DOUBLE EXPANSION JOINTS. 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. Rubber Expansion Joints differ in thet sense.

EXPANSION JOINTS. Any device containing one or more bellows used to absorb dimensional changes, such as those caused by thermal expansion or contraction of a pipeline, duct, or vessel.

GIMBAL EXPANSION JOINTS. A gimbal expansion joint is designed to permit angular rotation in any plane by the use of two pairs of hinges affixed to a common floating gimbal ring. The gimbal ring, hinges and pins must be designed to restrain the thrust of the expansion joint due to internal pressure and extraneous forces, where applicable. Consider the difference with concrete expansion joints or rubber expansion joints.

HINGED EXPANSION JOINT. A hinged expansion joint contains one bellows and is designed to permit angular rotation in one plane only, by the use of a pair of pins through hinge plates attached to the expansion joint ends. The hinges and hinge pins must be designed to restrain the thrust of the expansion joint due to internal pressure and extraneous forces, where applicable. Hinged expansion joints should be used in sets of two or three to function properly.

INTERNALLY GUIDED EXPANSION JOINT. An internally guided expansion joint is designed to provide axial guiding within the expansion joint by incorporating a heavy internal guide sleeve, with or without the use of bearing rings. The use of such expansion joints will assure installation without initial lateral or angular misalignment and can be installed in pipelines where reverse flow will be encountered. NOTE: The use of an internally guided expansion joint does not eliminate the necessity of using adequate external pipe guides.

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