarily, which also negatively affects the discharge rate of the air springs. SUMMARY OF THE INVENTION The present invention provides a discharge valve that is mounted directly to a height control valve and prohibits the height control valve from pressurizing the air springs by discharging the air from the air springs. The height control valve comprises a housing mounted in the frame and having an inner chamber. The height control valve also has an inlet gate, a discharge gate and a device gate. The input gate is adapted to fluidly connect the inner chamber to a source of pressurized fluid. The discharge gate is adapted to fluidly connect the interior chamber to the atmosphere. The device gate is adapted to fluidly connect the inner chamber with a height control member, which is mounted between the frame and the suspended member. Preferably, the height control member is expandable by pressurized fluid. The height control valve has a sensor that is operatively connected to the suspended member and detects a change in the height of the frame relative to the suspended member. The sensor is operatively connected to a controller disposed within the housing, which prohibits fluid communication between the device gate and the inlet gate and the discharge gate when the rack is at design height. A discharge valve is also mounted in the housing and has a fluid gate connected to the interior chamber of the housing and to the atmosphere. A valve element is disposed in the fluid gate and is selectively movable between a sealed condition in which the inner fluid communication chamber is sealed with the atmosphere through the fluid gate and a discharge condition in which the The inner chamber of the housing is in fluid communication with the atmosphere. Preferably, the valve element is a piston movably mounted within the fluid gate for reciprocating movement between a first position where the discharge valve is in the sealed position and a second position where the discharge valve is in the discharge condition . The discharge valve may have a trigger to move the piston between the first and second positions. The piston includes a head mounted on a rod, the head disposed within the fluid gate and the rod extending from the fluid gate to the inner chamber through an inlet opening in the discharge valve. A seal is fixedly mounted on the rod to seal the opening of the discharge valve in the fluid gate with respect to the interior of the housing and to fluidly connect the fluid gate to the interior of the housing during the actuation of the piston. When the fluid gate is fluidly connected to the interior of the housing, the piston rod forbids the controller to fluidly connect the input gate to the device gate. In one aspect of the invention, the piston can be moved between first and second positions to place the discharge valve in a sealed condition or a discharge condition. A spring can be used to resist movement of the piston of the first and second positions. Alternatively, a spring may be used to urge the piston from the first to the second position. The piston prohibits air from the inlet gate from entering the inner chamber of the "height" control valve when the valve is in the discharge condition In another aspect of the invention, the unloading valve has an inlet port. discharge valve that fluidly connects the fluid gate to the interior of the housing and the inlet port of the discharge valve is on one side of the housing of the height control valve and the inlet gate and the device gate are in the In another aspect of the invention, the height control valve may be a time delay valve Brief Description of the Drawings The invention will now be described with reference to the drawings, wherein: 1 is an exploded view of a height control valve and discharge valve assembly according to the invention; Figure 2 is a sectional view of the assembled spring return assembly of Figure 1; Figure 3 is a sectional view of the height control valve of Figure 1 with the discharge valve in the sealed position; Fig. 4 is a sectional view of the height control valve of Fig. 1 with the discharge valve in the discharge position; Figure 5 is a sectional view of a second embodiment of the height control valve with the discharge valve shown in the neutral position; Fig. 6 is a sectional view of the height control valve of Fig. 5 with the discharge valve shown in the discharge position; and Figure 7 is a sectional view of a third embodiment of the height control valve with the discharge valve shown in the neutral position. Description of Preferred Forms of Realization Referring now to the drawings and to the figure
