Abstract:
A passive cycle skipping valve comprising a pawl and a wheel comprising a first plurality of pins, wherein a distal end of the pawl is configured to engage any of the first plurality of pins where when the second pin is separated from the first pin by at least a threshold pin separation distance, the valve opens and when the second pin is not separated from the first pin by at least the threshold pin separation distance, the valve does not open.

Description:
FIELD OF THE INVENTION 
     Various implementations, and combinations thereof, are related to fluid valves and, more particularly, to passive cycle-skipping fluid valves. 
     BACKGROUND OF THE INVENTION 
     Fluid valves work by allowing and disallowing flow through the valve or, in the case of directional control valves, by directing the flow to alternating ports. In typical on/off valves there are three connection points: an input port where pressurized fluid is connected, an outlet port where fluid will flow when the valve is open, and an actuator connection point where a mechanical device causes the valve to open and close. Opening and closing of the valve can be accomplished via manual means, such as a home faucet, electrical means where an electrical signal actuates a solenoid, pneumatic means where compressed air (or gasses) actuate a diaphragm or piston, or hydraulic means where pressurized hydraulic fluid actuates a diaphragm or piston. In all of these cases the manual lever, electronic solenoid, pneumatic diaphragm or hydraulic diaphragm or piston move a part within the valve causing the valve to open or close. In all of these cases an external force or signal is required to make the valve switch between open and closed states. 
     SUMMARY OF THE INVENTION 
     In one implementation, a passive cycle skipping valve is presented. The passive cycle skipping valve comprises a pawl and a wheel comprising a first plurality of pins, wherein a distal end of the pawl is configured to engage any of the first plurality of pins where when the second pin is separated from the first pin by at least a threshold pin separation distance, the valve opens and when the second pin is not separated from the first pin by at least the threshold pin separation distance, the valve does not open. 
     In another implementation, a system is presented comprising a passive cycle skipping valve and a plurality of fluid emitters, wherein the passive cycle skipping valve controls the emission of at least one of the plurality of fluid emitters. The passive cycle skipping valve comprises a pawl and a wheel comprising a first plurality of pins, wherein a distal end of the pawl is configured to engage any of the first plurality of pins where when the second pin is separated from the first pin by at least a threshold pin separation distance, the valve opens and when the second pin is not separated from the first pin by at least the threshold pin separation distance, the valve does not open. 
     In yet another implementation, a method is presented for delivering a fluid from a pressurized line while skipping one or more pressure cycles. The method comprises disposing on a distal end of a conduit conveying a fluid having a first pressure, a passive cycle skipping valve comprising a pawl and a wheel comprising a first plurality of pins, wherein a distal end of said pawl engages a first pin of the first plurality of pins, rotating the wheel until a second pin of the first plurality of pins contacts the pawl, opening the valve when the second pin is separated from the first pin by at least a threshold pin separation distance, and not opening the valve when the second pin is not separated from the first pin by at least said threshold pin separation distance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like elements bear like reference numerals. 
         FIG. 1  is an exploded view of an exemplary embodiment of Applicants&#39; passive cycle skipping valve; 
         FIG. 2  an exploded view of the piston rod assembly of  FIG. 1 ; 
         FIG. 3  is an exemplary diagram of the pawl of the passive cycle skipping valve of  FIG. 1 ; 
         FIGS. 4A and 4B  are exemplary diagrams of the indexing wheel of the passive cycle skipping valve of  FIG. 1 ; 
         FIG. 5  is an exemplary diagram of the valve body of the passive cycle skipping valve of  FIG. 1 ; 
         FIG. 6A  is a perspective view of an exemplary diagram of the passive cycle skipping valve of  FIG. 1  in a first home position, or a non-pressurized state; 
         FIG. 6B  is a front view of the passive cycle skipping valve of  FIG. 6A ; 
         FIG. 6C  is a cross-section view of the passive cycle skipping valve of  FIG. 6A ; 
         FIG. 7A  is a perspective view of an exemplary diagram of the passive cycle skipping valve of  FIG. 1  in a trapped position, where no flow is allowed; 
