Abstract:
A valve assembly includes a check valve element in an output chamber. The check valve element opens to permit forward flow of fluid under pressure in the output chamber from an input port to an output port. The check valve element closes to block back flow of fluid under pressure in the output chamber from the output port toward the input port. The back flow of fluid under pressure exerts a closing force upon the check valve element from within the output chamber. A counter force generating element, or pilot element, communicates with the valve element, to selectively open the valve, even in the presence of back flow pressure. The counter force generating element may apply a counter force to the check valve element, which urges the valve element toward the opened condition. The counter force may be less than the closing force, so the check valve element remains closed.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/190,390, filed 28 Aug. 2008, and entitled “Flow Control Valve,” which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to fluid pressure operated systems and devices, particularly those required to maintain position while maintaining a fluid tight seal. 
     BACKGROUND OF THE INVENTION 
     Systems and devices using fluid pressure for lifting and holding position are known. These systems and devices typically include check valves, which prevent sudden and potentially damaging loss of pressure when the supply of pressurized fluid unexpectedly decreases or fails. Typically, the check valves are opened either by applying a lower pressure pilot fluid, or by applying manual pressure, sufficient to overcome the locking forces. 
     The amount of force required to open a check valve depends upon the area of the main check valve that is locked, and the magnitude of the pressure. For example, to unseat a main check valve having a 0.75 inch diameter, which is seated at a pressure of 100 psi, about 44 pounds of opening force must be applied. This opening force is more than a typical operator can apply, either manually or using a solenoid. Furthermore, the higher force on the main check seat imposes added wear and tear, which leads to reduced operating life. The requirement of large pilot pistons also increases the overall dimensions of the valve itself. 
     There remains a need for pilot operated check valves requiring reduced operating forces, which, in turn, will lead to increased operating life at higher pressures. There is also a need for pilot check valves having a more compact size. 
     SUMMARY OF THE INVENTION 
     The invention provides a valve assembly comprising an output chamber, or cartridge bore, for receiving a fluid under pressure. The output chamber has an inlet passage, or input reentrant bore, attachable to a source of fluid under pressure and an outlet passage, or output reentrant bore, attachable to a load. 
     The valve assembly includes a check valve element in the output chamber. The check valve element is operable in an opened condition, which permits forward flow of fluid under pressure in the output chamber from the source toward the load. The check valve element is also operable in a closed condition, which blocks back flow of fluid under pressure in the output chamber from the load toward the source. The back flow of fluid under pressure exerts a closing force upon the check valve element from within the output chamber. A back flow situation may arise, for example, because of a sudden, unanticipated loss of pressure in the inlet passage. The check valve element holds the load in this pressure change event. 
     According to the invention, the valve assembly further includes a counter force generating element, which is located within the output chamber and coupled to the valve element. The counter force generating element operates in response to pressure caused by the back flow of fluid in the output chamber. The element applies a counter force to the check valve element, which urges the valve element toward the opened condition. The counter force is, by purpose, less than the closing force, so the check valve element remains in the closed, load holding condition. Nevertheless, the presence of the counter force reduces the overall sealing forces applied by the check valve element, thereby reducing the magnitude of force which is ultimately required to unseat the check valve element when it is required to relieve the load pressure. Wear and tear on the check valve element is reduced. 
     In one embodiment, the counter force generating element applies the counter force from outside the output chamber. 
     In one embodiment, the valve assembly further includes a relief element located outside the output chamber and coupled to the check valve element. The relief element applies an external opening force, which, in combination with the counter force, moves the check valve element to the opened condition against the closing force in the output chamber. The opening force allows reverse flow from the output to input so that the load pressure can be relieved under controlled circumstances. 
     Since the counter force is present to reduce the overall magnitude of force required to unseat the check valve element, wear and tear on both the relief element and check valve element are reduced. Furthermore, due to the presence of the counter force, the relief element can be operated by typical manual force, or by force typically applied by an external mechanical actuator, like a solenoid. The presence of the counter force also makes possible the design of smaller valve assemblies. 
