Hydraulic jack with back pressure safety check

Claim 1

A SAFTEY CIRCUIT FOR A HYDRAULIC SYSTEM COMPRISING IN COMBINATION, A HYDRAULIC PUMP HAVING AN INLET IN FLUID COMMUNICATION WITH A RESERVOIR AND AN OUTLET, A FIRST FLUID CONNECTION BETWEEN SAID OUTLET AND SAID RESERVOIR, AND A SECOND FLUID CONNECTION BETWEEN SAID RESERVOIR AND THE INTAKE OF SAID PUMP, A RELEASE VALVE FOR OPENING, PARTIALLY OPENING OR CLOSING SIAD FIRST FLUID CONNECTION, A LIFT JACK OPERABLE BY SAID PUMP, A HYDRAULIC BACK PRESSURE SAFETY HOUSING FORMING AN END WALL OF SAID JACK, A CONDUIT IN FLUID COMMUNICATION WITH SAID FIRST FLUID CONNECTION, SAID HOUSING HAVING A FIRST BORE RECEIVING SAID CONDUIT AND A SECOND BORE IN COMMUNICATION WITH SAID JACK, FIRST AND SECOND PASSAGEWAYS BETWEEN SAID BORES, A CHECK BALL IN SAID FIRST PASSAGEWAY NORMALLY BLOCKING FLUID FLOW THERETHROUGH FROM SAID SECOND BORE TO SAID FIRST BORE AND PERMITTING RELATIVELY FREE FLOW FROM SAID FIRST BORE TO SAID SECOND BORE, A ONE WAY CHECK VALVE AND A RESTRICTION