Hydraulic pump: cavitation diagnosis due to inlet flow restriction

1. Problem description and scope

This manual is dedicated to diagnosing and correcting cavitation in hydraulic pumps caused by inlet flow restriction, low reservoir level, high working fluid viscosity, or air failure in the suction line. These problems occur in hydraulic systems of various types, including industrial machinery, production lines, and hydraulically actuated devices. Cavitation is considered critical because it can lead to pump failure, vibration, noise, and reduced system efficiency.

2. Security

Any work with hydraulic systems must be carried out in accordance with the Lockout and Tagout (LOTO) rules.

Do not turn off the system until the work is completed. During diagnostics, there may be dangerous leaks of working fluid, high pressure or accumulated energy.

Use personal protective equipment (protective gloves, glasses, noise insulation).

3. Necessary diagnostic tools

4. First assessment (checklist)

5. Systematic diagnostics

1. Symptom: Pump hums
   1. Check pump vibration
   2. If the vibration is higher than 8.5 mm/s, check the pressure in the absorber line
   3. If the pressure is less than 1.5 bar, check the level of the working fluid
   4. If the level is below 100 mm, fill
2. Symptom: The pump shuts off
   1. Check the temperature of the working fluid
   2. If the temperature is higher than 50°C, check the viscosity of the working fluid
   3. If the viscosity is higher than 100 cSt, change the type of working fluid
   4. If the viscosity is higher than 200 cSt, check the absorption line for leaks
3. Symptom: Pump does not respond to commands
   1. Check electrical connections
   2. If there is no current, check the machines
   3. If the current is higher than 15 A, check the coils
   4. If there are no turns, perform an audit

6. Matrix of determination of causes

7. Detailed analysis of reasons

7.1. Limiting the incoming flow

Inlet flow restriction occurs due to filter clogging, grid clogging, or insufficient flow. This leads to a decrease in pressure in the absorption line, which causes cavitation. Confirmation is performed by measuring the pressure in the absorption line. If the pressure is less than 1.5 bar, flow restriction occurs.

7.2. Low level of working fluid

A low level of working fluid can occur due to a leak, improper use or lack of filling. This leads to a decrease in pressure in the absorption line, which causes cavitation. Confirmation is performed by measuring the level of the working fluid. If the level is less than 100 mm, a low level occurs.

7.3. High viscosity of the working fluid

High viscosity of the working fluid can be caused by the wrong type of working fluid, high temperature or the use of old fluid. This results in reduced flow, which causes cavitation. Confirmation is done by measuring viscosity. If the viscosity is higher than 100 cSt, high viscosity occurs.

7.4. Air failure in the absorbing line

Air failure occurs due to leaks, loose joints, or lack of filling. This leads to the formation of air bubbles, which causes cavitation. Confirmation is made by measuring the presence of air. If air is present in the absorption line, an air failure occurs.

8. Step-by-step correction procedures

8.1. Limiting the incoming flow

1. Measure the pressure in the suction line
2. If the pressure is less than 1.5 bar, clean the filter
3. If the filter is clogged, replace the filter
4. Check the network for bandwidth
5. Fill the system to the level of 100 mm
6. Recheck pressure and vibration

8.2. Low level of working fluid

1. Check for leaks
2. If there are leaks, make repairs
3. Fill the system to the level of 100 mm
4. Check the level the next day
5. Recheck pressure and vibration

8.3. High viscosity of the working fluid

1. Measure the viscosity of the working fluid
2. If the viscosity is higher than 100 cSt, change the type of working fluid
3. Replace the working fluid with a suitable one
4. Check the temperature of the working fluid
5. Fill the system to the level of 100 mm
6. Recheck pressure and vibration

8.4. Air failure in the absorbing line

1. Check for air
2. If air is present, fill
3. Fill the system to the level of 100 mm
4. Check the connection for tightness
5. Recheck pressure and vibration

9. Preventive measures

10. Replacement parts and components

Go to the UNITEC-D catalog

11. Links

• ISO 4406:1999 – Standard for purity of hydraulic fluid
• DSTU 3023-95 – Requirements for hydraulic systems
• EN 12125:2002 – Requirements for hydraulic pumps
• UNITEC-D technical documentation
• Original technical documentation of the manufacturer