Inside Hydraulics Newsletter -- Issue 05

Filters that do more harm than good -- Part 1

Given that particle contamination in the hydraulic fluid reduces the service life of hydraulic components, it would seem logical that a system can never have too many filters. Well... not exactly.

Some filters can actually do more harm than good and therefore their inclusion in a system is sometimes misguided.

Pump inlet (suction) filters fall into this category. Inlet filters usually take the form of a 140 micron, mesh strainer which is screwed onto the pump intake penetration inside the reservoir.

Inlet filters increase the chances of cavitation occurring in the intake line and subsequent damage to, and failure of the pump. Piston-type pumps are particularly susceptible.

If the reservoir starts out clean and all fluid returning to the reservoir is filtered, inlet filters are not required since the fluid will not contain particles large enough to be captured by a coarse mesh strainer.

What does this mean?

I generally recommend removing and discarding inlet filters where fitted. The one possible exception to this rule is charge pump intakes on hydrostatic transmissions. If in doubt consult the pump manufacturer.

If you are involved in the design of hydraulic systems, think twice before specifying intake line filtration.