Why Does a Pneumatic Cylinder Fail? Causes of Failure and Diagnostics
Premature pneumatic cylinder failure may be caused by misalignment, side loads, contamination, manufacturing or assembly errors, or incorrect end-of-stroke cushioning. A leak is a symptom. Replacing the seals will not solve the problem if the installation still contains a scratched piston rod, a worn guide or a source of contamination.
This guide focuses on rod-type linear pneumatic cylinders. Always verify the requirements for the specific design and the actual operating conditions. Bore size and stroke alone are not sufficient selection criteria.
Pneumatic cylinder failure symptoms - what should be checked first?
A cylinder that does not move, loses force or runs unevenly may be affected by the air supply, directional control valve or driven mechanism. Check the complete pneumatic circuit and control system before removing the cylinder. The table shows possible causes and the first check. It is not a final diagnosis.
| Symptom | Possible causes | What to check |
|---|---|---|
| No extension or retraction | No control signal, faulty valve, no supply pressure, mechanical seizure | Control signal, valve switching, pressure at the cylinder and the mechanism |
| Loss of force under load | Pressure drop, back pressure, internal leakage or incorrect selection | Pressure in both chambers during the cycle and the actual load |
| Slow movement | Restricted flow, closed flow control or blocked silencer | Supply and exhaust paths in both directions |
| Jerky movement | Misalignment, variable friction, incorrect flow control or stick-slip | Guiding, settings and the permitted speed range |
| Leak at the piston rod | Damaged seal, scratched rod or worn guide | Rod surface, guide condition and side load |
| Continuous exhaust leakage | Valve leakage or leakage between cylinder chambers | Circuit condition and a test separating the possible sources |
| Impact at the end of stroke | Excessive speed or energy, incorrect cushioning | Mass, speed, settings and cushioning capacity |
Exhaust air during movement is normal. Continuous air discharge while the cylinder is stationary requires a circuit-based assessment. Noise near the valve does not identify the failed component by itself.
Manufacturing and overhaul errors - what damages seals?
Potential manufacturing nonconformities concern geometry, surfaces, cleanliness, component selection and assembly. During an overhaul, the same result may be caused by leaving a worn guide in place or using an incorrect seal kit. Early failure alone does not prove a manufacturing defect.
– Geometry and surfaces: incorrect bore or groove dimensions, loss of alignment, bent piston rod, scratches, burrs or unsuitable surface finish.
– Seals and guiding: incorrect seal profile, material or orientation, cut or rolled sealing lip, missing guide element or excessive guide wear.
– Assembly: chips, dust or cleaning residues left inside, incompatible grease, incorrect tightening, or incorrectly assembled cushioning components.
– Verification: failure to test leakage, full stroke and cushioning may leave a nonconformity undetected. A no-load test does not confirm operation in the machine.
Wear marks create diagnostic hypotheses. The cause must be confirmed by measurements, operating history and an inspection of the installation.
| Wear mark | What to verify |
|---|---|
| One-sided guide wear | Side load, alignment and mounting geometry |
| Longitudinal scratches | Hard particles, damaged surfaces and guide condition |
| Swollen or hardened seal | Chemical compatibility, temperature and service time |
| Cut lip on a new seal | Edges, chamfers and the seal installation method |
Pneumatic cylinder selection and installation errors - loads, alignment and mountings
Incorrect selection and installation increase friction and guide loads. Check alignment throughout the full stroke, joint movement and bracket stiffness. Tightening a cylinder against a distorted mounting surface does not correct the geometry.
– Side load: the piston rod is not a guide. The mass of a gripper and the moment from an offset load must be included in the design. A compensating coupling works only within its permitted range.
– Buckling: a long rod under compression requires a stability check. Free length, rod diameter, support conditions and force are relevant.
– Mountings: clevises, eyes and joints must allow the designed movement. Check the ISO 6431/15552 D32-D320 cylinder accessories and compatibility with the cylinder execution.
– Piston rod surface: never grip the working surface with pliers. Protect it against welding spatter, grinding dust and paint. Use the surfaces intended for tightening.
– Ports and tubing: check thread type, engagement depth, tightening torque and cleanliness. Sealant must not enter the air passages. Reversed ports or flow-control orientation changes cylinder behaviour.
Calculate force for both directions. In a single-rod cylinder, the effective area during retraction is smaller. Use the CPP PREMA S.A. calculator, then relate the result to the actual pressure and load. A force calculation does not replace an alignment or cushioning check.
Pneumatic cylinder operation - air quality, lubrication and cushioning
Operating errors include exceeding the permitted parameters and ignoring changes in the process. After increasing the workpiece mass or cycle speed, reassess flow, speed, temperature and end-of-stroke braking.
Contamination and incorrect lubrication
Contamination accelerates wear of working surfaces and seals. Check the filter, condensate drain and air quality at the point of use. A particle filter is not a dryer. Condensation may occur after the tubing cools below the pressure dew point.
