The most common hydraulic seals include rod seals, piston seals, symmetrical seals, static seals, as well as wipers, wear rings, U-cups, gaskets and cast iron piston rings. All hydraulic cylinder seals by size will be single or double acting. Single acting hydraulic seals head in one axial direction only. Double acting hydraulic seals go in both directions in order to produce a reciprocating motion. Hydraulic seals are made from different materials.
Such materials include nitrile, rubber, silicone, nylon and polyurethane. They also include bronze, nickel and glass-filled PTFE. There are even hydraulic seals that are molded straight from fabric reinforced rubber or leather. Rod seals are considered to be the most important in the composition of a hydraulic cylinder. These are radial internal seals. They press-fit into a housing bore. The sealing lip touches a shaft.
The failure of a rod seal could lead to fluid leakage. Rod seals are affected by changes to the rod surface as well as fluid temperatures. Such seals often experience the highest pressure variations. Piston seals, on the other hand, operate as radial seals. They are also known as external seals. These seals fit onto shafts where the sealing lip will be making contact with the housing bore. The seals are mounted on a piston head.
Piston seals are typically used in conjunction with bearings and guide rings. They are typically made from polyurethane. But there will be those that are also made from fabric reinforced rubber. The guiding force for utilizing such materials perhaps is that it gives added strength to the seals in which case the potential for any form of leakage is minimal. This has been but a brief expose of how hydraulic seals are being composed, making brief mention of its variants and materials.