Maintenance Guides 1 min read

Diagnostic Guide: Eliminating Misalignment and Creep of Hydraulic Cylinders

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

1. Description of the Problem and Scope of Application

This diagnostic manual is designed to identify and troubleshoot problems associated with drift and creep hydraulic cylinders in industrial systems. Displacement refers to unwanted movement of the cylinder when it is in a fixed position or under load, while creep is a slow, uneven movement. Both phenomena indicate internal leaks in the hydraulic system, leading to loss of efficiency, inaccurate positioning, and potential safety hazards.

The problem affects a wide range of industrial equipment, including presses, hoists, machine tools, manipulators, construction equipment and other systems that use hydraulic cylinders for linear movement.

Classification of Severity:

  • Critical: Uncontrolled displacement while holding the load, which poses an immediate threat to the operator or damage to the equipment.
  • Significant: Constant displacement resulting in inaccurate positioning, reduced productivity, or degraded product quality.
  • Minor: A slow creep that does not critically affect performance, but is an early sign of a potential malfunction.

2. Precautions

CAUTION: The following safety precautions MUST be observed before beginning any diagnostic or repair work on hydraulic systems.
LOCKOUT/TAGOUT (LOTO): Always perform the power lockout/tagout procedure in accordance with internal enterprise standards and the requirements of DSTU EN 1037:2018 and ISO 14118:2017 standards to prevent unexpected start-up or power-up.
EXPECTED ENERGY: Hydraulic systems store a significant level of energy under pressure. BE SURE to RELIEVE PRESSURE from the entire system before disassembling any components. Use appropriate pressure gauges to confirm no pressure.
PERSONAL PROTECTIVE EQUIPMENT (PPE): Always use safety glasses (DSTU EN 166:2017), gloves resistant to hydraulic fluids, protective clothing and protective shoes. Pressurized hydraulic fluid can cause serious injury or tissue injection.
HOT SURFACES AND LIQUIDS: Hydraulic fluid can be hot. Allow the system to cool before operating.
WORKING AT HEIGHTS: When working with lifted loads, use appropriate support devices and follow safety rules for working at heights.

3. Necessary Diagnostic Tools

Name of the Tool Specification/Model (Example) Range of Measurements Purpose
The manometer is hydraulic EN 837-1, accuracy class 1.0 or better 0-400 bar Pressure measurement at different points of the system.
Flow meter (turbine/ultrasonic) ISO 4006:1991, 0-200 l/min 0-200 l/min Measurement of hydraulic fluid flow to diagnose internal leaks.
Thermal imaging camera FLIR T540, range -20°C to 120°C -20°C to 120°C Detection of local overheating, indicating internal leaks or friction.
A set of adapters and hoses All necessary sizes and types of connections N/A Connecting measuring devices to the hydraulic system.
Digital multimeter Fluke 87V, TRMS VDC, VAC, Ohm, mA Diagnostics of electrical components (solenoids, sensors).
A set of torque wrenches ISO 6789-1:2017, from 10 Nm to 300 Nm 10-300 Nm Tightening connections with precise torque.
Caliper / Micrometer DSTU ISO 13385-1:2019, 0-300 mm 0-300 mm Measurement of the dimensions of seals and other components.

4. Initial Assessment Checklist

Before starting a detailed diagnosis, perform a visual inspection and collect information about the history of the malfunction. This will help narrow down the potential causes.

Item Rating What to observe/record The goal
Terms of use System pressure (bar), liquid temperature (°C), load (kN/t), cylinder movement speed. Determination of the effect of operating parameters on displacement.
Fault log Date of first detection, frequency, changes in work before the problem appeared. Establishing chronology and potential causes.
Visual inspection Visible fluid leaks, cylinder rod damage (scratches, corrosion), condition of hoses/pipelines, system contamination. Detection of external signs of damage.
Fluid level and condition The level of hydraulic fluid in the tank, color, smell, presence of bubbles, impurities (DSTU ISO 4406:2017). Assessment of hydraulic fluid quality.
Sounds and vibrations Unusual noises (cavitation, hissing), excessive vibrations. May indicate air in the system or damaged components.
Adjusting the valves Checking the current settings of the balancing valve, safety valves. Exclusion of incorrect settings.

