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.