         FIG. 7B  is a front view of the passive cycle skipping valve of  FIG. 7A ; 
         FIG. 8A  is a perspective view of an exemplary diagram of the passive cycle skipping valve of  FIG. 1  in a second home position, where flow will be allowed upon pressurization; 
         FIG. 8B  is a front view of the passive cycle skipping valve of  FIG. 8A ; 
         FIG. 9A  is a perspective view of an exemplary diagram of the passive cycle skipping valve of  FIG. 1  in a flow position wherein flow is allowed; 
         FIG. 9B  is a front view of the passive cycle skipping valve of  FIG. 9A ; 
         FIG. 9C  is a cross-section view of the passive cycle skipping valve of  FIG. 9A ; 
         FIG. 10  depicts a cross-section of the piston rod assembly of  FIG. 2  in the flow position; 
         FIG. 11A  is an exploded view of Applicants&#39; self-drain feature; 
         FIG. 11B  is a cross-section view of the self-drain feature of  FIG. 11A ; 
         FIG. 12A  is a block diagram of a typical installation of a drip circuit for plants; 
         FIG. 12B  is a block diagram of the installation of  FIG. 12A  illustrating the watering schedule of the depicted plants; 
         FIG. 12C  is a block diagram of the installation of  FIG. 12A  including Applicants&#39; passive cycle skipping valve; 
         FIG. 13  is a block diagram of an exemplary system wherein Applicants&#39; passive cycle skipping valve is used to control a large piloted valve; 
         FIG. 14  is a graph illustrating the flow from Applicants&#39; passive cycle skipping valve in gallons per hour under various fluid pressures; 
         FIG. 15A  is a cross-section view of an alternative embodiment of Applicants&#39; passive cycle skipping valve having a diaphragm and in the closed position; and 
         FIG. 15B  is a cross-section view of the passive cycle skipping valve of  FIG. 15A  in the flow position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the following description, this invention is described in preferred embodiments with reference to the figures in which like numbers represent the same or similar elements. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment, “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
       FIG. 1  is an exploded view of an exemplary embodiment of Applicants&#39; passive cycle skipping (PCS) valve  100  which allows output flow on predetermined pressure cycle intervals without an external pilot signal, the operation of PCS valve  100  being dependent only upon the pressurization and depressurization of the main supply line itself. As can be seen in the illustrated embodiment of  FIG. 1 , PCS valve  100  comprises piston rod assembly  132 , indexing wheel  106 , indexing wheel pivot pin  110 , pawl  104  having an integral return spring  212  ( FIG. 3 ), inlet fitting  146 , and outlet fitting  154  housed within valve body  102 . As will be appreciated by one of ordinary skill in the art, a pawl is a component that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Furthermore, it will be understood that the use of “wheel” for indexing wheel  106  is not limiting and includes any rotating part capable of performing the same function, such as, and without limitation, a gear, pinion, and spur wheel. 
     Valve body  102  is formed to include cavity  150  extending therethrough, wherein piston rod assembly  132  is disposed within cavity  150 . A cross-section of valve body  102  showing cavity  150  is depicted in  FIGS. 6C and 9C . As can be seen in the cross-section view of  FIGS. 6C and 9C , cavity  150  comprises piston bore  250 , piston rod bore  252 , clearance bore  253 , and exit bore  254 . As shown in  FIG. 1 , cavity  150  is sealed by inlet fitting  146  having o-ring  148  and outlet fitting  154  having o-ring  152 . Air filter  126  and vent retainer  128  are disposed within opening  130  of valve body  102 . 
     Referring now to  FIG. 5 , valve body  10  is further formed to include recess  158  having counter-bore  156 , wheel pivot pin  110 , and aperture  220 , wherein aperture  220  communicates with piston rod bore  252 . As can be seen in the illustrated embodiment of  FIG. 1 , indexing wheel  106  sits within counter-bore  156  such that wheel pivot pin  110  extends through aperture  214  ( FIGS. 4A and 4B ) of indexing wheel  106  and rotateably secures indexing wheel  106  within counter-bore  156 . Periphery  256  of counter-bore  156  is ratcheted such that anti-rotational spring  108  ( FIGS. 4A and 4B ) of indexing wheel  106  engages ratcheted periphery  256  of counter-bore  156 , as will be discussed in greater detail below. Pawl  104  sits within recess  158  such that bore  210  ( FIG. 3 ) of pawl  104  is aligned with aperture  220 , wherein pawl pivot pin  144  of piston rod assembly  132  extends through aperture  220  and bore  210  to movably secure pawl  104  to piston rod assembly  132 . Notch  213  ( FIG. 3 ) of pawl  104  abuts one of the pins  218  ( a )- 218 ( f ) ( FIGS. 4A and 4B ) of indexing wheel  106  while integral return spring  212  abuts wall  222  ( FIGS. 5 ,  7 B, and  9 B) of recess  158 . Pawl  104  is illustrated in  FIG. 3 . A front view and perspective view of indexing wheel  106  is presented in  FIGS. 4A and 4B  respectively. 
