Elbow pressure balanced expansion joints


Elbow pressure balanced expansion joints

An elbow pressure balanced expansion joints is designed to absorb externally imposed axial movement without imposing pressure loading on the system. This is accomplished by using two bellows both at line pressure tied together and acting in opposite directions. It is used where pressure loading on the piping or equipment is not acceptable.

While the joint balances out the pressure forces, the force required to move the joint itself is not balanced. Both the flow bellows and balancing bellows must be compressed or elongated in operation and the combined axial spring force acts on the piping or equipment. Since the forces needed to move the bellows of this joints are of low magnitude these are usually not objectionable.


These expansion joints are usually installed at change of direction. They may also be designed for in line operation.The complexity of the Elbow Pressure balanced Expansion Joint makes it an Expensive Unit . It’s use can be justified economically only in those cases where the problems created by the pressure loading would be even more expensive

This joint is used in applications where the pressure thrust loading on the anchors or the adjacent equipment is considered excessive. It is one type of the tied expansion joints that absorbs axial motion while restraining the pressure thrust. Due to this unique ability of these expansion joints , they provide ideal solution where a change in the direction of the piping occurs.

The design of the elbow joint uses flow and balancing bellows that are interconnected by the use of tie devices. The balancing bellows is subjected to the same line pressure as the flow bellows. As the flow bellows compresses, the tie devices make the balancing bellows extend by an equal amount. Since there is no change in the volume of the system, the pressure forces remain in balance.


When the flow bellows deflect laterally there is no volume change therefore the balancing bellows need only contain the proper number of convolutions required to absorb the axial movement of the system.The axial force to be considered in the design is only the force required to move the line bellows and balancing bellows.

The most common application of this elbow pressure balanced expansion joint is adjacent to a piece of equipment such as turbine or pump whose allowable nozzle loads compel to eliminate the pressure thrust.

In case of single Elbow joints when it is subjected to both axial and lateral movements both the anchors at the end of the piping run and the one on the machine are intermediate anchors and only directional guiding is required. By proper design the guide directly above the equipment can be made to absorb the axial movement forces of the expansion joint without imposing these on the equipment. The only force imposed on the equipment is the force which is required to deflect the expansion joint laterally.

When large amount of lateral movement is required or when the lateral forces must be held to a minimum an elbow pressure balanced universal expansion joint is used. In this design two bellows are used in the flow end of the expansion joint and a single bellows in the balancing end . The lateral movement is taken by the flow bellows in the same manner as a tied universal expansion joints.


Types of Elbow pressure balanced expansion joints

Double Universal Elbow Pressure Balanced Expansion Joint

Double Universal Elbow Pressure Balanced Expansion Joint

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Product Description


  • Absorbs axial and lateral movements while retaining the pressure thrust.
  • Eliminates main anchors.
  • Minimum guiding required.


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