Abstract:
A control valve system has two valve trains each of which has a series of valves which dynamically move between a deactuated position and an actuated position. An inlet of the valve system is connected to an outlet of the valve system when all of the valves are actuated and the outlet of the valve system is connected to an exhaust when all of the valves are deactuated. Each valve train includes a solenoid valve which when actuated moves the remaining valve members to their actuated position. The various valves of each valve train are interconnected with the valve of the other valve train such that actuation of all of the valves in a substantially simultaneous manner will connect the inlet of the valve system to the outlet of the valve system and deactuation of all of the valves in a substantially simultaneous manner will connect the outlet to the exhaust. The valve system monitors the dynamic movement of the valve members during its operation will move to a locked out condition when any valve is in a deactuated position and when one other valve is in an actuated position. In the locked out condition, the outlet of the valve system is corrected to the exhaust. The valve system will remain in this locker out condition until a resetting operation is performed. During a reset operation, the valve system can not actuate one of the valve trains because one of the valve trains is depressurized during the reset operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 09/330,937, filed Jun. 11, 1999, which is now U.S. Pat. No. 6,155,293, which is a continuation-in-part of U.S. Ser. No. 08/770,878, filed Dec. 20, 1996, which is now U.S. Pat. No. 5,927,324, which claims benefit of provisional application No. 60/033,016, which was filed on Dec. 16,1996. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a control valve. More particularly, the present invention relates to a dual poppet fluid control valve which includes an anti-tiedown device that prevents the control valve from operating if the control valve reset has been tied down. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Machine tools of various types operate through a valving system which interacts with a pneumatic controlled clutch and/or brake assembly. For safety reasons, the control valves which are used to operate these machine tools require the operator to actuate two separate control signal applying contacts essentially simultaneously. This requirement of simultaneous application ensures that the operator will not have his hand near the moving components of the machine tool when an operating cycle is initiated. The two control signal applying contacts can then be connected to the valving system which allows compressed air to be delivered to the machine tool to perform its operating cycle. 
     Safety rules and regulations require the valving system to be designed such that if a component in the valving system malfunctions, the valving system will not allow additional movement of the machine tool. In addition, the valving system must ensure that a new operation cycle of the machine tool cannot be initiated after a component of the valving system has become defective. 
     Prior art electromagnetic valving systems which are utilized for the operation of machine tools meet these safety requirements through the use of a double valve assembly. The double valve assembly, includes two electromagnetic supply valves which are normally closed. Each of the supply valves is moved to an open position in response to an electrical control signal. The two supply valves are arranged in series with respect to the source of compressed air. The double valve assembly also includes two exhaust valves which are normally open. Each exhaust valve is closed by a respective supply valve when it is opened. It is therefore necessary for the supply valves to be opened simultaneously otherwise, supply air will be exhausted from the system through one of the exhaust valves. The opening and closing of the valve units is monitored by sensing air pressures in the respective valve units and then comparing these two pressures. The monitoring and comparing of these two pressures is accomplished by using a single air cylinder which is separated into two chambers by a piston. The pressure in each valve unit is delivered to one of the chambers. Thus, unequal pressures in the valve units will cause movement of the normally static piston which will then interrupt the electrical signal to one of the valve units. This and other external electronic monitoring arrangements are expensive and require that electrical signal processing equipment be designed and utilized. 
     The continued development of the valving systems for machine tools has been directed toward more reliable, simpler and less costly valving systems which both meet and exceed the safety performance requirements in force today as well as those proposed for the future. 
     The present invention provides the art with a control valve system which operates entirely pneumatically thus eliminating the need for electrical monitoring and the associated controls. The control valve system includes a plurality of valves each of which open or close during the actuation or deactuation of the valves. The control valve system monitors the dynamic movement of the various valves of the system to ensure the proper functioning of the control valve system. The control valve system moves to a locked out position upon sensing a malfunction and remains in this locked out position until a resetting operation is performed. Thus, the operation of the control assembly is totally dynamic and the system does not rely on the monitoring of a static member to ensure its proper function. 
     The above-described invention clearly meets the requirement that valving systems for more reliable, simpler, and less costly valving systems which both meet and exceed the safety performance requirements in force today as well as those proposed for the future. In some such systems, however, operators sometimes attempt to maintain the reset in an operating position in order to attempt to prevent the machine from locking out in response to a malfunction. 
     The present invention also provides the art with a control valve system which operates entirely prenumatically. The control valve system includes a plurality of valves each of which open or close during the actuation or deactuation of the valves. The control valve system monitors the dynamic movement of the various valves of the system to ensure the proper functioning of the control valve system. The control valve system moves to a locked-out position upon sensing a malfunction and remains in this locked out position until a reset operation is performed. The control valve system also includes anti-tiedown capability which prevents operation of the control valve system to supply an output pressure while the reset operation is performed. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is a schematic circuit diagram of the control valve system of the present invention shown in a deactuated position; 
     FIG. 2 is a schematic illustration of the control valve shown in its deactuated position; 
     FIG. 3 is a schematic circuit diagram of the control valve system of the present invention shown in an actuated position; 
     FIG. 4 is a schematic illustration of the control valve shown in its actuated position; 
     FIG. 5 is a schematic circuit diagram of the control valve system of the present invention shown in an abnormal position; 
     FIG. 6 is a schematic illustration of the control valve shown in its abnormal position; 
     FIG. 7 is a schematic circuit diagram of the control valve system of the present invention shown in a locked out position; 
     FIG. 8 is a schematic illustration of the control valve shown in its locked out position; 
     FIG. 9 is a schematic illustration of the valving system in accordance with another embodiment of the present invention; 
     FIG. 10 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit of the present invention shown in a pre-start condition; 
     FIG. 11 is a cross sectional view of the control valve system shown in the pre-start condition; 
     FIG. 12 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit of the present invention shown in a reset position; 
     FIG. 13 is s cross-sectional view of the control valve shown in its reset position; 
     FIG. 14 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit of the present invention shown in a deactuated position; 
     FIG. 15 is a cross-sectional view of- the control valve shown in its deactuated position; 
     FIG. 16 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit of the present invention shown in an actuated position; 
     FIG. 17 is a cross-sectional view of the control valve shown in its actuated position; 
     FIG. 18 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit of the present invention shown in an abnormal position; 
     FIG. 19 is a cross-sectional view of the control valve shown in its abnormal position; and 
     FIG. 20 is a schematic circuit diagram of the control valve system having an anti-tiedown circuit according to another embodiment of the present invention shown in its deactuated position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIGS.  1  and  2  a control valve system in accordance with the present invention which is designated generally by the reference numeral  10 . Control valve system  10  is shown as a schematic fluid circuit in FIG.  1  and as a fluid control valve in FIG.  2 . 
