The Bendix® TR-2™ and TR-3™ valves are normally open, pilot-operated, inverting, on-off, two-way valves. As control pressure is reduced - to the point that the piston return spring or springs overcomes the force on the control piston - the valve will deliver full supply pressure at the delivery port. The TR-2 valve was used primarily in early Bendix® DD-3™ safety actuator control systems. It applied air pressure to the emergency diaphragm of the DD-3 actuators from a protected reservoir as control pressure is released from the lock mechanism. \nThe Bendix Trailer Line-Lock valve (most commonly referring to the Bendix® TR-3™ inversion valve or similar shut-off valves) is a component used to manage air signals to specific trailer systems, primarily lift axles. It "locks" or disrupts the air signal to prevent the service brakes from applying to an axle that is currently in the raised position.