Cylinder drift means a load or rod slowly changes position when it should remain still. It is often blamed on worn piston seals, but the cause can be elsewhere in the hydraulic circuit. A valve may leak internally, a load-holding device may not seat correctly, or a line may lose pressure. Temperature changes can also change pressure in trapped oil and create apparent movement.
First define the symptom
Record whether the cylinder extends or retracts, how much it moves, the load and machine position, oil temperature and whether the pump is running. Check whether the movement occurs immediately after stopping or develops after a long dwell. These details help distinguish a steady leakage path from thermal or structural effects. Compare the behavior with the machine’s approved holding requirement.
Possible leakage paths
Worn piston seals can allow oil to bypass between chambers. Rod seals may leak externally. A directional control valve, counterbalance valve or pilot-operated check valve can pass fluid when it should hold, and fittings or hoses may leak. The circuit arrangement matters: isolated oil volumes can respond differently to temperature and load than a cylinder connected to a return path. A visible dry rod does not rule out internal leakage.
Diagnose without creating a hazard
Secure the load and follow the machine’s lockout and pressure-release procedure before any inspection. Do not loosen a hydraulic line on a suspended load as an improvised test. A qualified technician can use pressure measurements and the manufacturer’s approved isolation or leakage procedure to identify the path. Record pressure on both cylinder ports and compare the result with the valve schematic and test criteria.
Fix the actual cause
Replacing piston seals may be appropriate when leakage is confirmed, but it will not repair a leaking valve or damaged cylinder bore. Check contamination and alignment before rebuilding; otherwise a new seal may fail quickly. For project-specific cylinders, send the original drawing, circuit schematic and drift observations to l'équipe d'ingénieurs de Yongjian.
Référence technique : Parker mobile cylinder troubleshooting manual. L'explication ci-dessus a été rédigée de manière indépendante à des fins de formation générale ; les valeurs de conception définitives doivent faire l'objet d'une analyse spécifique au projet.