Dynamic sealing is considerably more involved than static sealing. Not only does a seal have to prevent the flow of some medium, like in static sealing, but it also has to be able to perform that task while in motion and with frictional forces to consider. Additional consideration must also be given to the fluid compatibility as a volumetric increase in excess of 20% can lead to frictional and wear difficulties, while shrinkage of any kind (5% max) could lead to a lack of sealing contact. All of these considerations have lead Parker to develop a wide-range of sealing solutions for scenarios where dynamic movement is present.
Dynamic sealing can be broken down into two categories, reciprocating and rotational movement. Reciprocating movement describes the seal used in an application (usually a “piston-and-bore” radial seal application) in which the seal translates along a fixed line while maintaining adequate sealing force. Major considerations when designing a seal for reciprocating movement are stroke length, stroke speed, diameter of seal, and surface finish of the mating hardware. Typically, seals work best in reciprocating glands on short-stroke, small diameter applications. Rotational movement describes the seal spinning around a fixed axis while maintaining adequate sealing force in application. Rotary seal designs must take into consideration shaft diameter, shaft rotational speed (RPM), and surface finish of the mating hardware.
Each scenario presents its own set of challenges for sealing and require careful consideration of the sealing solution best suited for a particular application. Let us walk through several potential solutions and their advantage and potential pitfalls in meeting the needs of a dynamic seal.
O-rings still remain the simplest solution for sealing. While they may come with additional considerations, O-rings can functionally perform in properly designed reciprocating and rotary glands.
The sealing principles of X-rings are almost identical to that as O-rings. Sealing is achieved with radial squeeze in a piston/bore type gland.
Low Drag D-Ring
The D-ring was developed to solve the problem of an O-ring spiral failing, or rolling, either during installation or during service.