Abstract: The invention is particularly directed toward a safety device for a truck trailer having a valve, the valve having a casing rotatably mounting a valve spool therein. The casing has an air inlet, an air outlet, a vent outlet, and an alarm outlet. The spool has a passageway therethrough. The air inlet connects to connectable to an air compressor. The air outlet connects to the brakes of the trailer. The vent leads to the atmosphere. The alarm outlet leads to an alarm. The valve spool is selectivley rotatable within the casing to one of: a drive position where the valve connects the air inlet to the air outlet and blocks the vent and alarm outlets; a locked position where the valve connects the air outlet to the vent outlet and blocks the air inlet and alarm outlet; and an alarm position where the valve connects the air air inlet to the alarm outlet and blocks the air and vent outlets.

Abstract: The invention is particularly directed toward a safety device for a truck trailer having a valve, the valve having a casing rotatably mounting a valve spool therein. The casing has an air inlet, an air outlet,a vent outlet, and an alarm outlet. The spool has a passageway therethrough. The air inlet connects toconnectable to an air compressor. The air outlet connects to the brakes of the trailer. The vent leads to the atmosphere. The alarm outlet leads to an alarm. The valve spool is selectivley rotatable within the casing to one of: a drive position where the valve connects the air inlet to the air outlet and blocks the vent and alarm outlets; a locked position where the valve connects the air outlet to the vent outlet and blocks the air inlet and alarm outlet; and an alarm position where the valve connects the air air inlet to the alarm outlet and blocks the air and vent outlets.