1 in particular, a height control valve 10 of the type described in US Pat. Nos. 3,858,903; 3,884,454; and 4,726,571, the relevant material of which is incorporated herein by reference. The height control valve 10 of the present invention is similar in all respects to the height control valve described in these three patents, with the addition of the discharge valve, which is described in detail. Generally, the height control valve 10 comprises a shock absorber assembly 12, an air control assembly 14 and a spring return assembly capable of rotating 16. A discharge valve assembly 18 is fixedly mounted to the air control assembly 14. The air control assembly 14 is adapted to be mounted on a vehicle chassis or chassis (not shown) and controls the air flow to and from the "" height control valve. The spring return assembly 16 is adapted to operatively connect to a suspension member (not shown), such as a rear arm movably suspended from the vehicle frame. In the typical suspension, an air spring is disposed between the suspension member and the frame to resist vertical movement of the suspension member relative to the frame. It should be understood that in some applications, the air control assembly will be mounted to the suspension member while the spring return assembly will be operatively connected to the frame. The spring return assembly is rotatably mounted in the air control assembly 14, but with vertical displacement of the vehicle frame relative to the suspension member, the spring return assembly 16 is rotated with respect to the air control assembly 14. With such rotation beyond a predetermined distance, the air control assembly 14 will add air to or discharge air from the air spring in order to maintain the frame at a predetermined design height relative to the suspension member. The shock absorber assembly 12 dampens the response of the air control assembly 14 to such movement, and comprises a cushion housing 22 defining a cushion chamber (not shown) in which a damping fin 24 is received having a guide groove 26. A plate of base 28 is mounted in the damper housing 22"'by screws 30 for housing the damping chamber Preferably, an elastomeric seal 32 is disposed between the damper housing 22 and the base plate 28 to fluidly seal the damper housing 22 and the damping chamber The damping chamber is filled with a relatively viscous fluid to resist movement of the damping fin 24. The air control assembly 14 comprises an air control housing 40 defining an air control chamber 42. The air control housing further comprises an inlet gate 44, an air spring gate 46 and an outlet gate 48. The inlet gate 44 is adapted to be fluidly connected to a source of pressurized air (not shown), such as the vehicle air pressure system (not shown). The air springs gate 46 is adapted to connect fluidly to the air springs (not shown). The outlet gate 48 is fluidly connected to the atmosphere. The inlet gate 44 and the outlet gate 48 both have halves 52 and 50, respectively, such as a valve with a rod disposed therein. The air control chamber 42 is enveloped by the gasket 54, which is compressively mounted to the air control housing 40 by a mounting bracket 56 and screws 58. The mounting clamp 56 is used to mount the air control valve. height 10 to the vehicle frame, preferably, or another component "" of the vehicle chassis. Clogged openings 59 extend through the clamp 56 and are used to mount the discharge valve assembly 18. Only one of the capped openings 59 is used to assemble the discharge valve assembly 18. The other covered opening will be plugged by the cap 61. The two covered openings 59 allow the height control valve to be on the right or left. The air control housing 40 also has an annular opening 60 through which an arrow 62 extends. A dust screen 63 is disposed in the annular opening 60. The arrow 62 extends through the air control housing 40 and towards the damper housing 22. The arrow 62 has a wedge 64, which is inserted in the guide groove 26 of the damping vane 24. The arrow 62 further has a recessed portion 66 in which an actuator 68 is mounted by screws 70. A recess of the spring cup 72 is formed in the arrow 62 A series of O-rings 74, 76 and 78 are arranged in annular grooves formed in the surface of the arrow 62. The O-ring 74 fluidly seals the shock absorber assembly 12 relative to the air control assembly 14. The O-ring 76 fluidly seals the air control assembly 14 with respect to the atmosphere. The O-ring 78 fluidly seals the return spring assembly with respect to the atmosphere. Referring now to Figures 1 and 2, the spring return assembly 16 comprises a spring chamber block "86" having a cross bore 88 and an intersecting longitudinal bore 90 (Figure 2). 86 is rotatably mounted in the air control assembly 14 with the upper end of the arrow 62 received within the transverse bore 88. A partially hollow spring cup 92 is received within the longitudinal bore 90 and positioned so that the end of the spring cup 92 is disposed within the recess of the spring cup 72 of the arrow 62. A spring 94 is partially arranged within the hollow interior of the spring cup 92. The spring 94 and the spring cup 92 are retained within the longitudinal bore 90 by a plug 96 sealing the longitudinal bore 90. With the plug 96 disposed at the end of the longitudinal bore 90, the spring 94 is c ompressed between the plug 96 and the spring cup 92. Preferably, an O-ring 98 is mounted on the plug 96 to fluidly seal the spring chamber 86 relative to the atmosphere. The plug 96 is retained with respect to the spring chamber block 86 by means of a pin 99 which extends through the spring chamber block 86 and the plug 96. The spring return assembly 16 further comprises a lever arm mounted adjustable in the spring chamber block 86. The lever arm 100 has a circular opening 102 and an elongated opening 104. A circular protrusion 106 extending from the spring chamber block "" "36 is received