How to Diagnose No Power Failure of Hydraulic System | Complete Troubleshooting Guide

1.Basic external inspection

1.1Insufficient hydraulic oil level

  Low oil level exposes the pump suction port to air. The hydraulic pump continuously ingests air, failing to build working pressure, accompanied by abnormal noise and vibration.Judgment method: Check liquid level gauge after shutdown. Oil below minimum scale means abnormality. Watch for excessive foam in oil tank.

1.2Air leakage on suction line or blocked suction filter

  Loose pipe joints and damaged seals allow air to enter the pump. Blocked suction filter leads to poor oil absorption. The volumetric efficiency drops sharply and pressure cannot rise.Typical symptom: Sharp noise from hydraulic pump. The machine may move slightly without load, yet totally powerless under load.

1.3Coupling slipping or fracture

  The engine or motor rotates normally, but fails to drive the hydraulic pump shaft. Worn coupling rubber blocks or broken flat keys are common reasons.

2. Hydraulic pump failures

2.1 Variable pump displacement returns to zero

  Proportional piston pumps may suffer stuck control piston, broken spring or blocked servo spool. The swash plate stays at zero angle, so the pump outputs nearly zero flow.

2.2 Severe internal wear of pump with low volumetric efficiency

  Worn plungers, valve plates and cylinder blocks cause heavy internal leakage. Flow circulates inside the pump and pressure cannot rise. Typical feature: low pressure can be achieved without load, pressure drops to zero immediately under load, and pump housing overheats.

2.3 Failed pump pressure regulating assembly

  Stuck pressure regulating valve or broken spring makes relief valve stay open continuously. Oil flows back to tank directly without building pressure.

3. Relief valve stays open

  The relief valve controls system pressure. If debris jams the spool, or internal sealing fails, the relief valve remains open all the time. Oil discharged by pump returns straight to the tank, and system pressure cannot be established.

4. Directional valve circuit faults

4.1 Burnt solenoid coil or insufficient pilot pressure

  Electro-hydraulic directional valves require pilot pressure. Without control pressure, the main spool remains in neutral position. For M-type and H-type neutral function, the pump unloads continuously, leading to zero system pressure.

4.2 Directional spool stuck by contaminants

  The spool locks at neutral position, and pressurized oil cannot reach actuators. No response when operating control levers.

4.3 Disconnected control cable or lever for manual multi-way valve

  External control mechanism falls off, the valve spool cannot shift, and the circuit stays under unloading status.

5. Pipeline and actuator faults

5.1 Bursted pipeline or loose joint leading to massive leakage

  Damaged high-pressure pipe causes direct oil leakage, pressure cannot be maintained. Leak points can be observed visually.

5.2 Completely damaged piston seal inside cylinder

  Failed cylinder seal allows oil to circulate between two cylinder chambers. Pressure can build temporarily on gauge, but the cylinder cannot generate thrust. It is easy to misjudge as overall system no-power fault.

6. Standard on-site troubleshooting sequence

Step1: Check oil level, suction filter and air leakage of suction pipeline;

Step2: Confirm pump input shaft rotates synchronously with power source, rule out coupling failure;

Step3: Measure pressure at pump outlet to divide fault range:

① No pressure at pump outlet: faults lie in hydraulic pump or main relief valve;

② Pressure exists at pump outlet, cylinder keeps static after valve operation: faults exist in directional valve, control circuit or cylinder;

Step4: Test solenoid voltage and pilot pressure for electro-hydraulic directional valves;

Step5: Clean spools of relief valve and directional valve to eliminate jamming caused by impurities;

Step6: Inspect internal wear of hydraulic pump and arrange maintenance or replacement when necessary.

7.Important maintenance reminders

  Never disassemble high-pressure pipes with system pressurized. Release residual pressure before inspection. Do not replace hydraulic pump at the first time; prioritize checking relief valves and suction circuits which account for most low-cost faults. Clean oil tank and replace filter elements after maintenance to avoid repeated failures caused by pollutants.

  In conclusion： loss of hydraulic power is not only caused by broken hydraulic pumps. Air intake, continuously open relief valve, unloading neutral position of directional valve and failed control mechanism account for more than 70% of field faults. Follow the sequence from external to internal, simple to complex, shorten maintenance time and reduce repair costs effectively.