When axial deflections exist, and anchoring is not feasible or pressure loads are too high for sensitive equipment like pumps and turbines, the in-line pressure balanced expansion joint is a efficient method to solve a design problem. The principle of unit is that the axial pressure thrust is reacted by the pressure acting on a cross sectional area equal to the area of the working bellows.
Since this unit is entirely axial, the cross-sectional area needed to balance the pressure is placed around the outside of the unit. Because the pressure forces are generated by the pressure acting on the annular surface between the primary and outer or balancing bellows, the arrangement of the tie rods transfers and balances the pressure thrust. Now the forces needed to compress or extend the unit are only the result of the spring resistance of the bellows, thus main anchoring of the pipe or vessels is not required.
This expansion joint can be used to replace pipe loops or main anchor, and its cost advantage may be seen in reduced pumping energy by the elimination of pressure drop.