Externally Pressured Metal Bellows Expansion Joints Guide
Externally pressurized metal bellows expansion joints are built for one specific problem: high-pressure, high-temperature systems that also need long axial movement. Internally pressurized bellows tend to squirm under those conditions — buckling instead of flexing evenly. The externally pressurized design solves this by reversing the bellows' action: the flexible element sits inside a protective casing, so extension is absorbed as compression of the bellows, and the casing itself becomes a second containment barrier if the bellows ever fails.
Many of these types of expansion joints come with a drain that allow excess to be removed from the system. Pressurized steam systems are a common place you will find these type of expansion joints. Self-draining convolutions of the bellows element make it impossible for media to collect in the convolutions.
Some inherent features of this design include:
- Guide rings
- Full thickness cover
- Insensitivity to flow direction
- Meet EJMA guidelines for safety
The internal guide rings reduce the need for guides and anchors compared to internally pressurized bellows. These expansion joints do not require liners and are easy to insulate. The external casing protects the bellows element making installing easier and less time consuming with no critical surfaces exposed.
