Pressure Balanced Expansion Joints
Pressure Balanced Expansion Joints are used in piping systems to absorb axial movement and/or lateral movement while absorbing the pressure thrust forces. This is achieved by means of restraining devices interconnecting the flow bellows with an opposed balancing bellows which is also subjected to the same line pressure.
These assemblies are used where anchors are difficult to install. The usual application for this type of expansion joint is on a turbine casing or other type of rotating equipment.The expansion joint is designed to overcome the reaction load due to internal pressure. It is also used where the application of a main anchor would be impractical and costly.
For example, in a pipeline with Axial Unrestrained Expansion Joints, the maximum force on the anchors occurs at the change of direction in the piping. Such an anchor is called a main anchor.
The forces exerted at this point are composed of the internal pressure acting over the effective area of the bellows plus the spring forces of the bellows due to movement.
On large expansion joints or those operating under extremely high pressure, the internal pressure force is considerable. To eliminate this thrust, a Pressure Balanced Expansion Joint should be considered.
Pressure Balanced Expansion Joints are used at changes in direction of the piping, while an In-Line Pressure Balanced Expansion Joint can be installed directly in a straght run of pipe. The forces required to compress and elongate the bellows are the only ones which are imposed on the anchors or adjacent equipment during the operation cycle. In summation, the total axial force required to compress or elongate the expansion joint is the sum of the forces required to move both bellows elements in the system.
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