Abstract: A relief valve assembly (27) for use with first (15) and second (21) conduits, one communicating high pressure. The assembly comprises a housing (29,33) defining first (45) and second (47) ports, and a poppet seat (49). A poppet member (43) and the housing define a spring chamber (55), and a spring (39) is disposed to bias the poppet member toward the seat. The poppet member defines a shuttle cavity (51), a shuttle passage (53) communicating from the cavity to the spring chamber, and the poppet defining a seat (57), and a fluid passage (61P) communicating with the first port, and a seat (59), and a second fluid passage (63) communicating with the second port. A shuttle valve assembly (71,73,75) is provided, whereby the fluid pressure in whichever of the ports is at lower pressure is communicated to the spring chamber and adds to the force of the biasing spring.

Abstract: In order to achieve repeatable, consistent operation of a counterbalance valve, a poppet valve element within the valve has a radial bore therein in communication with a control fluid port and an axial bore therein which receives a rod that is anchored to a poppet valve cage that surrounds the poppet valve element. The poppet valve element is urged by a spring into engagement with a valve seat and pilot pressure is applied in opposition to the spring. By virtue of this arrangement, control fluid pressure is applied via the rod directly to the valve body in which the poppet valve element and cage are mounted. By changing the diameter of the rod and axial bore through the poppet valve element which receives the rod, the relief set pressure can easily be changed.