     As shown in  FIG. 1 , cover  114  and gasket  112  sit flush with valve body  102  and are secured to valve body  102  by screws  116 ( a )- 116 ( f ) inserted through blind apertures  118 ( a )- 118 ( f ) and apertures  120 ( a )- 120 ( f ) and into internally threaded apertures  122 ( a )- 122 ( f ) ( FIG. 5 ). 
     Turning to  FIG. 2 , an exploded view of Applicants&#39; piston rod assembly  132  is presented. As can be seen in  FIG. 2 , piston rod assembly  132  comprises piston rod  138  having pawl pivot pin  144  extending outwardly therefrom. Piston  136  is attached to a first end of piston rod  138 , wherein piston  136  is formed to include annular groove  202  for seal  149 . A second end of piston rod  138  is formed to include annular grooves  140  and  142  for o-rings  206  and  208 , respectively. Return spring  134  fits around piston rod  138  and sits between piston  136  and pawl pivot pin  144 . 
     Piston rod assembly  132  further includes fluid passage  203  and fluid passage hole  204 . Fluid passage  203  is drilled concentric to the outside diameter of piston  136  and extends the length of piston rod assembly  132  intersecting with fluid passage hole  204 , wherein fluid passage hole  204  extends inwardly between o-rings  206  and  208 . Fluid passage  203  and fluid passage hole  204  allow fluid to flow through PCS valve  100  when valve  100  is in an open “flow” position, as will be described in greater detail below. 
     In certain embodiments, fluid passage hole  204  intersects fluid passage  203  at a right angle. In other embodiments, fluid passage hole  204  intersects fluid passage  203  at an angle less than a right angle. In certain embodiments, piston rod assembly  132  comprises a plurality of fluid passage holes, each intersecting fluid passage  204 . 
     Applicants&#39; PCS valve  100  can be used with all fluids compatible with the materials of construction. PCS valve  100  can be made from several types of non-reactive elements to accommodate various fluids. Applicants&#39; PCS valve  100  can also operate in pneumatic circuits. For the purpose of this description, the term “fluid” will be understood to refer to all fluids that can be used with Applicants&#39; PCS valve  100  including, but not limited to, gases, air, water, and hydraulic fluid. 
     An alternative embodiment of Applicant&#39;s passive cycle skipping valve is presented in  FIGS. 15A and 15B  utilizing a diaphragm rod assembly. More specifically,  FIG. 15A  depicts alternative passive cycle skipping valve  190  in the closed, or no-flow, position and  FIG. 15B  depicts alternative passive cycle skipping valve  190  in the open, or flow, position. As can be seen in the illustrated embodiments of  FIGS. 15A and 15B , passive cycle skipping valve  190  comprises diaphragm  160  positioned between diaphragm cover  162  and diaphragm bell  164  and secured to rod  138  via threaded extension  166 , nut  168 , and o-ring  182 . Diaphragm  160 , diaphragm cover  162 , and diaphragm bell  164  are attached to one another via screws  170  and  172 , and to body  102  via screws  174  and  176 . In certain embodiments, additional screws may be employed as needed. 
     As is depicted in  FIG. 15B , as fluid enters via inlet  180  and fills chamber  251 , diaphragm  160  flexes and compresses spring  134  ( FIGS. 1 ,  2 ,  15 A,  15 B) moving rod  138  ( FIGS. 1 ,  2 ,  15 A,  15 B) laterally in piston rod bore  252  ( FIGS. 6C ,  9 C,  15 A,  15 B) such that fluid passage hole  204  ( FIGS. 2 ,  6 C,  9 C,  10 ,  15 A,  15 B) is within exit bore  254  ( FIGS. 6C ,  9 C,  10 ,  15 A,  15 B) allowing flow to pass through fluid passage  203  ( FIGS. 2 ,  6 C,  9 C,  10 ,  15 A,  15 B) and into exit bore  254 . 
     Applicants&#39; valve  100  is a passive counter skipping valve, allowing output flow on predetermined pressure cycle intervals without an external pilot signal. Rather, PCS valve  100  mechanically “counts” the pressurization and depressurization cycles of the supply line, allowing output flow after a predetermined number of cycles have lapsed.  FIGS. 6 ,  7 ,  8 , and  9  illustrate the flow cycle of Applicants&#39; PCS valve  100 . 
