Double Acting Relay is used for locking air in both the chambers of cylinderswhenever the supply pressure falls below the set value thereby keeping the actuator instay-put condition. The supply pressure connected to the signal port is sensed by the spring loadeddiaphragm and the thrust developed enable the valves to open thereby air enteringthrough the IN port get connected to the two output lines to respective cylinderchambers. The cut off setting is adjustable and can be done by adjusting the screwand locknut.