in the circular opening 102 of the lever arm while a bolt 108 extends through an opening 110 of the spring chamber block 86 and the elongated opening 104 of the lever arm 100 with a nut 112 and the roller 114 for fixed and adjustably mounting the arm of the lever arm. lever 100 to the spring chamber block 86. To adjust the position of the lever arm, the nut 112 is loosened and the lever arm is pivoted about the circular protrusion 106 within the range of the elongated opening 104 until the desired position is reached and the nut 112 is then tightened. Turning to Figures 3 and 4, the discharge valve assembly 18 comprises a discharge valve housing 120 which defines a discharge valve chamber 122 having a trigger opening 123 and an entry opening 125. A piston 124 is arranged inside the discharge valve chamber 122 and reciprocating inside the chamber between a first position where the air control chamber 42 is sealed relative to the discharge valve chamber 122 (figure 3) and a second position where the chamber The air control 42 is fluidly connected to the discharge valve chamber 122 (FIG. 4). A piston trigger 126 is mounted to the discharge valve housing 120 and serves to enable reciprocal movement of the piston 124. Preferably, the discharge valve housing 120 has one or more gates 128 that fluidly connect the discharge valve chamber. 122 to the atmosphere.
In addition, one end of the discharge valve housing 120 is preferably threaded at 130 so that the discharge valve assembly 18 can be threaded toward the capped opening 59 in the height control valve clamp cover 56. The discharge valve chamber 122 has a stepped profile which generally conforms to the shape of the piston 124. More specifically, the discharge valve chamber 122 comprises a series of diameter portions that are sequentially reduced. Initially, the outer portion 132 of the discharge valve chamber 122 is defined by threads 134 adjacent to the trigger opening 123. The outer portion 132 abuts a central portion 138, which terminates in an annular stop 140. Extending from the annular stop 140 is an arrow portion 142 terminating in an annular rim 144. A rod portion 146 of the discharge valve chamber 122 extends from the annular spine 144 to the inlet opening 125 of the discharge valve housing 120. The piston assembly 124 comprises a piston 150 having a head 152, the arrow 154 and the rod 156. The head 152 and arrow 154 each have an annular groove 158, 160 in which a ring is received in 0 162, 164. An annular seal platform 168 is mounted on the piston rod 156 outside the discharge valve chamber and holds a seal 170, preferably made of an elastomer. The seal 170 seals the inlet opening 125 of the discharge valve housing "" "120 to stop fluid communication between the air control chamber 42 and the discharge valve chamber 122. A spring 172 is axially mounted about of the piston arrow 154 within the central portion 138 of the discharge valve chamber 122 and is compressively retained between the piston head 152 and the stop 140 so that the seal 170 is biased against the entry opening 125 The piston trigger 126 is threadably mounted in the trigger opening 123 of the discharge valve housing 120. The piston trigger 126 preferably has an annular ring 174, which abuts the piston head 152 to limit displacement towards outside the piston 150. The piston trigger 126 also has a capped opening 176 extending therethrough.The piston trigger 126 is adapted to be fluidly connected to the source of the piston. The pressure fluid of the vehicle can be directed so that the pressurized fluid can be directed through the capped opening 176 and against the piston head 152 to move the piston 150 inward against the force of the spring 172. When air is discharged under pressure from the piston trigger 126, spring 172 biases piston 150 in contact with ring annulus 174 of piston trigger 126. Preferably, an O-ring 178 is disposed between a portion of piston trigger 126 and the discharge valve housing 120 to seal the threads of the opening 123. Likewise, an O-ring 180 is disposed between the mounting bracket 56 and the "unloading valve iloxing 120 to provide an additional seal. In operation, the height control valve 10 adjusts the air pressure in the air springs in response to the movement of the vehicle frame in the normal manner. As the vehicle frame is moved relative to the suspension member, the lever arm 100 moves accordingly, resulting in the corresponding rotation of the arrow 62. When the arrow 62 is rotated, the actuator 68 contacts correspondingly with either of the stems of valves 50 or 52 to discharge air from the air springs into the atmosphere or to add pressurized air to the air springs, as required. This operation is described more fully in U.S. Patent Nos. 3,858,903; 3,884,454; and 4,726,571, referred to above. When it is desired to completely discharge air from the air springs, the discharge valve assembly 18 is driven through the piston trigger 126, which directs air under pressure through the capped opening 176 and into the discharge valve chamber 122, where the pressurized air acts against the piston head 152. Upon finding the pressurized air the piston head 152, the force of the pressurized air acting on the surface area of the piston head 152 exceeds the force of the