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1. WO1981002768 - FLUID CIRCUIT WITH ZERO LEAK LOAD CHECK AND BY-PASS VALVE

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[ EN ]

CLAIMS

1. In a fluid circuit (10) having a fluid source (13), a fluid actuator (11), control means (16) for selectively communicating pressurized fluid to said actuator from said source, and check valve means (20,60,61) for isolating fluid pressure in said actuator in response to selective actuation of said control means, said check valve means including a load check valve (20) having a reciprocal spool (27), the improvement comprising said load check valve further including means (36) for communicating equalized fluid pressure from said actuator to opposite ends of said spool.
2. The fluid circuit of claim 1 wherein said check valve further includes poppet valve means

(28) for opening to communicate pressurized fluid from said source to said actuator.

3. The fluid circuit of claim 1 wherein said check valve further Includes means (3D for metering fluid flow from said actuator to said source in response to venting of fluid pressure from said actuator, said means defined in said spool.

4. The fluid circuit of claim 1 wherein said check valve further includes a fluid chamber (45,46) defined adjacent to each end of said spool, passage means (43,44) for communicating pressurized fluid from said actuator to each of said chambers, a reciprocal piston (51,52) disposed between each of said chambers and a respective end of said spool, and biasing means (53) for urging said spool in one direction of movement thereof.

5. The fluid circuit of claim 1 wherein said check valve means further includes at least one check valve (60 or 61) interconnected between said source and said load check valve.

b. The fluid circuit of claim 1 wherein said actuator includes a double-acting fluid cylinder (11) movable between extended and retracted conditions of operation and wherein said control means includes main control valve means (19) for movement between a first position for communicating pressurized fluid from said source to said cylinder to extend the same, a second position isolating said source from said cylinder, and a third position for communicating pressurized fluid from said source to said cylinder to retract the same, pilot control valve means (17) for communicating a pilot signal to said main control valve means to move it to its first, second, and third positions, vent valve means (66) for receiving a pilot signal from said pilot control valve means when said pilot control valve means actuates said main control valve means to its third position retracting said cylinder to open and exhaust pressurized fluid from said load check valve (20), and check valve means (61) for venting pressurized fluid from said cylinder in response to opening of said vent
valve means.

7. The fluid circuit of claim 1 wherein a pair of fluid actuators (11,12) is each connected to a said load check valve (20,20'), each of said actuators including an extensible and retractable fluid
cylinder, and control means (47) for interconnecting said load check valves to equalize the fluid pressure in said cylinders upon simultaneous extension or retraction thereof and to permit gradual retraction of said cylinders upon loss of fluid pressure between said load check valves.

8. The fluid circuit of claim 7 wherein said control means Includes resolver valve means (47') for movement between first and second positions (1) for moving to said first position to equalize the fluid pressure in said cylinders upon retraction of said cylinders and when the level of fluid pressure in one of said cylinders exceeds the level of fluid pressure in the other one of said cylinders, and (2) for moving to said second position gradually reducing the level of fluid pressure in said cylinders upon said loss of fluid pressure between said load check valves.

9. In a fluid circuit (10) having a pair of extensible and retractable fluid cylinders (11,12), load check valve means (20,20') for communicating fluid pressure to each of said cylinders to extend or retract the same, and control means (47) for
interconnecting said load check valve means to permit gradual retraction of said cylinders upon loss of fluid pressure between saicl load check valve means, the improvement comprising, said control means
including resolver valve means (47') for movement between first and second positions and (1) for moving to said first position to equalize the fluid pressures in said cylinders upon retraction of said cylinders and when the level of fluid pressure in one of said cylinders exceeds the level of fluid pressure in the other one of said cylinders, and (2) for moving to said second position gradually reducing the level of fluid pressure in said cylinders upon loss of fluid pressure between said load check valve means.