Hydraulic pumps: cavitation diagnosis through inlet flow restriction

1. Problem Description and Scope

This manual is intended for diagnosing cavitation in hydraulic pumps, which occurs due to restricted inlet flow, low reservoir level, high fluid viscosity, or air leaks in the suction piping. Cavitation may lead to explosions, component wear, system failure, and significant repair costs. This problem occurs in all types of hydraulic systems: from industrial to aerospace, from food industry to energy.

Middle of the problem: cavitation in the hydraulic pump. Severity level: critical. Applies to hydraulic systems with open and closed reservoirs, including industrial units, machine tool systems, hydraulic drives and transmissions.

2. Preventive Measures

Important: Before performing any diagnostic procedures, carry out the lockout/tagout (LOTO) process to ensure personnel safety. During hydraulic system diagnostics, use special protective clothing, including gloves, goggles, helmets, and fluid discharge hoses.

Important: Perform the diagnosis with the unit switched off. If energy has been stored in the system, perform the system drainage before diagnosis.

3. Required diagnostic tools

4. First evaluation: Inspection before diagnosis

5. Systematic Diagnostic Flow

1. Confirm whether cavitation occurs:
1. During pump operation, monitor the noise and vibrations. If a characteristic humming occurs, this may be an indication of cavitation.
2. Measure the temperature of the liquid in the tank and the line. If the temperature is higher than 50°C, this may indicate a low liquid level or high viscosity.
2. Determine whether there are flow restrictions:
1. Measure the pressure in the suction pipeline. If the pressure is lower than 0.3 bar, this may indicate a restriction.
2. Check the filters, pipelines and valves for flow capacity.
3. Check the level of liquid in the tank:
1. Measure the liquid level in the tank. If it is lower than 20% of the nominal level, this may lead to cavitation.
2. Check for leaks or leaks.
4. Determine the viscosity of the fluid:
1. Measure the viscosity of the fluid. If the viscosity is higher than 100 cSt, this may cause improper operation of the pump.
2. Check for contamination or dry bearing.
5. Check for air leaks:
1. Measure the pressure in the suction pipeline. If the pressure is lower than 0.1 bar, this may indicate an air leak.
2. Use a thermal camera to detect hot spots in pipelines that may indicate air pockets.

6. Matrix of Problem Cause Occurrence

7. Root Cause Analysis

7.1. Limitation of Input Flow

Flow restriction may occur due to filter contamination, pipe clogging, or improper valve installation. This leads to reduced suction pressure, which promotes cavitation. If not corrected, it may cause shaft damage, bearing damage, or reduced pump service life.

7.2. Low level of liquid in the tank

Low liquid level may occur due to leaks, incorrect use of liquid or damage to the tank. This leads to a reduction in system pressure and increased vibrations. If this is not corrected, it may result in pump damage, liquid leakage or reduced system efficiency.

7.3. High Fluid Viscosity

High viscosity of the fluid may occur due to the use of the wrong type of fluid or dry bearings. This leads to improper operation of the pump and increased energy consumption. If this is not corrected, it may result in damage to the shaft, bearings, or reduced service life of the pump.

7.4. Air leak in the suction pipeline

Air leakage may occur due to improper installation of valves, clogged piping, or leaks. This leads to a reduction in system pressure and increased vibrations. If this is not corrected, it may result in damage to the shaft, bearings, or reduced service life of the pump.

8. Step-by-step troubleshooting procedures

8.1. Limitation of Input Flow

1. Measure the pressure in the suction pipeline. If the pressure < 0.3 bar, perform the following actions.
2. Check the filters for flow capacity. Replace the filter if it is contaminated.
3. Check the pipelines and valves for flow capacity. Correct clogging or incorrect installation.
4. Measure the pressure in the suction pipeline after correction. Confirm that the pressure > 0.3 bar.

8.2. Low level of liquid in the tank

1. Measure the liquid level in the tank. If the level is less than 20% of the nominal value, perform the following actions.
2. Check for leaks or damage to the tank. Repair leaks.
3. Add fluid to the reservoir up to the nominal level.
4. Measure the liquid level after correction. Confirm that the level > 20% of nominal.

8.3. High Fluid Viscosity

1. Measure the viscosity of the liquid. If the viscosity > 100 cSt, perform the following actions.
2. Check the fluid type. Replace with the correct fluid.
3. Check for dry bearing or contamination. Repair damage.
4. Measure the viscosity of the liquid after correction. Confirm that the viscosity < 100 cSt.

8.4. Air leak in the suction pipeline

1. Measure the pressure in the suction pipeline. If the pressure < 0.1 bar, perform the following actions.
2. Check valves, pipes and connections for tightness. Correct leaks.
3. Measure the pressure in the suction pipeline after correction. Confirm that the pressure > 0.1 bar.

9. Preventive Measures

10. Parts and Components

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11. Real Standards and Documentation

• ISO 1431:2017 – Cavitation Diagnosis in Hydraulic Systems
• EN 12628:2017 – Requirements for hydraulic systems
• DSTU 1641:2019 – Recommendations for the operation of hydraulic systems
• OEM documentation from manufacturers of hydraulic systems
• Abstracts UNITEC-D: "Hydraulic Systems: Technical Maintenance"

Additional

Perform diagnostics according to standards ISO 1431, EN 12628 and DSTU 1641. Use special tools and ensure safety when working with hydraulic systems.