What are the possible causes of oil leakage in a hydraulic cylinder?
 

　　1. The sealing integrity between the hydraulic cylinder’s rod side and the cylinder itself is compromised, primarily due to piston‑rod wear, though aging can also contribute.

　　2. The sealing integrity between the hydraulic cylinder’s rod side and the cylinder liner is compromised. This is primarily due to long-term use causing seal aging; in many cases, excessive force applied during installation of the bearing end cap also crushes and damages the seals. Additionally, unscientific design practices at numerous domestic hydraulic cylinder manufacturers—often driven by cost‑cutting considerations—contribute to this issue.

　　3. Cracking of the high-pressure hoses connecting the hydraulic cylinder can also lead to leakage.

　　4. Oil leakage caused by defects on the cylinder head and the cylinder bearing end cover.
 

　　5. The hydraulic cylinder is bruised, pitted, or otherwise damaged with grooves and pits.

　　6. Mold growth in the grease causes an abnormal rise in the cylinder’s ambient temperature, accelerating the aging of the sealing rings.

　　7. Oil leakage caused by frequent operation beyond the cylinder’s pressure rating.

　　8. Oil seepage and leakage are primarily caused by deformation, aging, damage, or failure of the primary skeleton seals.

　　9. Under prolonged, high‑pressure, high‑temperature, and rapid operating conditions, the primary‑frame seal is highly susceptible to deformation and aging. Even the highest‑quality frame seals carry a risk of deformation under such circumstances; the difference lies only in the reduced likelihood of deformation for superior seals.

　　10. After the Y‑type skeleton seal deforms, the sealing skirt loses its supporting force, resulting in oil leakage.

　　During operation, cylinder manufacturers often encounter substantial dust and debris adhering to the cylinder rod. Contaminant‑resistant skeleton seals help prevent such particles from entering the cylinder, thereby protecting both the cylinder and the seal itself.

　　When the anti‑contamination skeleton seal is damaged, debris and dust enter the cylinder head directly, causing immediate harm to both the skeleton seal and the hydraulic cylinder. Under conditions of heavy dust accumulation, the skeleton seal can fail within just a few tens of minutes, resulting in severe damage to the inner lip.

　　The cylinder has turned black, with scoring on the inner bore. Under prolonged exposure to high temperatures and friction, lead from the coating material in the bore has adhered to the cylinder’s surface, indicating that the wear ring needs to be replaced. The wear ring (cup seal) plays a critical role in the cylinder: first, it provides wear resistance, and second, it helps to counteract lateral forces.

　　Once damaged and unable to be replaced, the cylinder is prone to blackening, oil leakage from the main‑frame seal (caused by ineffective dissipation of lateral impact forces that deform the seal), and cylinder‑knocking.

　　For wear rings, I personally recommend a material combination of polyester and glass fiber, as this blend offers superior processing performance compared to brass while delivering excellent results in terms of wear resistance, anti‑knock‑on cylinder characteristics, and the ability to accommodate metal debris.