     Referring now to FIG. 2, control valve system  10  comprises a housing  12  having a fluid inlet passage  14 , a fluid outlet passage  16 , a fluid exhaust passage  18 , a first valve bore  20 , a second valve bore  22 , a first fluid reservoir  24  and a second fluid reservoir  26 . Disposed within first valve bore  20  is a first valve member  28  and disposed within second valve bore  22  is a second valve member  30 . Located within inlet passage  14  in a coaxial relationship with first valve member  28  is a third valve member  32 . Also located within inlet passage  14  in a coaxial relationship with second valve member  30  is a fourth valve member  34 . A pair of solenoid valves  36  and  38  are attached to housing  12 . 
     A plurality of fluid passages interconnect valve bores  20  and  22  with inlet  14 , outlet  16 , exhaust  18 , reservoir  24 , reservoir  26 , valve  36  and valve  38 . A fluid passage  40  extends between inlet passage  14  and an intermediate chamber  42  formed by bore  20 . A restrictor  44  is disposed within passage  40  to limit the amount of fluid flow through passage  40 . A fluid passage  46  extends between inlet passage  14  and an intermediate chamber  48  formed by bore  22 . A restrictor  50  is disposed within passage  46  to limit the amount of fluid flow through passage  46 . 
     A fluid passage  52  extends between chamber  42  and a lower chamber  54  formed by bore  20 . A restrictor  56  is disposed within passage  52  to limit the amount of fluid flow through passage  52 . A fluid passage  58  extends between chamber  48  and a lower chamber  60  formed by bore  22 . A restrictor  62  is disposed within passage  58  to limit the amount of fluid flow through passage  58 . A fluid passage  64  extends between passage  52  and reservoir  24  such that restrictor  56  is located between chamber  42  and reservoir  24 . A fluid passage  66  extends between reservoir  24  and the input to solenoid valve  38 . A fluid passage  68  extends between passage  58  and reservoir  26  such that restrictor  62  is located between chamber  48  and reservoir  26 . A fluid passage  70  extends between reservoir  26  and the input to solenoid valve  36 . A passage  72  extends between the output of solenoid valve  36  and an upper chamber  74  formed by bore  20 . A passage  76  extends between the output of solenoid valve  38  and an upper chamber  78  formed by bore  22 . 
     A cross passage  80  extends between the lower portion of chamber  42  and the upper portion of chamber  48 . A cross passage  82  extends between the lower portion of chamber  48  and the upper portion of chamber  42 . A fluid passage  84  extends between passage  80  and outlet passage  16 . A fluid passage  86  extends between passage  82  and outlet passage  16 . Outlet passage  16  is in communication with exhaust passage  18  through two ports  88  and  90 . The upper portions of chambers  54  and  60  are in communication with atmospheric pressure through passages  92  and  94 , respectively. A reset passage  96  extends into housing  12  and is in communication with the lower portion of chambers  54  and  60  by communicating with passages  52  and  58 , respectively. A pair of check valves  98  and  100  are disposed between reset passage  96  and passages  52  and  58  respectively, to prohibit fluid flow between passages  52  or  58  to reset passage  96  but allow fluid flow from reset passage  96  to one or both passages  52  and  58 . 
     Disposed within bore  20  is valve body or member  102  and disposed within bore  22  is valve body or member  104 . Valve member  102  comprises an upper piston  106 , an intermediate piston  108  and a lower piston  110  all of which move together as a single unit. Upper piston  106  is disposed within chamber  74  and includes a valve seat  112  which opens and closes port  88  located between outlet passage  16  and exhaust passage  18 . Intermediate piston  108  is disposed within chamber  42  and includes an annular passage  114  which fluidly connects passage  40  to passage  52  when piston  108  is seated against housing  12 . Lower piston  110  is located within chamber  54  and includes a pair of seals  116  which seal inlet passage  14  from passage  92  and seal chamber  54  from passage  92 . Valve member  104  comprises a upper piston  118 , an intermediate piston  120  and a lower piston  122  all of which move together as a single unit. Upper piston  118  is disposed within chamber  78  and includes a valve seat  124  which opens and closes port  90  located between outlet passage  16  and exhaust passage  18 . Intermediate piston  120  is disposed within chamber  48  and includes an annular passage  126  which fluidly connects passage  46  to passage  58  when piston  120  is seated against housing  12 . Lower piston  122  is located within chamber  60  and includes a pair of seals  128  which seal inlet passage  14  from passage  94  and seal chamber  60  from passage  94 . 
     Valve member  32  is located around lower piston  110  and comprises a valve seat  130  and a valve spring  132 . Valve spring  132  biases valve seat  130  against housing  12  to prohibit fluid flow between inlet passage  14  and chamber  42 . Valve member  34  is located around piston  122  and comprises a valve seat  134  and a valve spring  136 . Valve spring  136  biases valve seat  134  against housing  12  to prohibit fluid flow between inlet passage  14  and chamber  48 . 
