Abstract: Improvements in devices designed to actuate the air brakes of a freight car when a derailment occurs; a device which operates to immediately detect a wheel derailment of a railway train and automatically brings the air brake system of the train into a state of emergency stop; a fail open system and apparatus including an air relief valve attached to a railway car and also connected to the air brake pipe of the air brake system, sensor cylinder and spring assemblies connected to the railroad car body at one end thereof and at the other end to the side frame of a railroad car truck adjacent the railroad car wheels, an oil reservoir in the air relief valve which, when full, maintains the air relief valve closed and not venting air from the air brake pipe, a piston with an elongate piston rod associated with an oil reservoir in each sensor cylinder, the end of the piston rod being attached to the truck side frame, a line communicating between the oil reservoirs of the air relief valve and each sensor cylinder so