5. Systematic Diagnostic Algorithm

  1. Is hydraulic cylinder displacement or creep observed?
    • YES: Go to step 2.
    • NO: The problem is not displacement/creep related. This manual does not apply.
  2. Set the cylinder in a fixed position under the load (if possible and safe).
    • IMPORTANT: Before performing this step, ensure that the load is securely locked mechanically to prevent an uncontrolled fall.
    • Measure displacement/creep rate (mm/min) and pressure in both cylinder chambers (bar).
    • Result: Document the metrics.
  3. External Leak Inspection:
    • Perform a thorough visual inspection of the cylinder, hoses, piping, and all connections for visible hydraulic fluid leaks.
    • If external leaks are detected:
      1. Determine the location of the leak (fitting, hose, stem seal).
      2. Probable cause: Damaged seals, loose connections, cracks in components.
      3. Actions: Replace damaged components, tighten connections to appropriate torque (see manufacturer's specifications). Go to step 9.
    • If NO external leaks are found: Go to step 4 (probably an internal leak).
  4. Diagnosis of internal leakage through cylinder piston seals:
    • IMPORTANT: Before disconnecting lines, make sure there is no pressure in the system.
    • Disconnect the supply lines from both cylinder chambers.
    • Mute one of the cylinder lines.
    • Apply operating pressure (eg 50% of the system's maximum operating pressure) to the open cylinder chamber.
    • Collect the fluid flowing from the blocked line (opposite chamber) over a period of time (e.g. 1 minute).
    • If the leakage volume exceeds the permissible values ​​(see section 6):
      1. Probable cause: Worn or damaged cylinder piston seals.
      2. Actions: Replace the piston seal kit. Go to step 9.
    • If the leakage volume is within normal limits: Go to step 5.
  5. Balancing (counterbalance) valve diagnostics:
    • If the cylinder is held by the counterbalance valve:
    • IMPORTANT: This inspection may require partial disassembly or bypass of the valve, which must be performed by qualified personnel.
    • Check valve opening pressure setting. It should be 1.3 - 1.5 times higher than the maximum pressure created by the load.
    • Measure the pilot pressure applied to the valve.
    • If the valve does not hold pressure or has excessive internal leaks (can be checked with a flow meter on the valve drain line):
      1. Probable cause: Balancing valve internal leakage, contamination, worn spool or seat.
      2. Actions: Repair or replace the balancing valve. Go to step 9.
    • If the balancing valve is working properly: Go to step 6.
  6. Diagnosis of check valves (Check Valves) / locking valves (Lock Valves):
    • If the system uses separate check valves or locking valves to hold the cylinder:
    • Check for dirt or damage preventing the valve from closing completely.
    • If valve does not close completely or leaks:
      1. Probable cause: Contamination, seat or ball/spool wear.
      2. Actions: Clean or replace the faulty valve. Go to step 9.
    • If the valves are working properly: Go to step 7.
  7. Pilot pressure diagnostics (for pilot controlled valves):
    • Measure the actual pilot pressure applied to the valve (eg distributor, balance valve).
    • If the pilot pressure is low or unstable:
      1. Probable cause: Internal leaks in the pilot pressure line, malfunction of the pilot pressure reducing valve, contamination.
      2. Actions: Repair leaks in pilot pressure line, repair or replace pressure relief valve. Go to step 9.
    • If the pilot pressure is normal: Go to step 8.
  8. Directional Control Valve diagnostics:
    • If all previous checks did not reveal a malfunction:
    • Plug the cylinder ports connecting to the distributor (leaving the distributor under pressure).
    • If the cylinder no longer moves, then the problem is in the distributor.
    • Probable Cause: Worn or damaged distributor spool leading to internal leaks between ports.
    • Actions: Repair or replace the guide distributor. Go to step 9.
  9. Verification and completion:
    • After repair, restore the system, check the fluid level.
    • Start the system and check for displacement/creep under working load.
    • Record the work performed in the maintenance log.

