When the bellows are restricted at both ends, the bellows will become unstable if the pressure in the bellows increases to a certain critical value. For the bellows working in the compression state, its greater compression displacement is, when under the pressure action, compression to each other between the bellows contact each other can produce a larger displacement value, also known as the structure allows greater displacement, it is equal to the bellows free length and greater compression length.

The larger displacement of bellows without plastic deformation is called the allowable displacement of bellows. After the deformation occurs under the action of force or pressure, when the force or pressure is removed, the bellows do not return to the original state.

Whether the bellows are stretched or compressed, at the initial stage of bellows displacement, its residual deformation is relatively small, generally less than the allowable zero offset value specified in the bellows standard. However, when the stretching or compression displacement gradually increases to more than a certain displacement value, it will cause a sudden increase in the zero offset value, which means that the bellows produce a relatively large residual deformation, so the bellows generally do not exceed this displacement.

The allowable compression displacement of bellows is larger than the allowable tensile displacement of bellows working in the compression state, so the bellows working in the compression state should be designed as far as possible. In general, the allowable compression displacement of the bellows of the same material and specification is 1.5 times the allowable tensile displacement.

The allowable displacement is related to the geometric dimension parameters and material properties of bellows. Generally, the allowable displacement of bellows is directly proportional to the yield strength and the square of the outside diameter, but inversely proportional to the elastic modulus of materials and the wall thickness of bellows. At the same time, relative wave depth and wave thickness also have some effects on it.

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