Pressure Balanced Bellows Expansion Joints are normally used where a change of direction occurs in a run of piping and pressure thrust to be absorbed.
The deflections are controlled by the tied universal type expansion joints so as to accept the lateral movements and the pressure balanced elbow is usually required to accept the axial deflections also present. Moreover a bellow is also incorporated beyond the elbow in order to accept the various movements present. This balancing bellow is connected by tie rods to the pipe beyond the universal section which enables the pressure thrust to be contained as tension in the tie rods.
The main features of these bellows is that apart from absorbing axial and lateral movements, the pressure forces remain in balance, the balance pressure thrust remains constant and there is no volume change.