Pressure control valve

Claim 1

A CONTROL VALVE COMPRISING A MAIN PASSAGE, A PISTON HAVING TWO SPOOLS INTERCONNECTED BY A SHAFT MEMBER AND MOVABLE IN SAID PASSAGE, BIASING MEANS BETWEEN THE END WALLS OF SAID PASSAGE AND THE ENDS OF SAID PISTON, A FIRST PASSAGE CONNECTING THE OUTSIDE OF SAID VALVE TO THE CENTRAL PART OF SAID MAIN PASSAGE ONLY, A FIRST BLEED PASSAGE CONNECTING SAID FIRST PASSAGE TO ONE END OF SAID MAIN PASSAGE, A SECOND PASSAGE BEING BIFURCATED AND CONNECTING THE OUTSIDE OF SAID VALVE WITH TWO PORTS WHICH ARE NORMALLY SUBSTANTIALLY CLOSED EACH BY ONE SPOOL OF SAID PISTON, A SECOND BLEED PASSAGE CONNECTING SAID SECOND PASSAGE TO THE OTHER END OF SAID MAIN PASSAGE SO THAT PRESSURE APPLIED IN ONE DIRECTION ACROSS SAID VALVE TENDS TO FULLY OPEN ONLY ONE OF SAID PORTS TO ALLOW FLOW THROUGH SAID VALVE BETWEEN SAID PORTS AND PRESSURE APPLIED IN THE OTHER DIRECTION TENDS TO FULLY OPEN ONLY THE OTHER OF SAID PORTS TO ALLOW FLOW IN THE OTHER DIRECTION THROUGH SAID VALVE, SAID RATE OF FLOW BEING A LINEAR FUNCTION OF THE PRESSURE DIFFERENCE ACROSS SAID VALVE.