       FIGS. 6A ,  6 B, and  6 C illustrate PCS valve  100  in a non-pressurized state. This is referred to as a “home position” of PCS valve  100 . As pressure is applied to inlet fitting  146  via a line connected to connection  103 , return spring  134  (depicted only in  FIG. 6C  for clarity) compresses and piston rod assembly  132  moves towards outlet fitting  154 . Pawl  104  attached to pawl pivot pin  144  of piston rod assembly  132  is moved linearly and notch  213  engages pin  318 ( a ) on indexing wheel  106 , the linear movement of pawl  104  causing indexing wheel  106  to rotate counter-clockwise. This counter-clockwise motion continues until pin  318 ( b ) of indexing wheel  106  is pushed up against pawl  104  as depicted in  FIGS. 7A and 7B . 
     As can be seen in the illustrated embodiment of  FIGS. 7A and 7B , pawl  104  is trapped between pin  318 ( a ), pin  318 ( b ), and wall  222  of recess  158 , preventing further rotation of indexing wheel  106  and liner movement of piston rod assembly  132 . In this non-flow position, referred to as the “trapped position,” piston rod o-rings  206  and  208  are both disposed within piston rod bore  252  thereby preventing fluid flow either out of the valve exit path or backwards toward the valve inlet fitting. The trapped position is maintained as long as fluid pressure is maintained in the supply line. When the pressure in the supply line decreases, return spring  134  (not depicted) decompresses, pushing piston  136  toward inlet fitting  146  and PCS valve  100  is returned to the home position. Anti-rotational spring  108  of indexing wheel  106  engages the ratcheted periphery  256  of counter-bore  156 , preventing indexing wheel  106  from rotating in a clockwise direction during the retraction stroke of piston rod assembly  132 . 
     As is shown in the illustrated embodiment of  FIGS. 8A and 8B , when the supply line next pressurizes and pressure is applied to inlet fitting  146 , piston  136  again moves towards outlet fitting  154 . During the linear motion of piston rod assembly  132 , notch  213  of pawl  104  engages pin  318 ( b ) of indexing wheel  106 , causing indexing wheel  106  to rotate counter-clockwise. This motion continues until pin  318 ( c ) of indexing wheel  106  is pushed up against the side of pawl  104  as shown in  FIGS. 9A ,  9 B, and  9 C. This is referred to as the “flow position” of PCS valve  100 . When in the flow position, o-ring  208  extends outwardly from piston rod bore  252  and into exit bore  254 , allowing fluid to flow through piston rod assembly  132  into outlet fitting  154  and out of PCS valve  100  via a line connected to connection  105 .  FIG. 10  depicts a cross-section of piston rod assembly  132  in the flow position. As is illustrated in  FIGS. 9A and 9C , o-ring  206  is maintained inside piston rod bore  252  preventing fluid flow back toward inlet fitting  146 . 
     When Applicants&#39; PCS valve  100  is in the flow position as shown in  FIGS. 9A and 9B , flow will be maintained until the inlet pressure decreases below the pressure necessary to compress return spring  134  (depicted in  FIG. 9C  only for clarity). When the inlet pressure decreases, return spring  134  pushes piston rod assembly  132  back toward the home position. Anti-rotational spring  108  of indexing wheel  106  engages the ratcheted periphery  256  of counter-bore  156 , preventing indexing wheel  106  from rotating in a clockwise direction during the retraction stroke of piston rod assembly  132 . 
     The embodiment of PCS valve  100 , as depicted in  FIGS. 6A-9B , has two flow positions and four trapped positions, as is indicated by the positions of the pins of indexing wheel  106 . Each time the supply line pressurizes and then depressurizes, valve  100  cycles through the flow and trapped positions described in connection with  FIGS. 6A-9B . 
     As will be appreciated by one of ordinary skill in the art, the number of home positions, flow positions, and trapped positions is determined by the arrangement of the pins of indexing wheel  106 , as the arrangement of pins dictates the cycle of PCS valve  100 . The embodiment of PCS valve  100  depicted in  FIGS. 6A-9B  is a tertiary valve, meaning that the exit flow is allowed every third time inlet pressure is applied. As can be seen in  FIG. 4A , which also depicts a tertiary valve, the spacing between pins  218 ( a )- 218 ( f ) varies, with the largest spacing, between pins  218 ( c ) and  218 ( d ) as well as  218 ( f ) and  218 ( a ). Thus, when pawl  104  engages pins  218 ( a ) or  218 ( d ), valve  100  will transition into the flow position. 
     Applicants&#39; PCS valve  100  can produce any cycle desired based upon the positioning of the index wheel pins. Cycles can be both symmetrical (e.g., binary, tertiary, etc.) and asymmetrical. Examples cycles achievable with Applicants&#39; valve  100  are presented in Table 1. Table 1 is illustrative only and not limiting. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Symmetrical Binary 
                 On-Off-On-Off-On . . . 
               
