Importance

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Abstract

A dual pressure vehicle air brake system (60, 61, 100, 101) made according to the invention includes first and second sources (62, 64) of pressurized air at, for example, 175 psi and 100 psi, respectively. A combination brake actuator (6) includes a conventional service brake chamber (8) adapted to accommodate the lower, second air pressure while the spring brake chamber (10) is made to accommodate the higher, first pressure. The use of the higher first pressure allows a stiffer actuator spring to be used and be fully deflected by the first pressure without substantially changing actuator piston areas and other elements of conventional combination brake actuators. A conventional modulated spring brake control valve (78) is used to supply air at the first pressure to the spring brake chamber. The service brake chamber is supplied with air at the second pressure through the outlet of a conventional service brake application valve (68). Compounding of brake forces, which could occur if both the service and spring brakes were applied simultaneously, may be reduced or eliminated using a conventional two-way check valve (50 ) or a novel shut off valve (102).

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First Claim