Dynamic Seals Commonly Used in Mechanical Industry Dynamic seals for reciprocating motion

In mechanical engineering, sealing is said to be dynamic when it is applied between two parts in relative motion, i.e. rotation and/or translation. When there is no movement between the parts, sealing is said to be static. The latter is covered in the article [BM 5 418].

Dynamic sealing is considerably more involved than static sealing. Not only must a seal prevent the flow of certain fluids, as in the case of a static seal, but it must also be capable of performing this task in motion and with friction forces to take into account.

Containing a gas or liquid, by its very nature, is not easy. The permissible leak rate depends on the nature of the fluid to be sealed; leakage of expensive, toxic, corrosive, explosive or flammable fluids must be kept to a minimum. Seal life and reliability are also major concerns for users, to reduce equipment and process downtime.

Seal failure can have multiple consequences, in terms of equipment availability, operation and safety. Common examples show that highly complex assemblies, such as landing gear, can experience major problems as a result of a simple leak. Good dynamic sealing reliability is not often easy to achieve.

Indeed, dynamic sealing calls on a number of physics and chemistry concepts, in which the properties of materials and dynamic contact surfaces play an important role. In addition, the problems to be solved are varied, involving a large number of parameters that are difficult to optimize simultaneously. The best solutions in mechanical sealing techniques in general, and dynamic sealing in particular, are almost always the result of skilful compromises.

This article deals with so-called translational dynamic seals in which the relative motion between sealing parts is linear. It gives an introduction to the different types and degrees of sealing, and then describes the different technologies of translational dynamic sealing according to each degree of sealing: rigorous, controlled and relative. Dynamic rotary seals are covered in [BM 5 420].

At the end of the article, readers will find a glossary and a table of the notations used.