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As the powerhouse of a hydraulic system, the hydraulic pump’s operating status directly impacts the performance and reliability of the entire system. Abnormal noise and insufficient flow are the two most common fault symptoms in hydraulic pumps, often serving as early warnings of more serious issues. This article systematically analyzes the causes, diagnostic methods, and corresponding treatments for these two types of faults, providing practical technical references for equipment maintenance personnel.
01. Typical phenomena of hydraulic pump failure
1. Abnormal Noise:
- Cavitation noise: Characterized by a high-frequency hissing or crackling sound, it typically occurs near the pump’s suction port. This is caused by air entering the oil or the collapse of bubbles.
- Mechanical noise: This noise manifests as a dull rumble, click, or continuous metallic friction. It is often caused by wear, damage, or installation issues within the pump’s mechanical components.
- Pressure pulsation noise: A periodic buzzing sound accompanied by noticeable fluctuations in the pressure gauge needle is typically caused by uneven leakage or unstable oil supply within the pump
2. Insufficient flow/drop in output pressure:
- The actuator (hydraulic cylinder, motor) experiences a significant slowdown in movement, with a noticeable sense of weakness.
- The system pressure fails to reach the setpoint or builds slowly.
- The pump temperature rises abnormally (this should be combined with the oil temperature for comprehensive evaluation).
02. Failure cause analysis
1. Causes of abnormal noise:
- Severe oil contamination (abnormal wear caused by solid particles).
- Poor oil anti-foaming properties and excessive bubbles (increased cavitation).
- Prolonged high oil temperature, leading to oil degradation and decreased viscosity.
- Worn or damaged bearings.
- Bent pump shaft or misaligned coupling.
- Severe wear, scoring, or breakage of internal moving parts (gears, vanes, plunger, slipper, port plate).
- Loose fasteners.
- Clogged oil suction filter or insufficient flow capacity.
- The oil suction line is undersized, too long, or has flattened or kinked components.
- The oil level in the tank is too low.
- The oil viscosity is too high (low-temperature startup) or too low (high temperature, incorrect oil selection).
- Poor seals in the oil suction line, causing air to be drawn in.
- Oil suction problems.
- Mechanical problems.
- Oil problems.
2. Causes of Insufficient Flow/Pressure Drop:
- Insufficient speed or power loss of the prime mover (motor/engine).
- Slippage or damage to the coupling.
- Internal wear of the pump (e.g., excessive clearance between the valve plate and the cylinder end face, between the plunger and the cylinder bore, or between the vanes and the stator/rotor slots).
- Low oil viscosity (exacerbated internal leakage).
- Suction-side issues: (Same as the suction issues with abnormal noise, resulting in insufficient pump suction).
- Decreased volumetric efficiency (increased internal leakage).
- Drive issues.
- Improper or failed relief valve setting: Premature pressure relief (need to investigate the relief valve itself).
- Severe system leakage: Although the pump output flow may be normal, significant oil leakage may result in insufficient effective flow (need to investigate the piping, fittings, actuator, etc.).
03. Diagnostic process and methods
1. Preliminary Inspection:
- Check the oil level, oil color, and cleanliness in the fuel tank.
- Check the suction filter’s differential pressure indicator or visually inspect its cleanliness.
- Touch the pump body and suction line to feel for temperature and vibration; listen for the location and characteristics of the noise source.
- Check all connections in the suction line for leaks (possibly due to air ingestion).
- Check the drive motor/engine for normal speed, coupling damage, and proper alignment.
2. Instrument Inspection:
- Pressure Gauge: Measure pressure at the pump outlet, along the system’s main pressure line, and before and after key valves to determine pressure buildup and differential pressure.
- Flow Meter: Install a flow meter at the pump outlet to directly measure actual output flow (the most accurate indicator of pump status).
- Thermometer: Measure pump casing and tank oil temperatures.
- Vacuum Gauge: Installed at the pump’s suction port to measure suction vacuum (to determine if suction resistance is excessive).
3. Isolation and Diagnosis:
- If conditions permit, disconnect the pump outlet piping and briefly measure the pump’s output flow and pressure under no-load conditions (pay attention to safe pressure relief) to preliminarily assess the pump’s performance.
- Compare the system’s performance under different operating conditions to determine whether the problem lies with the pump or with downstream valves or actuators.
04. Treatment measures and maintenance
1. General Solutions for Abnormal Noise and Insufficient Flow:
- Clean or replace clogged oil suction filters.
- Inspect and repair leaks, flattening, or kinking in the oil suction line; ensure the pipe diameter meets the requirements.
- Replenish the oil to the specified level.
- Select hydraulic oil with the appropriate viscosity based on the ambient temperature and operating requirements.
- Solving Oil Suction Problems.
- Replacing Hydraulic Oil and Filters: If the oil is severely contaminated, emulsified, degraded, or has poor anti-foaming properties, completely replace it with qualified new oil, clean the oil tank, and replace all filters.
- Check and Repair Leaks: Tighten joints and replace damaged seals (note the distinction between internal and external leaks).
2. Treatment for Pump Issues:
- Adjustment and Repair: Minor wear can sometimes be restored through professional repair (such as lapping the valve plate). Adjust the coupling alignment.
- Part Replacement: Replace worn or damaged bearings, shaft seals, and internal moving parts (repair kits available).
- Replacing the Hydraulic Pump: When internal wear is severe, key components (such as the housing or shaft) are damaged, or the cost of repair is prohibitive, a new pump is recommended. Always select a model that matches the original pump’s specifications (displacement, pressure rating, speed, and connections).
3. Preventive Maintenance Recommendations:
- Strict Oil Management: Regularly test oil cleanliness (particle count), viscosity, moisture, and acidity; replace hydraulic oil and filters regularly.
- Ensure Good Oil Suction Conditions: Regularly check the condition of the oil suction filter and piping; avoid excessively high or low oil temperatures.
- Monitor Operational Status: Perform daily inspections and pay attention to pump noise, vibration, and temperature fluctuations.
- Correct Operation: Avoid prolonged overpressure and overspeed operation; preheat the pump when starting at low temperatures.
- Professional Repair: Hydraulic pump disassembly and repair requires specialized knowledge and tools. It is recommended that this be performed by qualified personnel or under the guidance of a professional manufacturer.