spring 172 and directs the piston 150 inwardly until the spring 172 is completely compressed against the annular stop "" "140 of the valve housing At the same time, the seal platform 168 and seal 170 are moved away from the inlet opening 125 of the discharge valve housing to open the discharge valve chamber 122 relative to the discharge chamber. air control 42 so that the pressurized air in the air control chamber can exit through the discharge valve chamber and the gates 128 into the atmosphere In figure 4, the discharge valve a is in the unloading position and although the rod 156 is moved to the air control chamber 42, the O-ring 164 remains disposed on the gates 128 and will not interfere with the flow of fluid from the air control chamber 42. and the gates 128. In the unloading position, the piston rod 156 is adjacent to or abuts the actuator 68 to prohibit or limit the movement of the actuator 68 so that it can not operate the valve 52 in the inlet gate 44. It is It is important that during air discharge from the air springs is prohibited or limits the movement of the actuator 68 so that the actuator 68 can not rotate to pressurize the air springs because when unloading the air springs, the frame of the vehicle will be lowered, resulting in the lever arm 100 tending to rotate the arrow 62 and moving the actuator in contact with the valve 52 to fluidly connect the source of pressurized air to the air spring via the air control chamber "P.2. If the piston rod 156 does not prohibit or limit the movement of the actuator 68 so that the actuator 68 can not operate the valve 52 during the discharge of the air spring, the height control valve would simultaneously try to discharge the air spring and fill the air spring, placing a greater load on the vehicle's pressurized air system. Once the air spring is discharged, the pressurized air is removed from the piston trigger 126 and the spring 172 moves the piston 150 from the discharge position (Figure 4) to the sealed position (Figure 3) where the seal 170 seals the inlet opening 125 to the air control housing 40. Figures 5 and 6 illustrate a second embodiment of the height control valve according to the invention. The second embodiment of the height control valve is substantially identical to the embodiment illustrated in Figures 1 to 4, except for the alternative discharge valve 200. Therefore, similar reference numerals are used to identify similar parts, but the alternative discharge valve is identified with reference numerals beginning with 200. The alternative discharge valve 200 comprises a discharge valve housing 202 that defines a discharge chamber. discharge valve 204 having an outlet opening 222 and an inlet opening 224. The discharge valve chamber comprises an upper portion 206 defined by threads 208, the central portion 212, the annular stop 214, the arrow portion 216, the annular spine 218 and the stem portion 220. The discharge valve housing 202 further comprises a piston trigger 230. Preferably, the piston trigger 230 is a capped opening 232 disposed on one side of the discharge valve housing 202. and is adapted to be fluidly connected to the source of pressurized air of the vehicle. At least one gate 234 extends through the discharge valve housing 202 and fluidly connects the discharge valve chamber 204 to the atmosphere. The outlet opening 222 of the discharge valve housing 202 is sealed by means of a threaded plug 236 which is threaded into the threads 208 of the discharge valve housing 202. Preferably, a 0 209 ring or any other suitable type of seal is provided between the cap 236 and the discharge valve housing 202. A piston 240 comprises a piston head 242, a piston shaft 244 and a piston rod 246. Annular grooves 248 and 250 are respectively disposed on the piston head 242 and the piston shaft 244 and respectively receive O-rings 252 and 254. A seal pad 256 is mounted on the piston rod 246 and holds a seal 258 which seals the inlet opening 224 of the discharge valve housing 202 when the discharge valve chamber is sealed with respect to the air control chamber 42 (FIG. 4). A "" "spring 260 is mounted between the cap 236 and the piston head 242 and biases the piston inwardly so that the discharge valve 200 is always biased by the spring to the open or discharge position (FIG. 6). The operation of the discharge valve 200 is similar to the operation of the discharge valve assembly 18, except that the piston 240 is biased towards the discharge position, while the piston 150 is biased towards the sealed position. To move the discharge valve to the discharge position, pressurized air is released from the piston trigger 230 and the capped opening 232 so that the piston is moved downward by the force of the spring 260 and the seal 258 is moved away from the piston. the discharge valve inlet gate 224 for fluidly connecting the air control chamber 42 to the discharge valve chamber 204. In the discharge position, the end of the piston rod 246 is adjacent to or abuts the actuator 68 for prevent the rotational movement of the actuator. To close the discharge valve 200, pressurized air is directed to the discharge valve 200 via the piston trigger 230 or the capped opening 232 so that the piston head 242 is urged out against the force of the spring 260 to seal