Pressure Balanced Expansion Joint
The pressure balance expansion joint or bellow design, which basically is a combination of a Flow Bellow and a Balancing Bellow, comes handy in addressing many situations.
The axial thrust imposed by the imbalance area of the Bellow under internal pressure is a main concern in designing the Piping System employing such Bellows. The conventional method of designing such systems is by employing Main Anchors to absorb the above axial force. It is however not always practical (due to space/ access constraints) to achieve these conventional solutions. The excessive magnitude of the axial force could also become prohibitive in some instances.
The working principle of the above Bellow relies on the fact that since both Flow and Balancing Bellow have identical cross sectional area, they will produce equal, but opposite in direction, forces under the same internal pressure. If the ends of these Bellows are locked to each other by a suitably designed tie-rod, the above equal and opposite forces will cancel out to transmit no axial force on the end terminals of the connected piping. At the same time the above tie rod will not interfere with the Flow Bellow in absorbing axial/ lateral deflections.
1.0 Single Element Bellow installed at the 90 O turning of a piping profile
The sketches below show a typical arrangement of 3 such applications (refer Figure-13, Figure-14 and Figure-15 below. In all the 3 cases the Bellow is capable of absorbing primarily axial movement along with a small amount of lateral movement. Since the axial thrust due to internal pressure is cancelled out between the two Bellows the system requires only Intermediate Anchors wherever applicable.
2.0 In-line Pressure Balanced Bellow
A typical arrangement of the above application is shown in the accompanying sketch (Figure-16) below. The above arrangement is typically employed in the situations where the bellow is required to be, installed on a long line without the possibility of installing the Main Anchors. The common balancing Bellow effectively nullifies the imbalance axial force of the 2 flow Bellows, at the same it allows the required deflection to be absorbed within the assembly.
The piping end anchors are, therefore required to be designed as intermediate anchors only.
3.0 Double Element Bellow installed at the 90 O turning of a piping profile for absorbing
large lateral movements
A typical arrangement of the above application is shown in the accompanying sketch Fig.17 below. Where large amount of lateral deflections, are involved a Pressure Balanced Universal Joint (with tie rod) may best suit to the situation. By a proper design of the tie rods to rotate around its attachment points it is possible to absorb the lateral deflection by the combination of 2 flow bellows where as the balancing bellow is subject to only axial deflection.