Hydraulic Cylinder Seals for Construction Machinery

Common self-sealing, compression-type hydraulic cylinder seals used in construction machinery hydraulic cylinders primarily include O-rings, round rings, and square rings. These types of hydraulic cylinder seals offer advantages such as simple structure, ease of manufacture, and low cost. Therefore, they are widely used as dynamic and static seals in hydraulic transmission systems.

These elastic cylinder seals, when installed in the seal groove, experience 10-25% radial compression deformation, creating a high initial contact stress on the sealing surface, thereby preventing leakage of the sealing fluid in the absence of pressure. During operation, pressurized oil compresses the self-sealing, compression-type hydraulic cylinder seal, further deforming the seal ring and generating significant additional contact stress on the sealing surface, which increases with the pressure of the pressurized oil. This additional contact stress, combined with the initial contact stress, prevents leakage of the pressurized oil. However, when the operating pressure in the hydraulic cylinder exceeds 10 MPa, to prevent the synthetic rubber self-sealing compression-type hydraulic cylinder seal from being squeezed into the sealing gap and bitten or sheared off during the reciprocating motion of the hydraulic cylinder, causing seal failure and leakage, a harder synthetic resin retaining ring, such as a nylon retaining ring, a polyoxymethylene retaining ring, or a PTFE-filled retaining ring, must be installed on each pressure-bearing side of the synthetic rubber self-sealing compression-type hydraulic cylinder seal.

Because synthetic rubber self-sealing compression-type hydraulic cylinder seals experience significant compression deformation during operation, their static frictional resistance is particularly high, often more than twice their dynamic frictional resistance. Such high static frictional resistance can cause undesirable phenomena such as low-pressure creep and operational difficulties in some low-pressure hydraulic transmission systems. This is why self-sealing compression-type hydraulic cylinder seals are rarely used solely as dynamic seals.