1. Problem description and scope

This is a guide to diagnosing hydraulic pump cavitation caused by inlet flow restriction, low fluid level in the reservoir, high fluid viscosity, or an air leak in the suction line. Cavitation can lead to serious damages, fatigue of parts, reduced efficiency of hydraulic systems and unsafe working conditions. This manual is intended for hydraulic systems in mechanical engineering, metallurgy, chemical industry and energy.

2. Safety precautions

All work must be performed in compliance with the rules of blocking and marking (LOTO), the use of special clothing and personal protective equipment (PPE). Hazardous conditions may occur when diagnosing hydraulic systems, including fluid leaks and high pressure.

3. Necessary diagnostic tools

Name of the tool	Model/Spec	Measuring range	The goal
Multimeter	Fluke 87V	0–2000 Ω, 0–20 mA	Measurement of resistance and current in electric circuits
Thermal cameras	Fluke TiS10	-20°C to 550°C	Detection of uneven heating
Vibration analyzer	Keysight 35670A	0.1–100,000 Hz	Vibration measurement and malfunction detection
Time signature	Testo 825	0–1000 mm/s	Measurement of vibration speed
Pressure manometer	Testo 740	0–10 bar	Pressure measurement in the system

4. Check before starting diagnostics

Checkpoint	Description
Liquid level in the tank	Check if the fluid level is correct
Information about the duration of shutdown or system recovery	Confirm if the system has been turned off
Recent changes in the system	Check if piping or filters have been changed
Previous shutdown signals	Check the alarm log

5. Systematic diagnostic flow

Symptom: The pump makes a noise, sometimes with a "coffee" sound.
1. Check: Measure the pressure in the inlet line (0–10 bar). If the pressure is less than 1.5 bar, improper ventilation or restriction is possible.
2. Check: Measure the temperature of the liquid. If it exceeds 60°C, low viscosity or unstable level is possible.
Symptom: The pump does not meet the requirements.
1. Check: Measure the pressure in the tank. If it is less than 2 bar, check the fluid level and filters.
2. Check: Measure the vibration. If it exceeds 100 mm/s, cavitation is possible.
Symptom: Air leak in suction line.
1. Check: Use a thermal camera to detect uneven heating.
2. Check: Measure the pressure in the suction line. If the pressure is less than 1.2 bar, check the tightness.

6. Matrix of causes of defects

Symptom	Probable causes (most likely to least likely)	Diagnostic test	Expected result
Noise in the pump	Insufficient pressure in the inlet line Insufficient fluid level High viscosity of the liquid Air leak	Measure the pressure in the inlet line Check the fluid level Measure the temperature of the liquid Use a thermal camera to detect air leaks	The pressure is less than 1.5 bar The liquid level is less than 2 bar The temperature is more than 60°C Uneven heating
The pump does not meet the requirements	Insufficient fluid level Limiting the incoming flow High viscosity of the liquid	Measure the pressure in the tank Check the vibration Measure the temperature of the liquid	Pressure is less than 2 bar Vibration more than 100 mm/s The temperature is more than 60°C
Air leak in the suction line	Insufficient tightness Incorrect filter installation Insufficient line pressure	Use a thermal camera Measure the line pressure Check for tightness	Uneven heating The pressure is less than 1.2 bar Air leak

7. Analysis of root causes

7.1. Insufficient pressure in the inlet line

Insufficient pressure in the inlet line can be caused by restrictions in the piping, improper positioning of the pump, or insufficient liquid level in the tank. If the pressure during pump operation is less than 1.5 bar, this can lead to cavitation. Insufficient pressure causes uneven distribution of fluid and damage to internal parts.

7.2. Insufficient liquid level in the tank

A low fluid level in the tank can lead to a decrease in pressure and the appearance of air leaks. If the liquid level is less than 2 bar, this can lead to a higher level of cavitation. Insufficient fluid level causes uneven distribution of fluid and damage to internal parts.

7.3. High viscosity of the liquid

High fluid viscosity can lead to pressure drop and air leaks. If the temperature of the liquid is more than 60°C, this can lead to a decrease in viscosity. High fluid viscosity causes uneven distribution of fluid and damage to internal parts.

7.4. Air leak in the suction line

An air leak in the suction line can be caused by improper filter installation, improper sealing, or insufficient line pressure. If uneven heating or pressure less than 1.2 bar is detected, this may lead to air leaks. An air leak causes uneven distribution of fluid and damage to internal parts.

8. Step-by-step solution procedures

8.1. Insufficient pressure in the inlet line

Check the pressure in the inlet line. If the pressure is less than 1.5 bar, perform the following actions:
Check if there are restrictions in the pipelines. If so, clean or replace.
Check the fluid level in the tank. If the level is less than 2 bar, fill.
Check the pressure in the tank. If the pressure is less than 2 bar, fill.
Check vibration. If it is more than 100 mm/s, adjust.
Check the fluid temperature. If more than 60°C, measure the viscosity.

8.2. Insufficient liquid level in the tank

Check the fluid level in the tank. If the level is less than 2 bar, fill.
Check vibration. If it is more than 100 mm/s, adjust.
Check the pressure in the tank. If the pressure is less than 2 bar, fill.
Check the fluid temperature. If more than 60°C, measure the viscosity.
Check for tightness. If there are leaks, make repairs.

8.3. High viscosity of the liquid

Measure the temperature of the liquid. If more than 60°C, measure the viscosity.
Check vibration. If it is more than 100 mm/s, adjust.
Check the pressure in the tank. If the pressure is less than 2 bar, fill.
Check for tightness. If there are leaks, make repairs.
Check the fluid level. If less than 2 bar, fill.

8.4. Air leak in the suction line

Use a thermal camera to detect air leaks.
Measure the pressure in the suction line. If it is less than 1.2 bar, check the tightness.
Check vibration. If more than 100 mm/s, adjust.
Check the fluid level. If less than 2 bar, fill.
Check the pressure in the tank. If less than 2 bar, fill.

9. Preventive measures

The root cause	Preventive strategy	Monitoring method	Recommended interval
Insufficient pressure in the inlet line	Periodic check of pressure and fluid level	Manometer, thermal camera	Weekly
Insufficient fluid level	Filling the tank	Manometer	Weekly
High viscosity of the liquid	Measurement of temperature and viscosity	Thermal chamber, viscosities	Every month
Air leak	Periodic check of tightness	Thermal camera	Weekly

10. Relevant parts and components

Description of the part	Specification	When to replace	UNITEC-D category
The filter is hydraulic	Max. pressure 10 bar, temperature up to 60°C	After 1000 hours of operation	Hydraulics
Pipeline	The material is stainless steel	After 5000 hours of operation	Hydraulics
Reservoir	Max. volume 1000 l	After 10,000 hours of operation	Hydraulics
Manometer	Pressure up to 10 bar	After 2000 hours of operation	Hydraulics
Thermal camera	Temperature up to 550°C	After 1000 hours of operation	Diagnostics

For parts and components, visit the UNITEC-D website: https://www.unitecd.com/e-catalog/

11. Links

DSTU 2588-94: Hydraulic systems
EN 1284: Hydraulic systems
ISO 9001: Quality management systems
OEM printed instructions
UNITEC-D maintenance guides

Additional: This manual is intended for technical workers, reliability engineers and service managers in Ukrainian industry. It meets DSTU, EN, ISO standards, and uses CE, UkrSEPRO certifications.