I have been a mechanic all my life but not too much on hydraulics.The control valve has just three positions.up,stop and down.By the way this is an old 1963 JD 1010 Landscape loader.They were just like the backhoe but no backhoe attachment on them.Hydraulic pump on front of engine.There is no filter on it and looks like there never was a place for a filter adapter on it.Its just strait thru to the pump and no screen or anything.The oil is really clean and was changed about a month ago.It was also clean when I changed it and no sludge in bottom of tank.