     FIGS. 1 and 2 illustrate control valve system  10  in its deactuated position. Pressurized fluid from input passage  14  is biasing valve seats  130  and  134  against housing  12  closing communication between inlet passage  14  and both chambers  42  and  48 . Pressurized fluid is provided to passage  40  through restrictor  44 , to passage  52  through annular passage  114  through restrictor  56  and into chamber  54  to bias valve member  102  upward as shown in FIG. 2 seating piston  108  against housing  12 . Pressurized fluid also flows through passage  52 , through passage  64  to reservoir  24  and from reservoir  24  to the inlet of solenoid valve  38  through passage  66 . In a similar manner, pressurized fluid from input passage  14  is provided to passage  46  through restrictor  50  to passage  58  through annular passage  126  through restrictor  62  and into chamber  60  to bias valve member  104  upward as shown in FIG. 2 seating piston  120  against housing  12 . Pressurized fluid also flows through passage  58 , through passage  68  to reservoir  26  and from reservoir  26  to the inlet of solenoid valve  36  through passage  70 . Outlet passage  16  is in communication with exhaust passage  18  due to valve seats  112  and  124  being biased upward opening ports  88  and  90 . Intermediate chambers  42  and  48  are also open to exhaust passage  18  through cross passages  80  and  82 , respectively, through passages  84  and  86 , respectively. The fluid pressure below piston  110  and  122  of valve members  102  and  104 , respectively, bias valve members  102  and  104  upward maintaining control valve system  10  in the deactuated position. The connection between passages  40  and  52  through annular passage  114  and the connection between passages  46  and  58  through annular passage  126  maintain fluid pressure within chambers  54  and  60  and reservoirs  24  and  26 . 
     FIGS. 3 and 4 illustrate control valve system  10  in its actuated position. Both solenoid valves  36  and  38  have been substantially simultaneously actuated. The actuation of solenoid valve  36  connects passage  70  and thus reservoir  26  to passage  72 . Pressurized fluid is directed into chamber  74  to move valve member  102  downward as shown in FIG.  4 . The diameter of piston  106  is larger than the diameter of piston  110  thus causing the load which moves valve member  102  downward. In a similar manner, the actuation of solenoid valve  38  connects passage  66  and thus reservoir  24  to passage  76 . Pressurized fluid is directed into chamber  78  to move valve member  104  downward as shown in FIG.  4 . The diameter of piston  118  is larger than the diameter of piston  122  thus causing the load which moves valve member  104  downward. When valve members  102  and  104  move downward, an annular flange  140  on piston  110  unseats valve seat  130  and an annular flange  142  on piston  122  unseats valve  134 . Pressurized fluid flows from inlet passage  14  into the lower portion of chamber  42  through passage  80  to the upper portion of chamber  48  and through a gap  144  between valve member  104  and housing  12  to provide pressurized fluid to outlet passage  16 . Pressurized fluid also flows through passage  84  to outlet passage  16 . In a similar manner, pressurized fluid flows from inlet passage  14  into the lower portion of chamber  48  through passage  82  to the upper portion of chamber  42  and through a gap  146  between valve member  102  and housing  12  to provide pressurized fluid to outlet passage  16 . Pressurized fluid also flows through passage  86  to outlet passage  16 . The movement of valve members  102  and  104  downward seats valve seats  112  and  124  against housing  12  to close ports  88  and  90  to isolate outlet passage  16  from exhaust passage  18 . The fluid pressure within reservoirs  24  and  26  will initially be reduced when valves  36  and  38  are actuated by the fluid pressure will return to supply pressure at inlet  14  because reservoirs  24  and  26  are still open to inlet  14  and outlet  16  is isolated from exhaust  18 . 
     FIGS. 5 and 6 illustrate control valve system  10  in an abnormal position. In FIGS. 5 and 6, valve member  104  is located in its upward position while valve member  102  is located in its lower position. Both solenoid valves  36  and  38  are located in their deactuated position. Valve member  104  is located in its upward position similar to that shown in FIG.  1 . Pressurized fluid from inlet passage  14  is supplied to passage  46  through restrictor  50  to passage  58  through annular passage  126  through restrictor  62  and into chamber  60  to bias valve member  104  upward as shown in FIG. 6 seating piston  120  against housing  12 . Pressurized fluid also flows through passage  68  to reservoir  26  and from reservoir  26  to the inlet of solenoid valve  36  through passage  70 . Outlet passage  16  is in communication with exhaust passage  18  due to valve seat  124  being biased upward opening port  90 . Valve member  102  is located in its lower position which opens various passages to outlet passage  16  which, because the position of valve member  104 , is open to exhaust  18 . The upper portion of chamber  42  is open to exhaust through gap  146 . Pressurized fluid from inlet passage  14  is bled to exhaust through passage  40  and through the upper portion of chamber  42  through gap  146 , through outlet passage  16 , through port  90  to exhaust passage  18 . In addition, pressurized fluid from inlet passage  14  will bleed to exhaust  18  by entering the lower portion of chamber  42 , flow through passage  80 , through passage  84 , through outlet passage  16 , through port  90  and into exhaust passage  18 . Pressurized fluid in passage  52  and thus chamber  54  is also bled to exhaust through restrictor  56  which removes the biasing being applied to valve member  102 . A leak path also exists from inlet  14  to the lower portion of chamber  42  to the upper portion of chamber  42  via a gap between piston  108  and the walls of bore  20 . From the upper portion of chamber  42 , fluid pressure may escape as described above. Yet another leak path exists from the lower portion of chamber  42  through passage  80 , from upper portion to lower portion of chamber  48 , and through passage  82  into upper portion of chamber  42 . From the upper portion of chamber  42 , fluid pressure may escape as described above. In addition, fluid pressure in reservoir  24  is bled to exhaust through restrictor  56  removing the pressurized fluid being supplied to solenoid valve  38  through passage  66 . The amount of time for chamber  54  and reservoir  24  to bleed to exhaust will depend upon the size of chamber  54 , reservoir  24  and restrictor  56 . With the release of pressurized air from chamber  74  above piston  106  and the presence of pressurized air within inlet passage  14  acting against the bottom of valve seat  130 , valve spring  132  will move valve member  102  to an intermediate position where valve seat  130  is seated against housing  12  but piston  108  is not seated against housing  12 . This condition is shown in FIGS. 7 and 8. 
