Hydraulic Cylinder Troubleshooting: Causes of Slow, Uneven or Stuck Movement

Cylinder will not retract fully

Usually air trapped in the cap end, a rod seal that has swollen, or a restriction in the return line. Bleed the cylinder at the highest point with the rod fully extended, and check the return filter and the rod seal material against the fluid and temperature in service.

Slow extension

Check actual flow at the cylinder. A pump that delivers less than the catalogue figure, a relief valve that opens early, or a suction restriction will all produce slow extension. Confirm the pump speed and displacement, and verify the relief setting at the operating pressure.

Judder or chatter

Cavitation on the rod end is the usual cause: air in the supply, a suction strainer blocked, or fluid above its vapour pressure at the inlet. Bleed the system and check the suction line.

Cylinder drifts down under load

External leakage past the piston seal, or internal leakage that is not being replaced by the pump. On a cylinder that has been running with contaminated fluid, replace the seals as a set and flush the system before refitting.

Heat in the cylinder

Heat is produced when the oil is throttled across the cylinder or when the pump is oversized for the duty. Check the pressure relief setting and the flow required for the working speed.

Preventive maintenance

Keep the fluid clean and within its viscosity specification, check the rod for scoring at every seal change, and replace the complete seal kit rather than mixing seal materials from different suppliers.