Water Chamber Piston helps Counter Pipeline Thrust Forces

Flexible expansion joints have been used for many years with great success. They protect pipelines while crossing shear plains such as seismic faults...

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Flexible expansion joints have been used for many years with great success. They protect pipelines while crossing shear plains such as seismic faults, or provide protection of a structure’s pipeline system from either a seismic event or from gradual soil subsidence. They have, however, one drawback; they generate an axial imparting force while under pressure.

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While this imparting force or thrust is easy to accommodate with a pipeline that stretches across a rural landscape, it becomes cumbersome and costly in municipal settings to engineer and build a restraint system that can isolate these imparting thrusts without interfering with the purpose of the unit, which is to protect the pipeline from sudden or gradual movement generated by the environment and not the imparting thrust.

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The Force Balanced Flex-Tend® Flexible Expansion Joint, available from EBAA Iron, can accommodate pressure induced thrust forces by using an additional water chamber piston that acts in the equal and opposite direction of the imparting thrust and hence neutralizes the thrust forces. This neutralization of the pressure thrust allows designers to use flexible expansion joints in applications were bulky thrust blocks or other means of force restricting devices are not suitable.

With this new joint, a flexible expansion joint can now be placed into a system as easily as putting in a spool piece of pipe, rather than having to either dig out large areas for a thrust retaining walls and blocks, or by engineering costly lateral bracing that must be supported by structures that may not have been designed to take these forces.

Another concern is the addition of a needed flexible expansion joint to protect a pipeline system that serves a structure or uses a structure to make a crossing of some type. Most structures, such as water storage tanks, base isolated buildings, and bridges, were not designed to restrain the imparting thrust of a typical expansion joint, thus adding considerable cost in developing a restraint that can isolate the thrust without hampering the unit’s ability to move as needed to protect the pipeline. The Force Balanced Flex-Tend solves all these problems while giving the designer and owner the security of knowing his pipeline systems were protected from shear.

Municipalities are also experiencing a common theme in their maintenance and expansion programs for their water and wastewater needs: Congestion. The shear amount of buried utilities is already staggering and the future only holds more as cities grow and not only add more buried utilities but increase the size of the existing water and wastewater pipeline systems. In this existing and anticipated congestion, the Flex-Tend joint can protect pipeline systems from movement as would any other flexible expansion joint, but also can do so with a smaller and overall less expensive footprint, allowing room for the existing or future utilities that may one day join it.

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