a compressed air unloader for unloading compressed air used in the compressed air braking and suspension circuits of a motor vehicle is disclosed . the unloader includes a housing with an internal air chamber , an air inlet for passing compressed air into the air chamber , a compressed air outlet , and a controlled outlet valve in the compressed air outlet for venting compressed air in the air chamber to the atmosphere when the valve is opened . an electronic control unit opens and closes the outlet valve . the air chamber also has an air chamber check valve and a pressure sensor downstream of the check valve . an integral multi - circuit control valve assembly is formed within the housing , the control valve assembly including a plurality of generally identical control and monitor units positioned downstream of the air chamber check valve and the pressure sensor , each of the control and monitor units comprising a control and monitor unit check valve opening against the direction of the air flow therethrough , an overflow valve for passing compressed air from the control and monitor unit , an actuator for operating the overflow valve , and an air pressure sensor positioned downstream of the control and monitor unit check valve .