Hydraulic actuator and control unit

Claim 1

A HYDRAULIC ACTUATOR AND CONTROL UNIT COMPRISING A BODY HAVING A CYLINDER, A PISTON RECIPROCABLE IN SAID CYLINDER; SAID PISTON HAVING PISTON ROD MEANS SLIDABLY ENGAGING STUFFING BOX MEANS AT BOTH ENDS OF SAID CYLINDER, MEANS FOR ATTACHING ONE END OF SAID CYLINDER AND ONE END OF SAID PISTON TO SEPARATE ELEMENTS OF MECHANISM TO BE GIVEN RELATIVE MOVEMENT BY SAID ACTUATOR, A HYDRAULIC FLUID INLET PORT IN SAID BODY, A HYDRAULIC FLUID OUTLET PORT IN SAID BODY, A CONTROL VALVE MEANS IN SAID BODY NORMALLY OCCUPYING A POSITION IN WHICH BOTH ENDS OF SAID CYLINDER ARE SUBJECTED TO EQUAL PRESSURES AND SAID VALVE MEANS BEING OPERABLE IN OPPOSITE DIRECTIONS FROM SAID NORMAL POSITION TO ADMIT PRESSURE FLUID FROM SAID INLET PORT TO A SELECTED END OF SAID CYLINDER AND SIMULTANEOUSLY CONNECTING THE OPPOSITE END OF SAID CYLINDER WITH SAID OUTLET PORT, MEANS LIMITING THE EXTENT OF MOVEMENT OF SAID CONTROL VALVE REALTIVE TO SAID BODY, A VALVE SEAT IN SAID BODY, A VALVE ELEMENT RESPONSIVE TO DIFFERENTIAL PRESSURES NORMALLY ENGAGING SAID VALVE SEAT; ONE SIDE OF SAID VALVE ELEMENT BEING EXPOSED TO THE PRESSURE IN SAID INLET PORT AND SAID INLET PRESSURE TENDING TO HOLD SAID VALVE ELEMENT ON SAID SEAT AND THE OTHER SIDE OF SAID VALVE ELEMENT BEING EXPOSED TO PRESSURE OF FLUID BEING DISCHARGED FROM EITHER END OF SAID CYLINDER, AND SPRING MEANS CONSTANTLY IMPOSING A BIAS IN ADDITION TO THAT OF THE INLET PRESSURE TO SAID ONE SIDE OF SAID VALVE ELEMENT WHEREBY SAID VALVE ELEMENT IS YIELDINGLY MAINTAINED ON SAID SEAT TO PREVENT FLUID FLOW THROUGH SAID VALVE SEAT IN A DIRECTION TOWARD SAID ONE SIDE OF SAID VALVE ELEMENT UNLESS IT IS UNSEATED BY PRESSURE OF FLUID ISSUING FROM SAID CYLINDER IN RESPONSE TO ABNORMAL LOADS ON THE ELEMENTS OF A MECHANISM CONNECTED TO SAID ACTUATOR SUFFICIENT TO EFFECT MOVEMENT OF SAID BODY RELATIVE TO SAID CONTROL VALVE WITH RESULTANT CREATION OF PRESSURES ON SAID OTHER SIDE OF SAID VALVE ELEMENT WHICH ARE GREATER THAN THE COMBINED LOAD IMPOSED ON SAID ONE END THEREOF BY SAID SPRING MEANS AND THE INLET PRESSURE.