Hydraulic Oil Filters Hydraulic oil filtration unit or oil transfer unit is used to filter the equipment’s hydraulic oil from impurities. According to the degree of impurities present in the hydraulic oil, the type of filter required is determined in terms of its ability to filter the oil, i.e. the filter pores (microns) required for the filtration process, as well as the capacity of the pump used for the discharge speed and the required pressure. It is a very important process for any equipment to clean it from impurities that affect the operation and capacity of the equipment.