Metal Bellows Correctedn 7/11/00 2:41 PM Page 11
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 AU
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.
UNIVERSAL TIED AUT
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.
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