External Pressure Expansion Joints are designed for large axial deflections and high pressures. Normal bellows under such conditions are subject to "Squirming" and instability.
By applying external pressure, the bellows become stable, it changes from a bellows in
compression subject to buckling, to a stable bellows in tension.
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| In Fig.1
we take a bellows with a high "Length /
Diameter" ratio. |
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In
Fig. 2 we
apply pressure. After a certain pressure, the bellows twist and buckle.
This is a "Squirm". |
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| In
Fig. 3 we take the bellows and fix in a case to apply external pressure. |
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In
Fig. 4 we
apply pressure. As pressure
increases bellows straightens up.
The bellows is self - aligned.
We can apply pressure up to bursting
pressure without any deformation.
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