An In-Line Pressure Balanced Assembly is designed to absorb small amounts of axial and lateral movement while counteracting the pressure thrust in a system. This is achieved with a series of rods similar to the Pressure Balanced Elbow Assembly and a balancing bellows with twice the effective area as the line bellows. The elimination of the elbow is what makes this expansion joint unique.

The diagram shows that the effective area of the balancing bellows (EB) is twice that of the line bellows (EA). These forces act across the tie rods that are attached to the tie plates. As the line bellows are compressed, the balancing bellows is extended causing no volume change. No change in volume means no increase or decrease in pressure as the expansion joint moves.

This type of expansion joint is usually seen between two pieces of load sensitive equipment where minimum forces and moments are required. It is also used in installations where the application of a main anchor would not be practical. 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.