               
                   
                 Symmetrical Tertiary 
                 On-Off-Off-On-Off-Off-On . . . 
               
               
                   
                 Symmetrical Quertiary 
                 On-Off-Off-Off-On-Off-Off-Off-On . . . 
               
               
                   
                 Symmetrical Tertiary 
                 On-On-Off-On-On-Off . . . 
               
               
                   
                 Asymmetrical 
                 On-Off-Off-On-Off-Off-Off-On . . . 
               
               
                   
                 Asymmetrical 
                 On-On-Off-On-Off-Off-On . . . 
               
               
                   
                   
               
             
          
         
       
     
     In certain embodiments, indexing wheel  106  is two sided, thus having a first set of pins on a first side and a second set of pins on a second side. In such an embodiment, a user can alter the cycle of PCS valve  100  by flipping indexing wheel  106 . By way of example and not limitation, by flipping indexing wheel  106 , a user could change PCS valve  100  from a binary cycle to a tertiary cycle. In certain embodiments, the pins of indexing wheel  106  are moveable. In such an embodiment, a user can set the cycle of PCS valve  100  by altering the spacing between the pins. 
     In certain embodiments, Applicants&#39; PCS valve  100  further comprises a self-drain feature to allow bi-directional flow through valve  100  when the pressure in valve  100  is less than about 3 psi. By “about 3 psi,” Applicants mean 3 psi plus or minus 5%. An exemplary embodiment of Applicants&#39; self-drain feature is presented in  FIGS. 11A-B . As can be seen in the illustrated embodiment of  FIG. 11A , Applicants self-drain feature includes spherical bearing  302 , spring  304 , o-ring  306 , and threaded drain cap  308 , wherein drain cap  308  screws into a threaded bore located at the end of piston rod assembly  132  (illustrated in  FIG. 11B ). A cross-section view of Applicants&#39; self-drain feature is presented in  FIG. 11B . As can be seen in  FIG. 11B , drain cap  308  further comprises drain  314 . 
     When fluid pressure within piston rod assembly  132  is greater than about 3 psi, spherical bearing  302  will compress spring  304  until bearing  302  is against o-ring  306 , preventing fluid from flowing through drain  314 . As the pressure within piston rod assembly  132  decreases, spring  304  will decompress, allowing fluid to drain through drain  314 . 
     A threshold of about 3 psi for fluid to drain from PCS valve  100  is exemplary only. Applicants&#39; self-drain feature can be adjusted to drain at any pressure by adjusting the strength of spring  304 . 
     Turning now to  FIGS. 12A-C , an example of Applicants&#39; PCS valve  100  is presented to further illustrate to persons skilled in the art how to make and use the invention. This example is not intended as a limitation, however, upon the scope of the invention, which is defined only by the appended claims. 
