Terminology associated with the piston and seal rings are utilized interchangeably. Terms applied to piston rings and seal rings identify rings that have gaps or splits. They also refer to seals’ function in the prevention of fluid passages. Gaps or splits improve sealing capabilities. They do this by providing improved conformation to sealed surfaces. And they do this by facilitating installations that result in reduced leakages. Designs of piston and seal rings are informed by pressure differentials, operating temperatures, sealed fluid viscosities, the co-efficiencies of friction, corrosion formation, material compatibilities and linear or rotational movements, as well as relative speeds of movements.
Best quality piston rings are designed to seal onto the so-called OD of the ring. They are also designed to seal onto the ID of a ring. This has to do with enabling expanding and contracting motions respectively. In response to most piston rings experiencing leakages at its gaps, numerous gap designs have been developed. One such design is the step seal. This produces gap ends that overlap with its surface at an angle to a ring’s OD. Another design is that of the step joint whereby gap ends are allowed to overlap with its surfaces parallel to the side of a ring.
This latter design is able to provide far better sealing capabilities over a standard butt joint or straight cut gap. And the hook joint is being used to facilitate installations in areas where access is limited.
Both piston and seal rings utilize fluids on the high pressure side of a ring in order to seal against moving surfaces and the surface of the ring groove. The ring tension produced forms part of the wall dimension, the ring’s relaxed gap and provides elasticity for affected material. Tension can be increased by way of using expanders or contractors.