Pitch of a convolution - Bellows Terminology

The length of a single convolution of a bellows, measured either from root to root or crest to crest. 

This length can be calculated by, 
Pitch = Bellows convoluted length / Number of convolutions

ROOT and CREST - Bellows Terminology

The ROOT of a convolution is the curved profile located at the inner diameter of the bellows.

The CREST of a convolution is the curved profile located at the outer diameter of the bellows.

What are Tie Rods? Why do we need them ?

TieRods are devices, in the form of rods or bars that are attached to the expansion joint assembly whose primary function is to continuously restrain the full bellows pressure thrust during normal operation while permitting only lateral deflection.

Angular rotation can be accommodated only if 2 tie rods are used, located 90 deg opposed to the direction of rotation.

Pressure-Balanced Expansion Joint

A pressure-balanced expansion joint is designed to absorb axial movement and/or lateral deflection while restraining the pressure thrust force of the bellows. This is done by means of interconnecting the flow bellows with an opposed bellows also subjected to a line pressure. 

This type of expansion joint is usually used when a change in direction usually occurs in a run f the pipe.

Gimbal Expansion Joint

A gimbal expansion joint is designed to permit angular rotation in any plane by the use of 2 pairs of hinges affixed to a common floating gimbal ring.

Universal tied, swing, hinged and gimbal expansion joints, are normally used for the restraint of pressure thrust forces.

Hinged Expansion Joint

A hinged expansion joint contains one bellows and it is designed to allow the angular rotation in one plane using a pair of pins running through plates attached to the expansion joint ends. In order to function properly, a hinged expansion joint should be used in sets of two or three.

Swing Expansion Joint

A swing expansion joint is designed to absorb lateral deflection and/or angular rotation in one plane only using swing bars, each of which is pinned at or near the ends of the unit.

Universal Tied Expansion Joint

Tied Universal Expansion Joints are used whenever there is a necessity to eliminate the pressure thrust forces of an assembly from a piping system. However, in this case, the expansion joint will absorb lateral movements but will not absorb any axial movement due to the tied lengths. 

Universal Expansion joint

A universal expansion joint, similar to a double expansion joint, contains two bellows joined by a common connector to absorb any combination of three basic movements. A universal expansion joint is capable of accommodating for greater amounts of lateral movements in comparison to a single expansion joint.

Double Expansion Joint

A double expansion joint consists of two bellows joined together using a common connector anchored to a rigid part of the installation using an anchor base. The anchor base is attached to the common connector either at the time of installation or at the time of manufacturing. The anchor base allows each bellows of the assembly to work independently as a single unit. Double expansion joints look similar to an universal expansion joint but should not be confused with it.

Single Expansion Joint

This is the simplest form of an expansion joint. It is made up of one bellow (single bellows construction), which absorbs all the movement in the pipe section into which the expansion joint is installed.

Types of expansion joints

  • Single Expansion Joint
  • Double Expansion Joint
  • Universal Expansion Joint
  • Universal Tied Expansion Joint
  • Swing Expansion Joint
  • Hinged Expansion Joint
  • Gimbal Expansion Joint
  • Pressure-Balanced Expansion joint

Raised Face Slip On Flange Data Sheet

A data sheet containing the Nominal Pipe Size, Outside Diameter, Thickness, Raised Face Diameter, Length, Thru Hub, Hub Diameter, Bore, Approximate Weight, Bolt Circle, Number of Holes and the Diameter of the holes of the Flanges.

Expansion joint accessories

  • Liners
  • Weld Ends
  • Flanges
  • Collars
  • Hollow Reinforcing Rings
  • Solid Root Rings
  • Equalizing Rings
  • Control Rods
  • Limit Rods
  • Tie Rods
  • Pantographic Linkages

What is an expansion joint ?

According to the Expansion Joint Manufacturers Association (EJMA), an Expansion joint is a device that is made up of one or more metal bellows to absorb any dimensional changes caused by thermal expansion or contraction of a pipe-line, duct or vessel.