Fail Safe Air lock Relay as the name suggest has an extra line of safety built in to it for very critical situations. It is used for locking air in both the chambers of cylinderswhenever the supply pressure falls below the set value thereby keeping the actuator in stay-put condition. The supply pressure connected to the signal port is sensed by the spring loaded diaphragm and the thrust developed enable the valves to open thereby air entering through the IN port get connected to the two output lines to respective cylinder chambers. The cut off setting is adjustable and can be done by adjusting the screw and locknut. In addition to the Air Lock function it has a extra let of valve to lock the air in case of a failure.