6. Malfunction-Cause matrix

Symptom Probable Causes (by probability) Diagnostic Test Expected Result (if the cause is confirmed)
Constant displacement of the cylinder in one direction 1. Internal leakage through piston seals of the cylinder
2. Internal leakage of the guide distributor
3. Balancing/blocking valve failure		 1. Test for internal leakage of piston seals (section 5, step 4).
2. Checking the pressure on the choked ports of the distributor.
3. Balancing/blocking valve leak test (section 5, steps 5, 6).		 1. Liquid leakage > 10-15 ml/min per 100 mm of piston diameter at 70 bar.
2. Pressure drops at blocked ports.
3. The valve does not hold pressure, or there is a leak at the drain.
Uneven cylinder creep (jerks) 1. Air in the hydraulic system
2. Contamination of hydraulic fluid/valves
3. Cylinder rod/sleeve friction		 1. Visual inspection of the tank for the presence of bubbles, listening to the pump.
2. Fluid analysis for contamination (ISO 4406:2017), valve disassembly/inspection.
3. Visual inspection of the rod, measurement of friction force.		 1. Visible bubbles, pump noise.
2. Liquid purity class below normal (> 18/15/12), foreign particles in valves.
3. Scratches on the rod, increased effort of the cylinder movement.
Displacement of the cylinder only under heavy load 1. Incorrect adjustment or wear of the balancing valve
2. Internal leakage of piston seals		 1. Checking the balancing valve settings, leak test at maximum load.
2. Test for internal leakage of piston seals (section 5, step 4) at maximum operating pressure.		 1. Valve opening pressure is too low, or leakage at high pressure.
2. Increased leakage volume at high pressure.
Sudden increase in displacement 1. Seal damage (tear)
2. Contamination/jamming of the valve		 1. Quick test for internal cylinder leakage. Visual inspection of seals.
2. Valve disassembly and inspection.		 1. A very large volume of leakage.
2. Detection of foreign particles, jamming of the spool.
Displacement after a long period of inactivity 1. Shrinkage or deformation of seals
2. Air in the system		 1. Test for internal leakage after long idle time.
2. Pumping the system.		 1. Increased leakage of seals.
2. Bleeding eliminates the problem.

7. Analysis of the Root Causes of Each Malfunction

Internal leakage through the piston seals of the cylinder

WHY this happens: Piston seals (cuffs) wear out over time due to friction against the inner surface of the cylinder liner, temperature effects and chemical degradation of the hydraulic fluid. Abrasive particles in the fluid (dirt, metal shavings) can accelerate wear. Inappropriate seal type for the application (temperature, pressure, speed) or improper installation are also causes.

HOW to confirm: Piston seal internal leakage test (section 5, step 4). Disassemble the cylinder and visually inspect the seals for cracks, tears, hardening or excessive wear. Measurement of the residual thickness of seals.

WHAT damage is caused by: Constant loss of position, excessive use of pump energy to maintain position, increased fluid temperature due to leakage, accelerated wear of pump and other components due to circulation of contaminated fluid (if the seal fails). Can lead to emergency situations when working with cargo.

Internal leakage of the guide distributor

WHY this happens: Wear of the valve spool and/or distributor housing, resulting in increased clearances between the moving parts. This allows fluid to flow between the operating ports when the distributor is in the neutral or locked position. Contamination of the fluid can cause abrasive wear or jamming of the spool in the wrong position.

HOW to confirm: Cylinder port blanking test (section 5, step 8). Disassembly of the distributor and visual inspection of the spool and housing for scratches, abrasions, erosion. Checking the elasticity of the spool return springs.

WHAT damage is caused by: Uncontrolled movement of the actuator, overheating of the system due to constant leakage under pressure, loss of positioning accuracy. May cause production cycle failure and product damage.

Malfunction of the balancing (counter-balancing) valve

WHY this happens: Internal leakage due to worn seats, spool, or contamination preventing the valve from fully closing. Incorrect opening pressure setting (too low) or spring damage. Also, missing or insufficient pilot pressure can cause it to malfunction.

HOW to confirm: Check opening pressure and pilot pressure settings (section 5, step 5). Pressure valve drain port leak test. Visual inspection after disassembly for contamination or damage to internal components.

WHAT damage is caused by: Uncontrolled fall of cargo (especially when working with lifting mechanisms), which is a critical safety threat. May result in serious injury to personnel and destruction of equipment.

