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As the name implies, a hinged unit has one bellows, can be either non-equalizing or self-equalizing type, and is designed to permit angular rotation in only one plane by the use of a pair of hinges attached to the ends of the Expansion Joint. The hinge pins have a common axis perpendicular to the longitudinal center line of the bellows and located exactly in the center of the bellows length. Hinges must be designed to withstand the full pressure thrust load plus any other external forces, such as the weight of the piping, the wind loads, the force to deflect, and so forth, which will be applied. Hinged Expansion Joints should be used in pairs, or sets of three, to function properly.

The use of Hinged Expansion Joints not only reduces thrust loads applied to anchors, but may also permit installation of anchors at more advantageous locations. Their use, however, does not eliminate the installation of adequate alignment guides.


Swing Type Expansion Joint

A Swing Type Expansion Joint is a modification of the Hinged Expansion Joint, in which two bellows are attached to a common center nipple, and the outboard ends of the assembly are tied together by the use of two swing bars attached to the ends by hinge pins. This type of unit is designed to absorb lateral deflection and/or limited angular rotation in one plane only.


Gimbal Type Expansion Joint

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A Gimbal Type Expansion Joint is another variation of the Hinged Type Expansion Joint. However, this type unit Wlll absorb angular rotation in any plane. This is accomplished by the use of two pairs of half hinges, two half pairs attached to each end of the Expansion Joint with the pin ends attached 90 deg apart to a floating ring. This creates an Expansion Joint which will generate a cone of rotation equal to twice the allowable angular rotation of the bellows when one end of the joint is considered to be held fixed. The gimbal attachment, like the hinge attachment, must be designed to withstand the pressure thrust and all other externally applied loads. The use of two Gimbal Expansion Joints will absorb movement in multi-plane systems with some bending applied to the piping (A). Two Gimbal Expansion Joints used in conjunction with a Hinged Expansion Joint will permit the absorption of axial movement of two segments of piping With any angle of intersection (B).