The filter is a fine mesh screen which is used to remove impurities from oil, water, and air on the ship. Filters are mounted in pairs as a duplex system so that one can be used and other is kept on standby at a time.

The filter can be utilized both in low pressure (suction) and discharge (high pressure) side of the system and is used to remove the smallest part of dirt which is carried away in the system. The cleaning frequency of filters depends on the type of the filter and is decided by the manufacturer. The schedule is generally included in the planned maintenance system on board.