Replacement for Filtermart 90343 Suction Strainer

A partially blocked suction strainer is one of the most common causes of hydraulic pump damage — and one of the most misdiagnosed, because the symptoms look like other problems.
The primary indicator is pump cavitation: a high-pitched whine or grinding noise caused by the fluid vapor pressure dropping below the cavitation threshold when inlet flow is restricted. From there you’ll see erratic actuator speed, loss of system pressure, spongy cylinder response, and rising pump temperature. Severe restriction pulls air past inlet gaskets and fittings, giving you milky or foamy fluid in the reservoir.

Clean and inspect at every hydraulic fluid change — every 1,000–2,000 hours for most industrial systems, every 500 hours for mobile equipment in dirty environments.
For new and recently rebuilt systems, pull the strainer after the first 50–100 hours. Break-in contamination hits hard — pipe scale, assembly residue, and component wear debris load the strainer fast before the system settles into steady-state cleanliness.
Wire mesh strainers can usually be backflushed with clean solvent or hydraulic fluid and reused, as long as the mesh is intact and the end caps look good. Any strainer that’s been partially collapsed by a high-restriction event should be replaced, even if it looks clean — structural deformation compromises the bypass valve and reduces effective filtration area. Cellulose and synthetic media strainer elements are disposable and shouldn’t be cleaned and reinstalled.

Most suction strainers include an integral bypass valve — a spring-loaded check that opens at 1–3 PSID when the mesh is clogged. Its job is simple: if the strainer blocks up and can’t pass enough flow, the bypass valve opens and lets fluid get to the pump, even if that fluid hasn’t been strained. A clogged-and-bypassing pump survives. A clogged pump with no bypass path cavitates in seconds.
Some designers skip the bypass valve and install a vacuum switch at the pump inlet that triggers a shutdown or alarm at high restriction. That’s fine for applications where allowing unfiltered flow is unacceptable — but you need one or the other. A strainer with a failed bypass valve in a clogged condition is the worst outcome.