Peter William Backes, Age 652160 Eagle Ridge Dr, Mankato, MN 56003

5778672, Jul 14, 1998

Oct 17, 1996

8/733229

Douglas Michael Durant - Waterloo IA
Peter William Backes - Searcy AR

Deere & Company - Moline IL
Vickers, Inc. - Searcy AR

B60T 1300
F15B 700

605471

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 reservoir 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 piston form a high volume prefill chamber and a high pressure chamber. The high pressure 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 communicates the high pressure chamber to an outer surface of the high pressure piston. The bleed 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 the high pressure piston. The bleed groove is positioned so that the bleed orifice is open to the reservoir port via the prefill chamber during initial piston movement, and closed upon movement of the high pressure piston a predetermined distance beyond the position wherein the metering groove is first communicated with the inlet.