Hydraulic Seals

Hydraulic seals describe a class of seals that are used in applications with either rotary or reciprocating motions. Hydraulic seals are exposed to hydraulic fluids such as hydrocarbon and phosphate ester and are designed for high-pressure dynamic applications such as hydraulic cylinders. Hydraulic seals usually need to be higher friction seals than pneumatic seals but often operate under lower operating speeds.

The sealing orientation for hydraulic seals can include internal (rod seal), external (piston seal), symmetrical or axial seal. With the internal (rod) seal, the seal is fit into a housing bore and the sealing lip touches the shaft. With the external (piston) seal, the seal is placed onto a shaft and the sealing lip touches the housing bore. Since symmetric seals are the same on both sides they will function as either a rod or a piston seal. The axial seal fits axially against the housing.

Rotary applications need only one hydraulic seal (single acting) because it can seal in the one axial direction the application is moving. However, a reciprocating application will need two hydraulic seals (double acting), one for each of the directions.

The life of hydraulic seals is dependent on many factors including the maximum operating speed, maximum operating temperature, maximum operating pressure and the vacuum rating. When ordering hydraulic seals you will want to know the shaft outer diameter or seal inner diameter, housing bore diameter or seal outer diameter, the axial cross section and the radial cross section.