     Additional advantages of the invention include: 
     1. A seal on the piston rod to allow for a smaller design and ease of manufacture. 
     2. Coned shaped poppet for increased flow from input to output. 
     3. End cap spring inside of the rod for a more compact package and less impact due to a decrease in piston rod weight. 
     4. The bearing sleeve design allows for a more compact design and greater concentricity between the piston and the bore. 
     5. The sleeve may now be an integral part of the piston, eliminating an extra part. 
     6. Changed shape of poppet shortens the valve length. 
     7. The valve assembly provides a fluid tight design, which eliminates drift due to leaky or worn spools. 
     Generally, a valve according to the present invention has a valve body that includes a cartridge bore that has a piston bore, an input counterbore, an output counterbore, and a bearing counterbore. The input counterbore and the output counterbore meet at a sealing ledge, or poppet seat. An input reentrant bore, which intersects the input counterbore, is formed into the valve body. An output reentrant bore, which intersects the output counterbore, is formed into the valve body. Also, a pilot reentrant bore, which intersects the piston bore, is formed into the valve body. 
     A piston cartridge disposed at least partially within the cartridge bore. The piston cartridge includes a longitudinal piston rod, a first piston head secured to one end of the piston rod, and a second piston head secured to a second end of the piston rod. The second piston head is disposed in the piston bore of the cartridge bore. The piston cartridge also includes a poppet member slidably disposed on the piston rod within the output counterbore and a poppet bias spring located between the poppet member and the first piston head. The poppet bias spring biases the poppet member in a poppet bias direction against the sealing ledge or poppet seat. 
     An embodiment of a valve according to the present invention has an end cap spring acting against the first piston head, biasing the piston rod in the poppet bias direction. 
     An embodiment of a valve according to the present invention may have a bearing sleeve inserted into the bearing counterbore, extending into the output counterbore, wherein the first piston head is disposed in the bearing sleeve. 
     According to an embodiment of a valve according to the present invention, the valve body may be formed as a unitary member. 
     According to an embodiment of a valve according to the present invention, the valve may also include a flow control mechanism. The flow control mechanism includes a mounting plate including a threaded adjusting aperture formed therethrough and a threaded adjusting screw extending through said adjusting aperture. A lock nut may be threaded onto the adjusting screw and be adapted to selectively prevent rotation of the adjusting screw with respect to the mounting plate. The mounting plate is preferably coupled to the valve body to cover said bearing sleeve counterbore and the adjusting screw extends into the output counterbore. 
     An embodiment of a valve according to the present invention may include an adjustable pilot mechanism. The adjustable pilot mechanism preferably includes a mounting plate including a threaded adjusting aperture formed therethrough, a threaded adjusting screw extending through the adjusting aperture and a lock nut threaded onto the adjusting screw and adapted to selectively prevent rotation of the adjusting screw with respect to the mounting plate. The mounting plate is preferably coupled to said valve body to cover said bearing sleeve counterbore and the adjusting screw preferably abuts the end cap spring. A counterbalance mechanism may also or alternatively be provided. The counterbalance mechanism may include a counterbalance reentrant bore formed into the valve body and intersecting the pilot reentrant bore and the output reentrant bore. 
     An embodiment of a valve according to the present invention may include a sensor reentrant bore formed into the valve body where the sensor reentrant bore is in fluid communication with the output counterbore and spaced from the output reentrant bore. 
     An embodiment of a valve according to the present invention may further or alternatively include an auto release mechanism. The auto release mechanism may include a release housing having a sensor input port, a control input port and a release output port. The auto release mechanism may also include a release piston adapted to selectively allow flow from the sensor input port to the release output port, wherein the release piston is biased open by a release piston bias spring and may be closed by applying a fluid pressure to the piston through the control input port. The auto release mechanism may further include a needle valve to adjust a flow of fluid through the sensor input port. 
     An embodiment of a valve according to the present invention may further or alternatively include a manual release mechanism accessible from without the valve body, adapted to selectively release fluid from the output counterbore. The manual release mechanism may be a plunger extending through the valve body and abutting the piston cartridge within the piston bore. 