the discharge valve 200 moving the seal pad 256 and the seal 258 butt to the end of the discharge valve housing 202. FIG. 7 illustrates a third embodiment of "a height control valve in accordance with FIG. The third embodiment of the height control valve is substantially identical to the embodiment described in Figures 1-4, except for the alternative relief valve 300. Thus, similar reference numerals are used. to identify similar parts, but the alternative discharge valve is identified with reference numbers beginning with 300. The alternative discharge valve 300 comprises a housing discharge valve 302 defining a discharge valve chamber 304 having an outlet opening 322 and an inlet opening 324. The discharge valve chamber 304 comprises an upper portion 306 defined by threads 308, the central portion 312 , the annular stop 314, the arrow portion 316, the annular spine 318, and the stem portion 320. The discharge valve housing 302 further comprises a piston trigger 330 which is threadably mounted in the outlet opening 322 of the housing of discharge valve 302. Piston trigger 330 has a capped opening 332 extending therethrough to fluidly connect discharge valve chamber 304 to a source of pressurized air. An O-ring 334 is preferably disposed between the piston trigger 330 and the discharge valve housing 302. At least one gate 336 extends through the discharge valve housing 302 and fluidly connects the valve chamber of P '. It's loading 304 into the atmosphere. A piston 340 is mounted within the discharge valve housing 302 for reciprocal movement within the discharge valve chamber 304. The piston 340 comprises a piston head 342 and a piston arrow 344. Annular grooves 348 and 350 are disposed respectively on the piston head 342 and the piston shaft 344 and respectively receive O-rings 352 and 354. The O-ring 352 seals the portion of the discharge valve chamber 304 disposed inwardly of the piston head 342 with respect to the portion of the discharge valve chamber 304 between the piston head 342 and the piston trigger 330. The O-ring 350 seals the rod portion of the discharge valve chamber 304 from the air control chamber 42 when the discharge valve 300 is in the sealed condition, as illustrated in Figure 7. The piston arrow 344 has a plane 346 extending substantially along the length of the piston arrow 344. A spring 360 is compressively mounted between the piston head 342 and the spine. annular 318 for urging the piston 340 outward toward the piston trigger 330 and toward sealed condition. In order to move the discharge valve 300 to the discharge condition, pressurized air is directed to the discharge valve chamber 302 through the threaded opening 332 of the piston trigger 330 so that the pressurized air acts on the discharge head. piston 342 for moving the piston 340 inwardly against the spring force 360. The piston 340 will continue to move inwardly until the spring 360 is fully compressed or the piston head 342 contacts the stop
314. As the piston 340 moves inward, the piston arrow 344 extends beyond the entry opening 324 until the end of the piston arrow 344 is abutting at or adjacent the actuator 68 to prevent rotational movement of the actuator 68. In this position, the O-ring 350 is no longer in seal engagement with the rod portion 320 of the discharge valve chamber 304 and the plane 346 extends outwardly from the rod portion 320 and into the control chamber of air 42. In this way, with the absence of the seal provided by the O-ring 350, the plane 346 forms a channel between the piston shaft 344 and the rod portion 320 of the discharge valve chamber 304 of the housing discharge valve 302 so that an air control chamber 42 can pass through the gates 336 to the atmosphere via the channel between the plane 346 and the discharge valve housing 302. To close the discharge valve 300, pressurized air is removed from the piston trigger 330 and discharged. The spring 360 then biases the piston 340 towards the piston trigger 330 until the piston head 340 makes contact with the piston trigger 330. As the piston moves outward, the O-ring 350 is disposed within the piston portion. 320 of the discharge valve chamber 304 and forms a seal of the "discharge" valve 304 with respect to the discharge valve housing 302 to fluidly seal the air control chamber 42 relative to the discharge valve chamber 304 and floodgates 336. Although particular embodiments of the invention have been illustrated, it will be understood, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art, particularly in light of the previous teachings. Reasonable variations and modifications are possible within the scope of the foregoing description of the invention, without departing from the spirit of the invention. For example, it is not necessary for the piston trigger 126 to facilitate the use of pressurized air. Within the scope of the invention is the fact that the piston trigger comprises any type of electrical, mechanical or electromechanical device that can reciprocally move the piston 150. The piston trigger can be a solenoid-operated device that makes contact with the head of piston 152 to move the piston 150. The piston trigger may also comprise a solenoid in combination with the piston so that by energizing the solenoid, the piston is moved directly.