An Externally Pressurized Pressure Balanced Assembly is very similar to an In-Line Pressure Balanced assembly but it is capable of large amounts of axial movement. This is achieved by pressurizing the bellows externally, eliminating the possibility of bellows squirm. This design has the added benefit of being self guided with self draining convolutions. Again, no elbow is needed in this system.

The diagram above shows how the expansion joint is pressurized. The canceling thrust forces of the line bellows and the balance bellows cause this style to be completely pressure balanced eliminating the need for main anchors. There is no change in pressure when the expansion joint is moved because the volume does not change. As the line bellows (A) are compressed, the balancing bellows (B), which has twice the effective area as (A), is extended causing no volume change.

This type of expansion joint is also seen between two pieces of load sensitive equipment where minimum forces and moments are required. It is commonly used in steam line installations where pipe main anchors are far apart. The only loads seen by the equipment are the sum of the axial force required to compress or extend the line bellows and balancing bellows in the expansion joint. Modified versions of this style are used in direct burial applications.