Programmed unbalanced load valve system

摘要

A valve system for an unbalanced load having a first two stage valve assembly operable for raising the 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 when the second stage poppet moves for substantially zero flow jerk. In addition, the raise valve assembly has a pilot line coupled directly to the load so that high pressure oil is instantly available to actuate the second stage poppet. The lower valve assembly has a dashpot to decrease the rate of opening of that second stage poppet.