An O-ring is a rubber ring with a circular cross-section, and it is the most widely used sealing element in hydraulic and pneumatic systems.
The O-ring seal is a bidirectional sealing element. The initial compression of the O-ring during installation, either radially or axially, determines its initial sealing capability.
The force generated by the system pressure acting on the O-ring constitutes its total sealing force; this sealing force increases with increasing system pressure.
Under pressure, the shape of the O-ring resembles that of a liquid with high surface tension. Pressure is transmitted equally in all directions.