the necessary pressure upstream of the coalescer filters and the polishing filters for their efficient operation there is a continuous stream passing through conduit 65 into the separator chamber 34 which is operating at a lower pressure than the coalescer chamber and the final or polishing filters resulting in check valve 66 being open in this stage of the operation even though the major part of fluid passing through conduit 65 may be water any oil contained therein will tend to rise to the top of the separator chamber as it passes into the separator chamber simultaneously substantially oil free water is vented through conduit 70 for overboard discharge as the oil level in the separator chamber 34 moves downwardly the probe 83 senses the change from water to oil for example by the differing resistance of the two fluids to electrical current this signal is communicated to the power and sensing circuit where it is stored in the logic therein as the oil passes the lower probe 84 a similar signal is sent to the power and sensing circuit to indicate the oil has reached a predetermined level so that the pump circuit should be reversed to discharge oil through conduit 87 the power and sensing circuit is designed to stop the pump 16 and to reverse direction of the pump 16 after an appropriate wait referring to fig2 the check valves are shown in a position they will assume upon.