Pilot operated balanced relief valve with accumulator

Claim 1

A PRESSURE RELIEF VALVE FOR A SUBSTANTIALLY NON-COMPRESSIBLE FLUID, SAID VALVE COMPRISING A VALVE BODY HAVING A VALVE CHAMBER, INLET AND OUTLET PORTS IN SAID VALVE CHAMBER, A VALVE SEAT PROVIDED IN SAID VALVE CHAMBER BETWEEN SAID PORTS, A VALVE COOPERATING WITH SAID SEAT AND HAVING A LARGE CONTROL PISTON CLOSELY FITTED IN ONE END OF THE VALVE CHAMBER IN THE VALVE BODY AND COOPERATES THEREWITH TO DEFINE A CONTROL CHAMBER IN SAID ONE END, SAID VALVE ALSO HAVING A SMALL PISTON CLOSELY FITTED IN AN OPPOSITE END OF THE VALVE CHAMBER, SAID LARGE PISTON HAVING A LIFT AREA ALWAYS SUBJECT TO PRESSURE AT THE INLET PORT AND HAVING AN OPPOSITE AREA PROVIDING A HOLD DOWN AREA SUBJECT TO PRESSURE IN THE CONTROL CHAMBER, SAID SMALL PISTON HAVING AN END AREA IN THE OPPOSITE END OF THE VALVE CHAMBER PROVIDING A LIFT AREA SUBSTANTIALLY EQUAL TO THE DIFFERENCE OF THE HOLD DOWN AREA AND THE LIFT AREA OF THE LARGE PISTON, PASSAGE MEANS BETWEEN THE CONTROL CHAMBER AND THE OPPOSITE END OF THE VALVE CHAMBER SO THAT THE LIFT AND HOLD DOWN AREAS OF THE VALVE PROVIDE SUBSTANTIALLY HYDROSTATIC BALANCE OF THE VALVE WHEN THE PRESSURE IN THE CONTROL CHAMBER IS EQUAL TO THE PRESSURE AT THE INLET PORT, SPRING MEANS ACTING ON SAID VALVE TO URGE SAID VALVE AGAINST SAID SEAT, A PILOT VALVE MOUNTED ON SAID VALVE BODY AND OPERABLE IN RESPONSE TO THE PRESSURE IN SAID CONTROL CHAMBER EXCEEDING A PREDETERMINED VALUE TO CAUSE SAID VALVE TO OPEN AND LIMIT THE PRESSURE AT THE INLET PORT TO SAID PREDETERMINED VALUE, SAID CONTROL CHAMBER HAVING A MINIMUM AXIAL LENGTH TO LIMIT THE LIFT OF THE CONTROL PISTON TO A DISTANCE SUFFICIENT FOR RATED FLOW THROUGH THE VALVE WHEN THE PILOT VALVE IS OPEN SO AS TO NORMALLY HAVE A