Externally pressurized expansion joints is an excellent answer for large axial displacement needs. When large displacements are present in a system, more convolutions are needed to handle these large axial movements. Then, designing the bellows  becomes a challenge for the expansion joint engineer due to “column squirm” (instability due to internal pressure / buckling of bellows) concerns. Solution to this challenge is to pressurize the “bellows” externally.

These units are very robust and safe. They have an in-built (part of the design) inner sleeve and outer cover. Outer cover protects the bellows from external damages during shipping, installation and operation. It also makes this unit suitable for underground usage. Inner sleeve provides smooth flow and prevents pressure losses.

These units are not suitable for lateral movements.

They can be provided with pipe ends, or welded / rotating flange connections supplied in accordance with many industrial norms or special drillings.