3.1 Introduction

Sealing of rotary shafts covers a very wide range of equipment and applications including domestic equipment, all types of automotive and power plant machinery, industrial pumps, aircraft gas turbines, power generation turbines, and large industrial and pipeline compressors.

Each application presents an individual set of demands based around the space, weight, price and reliability demands of the user. A number of individual types of rotary seal have evolved and each has an individual place based around a range of applications. Within each class of seal the range of applications can vary enormously. Hence mechanical seals can be found on equipment as diverse as a domestic washing machine and aircraft gas turbines. Within any one application area it is quite usual for one type of seal to predominate, but at the boundaries in operating conditions between seal types then different seal types may be selected depending on the space envelope, friction, leakage and reliability objectives. For example, at low pressures there is a choice between using either a mechanical seal or lip seal. Examples include the stern shafts on ships and hydraulic pump and motor shafts. The selection will depend on individual manufacturer or user preference, and can also change as developments move the relative benefits of one seal type to another. A pertinent example are the recent developments in lip seals to work at four to seven bar as described in section 3.2.9

If the reader is contemplating seal selection for a new piece of equipment it is...