Hydraulic Power Unit Can Not Hold Pressure ？ Causes, Complete Troubleshooting & Solutions

1. Hydraulic Power Unit Pressure Loss Phenomenon

Hydraulic power unit pressure loss is a common hydraulic failure. Typical symptoms: continuous pressure drop on the pressure gauge, hydraulic cylinder sinking, mold unlocking, workpiece rebound and frequent pressure compensation. Most pressure holding failures are not caused by gear pump damage, but by valve internal leakage, seal damage and air intake.

2. Common Causes of Pressure Holding Failure

2.1 Check Valve Internal Leakage & Stuck

The check valve is the core pressure holding component. Dirt blockage, worn sealing surface and spring fatigue will cause hydraulic oil backflow and pressure loss.

2.2 Relief Valve Failure

Worn spool, stuck impurity and invalid spring cause unstable pressure and continuous system pressure relief.

2.3 Hydraulic Cylinder Internal Leakage

Aging and damaged piston seals lead to internal oil leakage, causing cylinder sinking and pressure dropping under load.

2.4 Gear Pump Internal Wear

Long-term operation causes large internal clearance of the mini high-pressure gear pump, resulting in high-pressure oil backflow and poor pressure holding performance.

2.5 External Oil Leakage

Loose joints, aging gaskets and damaged oil pipes cause slight oil leakage and system pressure loss.

2.6 Dirty & Deteriorated Hydraulic Oil

Impurities and emulsified oil cause valve jamming and poor sealing, resulting in pressure failure.

2.7 Air Intake & Pump Cavitation

Loose suction pipe causes air entering the hydraulic system, leading to unstable pressure and fast pressure relief.

3. Step-by-Step Troubleshooting Method

Step 1: Visual Inspection

Check oil leakage on pipes, joints, cylinders and valve blocks. Confirm sufficient oil level to avoid pump cavitation.

Step 2: Eliminate External Leakage

Tighten all pipe joints, replace aging gaskets and damaged oil tubes.

Step 3: Test Valve Block Pressure Holding

Isolate the cylinder and keep pressure on the valve block. If pressure drops quickly, the check valve or relief valve is faulty. Clean or replace the valve core.

Step 4: Test Cylinder Internal Leakage

Keep pressure on the hydraulic cylinder alone. If the cylinder sinks or pressure drops, replace the cylinder oil seal.

Step 5: Test Gear Pump Performance

If all valves and cylinders work normally but pressure still drops, the gear pump is worn out and needs replacement.

Step 6: Check Oil Quality & Air Intake

Replace deteriorated hydraulic oil, clean the filter and check the tightness of the suction pipeline.

4. Professional Solutions

4.1 Clean or replace faulty check valves and relief valves to solve internal leakage.

4.2 Replace all aging cylinder sealing rings to eliminate cylinder internal leakage.

4.3 Replace worn mini high-pressure gear pumps to restore system pressure stability.

4.4 Replace damaged pipes and gaskets to prevent external oil leakage.

4.5Use qualified hydraulic oil and regular filter replacement to keep the system clean.

5. Daily Maintenance Tips

Regularly replace hydraulic oil and filters; inspect pipeline tightness daily; avoid long-term high-pressure standby of the hydraulic system, effectively reducing pressure loss failure rate and extending the service life of gear pumps and hydraulic valves.