Axial and Lateral Movements on Universal Expansion Joints
The universal expansion joint consists of two bellows separated by a pipe section or spool. The primary purpose of this arrangement is to have a unit which will accept large amounts of lateral deflection. The amount of lateral deflection they can accept is a function of the amount of angulation each bellows can absorb and the distance between the bellows. For a given bellows element, the amount of lateral deflection capability can be increased or decreased by simply changing the length of the center spool. In our Expansion Joint Catalog, three standard overall lengths are given with their lateral movement capability. If the piping problem requires greater capability, then the overall length can be increased to suit.
Since deflections are the result of piping thermal expansion, and universal expansion joints are usually long, our units are designed so that the thermal expansion within the tie rods is absorbed as axial compression by the two bellows elements. In this way, the overall length of the unit does not change when the piping is in service. The standard units in our Expansion Joint Catalog have all been designed to accept the thermal expansion of their length within the tie rods when the temperature is up to the design temperature shown.
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Universal expansion joints are usually supplied with tie rods. Tie rods connect the ends of the unit to each other and restrain the pressure thrust load. This unit cannot accept any externally applied axial deflections. The thermal expansion of the distance between the tie rods —within the expansion joint— will be taken by the bellows element, as described above. The tie rods usually come in sets of two or more, equally distributed around the circumference of the expansion joint. When only two are provided, 180 degrees apart, the expansion joint is free to bend, or deflect angularly, as well as laterally. With three or more tie rods, since rods are loaded equally by the pressure thrust, only lateral deflections are possible without significant forces being applied by the adjacent piping.
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