The Argo Hytos E Series Return-Suction filters are For operation in 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 three 7.3 psi check valves 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 pressure relief valve prevents too high back pressure and protects the shaft seals against damages. As this valve leads the oil directly into the tank there is no direct connection between the return line and the connection of the feed pump, no by-pass valve function. Two emergency-suction valves with 300-micron protection strainer supply the feed pump in case of a short term of lack of oil. During normal operation, a lack of oil may definitely not occur.