TL;DR
Low hydraulic pressure is most often a worn main pump, drifted relief valve, or leaking line. Measure standby and relief pressure before pulling the pump.
What you might see
- slow or sluggish boom and stick
- system pressure below rated spec
- hydraulic oil temperature rising fast
- pump noise louder than normal
Likely causes
Main hydraulic pump worn, reduced volumetric efficiency from piston/swash plate wear
Main system relief valve set too low or sticking open
Internal leakage in a hydraulic cylinder or motor worn past tolerances
Low hydraulic oil level or severely contaminated oil thinning film strength
Required tools
- Calibrated hydraulic pressure gauge with appropriate test-point adapters
- Hydraulic oil sample kit
- IR thermometer
- LOTO kit
Safety first
- Engage the hydraulic lockout lever before leaving the cab or working near any actuator. Unsupported implements can fall.
- Hydraulic oil under high pressure can inject through skin. Never check for leaks with bare hands.
- Falling material hazard: keep clear of the bucket and boom during all tests.
Procedure
- 1
Park the shovel on level ground, lower the bucket to the ground, and shut down the engine.
Warning: Engage the hydraulic lockout lever in the cab before leaving the operator station. - 2
Check the hydraulic oil level in the reservoir sight glass. Top up if low with the specified grade.
- 3
Connect a calibrated hydraulic pressure gauge to the test point on the main pump outlet.[1]
- 4
Start the engine and warm the hydraulic oil to operating temperature (above 50 degC).
- 5
Read standby pressure with controls at neutral, then activate a function against the relief and read relief pressure. Compare both values to the Caterpillar specification for this machine.[1]
- 6
If standby pressure is in spec but relief pressure is low, adjust or replace the main system relief valve.
- 7
If both pressures are low, take a hydraulic oil sample for particle count and viscosity analysis. Pump wear produces metallic fines.
- 8
Inspect all visible hydraulic lines and fittings for external leaks. Wet dust on lines near fittings indicates a seeping joint.
- 9
If pump wear is confirmed by low efficiency and metallic contamination, schedule a pump overhaul at the next planned maintenance stop.
Sources
Caterpillar CAT 6060 / 6090 Hydraulic Mining Shovel / Excavator general technical documentation, Caterpillar
Caterpillar hydraulic shovel service and maintenance documentation, hydraulic pressure test procedures (general)
More guides for Caterpillar CAT 6060 / 6090
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Engine overheating is most often a plugged radiator or failed thermostat. Check coolant level, inspect the radiator core for dust packing, and test the thermostat before running again.
How to detect swing bearing wear on a Caterpillar CAT 6060 / 6090 shovel
Swing bearing wear shows as axial play above 3 mm and metallic grease. Measure play at the rim and pull a grease sample before planning a bearing changeout.
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