Air in the hydraulic system

WHY this happens: Insufficient fluid level in the tank, leak in the pump suction line, failure of the pump seals, incorrect filling procedure or system bleeding after repair. Air forms bubbles that compress under pressure, causing uneven movement.

HOW to confirm: Visual inspection of the hydraulic fluid in the tank (presence of foam, bubbles). Listening to the pump (characteristic cavitation noise). Pumping the system.

WHAT damage is caused by: Pump cavitation (accelerated wear), uneven movement of the cylinder (creep), reduction of system efficiency, increase in noise and vibration, deterioration of product quality due to inaccurate positioning.

Contamination of hydraulic fluid and valves

WHY this happens: Inefficient filtration, liquid contamination during topping up or repairs, ingress of foreign particles through leaky seals, wear of internal system components. Dirt particles can get stuck in small valve gaps, preventing them from closing completely or causing abrasive wear.

HOW to confirm: Laboratory analysis of a sample of hydraulic fluid for compliance with the purity class (DSTU ISO 4406:2017). Valve disassembly and visual inspection for deposits or stuck particles.

WHAT damage is caused by: Wear of seals and components, valve jamming, pump malfunctions, reduced system efficiency, fluid overheating. This is one of the most common reasons for failure of hydraulic systems.

8. Step-by-Step Troubleshooting Procedures

8.1. Replacement of hydraulic cylinder piston seals

  1. Security: Perform the LOCKOUT/TAGOUT (LOTO) procedure and depressurize the system. CAUTION: Provide mechanical support for any lifted loads.
  2. Disassembly: Disconnect the hydraulic lines from the cylinder. Remove the cylinder from the equipment.
  3. Disassembly: Fix the cylinder in a vise (by the body, not by the rod). Unscrew the cylinder cover (rod side) and the rear cover. Carefully remove the piston with the rod.
  4. Inspection: Carefully inspect the cylinder rod and the inner surface of the sleeve for scratches, burrs, corrosion. The minimum allowable depth of scratches on the rod is 0.05 mm. If the damage is significant, the cylinder may need to be repaired or replaced.
  5. Removing Old Seals: Carefully remove the old piston seals, back-up rings and guide bands from the piston.
  6. Cleaning: Thoroughly clean all cylinder components (piston, rod, sleeve, caps) from liquid residues and dirt. Use recommended cleaners compatible with hydraulic systems.
  7. Installing new seals:
    • Use only original or high-quality analog seals that meet the manufacturer's specifications (eg ISO 5597, EN 813).
    • Lubricate new seals with clean hydraulic fluid before installation.
    • Install the seal carefully using special installation tools to avoid damage. Ensure the seals are oriented correctly.
  8. Assembly: Assemble the cylinder in reverse order. Tighten the threaded connections to the recommended torque (see the cylinder manufacturer's manual).
  9. Installation: Install the cylinder in place and connect the hydraulic lines.
  10. Bleeding: Start the system and bleed the cylinder thoroughly, making several full strokes under no load to remove air.
  11. Verification: Verify no displacement/creep under working load. Check for external leaks.

8.2. Balancing valve repair/replacement

  1. Security: Perform the LOCKOUT/TAGOUT (LOTO) procedure and depressurize the system.
  2. Disassembly: Disconnect the hydraulic lines from the valve and remove it.
  3. Disassembly and Cleaning: Carefully disassemble the valve. Thoroughly clean all components (body, spool, springs, saddles) from dirt and deposits.
  4. Inspection: Inspect spool and saddles for wear, scratches, or corrosion. Check the springs for deformation. If the components are significantly worn or damaged, replace the entire valve or use a repair kit from the manufacturer.
  5. Reassembly: Reassemble the valve using new seals (O-rings, back-up rings). Tighten all threaded connections according to the manufacturer's recommendations.
  6. Installation: Install the valve in place and connect the hydraulic lines.
  7. Adjustment:
    • Set the valve opening pressure (if adjustable) to 1.3 - 1.5 times the maximum load pressure.
    • Measure the pressure using a calibrated pressure gauge.
  8. Verification: Carry out a functional check of the valve under working load, check that there is no displacement of the cylinder.

