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During hydraulic system operation, operators often encounter a puzzling problem: the pressure gauge indicates normal system pressure, but the cylinders fail to deliver sufficient push force. This failure not only impacts production efficiency but can also harbor significant equipment risks. This article will analyze the causes of this phenomenon from a professional perspective and provide systematic solutions.
01. Failure mechanism analysis
Normal hydraulic system pressure only indicates that the power source output pressure has reached the rated value. However, the cylinder’s output thrust depends on two key factors:
Push force = Pressure × Effective Area
Therefore, normal system pressure does not guarantee that the cylinder will generate sufficient output push force.
02. Analysis of the main causes
1. Internal leakage of hydraulic system
Internal cylinder leakage:
Worn or damaged piston seals can cause leakage from the high-pressure chamber into the low-pressure chamber, reducing the effective operating pressure. Scratches or wear on the cylinder barrel tube wall exceeding the allowable range can also cause internal leakage. Excessive clearance between the piston and the cylinder barrel tube can also cause leakage.
Internal valve manifold leakage:
Worn spools in the reversing valve can cause internal leakage exceeding the allowable limit. Poor sealing of hydraulic locks or counterbalance valves can cause the pressure-maintaining function to fail. An underset or seal failure in the overload relief valve can also cause pressure loss.
2.Abnormal Mechanical Resistance
Cylinder installation coaxiality deviation outside the allowable range can increase motion resistance. Overtightening or poor lubrication of the guide rail or slider can increase the coefficient of friction. Mechanical interference or sticking in the actuator can also reduce effective push force.
3.Pressure measurement error
Improper pressure measurement point selection may not accurately reflect the operating pressure. Incorrect settings of remote pressure regulators or pressure reducing valves can cause actual operating pressure to be lower than the displayed value. Inaccurate or damaged pressure gauges can also lead to reading errors.
4. Sealing System Failure
Improper seal selection and mismatch with the working medium or operating conditions can shorten seal service life. Improper seal installation or initial damage can lead to premature failure. Oil contamination exceeding NAS Level 9 can accelerate seal wear.
5. Excessive oil return backpressure
A clogged oil return filter can increase oil return resistance. An insufficient oil return line diameter or excessive elbows can create a throttling effect. Insufficient flow capacity of the reversing valve can also lead to increased backpressure.
03. Systematic troubleshooting process
Step 1: Pressure Verification
Install a calibrated pressure gauge directly at the cylinder inlet to measure the actual operating pressure. Compare the system pressure to the operating pressure. Normally, the difference should not exceed 0.5 MPa.
Step 2: Leak Detection
Perform a pressure holding test: Move the cylinder to the end of its stroke, maintain the rated pressure for 5 minutes, and record the pressure drop. A normal system pressure drop should not exceed 10% of the rated value.
Step 3: Mechanical Inspection
Use a laser alignment tool to check the cylinder’s mounting alignment. The deviation should be within 0.05 mm/m. Manually test the actuator’s travel resistance. Abnormal resistance often indicates a mechanical problem.
Step 4: Seal Inspection
Disassemble and inspect the seals for integrity and ensure the seal groove dimensions meet the standards. Use a particle size analyzer to analyze the oil contamination to ensure it meets NAS Class 9 or higher standards.
Step 5: Oil Return Test
Install a pressure gauge in the oil return line to measure the back pressure. Normally, it should be below 0.3 MPa. Check the filter’s differential pressure indicator and replace any clogged filter elements promptly.
