A control unit assembly for a medical device wherein the assembly comprises a control unit (10) and a docking unit, the docking unit located on the medical device wherein the control unit comprises a pump, at least one conduit and control means for controlling the flow of fluid from the pump through the conduit; and the docking unit comprises a detachable fluid transfer connector which connects the conduit to an inflatable cell of the device. One of the detachable fluid transfer connector is an air inlet connector which provides air to the pump and which is provided with a filter (24). The control unit further comprises a plurality of valves located between the pump and the conduits, the plurality of valves being arranged in a ranked structure.