4.20
Symptom Possible Cause Corrective Action
Noisy Pump Air in the system Tighten loose ttings. Replace cracked hoses and damaged parts.
Maintain hydraulic oil level in tank. Keep 3/4 full.
Cavitation (vacuum in pump) Open clogged or restricted intake line or plugged air vent in tank.
Loose or worn parts Replace worn gaskets.
Ensure the oil is the proper type and clean.
Stuck pump vanes, valves, pistons Dis-assemble pump and clean with solvent and dry thoroughly before reassembling. Do
not use hard tools, les, or emery cloth on machined surfaces. Replace rusted parts.
Pump/Drive misalignment Maintain constant oil temperature.
Overheating Outside temperature thickens oil Use oil with higher viscosity index. See uid manufacturers recommendations.
Low oil Maintain hydraulic oil level in tank. Keep 3/4 full.
High discharge pressure Parts misalignment Check parts for excessive friction. Replace if necessary. Ensure all parts are aligned.
Pump not pumping Shaft turning in wrong direction Shut the machine o immediately! Replace existing pump with one that turns in the
correct direction.
Intake clogged Clean tank and maintain oil at 3/4 full.
Air leak in intake Tighten or replace ttings, hose, or damaged parts.
Oil to thick Drain tank and replace with oil of the proper viscosity.
Low system pressure Relief value setting to low Block pressure line beyond relief valve and check line pressure with a pressure gauge,
adjust relief valve setting so uid ows to point of use.
Relief valve stuck open Clean dirty relief valve. Check oil for dirt and deterioration. Change if necessary.
Broken, worn, or stuck parts Block pressure line beyond relief valve and check line pressure with a pressure gauge. No
pressure buildup and functional relief valve indicate mechanical problems. Inspect pump
for worn or broken parts. Replace if necessary.
Valves sticking or binding Check oil for deterioration (e.g.: dirt, sludge, varnishes, and lacquers). Change if necessary.
Inspect pump parts for misalignment, wear, or damage. Replace if necessary.
Sluggish start-up Oil too thick at starting
temperature
Run the machine for short period and see if the oil thins out. If not, change the oil to a
lighter viscosity. See uid manufacturers recommendations.
Table 4.6 • Hydraulic Pump Troubleshooting Guide
General Maintenance • Hydraulics
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