Programmed valve system used for positioning control

摘要

A programmed valve system for positioning control having a first two stage valve assembly operable for raising a load and a second two stage valve assembly for lowering the load. Each of the second stages has a poppet with a parabolic contour which is dimensioned with orifice parameters to provide substantially linear flow rate change for minimized shock when one of the second stage poppets closes and the other opens. In the raise assembly, the pilot stage outlet orifice has a cross-sectional area substantially larger than that of the inlet orifice so that the second stage poppet opens much more rapidly than the closing thereof thereby to minimize overshoot when the pilot stage is actuated to the open position.