     FIGS. 7 and 8 illustrate control valve system  10  in a locked out position. When valve seat  130  urges valve member  102  upwards due to the biasing of valve spring  132 , valve seat  130  pushes against annular flange  140  to move valve member  102 . Because of a lost motion attachment between valve seat  130  and piston  110 , when valve seat  130  engages housing  12 , piston  108  has not yet engaged housing  12 . Additional movement of valve member  102  is required to seat piston  108  against housing  12  and connect passage  40  to passage  52  and provide pressurized fluid to chamber  54  and reservoir  24 . Without the seating of piston  108  to housing  12 , the upper portion of chamber  42  and thus passages  40  and  52  are open to exhaust  18  through gap  146 , outlet passage  16  and ports  88  and  90  and exhaust passage  18 . Thus reservoir  24  is open to exhaust along with passage  66  and the input to solenoid valve  38 . Chamber  54  is also open to exhaust eliminating any biasing load which would urge valve member  102  upward to seat piston  108  against housing  12 . An annular shoulder  150  located on piston  110  and open to inlet passage  14  biases valve member  102  downward with annular flange  140  being urged against valve seat  130  to keep valve member  102  in its intermediate position and control valve system  10  in its locked out position. A similar shoulder  152  is located on piston  122 . 
     When it is desired to move control valve system  10  from its locked out position to its deactuated position shown in FIG. 1, pressurized fluid is supplied to reset passage  96 . Pressurized fluid being supplied to reset passage  96  opens check valve  98  and pressurized fluid fills reservoir  24  and chamber  54 . Restrictor  56  will limit the amount of fluid bled off to exhaust during the resetting procedure. Once reservoir  24  and chamber  54  are filled with pressurized fluid, the fluid within chamber  54  acts against piston  110  to move valve member  102  upward to seat piston  108  against housing  12 . Fluid passage  40  is again in communication with passage  52  and control valve system  10  is again positioned in its deactuated position as shown in FIGS. 1 and 2. 
     While the above description of FIGS. 5 through 8 have been described with valve member  102  being located in its intermediate and locked out position and valve member  104  being located in its deactuated position, it is to be understood that a similar locked out position of control valve system  10  would occur if valve member  102  were located in its deactuated condition and valve member  104  were located in its intermediate and locked out condition. The resetting procedure of applying pressurized fluid to reset passage  96  would cause the pressurized fluid to open check valve  100  to fill reservoir  26  and chamber  60 . The pressurized fluid in chamber  60  would lift valve member  104  to seat piston  120  against housing  12  reconnecting passage  46  with passage  58 . 
     Thus, control valve system  10  is a fully fluid operating valve system which has the capability of sensing an abnormal condition and responding to this abnormal condition by switching to a locked out condition which then requires an individual to go through a resetting operation before control valve system  10  will again function. 
     FIG. 9 illustrates another embodiment of the present invention. In the embodiment shown in FIGS. 1-8, piston  108  includes annular passage  114  located in an upper surface of piston  108  to fluidically connect passage  40  with passage  52 . FIG. 9 illustrates a piston  108 ′ which fluidically connects a passage  40 ′ with a passage  52 ′ through a passage  114 ′ located on the external surface of piston  108 ′. In a similar manner, piston  120  of valve member  104  could be replaced with piston  108 ′. Fluid passage  40 ′ is the same as fluid passage  40  and fluid passage  52  is the same as fluid passage  52  with the exception that passages  40 ′ and  52 ′ enter chamber  42  through a vertical wall whereas passages  40  and  52  enter chamber  42  through a horizontal wall. The operation of the embodiment shown in FIG. 9 is identical to that described above for FIGS. 1 through 8. 
     FIGS. 10 through 19 illustrate a control valve system having anti-tiedown capability in accordance with the present invention which is designated generally by the reference numeral  510 . It should be noted that in FIGS. 10 through 19, like reference numerals designate like or corresponding parts throughout the several views. It should also be noted that like or corresponding parts from FIGS. 1 through 8 will have added  500  to the reference numerals of FIGS. 1 through 9. Control valve system  510  is shown as a schematic fluid circuit in FIG.  10  and as a fluid control valve in FIG.  11 . 
     Referring now to FIG. 11, control valve system  510  comprises a housing  512  having a fluid inlet passage  514 , a fluid outlet passage  516 , a fluid exhaust passage  518 , a first valve bore  520 , a second valve bore  522 , a first fluid reservoir  524 , and a second fluid reservoir  526 . Disposed within first valve bore  520  is a first valve member  528 , and disposed within second valve bore  522  is a second valve member  530 . Located within inlet passage  514  in a coaxial relationship with first valve member  528  is a third valve member  532 . Also located within inlet passage  514  in a coaxial relationship with second valve member  530  is a fourth valve member  534 . A pair of solenoid valves  536  and  538  are attached to housing  512 . 
     A plurality of fluid passages interconnect valve bores  520  and  522  with inlet  514 , outlet  516 , exhaust  518 , reservoir  524 , reservoir  526 , solenoid valve  536  and solenoid valve  538 . A fluid passage  540  extends between inlet passage  514  and an intermediate chamber  542  formed by bore  520 . A fluid passage  546  extends between inlet passage  514  and an intermediate chamber  548  formed by bore  522 . 
