A service brake inspection system engages service brake air lines downstream of a foot operated activation valve thereof to provide continuous engagement of the service brakes during inspection. The system includes a manually controlled air line which supplies air to a source port of an inversion valve. The inversion valve further includes an outlet port which is engaged to air lines supplying the vehicle service brake system via a double check valve in each of the primary and secondary service brake air lines, each being downstream of the foot operated valve. A third control port is connected to an air line disposed between a hand operated valve for exhausting the air lines to the spring parking brakes to set the parking brakes of the vehicle on. When the hand operated exhaust valve is set on, the pathway from the source to the outlet port in the inversion valve is opened to cause the service brakes to be continuously engaged for inspection.

An pneumatic system (10) for a tractor trailer truck (6) which increases compressed air flow to the trailer reservoir (52) whenever the tractor (7) is parked. This decreases the time it takes to charge the trailer reservoir (52) to a sufficient pressure to release the trailer brakes allowing the truck (6) to move. In normal over the road operation the trailer reservoir (52) is charged through a tractor protection control valve (14) which is mounted on the tractor dash. However when the tractor (7) is parked and a tractor park valve (12) which is mounted on the tractor dash is pulled out compressed air from the tractor secondary reservoir (42) is delivered with an increased flow rate to the trailer supply line (50). When the tractor park control valve (12) is pushed in releasing the tractor parking brake the trailer charging reverts back to charging through the dash mounted tractor protection control valve (14). Pulling the tractor protection control valve (14) out vents the trailer supply line (50) in both the fast and normal charge mode.

A brake system for a tractor-trailer vehicle includes a service brake system and a park brake system. The service and park brake systems are used to brake both a tractor and a trailer towed by the tractor. A trailer hand control valve is actuated by a vehicle operator to brake the trailer. The park brake system includes a park brake control valve that receives input commands from the vehicle operator to apply and release park brakes on the tractor and the trailer. An interlock valve assembly fluidly connects the park brake control valve to primary and secondary air supplies. The trailer hand control valve is also fluidly connected to the interlock valve assembly. The interlock valve assembly includes an outlet port that supplies an air signal to the trailer from one of the primary air source, secondary air source, or trailer hand control valve via a single connection line.