Abstract: A hydraulic control system including a source (11) of fluid having a pressure responsive means (15) and an actuator. A main control valve (21) has ports (27,29) communicating with the actuator ports by means of first (41) and second (43) conduits, and means to generate a load pressure (45). A pressure spike suppression valve (51) has ports connected across the conduits, the valve including a spool (65) moveable between a first position blocking communication between the ports, and a second position permitting communication. The valve (51) defines a spring chamber (67) including a spring (69) biasing the spool toward the first position. The valve defines a load signal passage (83) to communicate the load pressure to a chamber also to bias the spool toward the first position. The valve defines a pressure chamber (81) in communication with the source, fluid pressure therein biasing the spool toward the second position.

Abstract: A rotary fluid pressure device (11) having a housing (13,31), inlet and outlet ports (21,23), a gerotor gear set (15), a valve member (51) and an input-output shaft (49). A seal assembly (73) is disposed radially between the shaft (49) and the housing (31). The seal assembly comprises, in the order of leakage flow from a case drain region (63), a high pressure shaft seal (77), an annular chamber (71) in which is disposed a rigid back-up member (79;91) for the seal (77), a drain passage (81) communicating from the annular chamber (71) to a case drain port (47), and a low pressure shaft seal (83). The back-up member (79;91) may cooperate with either the housing (31) or the seal (77) or the input-output shaft (49) to define a fluid passage (87,89;93,95), so that any leakage flow past the high pressure shaft seal (77) flows through the drain.