Patent ID: 7455369

Claim:
A spring-actuated parking brake system for a vehicle, comprising at least one spring brake actuator in fluid communication with a fluid source via a supply line, a pressurized fluid supply valve, a shutoff valve disposed between said supply valve and said at least one actuator, said supply valve and said shutoff valve each being switchable to a bidirectional fluid flow-enabled position in which said at least one actuator is in fluid communication with a pressure sink to effect pressure relief of said at least one actuator and to engage a parking brake, said supply valve being switchable to a fluid supply position effecting fluid communication with said fluid source and said shutoff valve being switchable to said bidirectional fluid flow-enabled position to place said at least one actuator in fluid communication with said fluid source and to inject pressure into said at least one actuator to release said parking brake, and, when said parking brake is released, said shutoff valve being automatically switchable to a shutoff position to decouple said at least one actuator from said supply line, and to prevent depressurization of said at least one actuator and actuation of said parking brake when said supply line is broken, and said supply valve being switchable to said bidirectional fluid flow-enabled position to place said supply line in communication with said pressure sink.