A bidirectional check valve that includes a housing having an internal cavity with fluid openings at axially opposed ends. A first valve element comprises a cup-shaped sleeve having a base adjacent to one axial end of the cavity and a sidewall axially slidably embraced by the housing within the cavity. A first fluid passage extends through the base of the sleeve adjacent to one of the cavity openings. A second valve element comprises a spool telescopically slidably received within the sidewall of the sleeve. A second fluid passage extends through the spool end from adjacent the second end of the housing cavity to internally adjacent the sidewall of the sleeve. A fluid passage is formed between the radially opposed surfaces of the sleeve and the spool for passing fluid therethrough as a function of axial position of the sleeve and spool with respect to each other. A coil spring is captured in compression between the sleeve and the spool so as to urge the valve elements toward respective ends of the housing cavity. The fluid passage between the radially opposing surfaces of the sleeve and spool comprises at least one channel formed in the outer wall of the spool. The channel has a cross section to fluid flow that varies as a function of axial position of the valve elements with respect to each other. To restrict fluid passage at high flow rates, one or both of the housing fluid openings may comprise a damping orifice of preselected diameter.

A quick release valve for a vehicle fluid pressure braking system includes a housing having inlet, exhaust and delivery ports. A bead circumscribes the inlet port to provide a valve seating area for a flexible diaphragm within the valve housing, and the exhaust port includes a projecting portion which preloads the flexible diaphragm into engagement with the bead circumscribing the inlet port. Accordingly, pressure variations between the ports cannot force the flexible diaphragm to vibrate to create an undesirable honking noise. Furthermore, the circumferentially extending bead assures a pressure-tight seal with the flexible diaphragm, and also establishes a predetermined sealing area for the diaphragm, thereby reducing valve hysteresis by preventing sealing of the diaphragm at varying areas on the housing.

An air brake control system for use in truck trailers having at each axle compressed-air brakes including spring brakes and service brakes, and each trailer being coupled to receive compressed air through an emergency (supply) gladhand and to receive service brake signals through a service (control) gladhand, the invention comprising an integrated brake valve system for each axle of each trailer, including a common valve housing; a spring brake valve cluster having a non-return check valve connected to receive and pass air pressure from the emergency gladhand and to deliver it directly to the spring brakes and an air pressure responsive shuttle operative to open the check valve whenever the emergency line pressure falls below a predetermined spring brake isolation pressure above which the spring brake holding pressure is not affected by fluctuations of the emergency gladhand pressure; and including an air tank supply valve cluster connected between the emergency gladhand and the tank and operative to sense pressure in the emergency gladhand and to open at a tank-filling threshold pressure above the predetermined spring brake isolation pressure to pass air to the tank and having a tank protecting check valve to prevent backflow of air from the tank; and including a pressure amplifying service brake relay valve cluster connected between the tank and the service brakes to supply and modulate air to the latter responsive to variations in the service gladhand pressure.

A hydraulic control system that comprises a hydraulic pressure line, a hydraulic fluid control mechanism and a lag network coupling the pressure line to the control mechanism for restricting flow of hydraulic flow therethrough, and thereby delaying and damping response of the control mechanism to fluid pressure fluctuations at the hydraulic line. The lag network comprises check valve that includes a flow passages interconnecting the hydraulic line and the control mechanism, a valve element, and a spring resiliently urging the valve element to close the passage, such that resistance to fluid flow increases as fluid flow decreases between the hydraulic pressure line and the control mechanism. Preferably, a pair of such check valves are connected in parallel between the hydraulic pressure line and the control mechanism for controllably restricting fluid flow in both directions. To offset decreasing resistance as a function of increasing fluid flow through the check valve or valves, an orifice that exhibits increasing resistance as function of fluid flow may be connected in series with the valves.

A valve assembly for selectively controlling application of a spring brake in a truck brake system having primary and secondary circuits is provided. A spring brake valve is modified to incorporate a balance piston having an integral quick release valve. This reduces the number of components, complexity, and service problems while maintaining all of the advantages associated with monitoring the function of the primary circuit.