Hydraulic Repair Guides

31 Expert Hydraulic Repair & Diagnostic Fixes

10/31/2025

The Certified Specialist’s Quick Guide to Troubleshooting Common System Failures.

Don't let hydraulic failure cost you valuable time. Our Certified Fluid Power Specialists have compiled a comprehensive guide to quickly diagnose and address the most common problems from mysterious pump noise to excessive heating. Stop guessing and start fixing with this step-by-step repair guide.

Section A: Pump and Flow Diagnostics
This section addresses issues related to the core of the system.

Trouble Area 1: Intake, Air, and Fluid Issues

Restricted Inlet (Cause 1): Always check the line from the reservoir to the pump. Be sure filters and strainers are not clogged.
Air Leaks (Cause 2): Check pump intake piping joints and the pump shaft seal. Test by pouring oil on joints or the seal while listening for a change in the sound of operation.
Air Entrainment (Cause 3): This occurs if the oil level is low or the return line is installed above the oil level. Check the oil level and the position of the return line.
Reservoir Air Vent (Cause 4): Air must be allowed to be breathed into the reservoir. Clean or replace the breather.
Filter or Strainer (Cause 8): Keep filters clean enough to permit adequate flow. Be sure the original filter has not been replaced with one of smaller capacity.

Trouble Area 2: Mechanical Pump Failures

Pump Rotation or Speed Incorrect (Cause 5): First find out the speed recommended by the manufacturer, then check the pump speed. Reversed leads on 3-phase motors are a common cause of wrong rotation.
Pump Out of Line with Motor (Cause 9): Check the alignment. Misalignment may be caused by temperature variation or incorrect belt tension.
Pump Head Too Loose (Cause 10): Test by pouring oil over the pump head. Replace the faulty gasket or tighten the head as necessary.
Pump Head Too Tight (Cause 11): If a pump was recently overhauled, follow manufacturer instructions. Too tight reduces clearances and increases rubbing friction.
Stuck Pump Vane (Cause 12): Inspect the vane-type pump for wedged chips or sticky oil, then clean and re-assemble.
Pump Malfunction (Cause 14): Look for mechanical trouble in the pump and replace worn and broken parts if appreciable pressure is not developed after blocking the system.
Dirt in Pump (Cause 20): Dismantle and clean the pump.

Section B: Fluid Quality and System Component Issues
This section focuses on oil quality, valve operation, and overall system integrity.

Trouble Area 3: Valve and Pressure Control

Relief Valve Not Functioning (Cause 15): The valve setting may not be high enough, or the spring inside may be broken. Check the seat for score marks or replace the spring and re-adjust the valve.
Incorrect Control Valve Setting (Cause 16): If direction control valves are unintentionally set at the neutral position, oil can return to the reservoir without resistance, causing little pressure to develop.
Internal Leakage (Cause 17): Determine the location of the leakage in valves, cylinders, or pumps by progressively blocking off various parts of the circuit.
Excessive Pressure (Cause 18): Check the relief or regulator valve's maximum setting to ensure it is not exceeding the pump rating.
Valve Deposits (Cause 26): Repair or replace the valves. This is usually caused by a high sediment level or oil oxidation.
Pilot Pressure Too Low (Cause 27): Consult manufacturer instructions; pilot pressure typically runs about 50 psi.

Trouble Area 4: Leaks, Hoses, and Sealing

Restricted Lines (Cause 24): Check for crimped lines or internal obstructions.
Loosened Fittings (Cause 29): Tighten, reseal, or replace O-rings. Check fittings for signs of cracks or improper installation.
Dried or Worn Seals or O-rings (Cause 30): Replace or tighten worn components. Switching to seal-control oil may help.
Line Breakage (Cause 31): Check hose configuration for twists, tight bends, or sags, and install hose supports. Inspect for cheap hose quality or operator abuse.

Section C: Fluid Quality and Temperature

Oil Viscosity Too High (Cause 6): If oil is too heavy, some pump types cannot pick up prime. Drain and refill with oil of correct viscosity.
Oil Viscosity Too Low (Cause 7): Check pump manufacturer's recommendations. Oil with anti-wear agents is needed.
Low Fluid Level (Cause 19): Add recommended oil and check the level. Low supply means less oil to carry away heat, causing a temperature rise.
Fluid Contamination (Cause 22): Install an adequate filter or replace oil more often. Determine the source of the material and correct it.
Reservoir Too Small (Cause 25): The reservoir may be too small to provide adequate cooling or may vortex. Replace it with a larger reservoir or install a cooler.

Section D: Other Electrical and Component Wear

Packing Worn or Damaged (Cause 21): Tighten the packing gland or replace the packing. Abrasives in the oil may cause this, so check for points where abrasives are entering the system.
Oil Cooler Clogged (Cause 23): Try to blow it out with compressed air or use solvents.
Electrical Solenoid Problems (Cause 28): Make necessary electrical repairs.
Cavitation (Cause 13): Check for clogged or restricted intake line, plugged air vent in reservoir.

Solutions & Next StepsNeed to Pinpoint the Problem? Download Our Expert Cheatsheet.

The guide above details many common issues, but we know diagnostics can be complex. For a quick, scannable reference to identify the most likely cause for your system's exact symptoms, use our comprehensive Troubleshooting Cheatsheet.

DOWNLOAD: TroubleShooting Cheat Sheet

This guide was compiled and verified by the expert team at Progressive Power & Control. We are committed to providing Indiana's industrial sector with reliable parts, systems, and technical knowledge.

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