     Alternatively, the manual release mechanism may include a manual release reentrant bore in fluid communication with the output counterbore, and a fluted plunger disposed at least partially in the manual release reentrant bore. 
     An embodiment of a valve according to the present invention may further or alternatively include an output swivel including a throughbore in fluid communication with the output reentrant bore, and a swivel mounting plate stationarily coupled to the valve body, where the swivel mounting plate supports the output swivel in a rotatable relationship with the valve body. 
     An embodiment of a valve manifold according to the present invention includes a plurality of cascaded valves, where each valve includes a cartridge bore comprising a piston bore, an input counterbore, an output counterbore, and a bearing counterbore, where the input counterbore and the output counterbore meet at a sealing ledge. Each valve also includes an input bore which intersects the input counterbore, an output bore which intersects the output counterbore and a pilot bore which intersects the piston bore. Each valve in the manifold also includes a piston cartridge disposed at least partially within the cartridge bore. The piston cartridge includes a longitudinal piston rod, a first piston head secured to one end of the piston rod and a second piston head secured to a second end of the piston rod, where the second piston head is disposed in the piston bore. Each valve further includes a poppet member slidably disposed on the piston rod within the output counterbore, and a poppet bias spring located between the poppet member and the first piston head biasing the poppet member in a poppet bias direction against the sealing ledge. 
     Each valve may further include an end cap spring acting against the first piston head, biasing the piston rod in the poppet bias direction, and a bearing sleeve inserted into the bearing counterbore, extending into the output counterbore. The first piston head may be disposed in the bearing sleeve. 
     An embodiment of a valve manifold according to the present invention may include a first valve of the plurality of valves that has a pressure source bore in fluid communication with the input counterbore of the first valve, wherein the pressure source bore is in fluid communication with the input bore of a second valve of the plurality of valves. The pressure source bore of the first valve may be at least substantially diametrically opposed from the input bore of the first valve, across the input counterbore of the first valve. 
     An embodiment of a valve according to the present invention may include a valve body comprising a cartridge bore including a piston bore, an input counterbore, an output counterbore, and a bearing counterbore, said input counterbore and said output counterbore meeting at a sealing ledge. An input reentrant bore, which intersects the input counterbore may be formed in the valve body, and an output reentrant bore, which intersects the output counterbore, may also be formed in the valve body. The valve body may also include a pilot reentrant bore that does not intersect the cartridge bore, but rather intersects a pilot control reentrant bore formed in the valve body. A solenoid control reentrant bore, which intersects said piston bore is formed in the valve body. 
     A piston cartridge is disposed at least partially within the cartridge bore. The piston cartridge comprises a longitudinal piston rod a first piston head secured to one end of the piston rod, and a second piston head secured to a second end of the piston rod, where the second piston head is disposed in the piston bore. The piston cartridge also includes a poppet member slidably disposed on the piston rod within the output counterbore, and a poppet bias spring located between the poppet member and the first piston head biasing the poppet member in a poppet bias direction against the sealing ledge. The valve may further include an end cap spring acting against the first piston head, biasing the piston rod in the poppet bias direction, and a bearing sleeve inserted into the bearing counterbore, extending into the output counterbore. This embodiment may include a pilot control solenoid including a pilot fluid input port, a pilot fluid output port and an exhaust fluid port. The pilot fluid input port is in fluid communication with the pilot control reentrant bore and the pilot fluid output port is in fluid communication with the solenoid control reentrant bore, wherein the pilot fluid input port may be selectively placed in fluid communication with the pilot fluid output port and may be selectively placed in fluid communication with the exhaust fluid port. The first piston head is disposed in the bearing sleeve. 
     These and other features and advantages of the invention will become apparent from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a fluid flow system according to the present invention. 
         FIGS. 2A and 2B  are exploded cross-section views of an embodiment of a check valve according to the present invention. 
         FIG. 3A  is a cross-section view of an embodiment of a check valve according to the present invention including a flow control option. 