8.3. Removing air from the hydraulic system

  1. Safety: Make sure all moving parts are locked before starting.
  2. Fluid Level Check: Make sure the hydraulic fluid level in the tank is at the MAX mark.
  3. Bleeding the cylinder:
    • Start the pump and pressurize the system.
    • Slowly move the cylinder from one end position to the other several times, under no load, with the air bleed ports open (if provided) or loosened (very carefully).
    • Watch for air escaping from the system (bubbles in the tank).
  4. Bleeding other components: If there are other components (eg valves with air bleed ports), follow the same steps.
  5. Check: After pumping, check the absence of bubbles in the tank and the stable operation of the cylinder.

9. Precautions

Root Cause Prevention Strategy Monitoring method Recommended Interval
Worn cylinder piston seals Use of high-quality seals (ISO 5597), compliance with fluid purity. Regular cylinder internal leak test. Annually or every 2000 operating hours.
Internal leakage of the guide distributor Maintaining the purity of the hydraulic fluid (ISO 4406:2017), choosing the appropriate distributor. Monitoring of working pressure, distributor leakage test. Annually or when productivity decreases.
Malfunction of the balancing valve Correct selection and adjustment of the valve, regular inspection. Pressure setting check and valve functional check. Every 6 months or 1000 working hours.
Air in the hydraulic system Maintenance of liquid level, regular inspection of suction lines, correct pumping. Visual inspection of the liquid in the tank, listening to the pump. Daily (level), weekly (line review).
Contamination of hydraulic fluid and valves Use of quality filters (ISO 16889), regular control of liquid purity. Analysis of liquid samples (ISO 4406:2017), filter contamination control. Quarterly or every 500 working hours (analysis), according to filter indicators.

10. Spare Parts and Components

To ensure trouble-free operation of the equipment, UNITEC-D recommends using only high-quality spare parts that meet international standards (ISO, EN) and have CE, UkrSEPRO certificates.

Description of the Part Specification When to Replace Category UNITEC
A set of cylinder piston seals Material: NBR, FKM, PTFE (depends on temperature and liquid); Profile: U-shaped, compact. If an internal cylinder leak is detected, scheduled replacement. Seals and Cuffs
A set of cylinder rod seals Material: NBR, FKM, PUR; Profile: V-shaped, compact. When an external leak is detected along the stem. Seals and Cuffs
Balancing valve (complete assembly) Type: cartridge or case; Pressure range: 0-350 bar; Size: As per OEM specification. In case of impossibility of repair, excessive internal leakage. Hydraulic valves
Repair kit for balancing valve O-rings, seats, springs (depending on the valve model). In the case of minor leakage or contamination, if the components do not have significant wear. Valve repair kits
Guide distributor Type: spool (2/2, 3/2, 4/3); Management: electric (12/24 V DC), mechanical; Standard size: CETOP 3, 5, 7. With significant internal leakage between the ports, jamming of the spool. Hydraulic Distributors
Hydraulic fluid Type: HLP ISO VG 46/68 (according to the manufacturer's recommendations); Purity Class: ISO 4406:2017 18/15/12 or better. In case of pollution, degradation, or for topping up. Hydraulic fluids
Hydraulic filters Degree of filtration: 10 μm (absolute); Type: reverse flow, pressure. According to the maintenance schedule or when the pollution indicator is activated. Hydraulic Filters

Look for these and other components in our e-catalog: www.unitecd.com/e-catalog/

11. Links

  • DSTU EN 1037:2018. Machine safety. Unexpected startup prevention.
  • ISO 14118:2017. Safety of machinery — Prevention of unexpected start-up.
  • DSTU EN 166:2017. Means of individual eye protection. Requirements
  • DSTU ISO 4406:2017. Hydraulic drives. liquids A method for coding the level of pollution by solid particles.
  • ISO 4006:1991. Measurement of fluid flow in closed conduits.
  • ISO 6789-1:2017. Assembly tools for screws and nuts — Hand torque tools.
  • DSTU ISO 13385-1:2019. Geometric characteristics of products (GPS). Devices for measuring linear dimensions. Part 1. Vernier calipers.
  • ISO 5597. Hydraulic fluid power — Cylinders — Dimensions of rod and piston seals.
  • EN 813. Personal fall protection equipment — Sit harnesses.
  • Operation and maintenance manuals from hydraulic equipment manufacturers (OEM).
  • Related UNITEC Hydraulic Service Manuals.

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