2.1 Introduction

The designs and types of sealing methods for static duties cover a vast range. To discuss the various types it is useful to divide them into two basic categories, seals and gaskets. Seals are typified by an elastomeric O-ring in a seal groove and gaskets by fibrous materials clamped between a pair of flanges.

Seals, within this context are designed such that they are expected to be self-energizing whereas it is normal for gaskets to be clamped with sufficient force that the pressure is resisted by the stored energy within the gasket. Hence the relative assembly loadfor a seal may be much lower than a gasket for the same duty.

There are many variations on these two individual themes and several that cover a grey area between them. The selection will depend on a number of factors. These include:

• Temperature range.

• Pressure range.

• Fluids to be sealed.

• Environment.

• Environment.

• Integrity of sealing required.

• Material of counter-faces.

• Life requirement.

• Maintenance requirements.

• Volume to be manufactured.

• Assembly methods.

• Testing and inspection criteria.

• Degree of flexibility and relative movement of counter-faces.

• Requirement to withstand pressure, thermal or mechanical shock.

• Industry standards and practice.

• Sterility and hygiene requirements.

• Established custom and practice within a particular industry.

Hence the type of static seals chosen for an automotive gearbox casing, a pipe joint in a food plant, a vacuum chamber working in electronics manufacture, or a high pressure steam pipe in a process plant may all be very different. The reasons will be driven...