Suction Filters Suction filters are used as safety filters to protect pumps from gross contamination which can cause them to grip. They are available in 3 styles : * STR series immersed filters * FAS external filters, for mounting externally above the oil level * SF2 external filters, for mounting semi-immersed under the oil level SF2 semi-immersed filters, which shut off oil flow while the filter element is being replaced, replace the butterfly valves usually used for servicing hydraulic pumps.