Universal expansion joints contain two bellows with a connecting tube or centerline spool between them. It is usually equipped with a limit lever or a full push-pull lever, depending on the conditions of use. Tie rods or limit rods stabilize the center tube connection and distribute the movement evenly between the bellows. Tie rods are required if full compression thrusts and other externally applied loads need to be absorbed.
Universal expansion joints are typically designed to absorb any combination of axial and lateral motion and angular rotation in multiplanar piping arrangements. They are great for absorbing large amounts of lateral displacement. The amount of lateral displacement can vary widely, as any increase in the length of the center tube cross will correspondingly increase the allowable lateral deflection. In installations involving significant thermal changes, where the pipe height changes or there is an offset, it is often possible to install a universal bellows expansion joint in the offset or drop leg, which will absorb more lateral movement than can be compressed by the standard unit absorb. The installation of a universal expansion joint in this situation usually reduces construction costs considerably. The simplest form of universal expansion joints is the double expansion joint, which has two bellows separated by a centerline axis and does not require a tie rod, as they are typically used in low pressure exhaust type applications with significant lateral deflection.
Tied Universal Expansion Joints are usually composed of two sets of short tie rods, one on each bellows, or an integral tie rod. Devices with two sets of short rods are primarily used to limit movement and stabilize connecting pipe sections. Units with integral tie rods are designed to absorb full compression thrust, stabilize connecting pipe sections, and absorb all external loads present, such as wind loads and the weight of central pipe joints, where the unit is particularly long.