     A fluid passage  552  extends between chamber  542  and a lower chamber  554  formed by bore  520 . A restrictor  556  is disposed within passage  552  to limit the amount of fluid flow through passage  552 . A fluid passage  558  extends between chamber  548  and a lower chamber  560  formed by bore  522 . A restrictor  562  is disposed within passage  558  to limit the amount of fluid flow through passage  558 . Reservoir  524  forms part of passage  552  such that restrictor  556  is located between chamber  542  and reservoir  524 . 
     A restrictor  553  is disposed within passage  552  between reservoir  524  and lower chamber  554  to limit the amount of fluid flow between lower chamber  554  and reservoir  524 . A fluid passage  566  extends between reservoir  524  and the input to solenoid valve  538 . Reservoir  526  forms part of passage  558  such that restrictor  562  is located between chamber  548  and reservoir  526 . A restrictor  559  is disposed within passage  558  between reservoir  526  and lower chamber  560  to limit the amount of fluid flow between lower chamber  560  and reservoir  526 . 
     A fluid passage  570  extends between reservoir  526  and the input to solenoid valve  536 . A passage  572  extends between the output of solenoid valve  536  and an upper chamber  574  formed by bore  520 . A fluid passage  576  extends between the output of solenoid valve  538  and an upper chamber  578  formed by bore  522 . 
     A cross passage  580  extends between the lower portion of chamber  542  and the upper portion of chamber  548 . A cross passage  582  extends between the lower portion of chamber  548  and the upper portion of chamber  542 . A fluid passage  584  extends between passage  580  and outlet passage  516 . A restrictor  585  is disposed within passage  584  to limit the amount of fluid flow through passage  584 . A fluid passage  586  extends between passage  582  and outlet passage  516 . A restrictor  587  is disposed within passage  586  to limit the amount of fluid flow through passage  586 . Outlet passage  516  is in communication with exhaust passage  518  through two ports  588  and  590 . The upper portions of chambers  554  and  560  are in communication with exhaust port  18  through passages  592  and  594 , respectively. 
     A reset passage  596  extends through housing  512  and is in communication with the lower portion of chambers  554  and  560  by communicating with passages  552  and  558 , respectively. A pair of check valves  598  and  600  are disposed between reset passage  596  and passages  552  and  558  respectively, to prohibit fluid flow between passages  552  or  558  to reset passage  596  but allow fluid flow from reset passage  596  to one or both passages  552  and  558 . 
     Disposed within bore  520  is valve member  602  and disposed within bore  522  is valve member  604 . Valve member  602  comprises an upper piston  606 , an intermediate piston  608  and a lower piston  610 , all of which move together as a single unit. Upper piston  606  is disposed within chamber  574  and includes a valve seat  612  which opens and closes port  588  located between outlet passage  516  and exhaust passage  518 . Intermediate piston  608  is disposed within chamber  542  and includes an annular passage  614  which fluidly connects passage  540  to passage  552  when piston  608  is seated against housing  512 . Lower piston  610  is located within chamber  554 . A pair of seals  616  seal inlet passage  514  from passage  592  and seal chamber  554  from passage  592 . 
     As described above, valve member  602  comprises an upper piston  606 , and intermediate pistons  608 , and a lower piston  610 , all of which move together as a single unit. The respective pistons  606 ,  608 , and  610  each include central bores through which passes a valve stem  660 . Valve stem  660  includes a pair of lands  662  which provide end stops for one or more of the respective pistons. For example, upper piston  606 , valve seat  612 , and spacer  664  are seated on an upper land  662 . A nut  666  threadably engages a threaded portion of valve stem  660  to maintain upper piston  606 , valve seat  612 , and spacer  664  against upper land  662 . Similarly, a lower land  662  provides an end stop for intermediate piston  608 , a spacer  668 , and lower piston  610 , which are retained against the lower land  662  via a nut  670  which threadably engages a lower end of valve stem  660 . Spacer  668  is formed so that valve member  602  moves independently from valve member  532 . 
     Valve member  604  comprises an upper piston  618 , an intermediate piston  620  and a lower piston  622  all of which move together as a single unit. Upper piston  618  is disposed within chamber  578  and includes a valve seat  624  which opens and closes port  590  located between outlet passage  516  and exhaust passage  518 . Intermediate piston  620  is disposed within chamber  548  and includes an annular passage  626  which fluidly connects passage  546  to passage  558  when piston  620  is seated against housing  512 . Lower piston  622  is located within chamber  560 . A pair of seals  628  seal inlet passage  514  from passage  594  and seal chamber  560  from passage  594 . 
     As described above, valve member  604  comprises an upper piston  618 , an intermediate piston  620 , and a lower piston  622 , all of which move together as a single unit. The respective pistons  618 ,  620 , and  622  each include central bores through which passes a valve stem  674 . Valve stem  674  includes a pair of lands  676  which provide end stops for one or more of the respective pistons. For example, upper piston  618 , valve seat  624 , and spacer  678  are seated on an upper land  676 . A nut  680  threadably engages a threaded portion of valve stem  674  to maintain upper piston  618 , valve seat  624 , and spacer  678  against upper land  676 . Similarly, a lower land  676  provides an end stop for intermediate piston  620 , a spacer  682 , and lower piston  622  are retained against the lower land  676  via a nut  684  which threadably engages a lower end of valve stem  674 . Spacer  682  is formed so that valve member  602  moves independently from valve member  534 . 
     Valve member  532  is located around spacer  668  and comprises a valve seat  630  and a valve spring  632 . Valve spring  632  biases valve seat  630  against housing  512  to prohibit fluid flow between inlet passage  614  and chamber  642 . Valve member  534  is located around spacer  682  and comprises a valve seat  634  and a valve spring  636 . Valve spring  636  biases valve seat  634  against housing  512  to prohibit fluid flow between inlet passage  514  and chamber  548 . 
