Applications

Single Expansion Joints AS have one bellows. Axial compression and extension, lateral and angular movement can be accommodated. These expansion joints do not restrain the internal pressure thrust. The piping designer must provide the system with separate anchoring and guiding to resist the pressure thrust. Where small thermal movements are involved and proper anchoring and guiding is feasible, a single expansion joint is the most economical installation.

Tied Single AT Expansion Joints also have one bellows, except the overall length is restrained by tie rods designed to contain pressure thrust. A tied single is usually designed for lateral offset so that the tie rods can remain fully engaged and loaded with the pressure thrust force. A two tie rod design can accept angular deflection in a single plane.

Universal AU Expansion Joints consist of two bellows separated by a pipe spool. This configuration accommodates large lateral movements, in addition to axial compression and extension and angular deflection. These expansion joints have no restraints to resist pressure thrust and like the singles, the piping designer must provide separate anchoring to handle pressure thrust.

Universal Tied, AUT Expansion Joints contain two bellows separated by a pipe spool and tie rods designed to contain the pressure thrust force. These expansion joints are generally designed to accommodate lateral movement only. A universal expansion joint can be designed to have a very low lateral spring force to minimize forces on adjacent equipment. A two tie rod design can also accept angular deflection in a single plane.

The tie rods are usually at or near ambient temperatures and, therefore, do not expand and contract as a function of the temperature of the media within the pipe. As a result, the thermal expansion of the length of pipe between the tie rod end plates is forced into the bellows as an axial movement. The bellows design must accommodate this axial thermal expansion as well as the specified lateral movement.

Sometimes a universal expansion joint has a very heavy center spool that can exert excessive weight on the bellows elements. To protect the bellows elements from excessive lateral loads, a support system such as a slotted hinge can be installed across the individual bellows elements to support the dead weight of the center spool.

Hinged Expansion Joints AH have a single bellows with overall length restrained by hinge hardware designed to accommodate pressure thrust. A hinged expansion joint allows angular movement in a single plane.

Gimbal AG Expansion Joints have a single bellows and gimbal hardware designed to resist pressure thrust. The gimbal expansion joint hardware operates like the universal joint on a drive shaft to accommodate angular movements in any plane.

Applications

Standard Liners (part number L)

Liners can be installed inside the expansion joint to protect the bellows from damage. Liners should be specified by adding the letter L to the part number when the following conditions exist:

• Smooth flow or low pressure drop is required.
• Velocities which may produce flow induced vibrations described below.
• For air, steam and other gases
  • Up to 6" Dia. flow greater than 4 ft/sec per inch of Dia. (Up to 150 mm Dia. flow greater than 0.05 M/sec per mm of Dia.)
  • Over 6" Dia. flow greater than 24 ft/sec (over 150-mm Dia. flow greater than 7.5 M/sec)
• For water and other liquids
  • Up to 6" Dia. flow greater than 1.67 ft/sec per inch of Dia. (up to 150 mm Dia. flow greater than 0.02 M/sec per mm of Dia.)
  • Over 6" Dia. flow greater than 10 ft/sec (over 150 mm Dia. flow greater than 3.0 M/sec)

Covers (part number C)

Covers should be specified when:

• Protection from falling objects or protection from traffic is needed.
• Protection of personnel is needed.
• Insulation will be applied over the expansion joint.
• When high flow velocities may exist around the outside of the expansion joint, such as in the exhaust of a steam turbine.

Senior Flexonics Pathway always recommends a cover. The small cost for the cover is insurance against costly downtime due to damage. The standard cover is a removable design.