FEXIBLE JOINT
Metal Expansion Joint, Functions and Types
Referring to the EJMA (Expansion Joint Manufacture Association), a Metal Expansion Joint is a device consisting of one or two bellows used to absorb dimensional changes caused by thermal expansion or contraction in a piping system, ducting, and vessel. Metal Expansion Joints can also sometimes be used to dampen vibrations. Other functions of Metal Expansion Joints include absorbing thermal movement, absorbing axial, lateral, angular & torsion movement, and withstanding pressure thrust.
There are various types of Metal Expansion Joints, including:
- Single Expansion Bellows: Having one bellows, capable of accommodating axial compression & expansion, lateral, and angular movement. This type of expansion joint cannot withstand internal pressure thrust, and the piping design must have a separate system to withstand pressure thrust.
Universal Expansion Bellows: Has two bellows connected to the spool pipe, capable of absorbing greater axial and lateral movements compared to a Single Expansion Joint. - Tied Expansion Bellows: Has one bellows, total length limited by a tie rod, which is acceptable for withstanding pressure thrust. When designed to withstand high pressure, it is usually not acceptable to absorb axial movement and only to absorb lateral movement. If this expansion joint is designed with 2 tie rods, it can also absorb angular movement.
- Double Tied Expansion Bellows: Consists of two bellows connected by a spool pipe, designed to absorb large lateral movements because it is provided with tie rods, this type of expansion joint is capable of withstanding pressure thrust, not designed to absorb axial movement, and if designed with more than two tie rods, angular movement is not acceptable.
- Hinge Expansion Bellows: Has a single bellows and its length is limited by an additional hinge mechanism which is very strong to withstand pressure thrust and can only absorb angular movement in one axis.
Hinge Universal Expansion Bellows: Consists of two bellows connected by a spool pipe, the ability to withstand pressure thrust is obtained from the hinge assembly pad on each bellows, and it is also only allowed to absorb angular movement in one axis.
Slotted Hinge Expansion Bellows: There are many variants of the "hinge" type, although they are designed to absorb angular movement, axial movement can be accepted because the hinge pin can move and there is a slot in the hinge construction design. The hinge structure can be designed to withstand full pressure thrust. - Multiply Exhaust Expansion Bellows: Designed to eliminate vibrations and specifically to relieve stresses from the turbocharger and isolate the exhaust from damage caused by vibrations.
- Gimbal Expansion Joint: Designed using a single bellows, it has the unique ability to withstand pressure thrust in the structure and can absorb angular movement in two axes. The structure consists of two hinge mechanisms.
- Gimbal Universal Expansion Bellows: Similar to a universal hinge. Designed with the ability to absorb large lateral movement in any plane.
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