Separate inputs for air pressure supply and parking brake control are provided to a parking brake control valve for a towed vehicle to enable manual release of the parking brakes using air pressure stored in either one of two mutually protected reservoirs on the towed vehicle without bleeding one source of stored air pressure into another.
A braking system control requires that a first or service braking system be actuated before a second or parking braking system can be released to prevent unexpected movements. A sensor senses that the service brakes are engaged and controls a device to release the parking brakes. A latch ensures that the parking brakes remain released. For example, a piston and check valve form the sensor and latch. Service brake pressure works against the piston. Above a threshold level, service brake pressure drives the piston to open a valve that provides pressurized air to a parking brake release system. Once released, the check valve directs parking brake release pressure to the piston to keep the valve open.
A valve assembly for an air pressure system includes an inlet valve, a first control valve, and a second control valve. The inlet valve includes an inlet port, an outlet port and a control port. The inlet valve inlet port communicates with the inlet valve outlet port when the inlet valve control port is above a threshold pressure. The first control valve includes an inlet port, an outlet port, an exhaust port, and a control member. The first control valve inlet port communicates with the inlet valve outlet port. The first control valve outlet port communicates with one of the first control valve inlet port and the first control valve exhaust port as a function of a position of the first control valve control member. The second control valve includes an inlet port, an outlet port, an exhaust port, and a control member. The second control valve inlet port communicates with the inlet valve outlet port. The second control valve outlet port communicates with one of the second control valve inlet port and the second control valve exhaust port as a function of a position of the second control valve control member.
A valve assembly for an air pressure system includes an inlet valve, a first control valve, and a second control valve. The inlet valve includes an inlet port, an outlet port and a control port. The inlet valve inlet port communicates with the inlet valve outlet port when the inlet valve control port is above a threshold pressure. The first control valve includes an inlet port, an outlet port, an exhaust port, and a control member. The first control valve inlet port communicates with the inlet valve outlet port. The first control valve outlet port communicates with one of the first control valve inlet port and the first control valve exhaust port as a function of a position of the first control valve control member. The second control valve includes an inlet port, an outlet port, an exhaust port, and a control member. The second control valve inlet port communicates with the inlet valve outlet port. The second control valve outlet port communicates with one of the second control valve inlet port and the second control valve exhaust port as a function of a position of the second control valve control member.