     A particular feature of this invention includes an anti-tiedown circuit  690  which inhibits actuation of first valve member  530  during a reset operation. The antitiedown circuit  690  includes an anti-tiedown valve  692 . A fluid passage  694  extends between inlet passage  514  to the input to solenoid  696 . A fluid passage  700  extends from the output of solenoid  696  to an input port  702  of anti-tiedown valve  692 . A reset port  698  fluidly connects to fluid passage  700  and provides an alternative, typically operator supplied, means for pressurizing fluid passage  700 . An actuation passage  704  extends between fluid passage  700  and actuation port  706 . A reservoir passage  708  extends between actuation passage  704  and fluid reservoir  710 . A restrictor  712  is disposed within actuation passage  704  to limit the amount of fluid flow through passage  704 . An outlet port  714  connects to reset passage  596 . A vent port  716  connects to passage  566 . 
     Anti-tiedown valve  692  comprises a valve body  718  which also forms part of housing  512 . Valve body  718  includes a central bore  720 . A valve spool  722  translates within central bore  720  between end structures  724 . At its upper end, valve spool  722  includes a valve seat  726  which opens and closes a passage between vent port  716  and upper exhaust port  728 . Valve spool  722  also includes an o-ring  730  which provides a seal between upper exhaust passage  728  and input port  702 . Similarly, o-ring  732  provides a seal between input port  702 , outlet port  714 , and lower exhaust port  734 . A third o-ring  736  provides a seal between outlet port  714  and lower exhaust port  734  when anti-tiedown valve  692  is an actuated position. A fourth o-ring  738  provides a seal between actuation port  706  and second exhaust port  734 . 
     FIGS. 11 and 12 illustrate control valve system  510  in an initial position. It should be noted that FIGS. 11 and 12 also illustrate control valve system  510  in a locked out position. A lockout condition occurs when at least one of the intermediate pistons  608  or  620  assumes the position shown in FIG.  11 . Displacement of the valves from a locked out to a deactuated position will be described with respect to first valve member  528 . However, displacement of second valve member  530  occurs in a similar manner. When valve seat  630  urges valve member  602  upwards due to the biasing of valve spring  632 , valve seat  630  pushes against annular flange  640  to move valve member  602 . Because first valve member  528  and third valve member  532  may move independently, when valve seat  632  engages housing  512 , piston  608  has not yet engaged housing  512 . Additional movement of valve member  602  is required to seat piston  608  against housing  512  and connect passage  540  to passage  552  and provide pressurized fluid to chamber  554  and reservoir  524 . Without the seating of piston  608  to housing  512 , the upper portion of chamber  542  and thus passages  540  and  552  are open to exhaust  518  through gap  646 , outlet passage  516 , ports  588  and  590 , and exhaust passage  18 . Thus reservoir  524  is open to exhaust along with passage  566  and the input to solenoid valve  538 . Chamber  554  is also open to exhaust eliminating-any biasing load which would urge valve member body  602  upward to seat piston  608  against housing  512 . A spring  686  urges intermediate piston  608  downward via valve stem  660 , with annular flange  640  being urged against valve seat  630  to keep valve member body  602  in its intermediate position and control valve system  510  in its startup (body valves) or locked out (one valve) position. A similar configuration applies to the other main valve. 
     When it is desired to move control valve system  510  from its initial, or locked out, position to its deactuated position shown in FIGS. 14 and 15, pressurized fluid must be supplied to reset passage  596 . Pressurized fluid being supplied to reset passage  596  opens check valves  598 ,  600 , and pressurized fluid fills reservoirs  554  and  560 . Restrictors  556  and  562  will limit the amount of fluid bled off to exhaust during the resetting procedure. Similarly, restrictors  553  and  559  will limit the amount of fluid entering respective reservoirs  524  and  526 . Once reservoirs  524  and  526  and chambers  554  and  560  are filled with pressurized fluid, the fluid within chambers  554  and  560  acts against pistons  610  and  622  to move valve members  602  and  604  upward to seat pistons  608  and  620  against housing  512 . Fluid passages  540  and  546  are again in communication with passages  552  and  558  and control valve system  510  is again positioned in its deactuated position as shown in FIGS. 14 and 15. 
     As best illustrated in FIGS. 12 and 13, in a particular feature of the present invention is that pressurization of reset passage  596  is controlled through a novel anti-tiedown circuit  690 , including an anti-tiedown valve  692 . Anti-tiedown circuit  690  prevents pressurization of reset passage without previous depressurization of reservoir  524  and passage  566 , thereby preventing solenoid  538  from providing fluid pressure to passage  576  and chamber  578 . This prevents displacement of first valve member  530  to an actuated position. Thus, anti-tiedown valve  692  prevents pressurizing outlet passage  16  during a reset operation. 
     To effect a reset operation when one or both of first valve member  528  or second valve member  530  is in a locked-out position, such as may occur during initial start up or a locked out condition, fluid passage  700  must be pressurized. Pressurization of fluid passage  700  can occur through reset activation of solenoid  696  which receives input fluid pressure from inlet passage  514  via fluid passage  694 . Upon actuation of reset solenoid  696 , inlet fluid pressure is applied to fluid passage  700 . Alternatively, valve housing  512  includes an optional reset port  698  which may be provided for use with a customer supplied reset fluid pressure. 
     Upon application of one of the alternative reset signals, fluid pressure and in passage  700  causes upward displacement of valve spool  722  resulting from pressurization of chamber  740 . The input fluid pressure applied through fluid passage  700  also pressurizes reservoir  710 . Upward displacement of valve spool  722  enables communication between fluid passage  566  and upper exhaust port  728 . This vents fluid pressure in reservoir  524  and fluid passage  566  to exhaust, thereby preventing actuation of first valve member  528 . Upward displacement of valve spool  722  also enables communication between pressurized fluid passage  700  and reset passage  596 , causing displacement of first valve member  528  and/or second valve member  530  to a deactuated position, as described above with respect to FIGS. 10 and 11. During this operation, fluid restrictors  553  and  559  limit fluid flow into respective reservoirs  524  and  526 . This ensures that a higher pressure will build in chambers  554  and  560 , thereby displacing pistons  608  and  620  upward to effect the reset operation. Further, so long as fluid passage  700  is pressurized, either by reset solenoid  696  or customer supplied reset signal  698 , fluid passage  566  will be vented through upper exhaust passage  728 , thereby insuring deactuation of first valve member  530 . 