         FIG. 3B  is an elevation view of the embodiment of  FIG. 3A . 
         FIG. 4A  is a cross-section view of an embodiment of a check valve according to the present invention including a counterbalance mechanism. 
         FIG. 4B  is an elevation view of the embodiment of  FIG. 4A . 
         FIG. 4C  is an elevation view of an embodiment of a check valve according to the present invention including a counterbalance pilot. 
         FIG. 5A  is a cross-section view of an embodiment of a check valve according to the present invention including an adjustable pilot mechanism. 
         FIG. 5B  is an elevation view of the embodiment of  FIG. 5A . 
         FIG. 6A  is a cross-section view of an embodiment of a check valve according to the present invention including a sensor port. 
         FIG. 6B  is an elevation view of the embodiment of  FIG. 6A . 
         FIG. 7A  is a cross-section view of an embodiment of a check valve according to the present invention including a remote controlled exhaust mechanism. 
         FIG. 7B  is an elevation view of the embodiment of  FIG. 7A . 
         FIG. 8A  is a cross-section view of an embodiment of a check valve according to the present invention including an alternate manual exhaust. 
         FIG. 8B  is an elevation view of the embodiment of  FIG. 8A . 
         FIG. 9A  is a cross-section view of an embodiment of a check valve according to the present invention including a solenoid controlled pilot. 
         FIG. 9B  is an elevation view of the embodiment of  FIG. 9A . 
         FIG. 9C  is a view taken along line  9 C- 9 C of  FIG. 9A . 
         FIG. 10A  is an elevation view of an embodiment of a check valve according to the present invention including an output swivel mount. 
         FIG. 10B  is an elevation view of the embodiment of  FIG. 10A . 
         FIG. 10C  is a cross-section view of the embodiment of  FIG. 10A . 
         FIG. 11A  is a front elevation view of an embodiment of a valve manifold including a plurality of valves according to the present invention. 
         FIG. 11B  is a bottom plan view of the embodiment of  FIG. 11A . 
         FIG. 11C  is a cross-section view of one of the plurality of valves of the embodiment of  FIG. 11A  schematically connected in a fluid system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     I. The System 
     Air pressure from the supply source  1  is connected to a control valve  2 . When the control valve  2  is energized to advance the air cylinder  4 , the air pressure goes into the check valve  100  and applies force to the poppet  230 . The poppet  230  is biased toward the seat  148  with a low force poppet spring  240  that opens when there is about a 1-2 psi pressure difference across the poppet  230 . With the poppet  230  open, the air moves into the air cylinder  4  raising the load  8 . 
     The air on the rod side of the cylinder  4  needs a passage to exhaust to atmosphere. The path is provided by a straight passage through the control valve  2  to atmosphere. 
     To lower the load, air pressure is applied to the rod side of the cylinder  4 , which is opposite the direction shown in  FIG. 1 . At the same time air is applied to the rod side, the opposite side needs a path to exhaust to atmosphere. In order for this to happen, the check valve  100  must be opened. This is accomplished by tapping air pressure off the retract line  9  or from an outside source and applying it to the pilot port  116 . The air pressure from the pilot port  116  opens the poppet  230  allowing air to flow from the output port  114  to the input port  112 , back through the control valve  2  and exhaust to atmosphere. 
     II. Valve 
     Turning now to  FIG. 2A  and  FIG. 2B , an embodiment  100  of a valve according to the present invention is shown. Generally, the valve  100  includes a valve body  102 , into which a plurality of bores are formed. A first bore  110  is a cartridge bore, which includes a piston bore  110   a , an input counterbore  110   b , an output counterbore  110   c , and a bearing sleeve counterbore  110   d . An input reentrant bore  112  and an output reentrant bore  114  may be formed in a spaced relationship into the valve body  102 . The input reentrant bore  112  intersects the cartridge bore  110  at the input counterbore  110   b  and the output reentrant bore  114  intersects the cartridge bore  110  at the output counterbore  110   c . A pilot reentrant bore  116  is formed into the valve body  102  and intersects the cartridge bore  110  at the piston bore  110   a.    
