Pressure control unit for hydraulic systems

Claim 1

A PRESSURE CONTROL UNIT FOR MAINTAINING THE PRESSURE IN A HYDRAULIC SYSTEM WITHIN PREDETERMINED LIMITS, COMPRISING A NORMALLY CLOSED DISCHARGE VALVE HAVING A DISCHARGE PORT, A VALVE MEMBER ADAPTED TO CLOSE SAID DISCHARGE PORT, SAID DISCHARGE VALVE HAVING A PRESSURE INLET PORT ASSOCIATED WITH ONE END OF SAID VALVE MEMBER AND A CONTROL PORT ASSOCIATED WITH THE OTHER END OF SAID VALVE MEMBER, MEANS IN SAID DISCHARGE VALVE PROVIDING COMMUNICATION BETWEEN SAID INLET PORT AND SAID CONTROL PORT, A CONTROL VALVE COMPRISING A BODY PORTION HAVING A PRESSURE CHAMBER, A DISCHARGE CHAMBER AND A CONTROL CHAMBER, SAID PRESSURE CHAMBER HAVING A PORT CONNECTED TO THE CONTROL PORT OF SAID DISCHARGE VALVE, SAID DISCHARGE CHAMBER HAVING A DISCHARGE PORT AND SAID CONTROL CHAMBER HAVING A PRESSURE INLET PORT, A PASSAGEWAY IN SAID CONTROL VALVE PROVIDING COMMUNICATION BETWEEN SAID PRESSURE CHAMBER AND SAID DISCHARGE CHAMBER, SAID PASSAGEWAY HAVING A PORT IN SAID PRESSURE CHAMBER DEFINING A VALVE SEAT, A PILOT VALVE CONTROLLING SAID SEAT, A PISTON IN SAID PRESSURE CHAMBER, A FIRST COIL SPRING OPERATIVELY INTERPOSED BETWEEN SAID PISTON AND SAID PILOT VALVE NORMALLY TO RETAIN THE LATTER ON SAID SEAT TO CLOSE SAID PASSAGEWAY, A SECOND COIL SPRING OF GREATER FORCE THAN SAID FIRST COIL SPRING REACTING AGAINST SAID PISTON IN THE OPPOSED DIRECTION TO SAID FIRST COIL SPRING, A PISTON IN SAID CONTROL CHAMBER, RIGID MEANS EXTENDING THROUGH SAID PASSAGEWAY AND COACTING WITH SAID SECOND PISTON AND SAID PILOT VALVE TO URGE THE PILOT VALVE AWAY FROM SAID SEAT, WHEREBY WHEN THE PRESSURE IN SAID PRESSURE CHAMBER AND SAID CONTROL CHAMBER RISES TO A PREDETERMINED VALUE, THE PISTON IN SAID PRESSURE CHAMBER WILL BE MOVED IN DIRECTION TO REDUCE THE FORCE OF SAID FIRST COIL SPRING AGAINST SAID PILOT VALVE AND THE PISTON IN SAID CONTROL CHAMBER WILL MOVE IN DIRECTION TO CAUSE SAID RIGID MEANS TO MOVE THE PILOT VALVE OFF ITS SEAT, THEREBY PERMITTING FLOW OF FLUID FROM SAID PRESSURE CHAMBE THROUGH SAID PASSAGEWAY INTO THE DISCHARGE CHAMBER, TO REDUCE THE PRESSURE IN SAID CONTROL PORT OF THE DISCHARGE VALVE TO PERMIT OPENING OF THE LATTER BY THE PRESSURE APPLIED TO THE INLET PORT THEREOF, SAID FIRST COIL SPRING BEING COMPRESSED WHEN THE PRESSURE IN SAID PRESSURE CHAMBER IS REDUCED BY THE MOVEMENT OF THE FIRST PISTON BY THE SECOND COIL SPRING TO SEAT SAID PILOT VALVE WHEN THE PRESSURE IN SAID CONTROL CHAMBER HAS FALLEN BELOW A PREDETERMINED AMOUNT.