Air service brake exhaust control system

An air service brake exhaust control system for controlling the exhaust air from an air service brake assembly, the assembly including a housing, a service chamber defined by said housing, a housing inlet formed in said housing and a fluidly communicating with said service chamber, and an actuator responsive to the pressure within said service chamber, the system comprising:

• a pilot check valve having a first port fluidly coupled to said housing inlet, a second port fluidly fluidly copled to said first port, check valve means for allowing relatively free fluid flow from said second port to said first port and for blocking fluid flow from said first port to said second port, a control port, and means, responsive to the presence of a control pressure at said control port of at least a first value, for overriding said check valve means to allow relatively free flow of fluid between said first and second ports;
• and
• exhaust valve means, having an ambient exhaust port, for fluidly connecting said second port to a service brake pressure source or to said ambient exhaust port;
• whereby when said control pressure is at least said first value and said second port is fluidly connected to the service brake pressure source, the fluid from said service brake pressure source is fluidly connected to said housing inlet to actuate said actuator;
• when said control pressure is at least said first value and said second port is fluidly connected to said ambient exhaust port, said housing inlet is fluidly connected to said ambient exhaust port to allow the fluid in said service chamber to be exhausted through said ambient exhaust port;
• and when said control pressure is less than said first value, fluid flow from said service chamber through said pilot check valve is blocked by said check valve means so the pressure within said service chamber is not dissipated by exhausting fluid within said service chamber through said ambient exhaust port.