     By way of example and not limitation,  FIG. 12A  illustrates the typical installation of a drip circuit for plants comprising timer-operated solenoid valve  502 , main line tubing  520 , and branch tubing  522 ,  524 ,  526 , and  528  connected to emitters  504 ,  508 ,  512 , and  516  for watering plants  506 ,  510 ,  514 , and  518 . Plants  506 ,  510 ,  514 , and  518  have a variety of irrigation needs and differ in terms of the volume of water needed and the frequency of watering cycles. Plants  506  and  510  are illustrated as container plants and need more frequent, lighter waterings. Plant  514  is an established tree and plant  518  is a cactus, both needing less frequent, deeper waterings than container plants  506  and  510 . However, as can be seen in the illustrated embodiment of  FIG. 12B , with the drip circuit illustrated, each plant receives the same amount of water at the same frequency. If sufficient water is provided to container plants  506  and  510  then plants  514  and  518  are overwatered. If this is compensated for by reducing the frequency of the waterings, plants  506  and  510  may not receive enough water. 
     As can be seen in  FIG. 12C , by using Applicants&#39; PCS valve  100  plants  506  and  510  can be watered frequently while plants  514  and  518  receive fewer waterings without altering the drip circuit. The embodiment of PCS valve  100  illustrated in  FIG. 12C  has a cycle interval ratio of 3:1, meaning there are three pressure cycles per output of valve  100 . Thus, if plants  506  and  510  are watered, by way of example and not limitation, three times per week, plants  514  and  518  will only receive water once per week. 
       FIG. 13  presents an exemplary system wherein Applicants&#39; PCS valve  100  is used to control a large piloted valve. As will be appreciated by one of ordinary skill in the art, a pilot valve is a small valve that controls a limited-flow control feed to a separate piloted valve, the piloted valve controlling a high pressure or high flow feed. Pilot valves are useful because they allow a small and easily operated feed to control a much higher pressure or higher flow feed, which would otherwise require a much larger force to operate. 
     In the illustrated embodiment of  FIG. 13 , drip circuit  600  comprises main line  620 , which connects to both pressure regulator  602  and pilot operated diaphragm control valve  606 , solenoid valve  604 , PCS valve  100 , branch lines  622 ,  624 , and  626 , and emitters  608 ,  610 ,  612 ,  614 ,  616 , and  618 . Emitters  608 ,  610 , and  612  are controlled by solenoid valve  604  where emitters  614 ,  616 , and  618  and pilot operated diaphragm control valve  606  is controlled by PCS valve  100 . Thus, in the illustrated embodiment of  FIG. 13 , emitters  608 ,  610 , and  612  will emit flow each time fluid is inputted into lines  622  and  624 , where emitters  614 ,  616 , and  618  and diaphragm control valve  606  will emit fluid based on the cycle interval ratio of PCS valve  100  even though line  620  to diaphragm control valve  606  is always pressurized. As is shown, PCS valve  100  in  FIG. 13  has a cycle interval ratio of 4:1. Thus, if water is input into lines  622  and  624  four times per week, flow will be allowed to emitters  614 ,  616 , and  618  and diaphragm control valve  606  only once per week. 
     Turning to  FIG. 14 , Applicants&#39; PCS valve  100  has been tested under a variety of conditions.  FIG. 14  illustrates the flow, in gallons per hour, from Applicants&#39; PCS valve  100  under various fluid pressures. As is shown, at 11.5 psi, Applicants&#39; PCS valve  100  opens and flow begins. The pressure at which valve  100  begins to allow flow at is dependent upon the strength of return spring  134 . By using springs of different strength, the pressure needed to operate valve  100  can be varied. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described implementations are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
     While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.