Bellows Expansion Joint Movements

Bellows Expansion Joint Movements 

There are four basic movements such as axial,lateral,angular and torsional that can be applied to bellows expansion joint.We introduce these four types movements for you as follow: 

1. Axial Movement(+/- mm)

Axial movement is the change in dimensional length of the bellows from its free length in a direction parallel to its longitudinal axis.Compression is always expressed as negative(-) and extension as positive(+). The units for axial spring rates displayed in N/mm. 

2. Angular Movement(+/- Degrees)

Angular movement is the rotation displacement of the longitudinal axis of the bellows toward to point of rotation. The convolutions at the inner most point are in compression(-) while those furthest away are in extension(+).The angular capability of a bellows is most often used with a second bellows.

The units for angular spring rates displayed in Nm/deg. 

3. Lateral Movement(+/- mm)

Lateral movement is the relative displacement of one end of the bellows to the other end in a direction perpendicular to its longitudinal axis(shear).Lateral movement can be imposed on a single bellows as depicted below but to a limited degree.A better solution is to incorporate two bellows in a universal arrangement as shown. This results in greater offset movements and much lower offset forces. 

The units for lateral spring rates displayed in N/mm. 

4. Torsional Movement(+/- Degrees)

Torsional movement is the roration about the axis through the center of a bellows(twisting).Torsion destabilizes an expansioin joint reducing its ability to contain pressure and absorb movement. If torsion is present in a piping system,hinges,slotted hinges or gimbals are recommended to combat the torsion.