Hydraulic lift control system and valve therefor

Claim 1

A HYDRAULIC LIFT CONTROL SYSTEM COMPRISING A VALVE THROUGH WHICH FLUID MAY FLOW TO AND FROM THE LIFT CYLINDER WHEN THE LIFT IS BEING RAISED AND LOWERED, THE VALVE ALLOWING FREE FLOW TO THE CYLINDER AND LIMITING THE MAXIMUMU RATE OF EXHAUST FLOW FROM THE CYLINDER, SAID VALVE HAVING A SPRING-BACKED PISTON MOVABLE IN RESPONSE TO CHANGES IN EXHAUST FLUID PRESSURE UPSTREAM THEREFROM, SAID VALVE HAVING VARIABLE-AREA ORIFICES SO CONTROLLED BY THE PISTON AS TO DECREASE AND INCREASE IN AREA RESPECTIVELY UPON INCREASE AND DECREASE IN SUCH PRESSURE, WHEREBY THE MAXIMUM RATE OF DESCENT OF THE LIFT CYLINDER DECREASES AS THE STATIC LOAD ON THE LIFT INCREASES, SAID VALVE COMPRISING A BODY HAVING A CYLINDER DIVIDED BY SAID PISTON INTO AN INLET CHAMBER AND A CONTROL CHAMBER, WITH SAID INLET CHAMBER ARRANGED TO RECEIVE EXHAUST FLUID FROM THE LIFT CYLINDER WHEN THE LIFT IS LOWERING, AND SAID VALVE BODY ALSO HAVING AN OUTLET OPENING FOR SUCH EXHAUST FLUID, THE PISTON-BACKING SPRING BEING ARRANGED TO RESIST MOTION OF THE PISTON IN A DIRECTION TO EXPAND SAID INLET CHAMBER, A FIRST VARIABLE-AREA ORIFICE CONNECTING THE INLET CHAMBER WITH THE CONTROL CHAMBER, AND A SECOND VARIABLE-AREA OPENING, THE AREAS OF BOTH OF SAID ORIFICES BEING CONTROLLED BY THE PISTON AND BEING DECREASED BY MOTION OF THE PISTON IN SAID DIRECTION.