Pressure regulator valve

Claim 1

A REGULATOR VALVE, COMPRISING: (A) A VALVE BODY DEFINING A PASSAGE, NORMALLY FORMING AN INLET, OPPOSED BORES COMMUNICATING WITH SAID PASSAGE, A VALVE CHAMBER COMMUNICATING WITH THE OPPOSED ENDS OF SAID BORES, AND A PORT, NORMALLY FORMING AN OUTLET, COMMUNICATING WITH SAID CHAMBER; (B) A VALVE ELEMENT FOR ONE OF SAID BORES TO PERMIT FLOW FROM SAID PASSAGE TO SAID PORT; (C) A PRESSURE-BALANCING PISTON SLIDABLE IN THE OTHER OF SAID BORES; (D) A STEM CONNECTING SAID PISTON AND VALVE ELEMENT FOR SIMULTANEOUS MOVEMENT THEREOF; (E) SAID PISTON DEFINING AN O-RING GROOVE CONTIGUOUS TO SAID STEM, AND NOTCHED PORTIONS AT THE PASSAGE SIDE OF SAID O-RING GROOVE INTERRUPTING SAID GROOVE AT DIAMETRICALLY OPPOSITE SIDES THEREOF AND TOWARD SAID PASSAGE, SAID NOTCHED PORTIONS HAVING FACES CONVERGING TOWARD SAID STEM; (F) A FLEXIBLE O-RING FITTING SAID GROOVE FOR SEALING ENGAGEMENT WITH THE WALLS OF THE SURROUNDING BORE AND ADAPTED, IN RESPONSE TO A CONDITION OF GREATER PRESSURE IN SAID PASSAGE THAN IN SAID CHAMBER, TO SEAL SAID PISTON IN SAID BORE; (G) SAID O-RING INCLUDING ARCUATE PORTIONS BRIDGING SAID NOTCHED PORTIONS, SAID NOTCHED PORTIONS BEING OF SUFFICIENT ARCUATE EXTENT AND SAID O-RING BEING SUFFICIENTLY FLEXIBLE THAT SAID O-RING IS DEFLECTABLE OVER SAID CONVERGING SURFACES CLEAR OF THE WALLS OF THE SURROUNDING BORE, THEREBY TO PERMIT BACK FLOW TOWARD SAID PASSAGE; (H) AND A SPRING-BACKED DIAPHRAGM EXPOSED TO SAID CHAMBER AND CONNECTED WITH SAID PISTON AND VALVE ELEMENT, SAID DIAPHRAGM BEING RESPONSIVE TO PRESSURE IN SAID CHAMBER TO CLOSE SAID VALVE ELEMENT ON RISE OF PRESSURE IN SAID VALVE CHAMBER TO A PREDETERMINED VALUE.