Oppose the effects of pressure thrust in applications where space limitations prevent the use of main anchors
This is a combination of single joints which oppose each other so that the internal pressure load of one balances the internal pressure load of the other. This prevents excessive loading due to pressure thrust, from being transmitted to pipe anchors, turbines or process equipment. The compressive forces of the two bellows are additive but these are usually negligible in comparison with the pressure forces. This type of joint is used where a pipeline changes direction. It absorbs axial or a combination of axial and lateral movements.
This figure shows a typical application of a pressure balanced expansion joint for a combined axial movement and lateral deflection. The anchor on the piping run and that on the turbine are intermediate anchors and only directional guiding is required. By proper design, the guide directly above the turbine can be made to absorb the axial movement forces of the expansion joint without transmitting these to the turbine. The only force imposed on the turbine is that which is required to deflect the expansion joint laterally.