Hydraulic Cylinder Leakage: Find the Source Before Resealing

Hydraulic cylinder leakage can be external or internal. Locate the path before ordering a rod seal: oil can travel along surfaces from a fitting, and a drifting cylinder can also have a valve fault.

Oil at the rod

After safe shutdown, clean the area and inspect the rod surface, gland and adjacent fittings. Repeated droplets or running oil need investigation. A slight film depends on the sealing design and duty; inspect changing leakage against the maker’s criteria rather than declaring every wet rod failed.

Oil at a port, gland joint or barrel

Trace the highest or earliest wet point. A connection leak may run toward the rod. Inspect the correct fitting seal, static gland seal and hardware before opening the cylinder. Cracks or damaged structural parts require a qualified repair assessment. Never search for a pressurized pinhole leak with your hand.

Drift with no external oil

Consider piston bypass, directional-valve leakage and load-holding components. A qualified technician must use the machine’s isolation procedure to separate these paths. Drift alone is not a piston-seal test; loading and circuit connections affect what movement is possible.

Oil from a breather

On a single-acting cylinder, confirm the breather’s function and the design’s normal behavior. Oil discharge can indicate fluid passing the piston seal, but inspect the arrangement and history before deciding. Do not block the breather to hide the symptom.

Build the repair evidence

Record the leak location, direction of travel, load, temperature, recent work and rate of change. Once the fault is isolated, inspect the matching seal, running surface and guidance. A repeat leak after resealing points to an unresolved cause or an incorrect installation, not automatically a defective new ring.

To connect this inspection with the next repair decision, see Hydraulic Cylinder Leaking From the Rod: What to Check First.