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Expansion Joint Glossary of Terms
Fustar Bellows has adopted and encourages the use of the definitions of expansion joints and related equipment as published by The Expansion Joint Mnufactures Association. The definitions are taken,in part,from the Fifth Edition of the EJMA Standards.
ANCHOR,DIRECTIONAL. A directional or sliding anchor,is one which is designed to absorb loading in one direction while permitting motion in another.It may be either a main or intermediate anchor,depending upon the application involved. When designed for this purpose,a directional anchor may also function as a pipe alignment guide.In the design of a direction chchor,and effort should be made to minimize the friction between its moving or sliding parts,since this reduce the loading on the piping and equipment and insure proper functioning of the anchor.
ANCHOR,INTERMEDIATE. An intermediate anchor is one which must withstand the bellows thrust due to flow,spring forces,etc.,but not the thrust due to pressure.
ANCHOR,MAIN. A main anchor is one which must withstand the full bellows thrust due to pressure,flow,spring forces,etc.
BELLOWS. The flexible element of an expansion joint consisting of one or more convolutions and the end tangents,if any.
CONTROL ROD. Devices, usually in the form of rods or bars,attached to the expansion joint assembly whose primary function is to distribute movement between the two bellows of a universal expansion joint.Control rods are not designed to restain pressure thrusts.
CONVOLUION. The smallest flexible unit of a bellows.The total movement capacity of a bellows is proportional to the number of convolutions.
COVER. A device used to provide limited protection of the exterior surface of the bellows of an expansion joint from foreign objects or mechanical damage. A cover is sometimes referred to as a shroud.
DOUBLE EXPANSION JOINT. A double expansion joint consists of two bellows joined by a common connector which is anchored to some rigid part on the installation by means of an anchor base.The anchor base may be attached to the common connector either at installation or at time of manufacture.Each bellows acts as a single expansion joint and absorbs the movement of the pipe section in which it is installed,independently of the other bellows.Double expansion joints should not be confused with universal expansion joints.
EQUALIZING AND REINFORCING RING.Devices used on some expansion joints fitting snugly in the roots of the convolutions.The primary purpose of these deveices is to reinforce the bellows against internal pressure.Equalizing rings are made of case iron,carbon steel,stainless steel or other suitable alloys and are approximately”T” shaped in cross section. Reinforceing rings are fabricated from tubing or solid round bars of carbon steel,stainless steel, or other suitable alloys.