1. A HYDRAULIC CONTROL APPARATUS FOR SUPPLYING FLUID PRESSURE TO AND RELEASING FLUID PRESSURE FROM A HYDRAULIC LOAD IN ACCORDANCE WITH THE LEVEL OF SUPPLY PRESSURE AND COMPRISING A HYDRAULIC LOAD HAVING AN INLET CONNECTION, A PILOT-OPERATED CHECK VALVE HAVING A PAIR OF FLUID PRESSURE PORTS AND A THROUGH FLOW PATH EXTENDING BETWEEN AND CONNECTING THEM AND HAVING A PILOT PRESSURE PORT, THE PORT AT ONE END OF SAID FLOW PATH BEING CONNECTED TO SAID INLET CONNECTION OF SAID HYDRAULIC LOAD TO PROVIDE FREE AND UNCHECKED CONDUCTION THROUGH SAID CHECK VALVE TOWARD SAID LOAD AND PILOT PRESSURECONTROLLED CONDUCTION THROUGH SAID CHECK VALVE IN A DIRECTION AWAY FROM SAID LOAD, A PRESSURE SUPPLY CONDUIT, CONTROL MEANS CONNECTED TO THE PORT AT THE OTHER END OF SAID FLOW PATH AND TO SAID PILOT PRESSURE PORT OF SAID CHECK VALVE ON THE ONE HAND AND TO SAID PRESSURE SUPPLY CONDUIT AND TO ATMOSPHERE ON THE OTHER, SAID CONTROL MEANS HAVING VALVE MEANS MOVABLE FROM A FIRST POSITION CONNECTING SAID PRESSURE SUPPLY CONDUIT AND ATMOSPHERE TO THE PORT AT THE OTHER END OF SAID CHECK VALVE AND ITS PILOT PRESSURE PORT RESPECTIVELY AND A SECOND POSITION REVERSING SAID FIRST POSITION CONNECTIONS, SAID VALVE MEANS HAVING A CONTROL PRESSURE PORT CONNECTED TO SAID PRESSURE SUPPLY CONDUIT AND BEING MOVABLE FROM SAID FIRST POSITION TO SAID SECOND POSITION IN RESPONSE TO PRESSURE IN SAID PRESSURE SUPPLY CONDUIT IN EXCESS OF A PREDETERMINED LEVEL.