3.4.1 Introduction

A mechanical seal is a device that uses a pair of ostensibly flat radial faces, one stationary and the other rotating, to form a dynamic seal. The faces are held in sealing contact, usually by a combination of the force of a spring and the system pressure. The face materials are selected to be a compatible tribological pair when operating in the sealed fluid. One of the faces will be well located either in the machine housing or on the shaft and the other face, loaded by the spring, will be permitted to float sufficiently to maintain the required sealing contact and face orientation. The selection of either a static or rotating floating component depends on the application and operating parameters.

This type of seal is now the primary method for providing the rotary shaft seal for containing the product in most types of rotary machines such as centrifugal pumps, rotary compressors, mixers and other process equipment. There are a wide variety of designs to suit individual applications and also facilitate the appropriate production volumes. To seal high pressures, difficult or hazardous fluids two or more seals may be used in a variety of configurations which are discussed in more detail in the relevant sections. The production requirements can vary from the very high volumes for domestic equipment, washing machines and dishwashers, or automotive water pumps to special one-off designs for large high pressure pumps or compressors.

This section describes the basic operating mechanism of...