BRAKE VALVE

摘要

A two stage brake valve communicates fluid pressure to a brake mechanism. The brake valve has an inlet for receiving pressurized brake fluid from a pump, a re servoir port, a stepped bore and a stepped piston member comprising a larger diameter prefill piston and a smaller diameter high pressure piston. The stepped bore and the stepped pi ston form a high volume prefill chamber and a high pressure chamber. The high pressur e piston has a metering groove which controls communication between the inlet and the brake mechanism. A bleed orifice is formed in the high pressure piston and commu nicates the high pressure chamber to an outer surface of the high pressure piston. The b leed orifice includes an annular bleed groove formed in an outer surface of the high pressure piston and a radial passage extending from the bleed groove to an interior of th e high pressure piston. The bleed groove is positioned so that the bleed orifice is ope n to the reservoir port via the prefill chamber during initial piston movement, and close d upon movement of the high pressure piston a predetermined distance beyond the positio n wherein the metering groove is first communicated with the inlet.