     Inserted into the cartridge bore  110  is a piston cartridge  200 . In a first embodiment, the piston cartridge  200  generally includes a longitudinal piston rod  202 , a first piston head  210 , a second piston head  220 , and a poppet member  230  slidably disposed on the piston rod  202  and located generally between the first and second piston heads  210 , 220 . The substantially free sliding movement of the poppet member  230  generally, without pilot pressure, checks air in one direction and allows free flow in the opposite direction. The first piston head  210  is connected to a first end  204  of the piston rod  202 , and the second piston head  220  is connected to a second end  206  of the piston rod  202 , which may include a threaded engagement means  208  to cooperate with the second piston head  220 . The first piston head  210  is preferably formed with an annular piston seal groove  212  about its circumference, which accommodates placement of a first piston seal  214 , such as a grooved elastomeric O-ring. The first piston head  210  also preferably provides a first poppet stop surface  216  and a piston bias bore  218  adapted to accept a piston bias spring, such as an end cap spring  256 . The second piston head  220  is preferably formed with an annular piston seal groove  222  about its circumference, which accommodates placement of a second piston seal  224 , such as a grooved elastomeric O-ring. The second piston head  220  also preferably provides a second poppet stop surface  226 . 
     The poppet member  230  is slidably disposed on the piston rod  202 , the piston rod  202  preferably extending through the poppet member  230 . Situated between the poppet member  230  and the piston rod  202 , there may be a rod gasket or seal  203  such as an elastomeric O-ring that is disposed in an annular groove  205  formed about the piston rod  202 . Situated between the poppet member  230  and the first piston head  210  is a poppet bias spring  240 , which biases the poppet member  230  in a bias direction  242 , which is generally towards the second piston head  220 . The poppet member  230  itself may generally be formed as a frustoconical member extending between a first end  232  and a second end  234 , and further including an annular sealing flange  236  disposed thereabout. The annular sealing flange  236  includes a sealing surface  238 , which, when the piston cartridge  200  is assembled, generally faces towards the second piston head  220 . Disposed on and/or recessed into the sealing surface  238  is a poppet gasket  239 , which may be formed of an elastomeric material. 
     The piston cartridge  200  may generally be assembled by situating the rod gasket  203  in the annular groove  205  provided on the piston rod  202 . The poppet bias spring  240  may be placed on the rod  202 , resting against the first piston head  210 . The poppet member  230  may be slid onto the piston rod  202  and the second piston head  220  may be secured to the piston rod  202 . The piston seals  214 , 224  are placed around their respective piston heads  210 , 220 . 
     As indicated above, the cartridge bore  110  is provided with a plurality of counterbores. The output counterbore  110   c , formed larger than the input counterbore  110   b , provides a poppet seat, or sealing ledge  148  and further provides sufficient clearance for sliding movement of the poppet member  230  and desired fluid flow. To maintain the piston cartridge  200  in a preferred orientation, a bearing sleeve  250  may be used. The bearing sleeve  250  includes a piston aperture  252 , into which the first piston head  210  may be situated, the bearing sleeve  250  circumferentially contacting the first piston seal  214 . Disposed around the bearing sleeve  250  is preferably a bearing sleeve seal  254 , such as an elastomeric O-ring, which is adapted to sealingly engage the output counterbore  110   c  provided in the cartridge bore  110 . 
     In the first embodiment  100 , the piston cartridge  200  and bearing sleeve  250  is maintained in the valve body  102  by a piston cover  130 , which generally extends to cover one side of the cartridge bore  110  and is secured to the valve body  102 , such as by using a plurality of threaded fasteners  132 . On the opposite end of the cartridge bore  110  from the piston cover  130 , a manual release mechanism  150  may be provided. The manual release mechanism  150  may include a manual release plunger  154 , and a plunger gasket  158 . The manual release plunger  154  is a flanged post that extends through the valve body  102  and into the piston bore  110   a.    
     This allows the release of air that may be trapped on either side of the air cylinder  4 . 