     Upon removal of the reset signal, either through reset solenoid  596  or customer supplied reset support  698 , biasing member  742  displaces valve spool  722  downward disabling communication between fluid passage  700  and reset passage  596 . Downward displacement of valve spool  722  resultantly closes off communication between fluid passage  700  and reset passage  596 , thereby relieving pressure to check valves  598 ,  600 . Downward displacement of valve spool  722  also causes reset passage  596  to vent through lower exhaust port  734 , thereby providing a continuous exhaust for reset passage  596  so that reset passage  596  is only pressurized during the reset operation and otherwise vented to exhaust. Also, valve seat  726  closes off communication between passage  566  and upper exhaust port  728 , thereby enabling pressurization of reservoir  526 . Reservoirs  524  and  526  are thus sufficiently pressurized to maintain a sufficient pressure in respective chambers  554  and  560  to maintain first valve member  528  and second valve member  530  in a deactuated position. 
     FIGS. 14 and 15 illustrate control valve system  510  in its deactuated position. Pressurized fluid from input passage  514  is biasing valve seats  630  and  634  against housing  512  closing communication between inlet passage  514  and both chambers  542  and  548 . Pressurized fluid is provided to passage  540 , to passage  552  through annular passage  614  through restrictor  556  to reservoir  524  through restrictor  553  and into chamber  554  to bias valve member  602  upward as shown in FIG. 15 seating piston  608  against housing  512 . Pressurized fluid also flows from reservoir  24  to the inlet of solenoid valve  538  through passage  566 . In a similar manner, pressurized fluid from input passage  514  is provided to passage  546  to passage  558  through annular passage  626  through restrictor  562  to reservoir  526  through restrictor  559  and into chamber  560  to bias valve member  604  upward as shown in FIG. 15 seating piston  620  against housing  512 . Pressurized fluid also flows from reservoir  526  to the inlet of solenoid valve  536  through passage  570 . Outlet passage  516  is in communication with exhaust passage  518  due to valve seats  612  and  624  being biased upward opening ports  588  and  590 . Intermediate chambers  542  and  548  are also open to exhaust passage  518  through cross passages  580  and  582 , respectively, through passages  584  and  586 , respectively. The fluid pressure below piston  610  and  622  of valve members  602  and  604 , respectively, bias valve members  602  and  604  upward maintaining control valve system  510  in the deactuated position. The connection between passages  540  and  552  through annular passage  614  and the connection between passages  546  and  558  through annular passage  626  maintain fluid pressure within chambers  554  and  560  and reservoirs  524  and  526 . 
     FIGS. 16 and 17 illustrate control valve system  510  in its actuated position. Both solenoid valves  536  and  538  have been substantially simultaneously actuated. The actuation of solenoid valve  536  connects passage  570  and thus reservoir  526  to passage  572 . Pressurized fluid is directed into chamber  574  to move valve member  602  downward as shown in FIG.  17 . The diameter of piston  606  is larger than the diameter of piston  610  thus causing the load which moves valve member  602  downward. In a similar manner, the actuation of solenoid valve  538  connects passage  566  and thus reservoir  524  to passage  576 . Pressurized fluid is directed into chamber  578  to move valve member  604  downward as shown in FIG.  17 . The diameter of piston  618  is larger than the diameter of piston  622  thus causing the load which moves valve member  604  downward. When valve members  602  and  604  move downward, an annular flange  640  on piston  610  unseats valve seat  630  and an annular flange  642  on piston  622  unseats valve  634 . Pressurized fluid flows from inlet passage  514  into the lower portion of chamber  542  through passage  580  to the upper portion of chamber  548  and through a gap  644  between valve member  604  and housing  512  to provide pressurized fluid to outlet passage  516 . Pressurized fluid also flows through passage  584  to outlet passage  516 . In a similar manner, pressurized fluid flows from inlet passage  514  into the lower portion of chamber  548  through passage  582  to the upper portion of chamber  542  and through a gap  646  between valve member  602  and housing  512  to provide pressurized fluid to outlet passage  516 . Pressurized fluid also flows through passage  586  to outlet passage  516 . The movement of valve members  602  and  604  downward seats valve seats  612  and  624  against housing  512  to close ports  588  and  590  to isolate outlet passage  516  from exhaust passage  518 . The fluid pressure within reservoirs  524  and  526  will initially be reduced when valves  536  and  538  are actuated, but the fluid pressure will return to supply pressure at inlet  514  because reservoirs  524  and  526  are still open to inlet  514  and outlet  516  is isolated from exhaust  518 . 
