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Diagnosing and correcting hydraulic cylinder runout and wear: internal leaks, oil seal inspection, control valve testing, and pilot pressure testing

Technical analysis: Troubleshooting hydraulic cylinder drift and creep: internal leak diagnosis, seal inspection, counte

Діагностика та виправлення відкидання та зношування гідравлічних циліндрів: внутрішні утечки, перевірка сальників, випробування клапанів контрольного засобу та перевірка тиску пілоту - UNITEC-D Indust
Діагностика та виправлення відкидання та зношування гідравлічних циліндрів у виробництві. Виконайте перевірку тиску пілоту, клапанів контрольного засобу, сальників та внутрішніх утечок. Використовуйте

1. Problem description and scope

This guide is intended to diagnose and correct hydraulic cylinder run-off and wear caused by internal leaks, damaged oil seals, faulty control valves, and incorrect pilot pressure readings. These problems can occur in high-load production hydraulic systems used in the automotive, aerospace, food, chemical and energy sectors. The middle of the problem is classified as critical because it can cause production to stop and equipment to malfunction.

2. Security

Wear personal protective equipment (PPE), including gloves, goggles, and helmets.
Perform a lockout/tagout process before working on hydraulic systems.
Check for stored energy before shutting down.
Avoid touching hot or glowing components.
When operating use chemical protection products with hydraulic fluids.

3. Necessary diagnostic tools

Name of the tool Model/Spec Measurement range The goal
Multimeter Fluke 87V 0–2000 Ω, 0–600 V, 0–20 A Checking electrical connections and resistances
Thermograph FLIR T1020 -20°C to 550°C Detection of uneven heating of components
Vibration analyzer BB3000 0-10,000Hz, 0-10mm/s RMS Diagnostics of vibration characteristics of hydraulic cylinders
Pressure manometer Testo 510 0–100 bar Checking system pressure and pilot pressure
Microscope Leica M205A 10–100x Checking the condition of oil seals and internal surfaces

4. First assessment (checklist)

Point action
1 Check the status of the hydraulic system and information about previous shutdowns.
2 Record the pressure and temperature values ​​of the system.
3 Check alarm reports and error codes.
4 Save changes in system settings.
5 Record the operating conditions (load, temperature, pressure).

5. Systematic diagnosis

  1. Symptom: Throwing cylinder without action.
    1. Pilot pressure check:
      1. Measure the pilot pressure with a manometer.
      2. The operating pressure of the pilot should be in the range of 10–20 bar.
      3. If the pressure is below 10 bar, check the control valve.
    2. Control Valves Check:
      1. Perform valve leakage test.
      2. The outflow should not exceed 50 ml/h.
      3. If the leakage is higher, replace the valve.
  2. Symptom: Cylinder wear under load.
    1. Checking the oil seals:
      1. Use a microscope to inspect the oil seals.
      2. Oil seals must be free of wear, leaks or chips.
      3. If the seals are damaged, replace them.
    2. Checking the internal pressure:
      1. Use a pressure gauge to measure the pressure.
      2. The pressure should not exceed 150–200 bar.
      3. If the pressure is higher, check for leaks.

6. Matrix of causes of defects

Symptom Probable reasons Diagnostic test Expected result
Dropping the cylinder without action 1. Low pilot pressure Measure pilot pressure The pilot pressure is less than 10 bar
Dropping the cylinder without action 2. Leakage of the control valve Checking the valve for leakage Leakage is more than 50 ml/h
Cylinder wear under load 1. Wear of oil seals Inspection of oil glands with a microscope Oil seals are worn out
Cylinder wear under load 2. Internal leaks Internal pressure check The pressure is above 200 bar

7. Analysis of root causes

7.1. Low pilot pressure

Low pilot pressure can be caused by improper valve settings, a leaking pilot line, or a damaged fan. This leads to a malfunction of the control valve, which causes the cylinder to drop. Measure the pilot pressure and check for leaks to confirm.

7.2. Check valve leakage

Valve leaks can be caused by worn internal components, pilot line leaks, or valve damage. This results in a loss of control over the hydraulic system, which causes the cylinder to drop. Perform a leak test to confirm.

7.3. Wear of oil seals

Wear of oil seals occurs due to constant load, high temperature or leakage of liquid. This leads to internal leaks, which causes cylinder wear. To confirm, inspect the oil seals under a microscope.

7.4. Internal leaks

Internal leaks can occur due to damage to internal surfaces, worn components, or incorrect valve settings. This results in a loss of control over the system, resulting in the cylinder being ejected. Take an internal pressure measurement to confirm.

8. Step-by-step correction procedures

8.1. Fix low pilot pressure

  1. Check the control valve setting.
  2. Set the pilot pressure in the range of 10–20 bar.
  3. Check the pilot line for leaks.
  4. Perform a pilot pressure measurement after installation.

8.2. Control valve leak correction

  1. Turn off the system and lock it.
  2. Remove the valve and check for leaks.
  3. Replace the valve with a new one if the leakage is higher than 50 ml/h.
  4. Perform a leak test after installation.

8.3. Repair of oil seals wear

  1. Turn off the system and lock it.
  2. Remove oil seals and check their condition.
  3. Replace oil seals with new ones if they are worn.
  4. Inspect the oil seals with a microscope after installation.

8.4. Fix internal leaks

  1. Turn off the system and lock it.
  2. Measure the internal pressure.
  3. Replace internal components if the pressure is above 200 bar.
  4. Perform internal pressure check after installation.

9. Preventive measures

The root cause Prevention strategy Control method Recommended interval
Low pilot pressure Periodic check of valve settings Pilot pressure measurement Monthly
Check valve leakage Regular replacement of the valve Leakage test Every 6 months
Wear of oil seals Periodic inspection of oil seals Inspection with a microscope Every 12 months
Internal leaks Periodic inspection of internal components Measurement of internal pressure Every 24 months

10. Production spare parts

Description of the component Specification When to replace UNITEC-D category
Oil seals for hydraulic cylinders Material: NBR, diameter: 50 mm After wear and tear 2300
Control device valve Pressure: 150 bar, power: 10 kW After leaking 2310
Manometer for hydraulic systems Range: 0–100 bar After damage 2320
Microscope for checking oil seals Scale: 10-100x After damage 2330

Here is the UNITEC-D Universal Parts Catalog: https://www.unitecd.com/e-catalog/

11. List of references

  • DSTU 2885-94: Hydraulic systems — design requirements
  • EN 1253: Hydraulic pipelines — performance requirements
  • ISO 5599: Hydraulic systems — requirements for operation
  • CE, UkrSEPRO certification
  • Original technical documents of manufacturers
  • Complete UNITEC-D maintenance guides

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