Hydraulic System Troubleshooting Guide

Low or No System Pressure

Overheating

• Check the reservoir fluid level — low fluid reduces heat dissipation capacity
• Inspect the heat exchanger (air/oil cooler or water/oil cooler) for fouling, blocked airflow or coolant failure
• Measure pressure drop across return filters — a clogged filter forces fluid through the bypass, reducing cooling
• Check for continuous relief valve operation — a stuck-open relief or a misadjusted compensator can generate continuous heat
• Measure case-drain flow on pumps and motors — excessive internal leakage generates heat
• Confirm the fluid viscosity grade matches the ambient and operating temperature range
• Check for internal leakage through closed-center directional valves — a worn spool can bypass flow at rest

Adding a cooler without finding the heat source treats the symptom, not the cause. Start by measuring flow and pressure where energy is being converted to heat.

Noisy Pump

• Check for cavitation: restricted suction strainer, collapsed suction hose, high fluid viscosity or insufficient reservoir head
• Check for aeration: loose suction-line fittings, low reservoir level, faulty shaft seal or excessive return-line turbulence above the fluid surface
• Inspect the pump coupling: misalignment, wear, or loose elements can produce noise that sounds like a pump problem
• Check for trapped air: bleed the pump case and the highest point in the circuit
• Measure case-drain flow: an increase over time can indicate wear that also changes pump sound
• Confirm the drive speed is within the pump's published range

Cavitation and aeration damage pumps quickly. A noisy pump should be investigated immediately — do not run it hoping the noise will go away.

Slow or Erratic Actuator

• Confirm the pump is delivering flow: measure flow at the pump outlet or use a flow meter in the pressure line
• Check for a partially shifted directional valve: a sticking spool or inadequate pilot pressure can restrict flow
• Inspect flow-control valves for contamination or incorrect setting
• Check for external leakage at cylinder rod seals, fittings or hoses
• Check for internal cylinder leakage: isolate the cylinder and check for piston bypass under load
• Confirm the load has not changed: increased mechanical friction, binding or additional weight
• Check for air in the circuit: bleed the system and inspect the suction side

Cylinder Drift Under Load

• Isolate the cylinder with a shut-off valve or by blocking the ports — if drift stops, the problem is in the valve, not the cylinder
• If drift continues with the cylinder isolated, the piston seal is bypassing internally
• Check the directional valve spool for wear — a closed-center spool with excessive clearance can allow creep
• Check the counterbalance or load-holding valve for contamination or incorrect setting
• For vertical loads, confirm the load-holding valve pilot ratio is appropriate for the application

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