1. Problem description and scope

This guide is intended to diagnose and solve problems with deflection and slippage of hydraulic cylinders that often occur in industrial installations. Deviation (drift) and creep (creep) occur when the cylinder does not stop or does not maintain its position after stopping the influence of the working rod. This can affect the accuracy, performance and safety of the installation.

2. Security

Any repairs to hydraulic systems must be performed after a lockout/tagout (LOTO) procedure and power off.
Use personal protective equipment (PPE) - gloves, goggles, overalls.
Before opening the system, check for stored energy (for example, opening a distributor or turning off the hydraulic pump).

3. Necessary tools

Name of the tool	Model/specification	Measuring range	The goal
Multimeter	Fluke 87V	0-2000 mA, 0-200 V, 0-2000 Ohm	Checking electrical connections and measuring voltage
Thermal camera	FLIR T650	-20°C to 1200°C	Detection of overheated or unevenly heated components
Vibration analyzer	Brüel & Kjær 3560	0.1 – 10,000 Hz	Detection of vibrations that may indicate an internal drain
Manometer	Testo 260	0 - 100 bar	Checking the pressure in the hydraulic system
Microscope	Leica M205A	100x – 1000x	Checking the condition of seals and surfaces

4. First examination: Check before starting diagnostics

A sign	action
Type of equipment	Determine the type of hydraulic cylinder (range, pressure, actuator)
Recent changes	Check if changes have been made to the system (e.g. installation of new seals, change of pressure)
A history of anxiety	View the alarm log to determine when the problem occurred
The behavior of the cylinder	Record whether sliding is felt when stopping work
Temperature	Check for overheating, which could indicate an internal drain

5. Systematic diagnostic flow

Checking the pressure in the system:
1. Measure the pressure in the system using a manometer. The pressure should be between 150-200 bar.
2. If pressure is higher, check for blinding or blockage.
Pilot pressure check:
1. Measure pilot pressure between 10-30 bar.
2. If it is higher or lower, check for blinding or valve wear.
Vibration check:
1. Use the vibration analyzer to measure the level of vibration. The normal level is up to 5 mm/s.
2. If the vibration is higher, check for wear or internal drain.
Checking thermograms:
1. Use a thermal camera to detect uneven heating.
2. Normal temperature is up to 60°C.
3. If the temperature is higher, check for an internal drain.
Measuring electrical parameters:
1. Measure current and voltage on electrical connections. Normal current - up to 200 mA.
2. If the current is higher, check for shorts or wear.

6. Matrix of differences of causes

Symptom	Probable causes (by probability)	Diagnostic test	Expected response
Cylinder deflection	Internal drain Seal wear Valve failure	Measure the pressure in the system Measure the vibration Use a thermal camera	Higher pressure - no blinding The vibration is higher - wear or drain Higher temperature - internal drain
Sliding	Wearing of seals Blinding of valves Change in pilot pressure	Check the condition of the seals Measure the pilot pressure Check for blinding	Wearing of seals - replacement required Higher pilot pressure - no blinding Blinding – no blinding

7. Analysis of reasons for each exception

7.1 Internal drain

An internal drain occurs when working fluid penetrates through worn seals or damage to the cylinder body. This leads to deflection and sliding. To confirm, use a thermal camera to detect overheating and a pressure gauge to measure pressure.

7.2 Wear of seals

Seal wear can occur due to excessive loading, high pressure or high temperature. This leads to loss of tightness and deviation. Use a microscope to examine the surfaces to confirm.

7.3 Malfunction of valves

Failure of the valves can result in a lack of controlled movement, causing slippage. Use a pressure gauge to measure pilot pressure to confirm.

8. Step-by-step solution procedure

8.1 Internal drain

Measure the temperature in the system with a thermal camera.
If the temperature is higher, open the system and check for blinding.
Use a pressure gauge to measure system pressure.
Replace seals and valves if worn.
Test the system after installing the new components.

8.2 Wear of seals

Use a microscope to examine the sealing surfaces.
If there is wear, replace the seal.
Check system pressure after installing new seals.
Use a thermal imager to detect overheated components.
Check the operation of the system after installing new seals.

8.3 Malfunction of valves

Measure the pilot pressure with a pressure gauge.
If the pressure is higher, check for blinding.
Replace the valve if it is worn.
Check the operation of the system after installing the new valve.

9. Preventive measures

The reason	Prevention	Monitoring	Periodicity
Internal drain	Regular replacement of seals	Thermal camera, manometer	monthly
Seal wear	Use of high-quality materials	Microscope, thermal camera	Quarterly
Malfunction of valves	Regular pressure check	Manometer	monthly

10. Replacement particles

Description of the component	Specification	When to replace	UNITEC-D category
Sealing	Diameter 50 mm, material nickel-plated steel	When wear is detected	CIL-50-100
Valve	Pressure 200 bar, diameter 15 mm	In the event of a malfunction	VAL-15-200
Cylinder body	Material is steel, diameter 60 mm	In case of damage	CYL-60-100

For replacement parts, visit our e-catalog: https://www.unitecd.com/e-catalog/

11. Links

DSTU 3045-95: Hydraulic systems - basic requirements
EN 12930: Hydraulic systems - standards
ISO 4401: Hydraulic fluids - requirements
OEM technical developments
UNITEC-D technical guides