What are Universal & Hinged Expansion Joints

Further to my previous post regarding different types of expansion joints, this post details out

1. Universal expansion joint

2. Hinged expansion joint

UNIVERSAL EXPANSION JOINT:

Universal expansion joints contain two bellows with multiple convolutions joined by a center pipe or spool. These joints, also known as double or tandem bellows expansion joints are used for the purpose of absorbing any combination of axial, lateral, or angular movements in a piping system.

When lateral movements are too excessive for a single axial expansion joint to accommodate or when there is a limitation on the amount of lateral forces allowed on the connecting piping or equipment, universal expansion joints are installed to accommodate these movements.

 

1.0 Bellow with tie rod installed in a Z shaped piping profile in a single plane

A typical arrangement of the above application is shown in the accompanying sketch below (refer Figure-10). Typically the assembly employs 2 Bellow elements tied across. The above bellow is purely lateral, and hence the axial expansion of the leg (excluding the expansion of the Bellow itself) housing the Bellow is, required to be accommodated by the Flexibility of the adjoining legs. To prevent the longer legs from rotating necessary Directional Guides are provided as shown. The End Anchors are required to be designed as Intermediate Anchors only.

 

2.0 Bellow with tie rod installed in a Z shaped piping profile in two planes

A typical arrangement of the above application is shown in the accompanying sketch (refer Figure-11) below. The arrangement is completely similar to that of the earlier situation except that the Bellow is subject to lateral deflection in a resultant plane derived from the magnitude of the 2 linear expansion components of the longer legs.

 

 

3.0 Bellow with pantographic linkage

A typical arrangement of the above application is shown in the accompanying sketch (Figure-12) below. Owing to the limited space between the 2 directly connected equipment nozzles the Bellow is required to absorb axial as well as lateral deflection. In such case the equipment nozzles must be designed to take the axial force due to Bellow imbalance area.

The Pantographic linkage is provided to distribute the expansion between the 2 Bellows and control their movements.

HINGED EXPANSION JOINT:

Hinged expansion joints are usually used in sets of 2 or 3 elements to absorb lateral deflection in one or more directions in a single plane. Each element of the assembly is subject to pure angular rotation by its hinge pin. Each pair of bellow element connected by a segment of pipe will act in unison to absorb lateral deflection in much the same way as universal joint in a single plane. The hinges are designed strong enough to take the axial pressure thrust and also to transmit the piping deflections in a plane perpendicular to the plane of hinge rotation.

The magnitude of the lateral deflection that could be absorbed by a hinged bellow is directly proportional to the length of spool piece connecting the bellow elements.

 

1.0 Two Element Bellow

A typical arrangement of the above application is shown in the accompanying sketch (Figure-18) below. Since the axial pressure thrust is absorbed by the hinges the piping end anchors need to be designed as intermediate anchors only. The position of the pipe guides on the axial pipes should provide adequate flexibility to absorb the expansion of the offset leg housing the bellow.

 

2.0 Three Element Bellow

A typical arrangement of the above application is shown in the accompanying sketch (Figure-19) below. The above arrangement is typically employed in the situations where the flexibility in Z shaped profile (in a single plane) is not sufficient to absorb the thermal expansion of the offset leg.