Cap seals offer a low friction seal for use in dynamic reciprocating applications. A plastic cap provides a seal against the dynamic sealing face, an O-ring is used to energise the plastic cap and operates in a static environment. The O-ring uses the system pressure to increase the sealing force acting on the cap. The cap also prevents extrusion of the O-ring energiser when used in high pressure applications.
The plastic cap is typically made from a low friction material, such as PTFE. Under low pressure conditions, liquid media can provide lubrication as it migrates between the dynamic sealing faces through a capillary effect. Cap seals are often referred to as wet seals as they allow a small amount of fluid to pass across the seal.
Cap seals can be offered in two different designs, a heavy duty cap or a low profile cap:-
The heavy duty cap provides a thicker cross section of sealing cap for use with high pressure, up to 40MPa, but require a non-standard groove for fitment. This thicker section allows for greater wear due to the higher sealing forces induced.
The low profile cap is generally for light to medium duty and can be retro fitted into standard O-ring grooves. The low profile cap provides good wear resistance and low friction due to the lower sealing forces induced.