The Argo Hytos E Series Return-Suction filters are for operation in mobile units with hydrostatic drives, when the return flow is under all operating conditions higher than the oil flow of the feed pump. The hydraulic oil returning from the circuit passes the filter element, is pressurized by a 7.3 psi check valve and supplied to the feed pump. The surplus oil flows filtered over the integral check valve into the reservoir. As the feed pump is always fed with pressurized oil, the risk of cavitation is minimized and full performance is available even during the critical cold start phase. An integral by-pass valve in the filter prevents too high back pressure - cold start, contaminates. A by-pass valve with a 200-micron protection strainer guarantees that only filtered oil can get into the feed pump.