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The spring rate is equal to the spring rate of both flow bellows plus the spring rate of the balancing bellows.

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Elbow Pressure Balanced Pipe Expansion Joint

Bellows squirm because they have surpassed the critical design pressure limit. This can occur in small diameter bellows with a large number of convolutions.

Example of Bellows Squirm
Example of Bellows Squirm

By using an in-line pressure balanced expansion joint.

In line pressure balanced expansion joint diagram
In-line pressure balanced expansion joint diagram

Yes, the rubber expansion joints do have spring rates and that are required to be input into the stress model.

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Rubber Expansion Joints

The spring rate is equal to the spring rate of both flow bellows plus the spring rate of the balancing bellows.

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Elbow Pressure Balanced Pipe Expansion Joint

The spring rate is equal to the spring rate of both flow bellows plus the spring rate of the balancing bellows.

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Elbow Pressure Balanced Pipe Expansion Joint

The preferred method to design universal expansion joints would be to use a larger diameter bellows and use a reducer at the end of the expansion joint. This would ensure angular rotation and axial movement between the two bellows.

 

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72″ Inch Tied Universal Thick-wall Expansion Joint

The expansion joint is designed to accommodate all the needed displacements. The tie-rods are part of the expansion joint and designed to absorb all the specified displacements.

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20″ Diameter Tied Universal Expansion Joint

Universal expansion joints are usually used when there is large lateral motion.

Tied universal expansion joint
Tied universal expansion joint