     III. General Valve Operation 
     Turning back to  FIG. 1 , an embodiment of a system according to the present invention is shown incorporating an embodiment of a check valve according to the present invention. A fluid source  1  is coupled through a valve  2  to the check valve  100  input bore  112 . 
     The output bore  114  is connected to the plunger side of an air cylinder  4 . The rod side of the air cylinder  4  exhausts out through the control valve  2  to the atmosphere. When fluid is pumped from the supply source  1 , it forces the plunger in the air cylinder  4  towards the rod side, thus extending the rod to lift a load  8 . To lower the load  8 , the flow control valve  2  is manipulated to connect the supply source  1  to the rod side of the cylinder  4  through the retract line  9 . However, the fluid on the plunger side of the cylinder  4  needs to be able to exhaust if the plunger is to move. Thus, a tap line may place the retract line  9  in fluid communication with the pilot port  116  on the valve  100 . In this way, the fluid pressure in the piston bore  110   a  forces the cartridge  200  against the bias of the end cap spring  156 , thereby unseating the poppet member  230 , thus opening the valve  100  and allowing the exhaust fluid from the plunger side of the cylinder  4  to enter the output bore  114 , past the poppet member  230 , out of the input bore  112 , and to exhaust out through the control valve  2  to the atmosphere. In the event of any loss of fluid pressure from the supply source  1 , however, the check valve  100  will close, thereby maintaining the cylinder  4  and load  8  in a substantially safe and static condition. 
     Advantages of the invention include smaller valves allowing for a more compact design and higher pressure capacity. 
     III. Control Valve Options 
     A. Flow Controls 
     A first option is a flow control option as shown in  FIGS. 3A and 3B . The flow control allows the operator to adjust the speed of flow without having to add an external flow control. This eliminates cost and makes for a more compact design. Metering out is the preferred method of controlling air cylinder speed. 
     The flow control meters airflow from the output port  114  to the input port  112 . This is accomplished by limiting the movement of the cartridge  200  when air is applied to the pilot port  116 . Air pressure applied to the pilot port  116  moves the entire cartridge assembly  200  away from the poppet seat  148 , causing the passage to open between the output port  114  and the input port  112 . An adjusting screw  29  extending through the housing  102  and into the output counterbore  110   c  limits cartridge  200  travel and therefore, limits the travel of the poppet  230 . A lock nut  30  is used to lock the adjusting screw  29  in position. A shock absorbing impact pad (not shown) may be installed in or on the piston rod  202  to limit the impact force between the piston rod  202  and the adjusting screw  29 . The end cap spring  256  keeps the poppet  230  in contact with the poppet seat  148  when the valve  100  is in the static, or non-piloted condition. A flow control cover plate  32  is used to close the end of the valve  100 . The cover  32  is threaded with fine threads in order to engage the adjusting screw  29  and allow for flow adjustment. The cover is secured with screws  21 . A small air passage  68  is machined into the flow control cover plate  32  to prevent back pressure. 
     B. Counterbalance 
     Another option is a counterbalance mechanism, as seen in  FIGS. 4A and 4B . The counterbalance valve can be adjusted to hold a load in position and maintain air pressure to hold that position. Because the counterbalance maintains a constant resistance pressure in the air cylinder, the load will not take off in a run-away condition when the load is lowered. 
     The counterbalance uses an air passage  34  that is drilled in the valve body  102  that intersects the output port  114  and the pilot port  116 . The pilot port  116  is sealed air-tight with a threaded plug  32  and sealant. The drilled hole is sealed with a stainless steel ball  33 . When air pressure increases on the output side  114 , the same pressure is now applied to the piston bore  110   a . If the air pressure increases enough to overcome the end cap spring  256 , the cartridge  200  will begin to open, allowing air to flow from the output port  114  to the input port  112 . The air pressure required to open the valve can be adjusted by turning the adjusting screw  35 . Turning the screw  35  clockwise will increase the pressure required to open the valve  100 , due to compression of the end cap spring  256 . Counterclockwise adjustment will reduce the pressure required to open the valve  100 . A locknut  36  will lock the adjusting screw  35  in place. 
