Glossary of Terms

Angular Rotation

The displacement of the longitudinal axis of the flexible element from its initial straight line position in an arc.

Axial Compression

The dimensional shortening of a flexible element or Bellows along its longitudinal axis.

Axial Extension

The dimensional lengthening of a flexible element along its longitudinal axis.

Axial Single Bellows

Single Bellows construction, designed primarily to absorb axial movements and can also be used for angular or lateral offset or misalignment.

Bellows

The flexible element of a flexible element, consisting of one or more convolutions and end cuffs, if any.

Braided Bellows

Designed to accommodate lateral and angular movement with absorption of pressure end loads, offering a cost-effective solution for moderate deflections in low-pressure systems. Titanium bellows can be supplied with stainless steel braid to minimise cost.

Convolution

The smallest flexible unit of a bellows. The total movement capacity of a bellows is proportional to the number of convolutions.

Cuff

The straight, unconvoluted portions at the ends of the bellows.

Cycle Life

The minimum number of complete cycles at the working conditions which a flexible element or Bellows is designed to withstand without failure.

Effective Area

The cross-sectional area of the Bellows over which the pressure is assumed to act, this is used for calculation of axial thrust.

E.J.M.A

Expansion Joint Manufacturers Association

Expansion Joints

Device containing one or more bellows used to absorb dimensional changes, such as those caused by thermal expansion or contraction of a pipeline, duct or vessel.

Externally Pressurised Bellows

In this type of joint, the duct pressure is transferred to the outer surface of the bellows, the pressure being held by the outer casing. This type of unit has applications where lateral movement must be accommodated in a rigid duct.

Flanged Ends

The ends of a flexible element equipped with flanges for the purpose of bolting the Expansion Joint to the mating flange flanges or adjacent equipment or piping.

Gimbal Bellows

Gimbal bellows act as universal joints in the duct and offer angulation through 360°. Together with absorption of duct end loads. The Senior Bird Bellows gimbal joint has been developed for minimum weight whilst retaining the advantage of full bellows-sealed construction and is supplied with vee flanges or weld ends.

Hinged Bellows

A Single Hinged flexible element containing one bellows, designed to permit angular rotation in one plane only, using a pair of pins through hinge plates, attached to expansion joint ends. Hinges and Pins are designed to restrain the thrust of the flexible element due to internal pressure.

Internal Sleeve

A device which shields the convolution from direct contact with the flow of the media, also referred to as a Liner.

Lateral Deflection

The relative displacement of the two ends of a flexible element perpendicular to its longitudinal axis.

Movement

The various dimensional changes which a flexible element is required to absorb, such as those resulting from thermal changes in a piping system.

Nadcap (NDT)

Performance review institute AS7114.

Nadcap (Welding)

Performance review institute AS7110.

Pressure Balanced Expansion Joints

Pressure balanced bellows are designed to absorb axial and lateral deflection without transmitting pressure loads to adjacent ducts. The ability to eliminate end load due to pressure is particularly valuable where space is limited and where ducts cannot be adequately restrained.

Shroud

A device used to provide limited protection of the external surface of the bellows from foreign objects or mechanical damage. It is sometimes referred to as a cover or external sleeve.

Spring Rate

The force (pounds or newtons) required to deflect the Bellows one unit of travel (inch or millimetre).

Weld Ends

The ends of a flexible element equipped with pipe suitably prepared for welding to adjacent equipment or piping.