Floating piston 1 is held in the neutral central position by springs 2 and 3. Fluid entering through port 4 opens left-hand check valve 5 and passes through port 6 to the working end of a hydraulic cylinder. At this, right-hand check valve 7 is moved to the right by piston 1 and the exhaust end of the hydraulic cylinder is connected to the tank. As soon as fluid delivery ceases, piston 1 is returned to its neutral position by springs 2 and 3, valves 5 and 7 close and lock the position of the piston in the hydraulic cylinder. Valves 8 and 9 are relief valves.
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