A backpressure check valve forces fluid through an orifice to the filter. The backpressure must not interfere with circuit operation.

Suction line strainer or filter

To prevent pump cavitation, components in this system must have low pressure drop and high capacity. Filter elements should be submerged in reservoirs so no part of the filter surface is exposed to air.

Pressure line bleed-off filter

An orifice between the pump discharge and filter assembly maintains a constant flow through the filter. This circuit generally is used on high-flow circuits because flow through the filter is lost as effective pump output.

Discharge line filter

This circuit filters oil immediately as it returns from the work station. Return line filters can tolerate a higher pressure drop than those in a suction line.

Pressure line filter

This circuit has the advantage of full-flow filtration but the disadvantage of high pressure drop. Often it can be used instead of a low-pressure return line filter to prevent building up backpressure.

Independent circuit

Sometimes called a kidney loop, this circuit filters full flow from a separate filter pump. These circuits often incorporate a heat exchanger and multiple filters.