     As seen in  FIG. 4C , a pilot can be added to the counterbalance by mounting a cover plate  92  to the pilot end of the valve so that the counterbalance can be opened with a pilot signal if desired. The cover plate  92  houses a piston  93  that is biased with a spring  94 , and is sealed with a seal  95 . An air passage  96  is machined into the cover plate  92  to prevent pressure buildup. When pressure is applied to the pilot port  97 , the piston  93  moves and applies a force to the manual release  154  and moves the cartridge  200  to the open position. 
     C. Adjustable Pilot 
     Another option is an adjustable pilot mechanism as shown in  FIGS. 5A and 5B . The adjustable pilot valve is designed for faster and quicker stopping. In some machines where long plumbing lines store large amounts of air, it may take a couple of seconds to empty those air lines. If the pilot port  116  is connected to these long lines, the stored pressure in the exhaust lines will hold the valve open until the pressure drops low enough to close the valve. The adjustable pilot design solves this problem by setting the valve to close at a desired pilot pressure. 
     The air pressure required to open the valve can be adjusted by turning an adjusting screw  35 . Turning the screw clockwise will increase the pressure required to open the valve, due to compression of the end cap spring  256 . Counterclockwise adjustment will reduce the pressure required to open the valve. A locknut  36  will lock the adjusting screw  35  in position so that the pressure setting doesn&#39;t change during operation. 
     D. Sensor Port 
     Another option is a sensor port as shown in  FIGS. 6A and 6B . A sensor port added to a standard valve allows the operator to monitor whether a device is pressurized. 
     A sensor port  39  can be added to allow for the insertion of a pressure sensor that will signal when pressure is trapped or exhausted in the output counterbore  114  of the valve. An air passage  37  in fluid communication with the output counterbore  114  is added to the valve body  102  and sealed with an O-ring  38 . A cover plate  40  can have a number of different port configurations. The cover plate  40  is secured with screws  21 . 
     E. Auto Release with Metered Exhaust 
     A pneumatically operated release mechanism, or auto release, may be used as shown in  FIGS. 7A and 7B . 
     Auto release is advantageous when the valve is buried in a system and/or not readily accessible for service. A pilot signal can be removed from the valve to release the trapped air to allow for safe servicing of the equipment. A needle valve  48  makes sure that the air pressure is release slowly, so that loads are gently lowered to the ground. 
     The auto release consists of an air passage  37  and O-ring seal  38 . An air signal is applied to a second pilot port  41  that can come from any air source. Air pressure is applied to the second pilot port  41 , which moves a piston  42  to seal on a piston seat  46 . The resulting seal is air-tight because of the O-ring  45  attached to the face of the piston  42 . When the air pilot signal is removed, the piston  42  moves away from the seat  46  causing an air passage to open to atmosphere through an exhaust hole  47 . The needle valve  48  allows for a controlled release of the exhaust air. An O-ring  49  on the needle valve  48  keeps the air from leaking past the needle. 
     F. Manual Exhaust to Atmosphere 
     A manual exhaust may be provided on a side of the valve opposite the piston bore  110   a , as shown in  FIGS. 8A and 8B . The advantage of this design is that it allows for a manual release when a solenoid is attached to the valve. It also allows the trapped air to be directly released to atmosphere without first going through a control valve. 
     A rear manual release button  50  can be added when a solenoid is attached to the location of the standard manual release  22 , or if otherwise desired. The button  50  is sealed with an O-ring  51  seated around a portion of the button  50  as shown. The button  50  is preferably fluted, or has grooves cut down a majority of its length that stop right above the O-ring  51 , to allow the O-ring  51  to seal between the manual release button  50  and the cover  20 . An outer O-ring  52  seals between the cover plate  20  and the valve body  102 . A manual release spring  53  keeps the manual release button  50  biased against the cover plate  20 . An air passage  54  in fluid communication with the output counterbore  114  completes the path that will allow air to exhaust to atmosphere when the rear manual release button  50  is depressed. 