Use additional lubrication only when the documentation for the particular series allows it. Do not add oil to the port as a way of treating stick-slip. An incorrect lubricant can be incompatible with the seals. Also assess dust on the piston rod, cleaning agents, temperature and scraper condition.
Excessive speed and incorrect cushioning
Higher speed increases the energy that must be absorbed. For the same mass, doubling the speed increases kinetic energy fourfold. End-of-stroke cushioning has a defined absorption capacity and does not replace speed control over the complete stroke.
Insufficient throttling may cause impact. Excessive throttling may prevent the cylinder from reaching the end position. Check the first movement after depressurisation and the valve sequence. Two cylinders supplied from the same source are not automatically synchronised.
Pneumatic cylinder diagnostics - the correct sequence
Start by comparing the symptom with the operating conditions. A correct pressure reading at the regulator does not confirm the pressure in the chamber during movement. The available force depends on the pressure on both sides of the piston, effective areas and friction.
Before any intervention, isolate and lock out energy sources, secure the load and release and verify residual pressure. Dynamic measurements must be performed by trained personnel during a controlled test with the required safeguards. Do not disconnect tubing under pressure.
– Record when the problem occurs: after installation, after a setting change, under load, after a stop or only in one direction.
– Check supply and exhaust: pressure during the cycle, filter, tubing, flow controls and silencer. Do not compensate for restricted flow by simply increasing pressure.
– Compare control with movement: valve signal, actual position and sensors. A missing end-position signal does not prove a cylinder failure.
– Assess mechanics and leakage: alignment, play, piston rod surface and the exact leakage location. Perform a valve-to-cylinder separation test according to the instructions on a secured circuit.
– Confirm the repair: both directions, full stroke, cushioning, leakage and position sensing under the intended load. Record the root cause, not only the replaced parts.
Repair, overhaul or replacement of a pneumatic cylinder?
An overhaul is justified when the construction is serviceable, the correct parts are available and the required performance can be restored. Damage to the tube, piston rod, guide or mounting requires a wider assessment than seal replacement. When comparing repair with a new cylinder, include downtime and the risk of recurring failure.
Prepare the cylinder identification, installation photographs, circuit diagram, operating pressure, mass, load direction and symptom description. CPP PREMA S.A. provides pneumatic cylinder overhaul, repair and service support. Pneumatic cylinders and installation components are available in the CPP PREMA S.A. online shop.
Pneumatic cylinder failures - technical FAQ
Why is a pneumatic cylinder leaking air?
Possible causes include damaged seals, scratches on working surfaces, a worn guide or a leaking connection. First determine whether the leakage is external or between the chambers. Replace a seal only after identifying what caused it to fail.
Why is air escaping through the exhaust of a 5/2 valve?
During movement, exhausting air from the chamber is normal. Continuous discharge after the cylinder stops may indicate leakage in the directional control valve or piston seal, depending on the circuit condition. The sound near the valve does not identify the failed component by itself.
Why does a pneumatic cylinder move jerkily?
Possible causes include variable friction, misalignment, incorrect flow control or operation at a very low speed for the selected design. Stick-slip is the repeated transition between stopping and moving. Adding oil without checking the instructions is not a valid diagnosis.
Why does a pneumatic cylinder lack force despite correct pressure?
The pressure gauge may show pressure upstream of a flow restriction or only pressure at rest. Check pressure during movement, back pressure, the actual load and leakage. Also consider the smaller effective area during retraction in a single-rod cylinder.
Does a pneumatic cylinder require lubrication?
It depends on the design. Many cylinders are factory-lubricated and operate without additional oil mist. Check the documentation for the particular series to confirm whether lubrication is allowed, which lubricant is compatible and how it must be applied.
Is replacing the seals enough?
Only when the remaining components are serviceable and the cause of the leakage has been removed. A scratched piston rod, worn guide or contaminated air can damage the new seal set again. Assess the complete cylinder and its operating conditions.
What causes a piston rod to bend?
Possible causes include a side load, collision or buckling under compression. Geometry, extension length, support conditions and force are relevant. Do not straighten and restart a bent piston rod without a technical assessment and root-cause analysis.
When is a pneumatic cylinder overhaul worthwhile?
An overhaul is worthwhile when the construction can be serviced, the correct parts are available and the repair can restore the required performance within an acceptable time and cost. Include downtime and recurrence risk in the comparison, not only the price of parts.
The key conclusion: remove the root cause before installing another cylinder
Leakage, loss of force or uneven movement are the start of the diagnosis. Long-term performance also depends on mounting, load guidance, air quality, control and the environment. Checking these factors helps determine whether the right solution is an overhaul, a new cylinder or a change to the application.
If the failure returns after replacing the seals, prepare the cylinder identification, installation photographs and operating conditions. Contact CPP PREMA S.A. for pneumatic cylinder overhaul, repair and service support.