Fluid Cleanliness
Contamination is the largest single cause of pump wear. Particles the size of the working clearances do the damage, and they are far too small to see. Sample the oil, act on the result, and change filters on condition rather than only on a calendar.
Filtration
A blocked filter on bypass is doing nothing. Fit and watch indicators, and change elements when they say so rather than at a fixed interval. After any pump repair, change filters early because the circuit will shed debris.
Oil Temperature
Hot oil is thin oil, and thin oil means less film between the moving faces. Check cooler airflow and fan operation, and treat a rising running temperature as a symptom rather than a nuisance.
The Suction Line
Look at it regularly. A hose that has collapsed internally, a partly blocked strainer or a loose joint drawing air will all cause cavitation, and cavitation shortens pump life dramatically.
Reservoir and Breather
A blocked breather pulls a vacuum on the tank and a missing one lets dirt straight in. Both are cheap to fix and both cause expensive damage.
Measurements Worth Recording
Case drain flow, delivered flow at working pressure and running oil temperature. Recorded over time these three numbers will tell you a pump is failing months before it stops.
Planning a Rebuild
Once flow has dropped noticeably or case drain has climbed, plan the rebuild rather than waiting for the failure. A planned rebuild costs a fraction of an unplanned one because you choose when the machine stops.