     G. Solenoid Controlled Pilot with Manual Release 
     It is sometimes easier to control the pilot signal with a solenoid valve that is piped to a constant pressure source, as shown in  FIGS. 9A and 9B . The check valve can be opened and closed by sending an electronic signal to the solenoid. 
     The solenoid valve  55  may be a normally closed 3-way, two-position, air valve that is shifted with AC or DC voltage. There are 3 ports on the valve, and 2 are directly connected to the valve body  102  through a sealed air passage. A pilot passage, or pilot control reentrant bore,  56  is in fluid communication with the pilot port  116  and a piston passage, or solenoid control reentrant bore,  57  is in fluid communication with the piston bore  110   a  in contact with the cartridge  200 . An exhaust port  58  on the solenoid  55  is open to the atmosphere. Air pressure is continuously supplied to the pilot port  116 . When the solenoid  55  is energized, it opens and allows air to flow from the pilot port  116 , through the pilot passage  56 , through the solenoid valve  55  and back into the valve body  102 , via the piston passage  57 . This causes the cartridge  200  to shift and open the valve. When the electronic signal is removed, the air passage through the solenoid valve  55  is closed and the air inside the piston bore  110   a  is released back through the piston passage  57  and out the exhaust port  58 . The manual release button  50 , if desired, may be moved to the back of the valve because the solenoid  55  is mounted in the original location of the manual release (see the previous section). 
     H. Swivel Design 
     Yet another option is a swiveling valve, as shown in  FIGS. 10A ,  10 B and  10 C. The swivel design allows for direct attachment to a pneumatic device, such as an air cylinder  4 , and the ability to rotate the valve to any rotational position when attached to an air cylinder  4 . This eliminates extra plumbing and makes for a compact design. Attaching the valve directly to the air cylinder  4  also helps to eliminate cylinder bounce. 
     The swivel design consists of a standard valve with a swivel  59  attached to allow the valve to be directly attached to the air cylinder  4  or other pneumatic devices. The swivel  59  is held in place with a swivel plate  60  and is sealed air-tight with an O-ring  61 . The air passage  62  through the valve body  102  provides a path from the output counterbore  110   c  to the swivel  59 . The swivel plate  60  is held in place with screws (not shown). 
     I. Manifold Mounted Cartridge 
     Another embodiment may include a plurality of cartridges  200  within the same valve body  63 , as shown in  FIGS. 11A ,  11 B and  11 C. The cartridge  200  can be mounted in manifolds, air cylinder end caps, and other devices to become an integral part of the product. This can save time and money, especially where mass production is involved. Because of the simple one-piece body design, the cavity for the cartridge can be machine from one side of the part and can be replaced in a very short time. 
     The design of the cartridge  200  allows it to be mounted in a machined manifold  63 . The sleeve bearing  250  design is less expensive to manufacture and maintain concentricity. The insertion of the end cap spring  256  inside of the first piston head  210  also allows for a lower profile design and a less expensive cover plate. The cost for multiple cartridge designs is significantly reduced with this new design. A single cover plate  64  can be used to cover several mounted cartridges, instead of each cartridge having an individual cover. 
     In this design, the input counterbores  110   b  of all of the cartridge bores  110  may be cascaded together through a common header channel  77  formed into the valve body, which is in fluid communication with a common input port  79 . The first adjacent valves  81  are provided with a pressure source bore  113 , also in fluid communication with each respective input counterbore  110   b . Thus, the pressure source bore  113  from a preceding valve is coupled to an input port  112  on an adjacent valve. Each respective output port  114  and respective pilot port  116  may be coupled to distinct pneumatic devices for control thereof. 
     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. For instance, it will occur that various combinations of the features herein described may be accommodated. For instance, while the preferred embodiment has been generally described as a pneumatic linear actuator, it is to be understood that an embodiment of the present invention may utilize or be utilized with any fluid motor. Furthermore, while the preferred embodiment has been described in connection with air as the fluid, it is to be understood that a valve according to the present invention would also function with other fluids such as oil and water. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.