In order to effectively reduce the failure rate of hydraulic cylinders, we must first understand the several states of hydraulic seals. When the seal is not installed, it has four dimensions, namely the inner diameter of the seal root, the outer diameter of the root, the inner diameter of the lip, and the outer diameter of the lip. When the seal is installed in the groove and has not yet worked, the groove size remains unchanged, while the seal size has changed completely. The four dimensions are the outer diameter of the seal root, and the outer lip diameter changes to the outer diameter of the groove at the same time; the inner lip diameter is the piston rod diameter, and the inner diameter of the root is the gap between the seal and the piston rod plus the piston rod diameter.

When the hydraulic cylinder starts to work and pressure is applied, the working state of the seal is: the inner and outer lips are close to the inner and outer walls and move slightly backward. The root of the seal is squeezed backward, and as the pressure increases, the force of the hydraulic oil on the seal also increases, and the overall deformation of the seal also increases. When the working cycle is completed and the cylinder is pressure-free, the seal returns to its original state. Repeated deformation and recovery until the effective amount of the two lips of the seal is completely lost, the seal is damaged.

Secondly, the tolerance of the hydraulic cylinder groove size needs to be matched with the seal. There are many forms of reciprocating seals, the most common ones are L-type, U-type, V-type, and Y-type, and most of them are lip seals. Reciprocating lip seals are widely used in reciprocating cylinders of hydraulic systems.

The pressure surface of this seal is lip-shaped, and there is a small amount of interference during installation, so that the lip edge and the sealing surface are fully in contact to produce a sealing effect. When the cylinder is working, as the pressure increases, its contact force and contact area increase, and the sealing performance increases with the increase in pressure. When the cylinder returns, the pressure decreases, the contact area and contact force decrease, and the sealing performance decreases accordingly.