Abstract: A reservoir for use in a hydraulic circuit is disclosed which includes a passive gas separating medium to separate gas from the hydraulic fluid as it circulates through the reservoir. The gas separating medium, which may be a membrane-type diffuser, is permeable to air, but not hydraulic fluid. This allows entrained air to diffuse through the membrane element after which it may be expelled to the atmosphere. The membrane diffuser is located within the reservoir housing in a low-pressure portion of the hydraulic circuit in a space between spaced apart double walls of the reservoir such that hydraulic fluid returning to the reservoir must first pass through the membrane. The membrane may have several concentric or spiral layers, depending upon the capacity of the circuit. Gas separated from the hydraulic fluid is withdrawn from the membrane diffuser structure and may be vented to atmosphere through a valve associated with the reservoir housing.

Abstract: A multiport selector valve incorporates a polished interface between a respective poppet of each port and a displaceable valve spool. A controlled gap exists between each poppet and its respective port fitting to pressurize a recess in which an O-ring is seated during operation of the valve. This results in the O-ring seal being urged against a confronting surface of the poppet which increases the contact force between optical surfaces of the poppet and the spool, particularly during periods of dynamic flow. The construction of the valve results in a unit of high reliability and useful life with attendant reduction of replacement costs.