     FIGS. 18 and 19 illustrate control valve system  510  in an abnormal position. In FIGS. 18 and 19, valve member  604  is located in its upward position while valve member  602  is located in its lower position. Both solenoid valves  536  and  538  are located in their deactuated position. Valve member  604  is located in its upward position similar to that shown in FIG.  15 . Pressurized fluid from inlet passage  514  is supplied to passage  546  to passage  558  through annular passage  626  through restrictor  562  and into chamber  560  to bias valve member  604  upward as shown in FIG. 19 seating piston  620  against housing  12 . Pressurized fluid also flows to reservoir  526  and from reservoir  526  to the inlet of solenoid valve  536  through passage  570 . Outlet passage  516  is in communication with exhaust passage  518  due to valve seat  624  being biased upward opening port  590 . Valve member  602  is located in its lower position which opens various passages to outlet passage  516  which, because the position of valve member  604 , is open to exhaust  518 . The upper portion of chamber  542  is open to exhaust through gap  646 . Pressurized fluid from inlet passage  514  is bled to exhaust through passage  540  and through the upper portion of chamber  542  through gap  646 , through outlet passage  516 , through port  590  to exhaust passage  518 . In addition, pressurized fluid from inlet passage  514  will bleed to exhaust  518  by entering the lower portion of chamber  542 , flow through passage  580 , through passage  584 , through outlet passage  516 , through port  590  and into exhaust passage  518 . Pressurized fluid in passage  552  and thus chamber  554  is also bled to exhaust through restrictors  553  and  556  which removes the biasing being applied to valve member  602 . A leak path also exists from inlet  514  to the lower portion of chamber  542  to the upper portion of chamber  542  via a gap between piston  608  and the walls of bore  520 . From the upper portion of chamber  542 , fluid pressure may escape as described above. Yet another leak path exists from the lower portion of chamber  542  through passage  580 , from upper portion to lower portion of chamber  548 , and through passage  582  into upper portion of chamber  542 . From the upper portion of chamber  542 , fluid pressure may escape as described above. In addition, fluid pressure in reservoir  524  is bled to exhaust through restrictor  556  removing the pressurized fluid being supplied to solenoid valve  538  through passage  566 . The amount of time for chamber  554  and reservoir  524  to bleed to exhaust will depend upon the size of chamber  54 , reservoir  524  and restrictors  553  and  556 . With the release of pressurized air from chamber  574  above piston  606  and the presence of pressurized air within inlet passage  514  acting against the bottom of valve seat  630 , valve spring  532  will move valve member  602  to an intermediate position where valve seat  630  is seated against housing  512  but piston  608  is not seated against housing  512 . This condition is shown in FIGS. 10 and 11. 
     While the above description of FIGS. 18 and 19 have been described with valve member  602  being located in its intermediate, and locked out position and valve body  604  being located in its deactuated position, it is to be understood that a similar locked out position of control valve system  510  would occur if valve member  602  were located in its deactuated condition and valve member  604  were located in its intermediate and locked out condition. 
     Thus, control valve system  510  is a fully fluidically operating valve system which has the capability of sensing an abnormal condition and responding to this abnormal condition by switching to a locked out condition which then requires an individual to go through a resetting operation before control valve system  510  will again function. Control valve system  510  further prevents operation of the valve during a reset operation. 
     The control valve systems  10  and  510  described above in FIGS. 1-19 are generally referred to as crossmirror valves because they are configured to include a monitoring feature integral to the design of the valve. These valves offer particular features to the customer. An alternative valve configuration may generally be referred to as a crossflow valve. A typical crossflow valve comprises a body and valve elements, but does not inherently include a monitoring circuit for detecting when the valve systems are in an abnormal configuration. Such a valve may be referred to as a double valve, and FIG. 20 illustrates a schematic circuit diagram for control valve system  810 , which defines yet another embodiment of the present invention. With reference to FIG. 20, control valve system  810  includes an inlet supply  814 , an outlet supply  816 , and an exhaust  818 . Solenoid valve  820  controls actuation of first valve member  824 . Similarly, solenoid valve  822  controls actuation of second valve member  826 . Solenoid valves  820  and  822  must be actuated within a predetermined time period, and respective first valve member  824  and second valve member  826  must actuate and deactuate within a predetermined time period in order to prevent transition of control valve system  810  to a locked out position. Control valve system  810  also includes a lockout spool  828  and anti-tiedown valve  830 . It should be noted that solenoid valves  820  and  822  are analogous to respective solenoid valves  36 ,  38  and  536 ,  538 , as described above. Similarly, it should be noted that main valve members  824 ,  826  are analogous to first valve members  28 ,  30  and  528 ,  530  described above. Similarly, anti-tiedown valve  830  is analogous to anti-tiedown valve  592  described above. 
     Lock out spool  828  is a four port, three position spool valve which monitors fluid pressure on fluid passages  832  and  834 , which reflect the pressure output by main valve members  824 ,  826 . When the pressures are generally equal, spool valve  828  assumes a centered position. When the pressure becomes unequal, lock out spool  828  shifts, thereby exhausting input pressure to port YA and exhausting control pressure applied to anti-tiedown valve  830  and solenoid valves  822 ,  824  to port YB. A lock out switch  836  includes a lockout pin  838 . Lock out pin  838  is biased in the direction of a notched member  840  which moves in accordance with a displaceable portion of lockout spool  828 . Notched member  840  includes a pair of notches, one of which lockout pin  838  engages as lockout member  840  shifts in accordance with the spool portion of lockout spool  828 . Once in a locked out position, fluid pressure must be applied to reset port  842  in order to return lockout spool  828  to its center position by pressurizing lock out pin  838  away from notched member  840  thereby enabling lock out spool  828  to return to its center position, so long as the pressure inputs on fluid passages  832  and  834  are generally equal. 
     Anti-tiedown valve  830  operates similarly as described above in order to provide a path from fluid passage  844  to exhaust through anti-tiedown valve  830  during reset. In operation, applying fluid pressure to reset port  842  displaces anti-tiedown valve  830  to an actuated position. In the actuated position, anti-tiedown valve  830  provides a path to exhaust for fluid passage  844 . Also when in an actuated position, anti-tiedown valve  830  provides a path from reset port  842  to reset pin  838 . The reset pressure pressurizes a chamber which overcomes the biasing force of a spring that biases reset pin  838  towards notched member  840 . During the reset operation, fluid pressure cannot be applied to either of solenoid valves  820 ,  822 , and thus cannot be applied to respective main valve members  824 ,  826 . This prevents application of inlet pressure on outlet supply  816 . Once fluid pressure is removed from reset port  842 , anti-tiedown valve  830  returns to its deactuated position, as described above with respect to FIGS. 10-19, enabling operation of main valve members  824 ,  826 . 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.