Backing ring
Cylinder attached to cuff to provide reinforcment.
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Bellows cuff
Plain cylindrical end of bellows extending beyond convolutions.
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Bellows element
The flexible membrane of bellows unit, consisting of one or more convolutions.
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Bellows expansion joint
A device containing one or more bellows elements used to absorb movements such as those caused by thermal expansion or contraction of a pipe line duct, or vessel.
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Centre pipe or tube
A length of pipe connecting the bellows elements to form a double bellows unit, the length of which is critical to the stability of the assembly.
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Cold pull-up or cold draw
Extension of bellows from free length so that maximum movement of bellows can be utilised.
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Convolution
The smallest flexible unit of a bellows. The total movement of a bellows being proportinal to the number of convolutions.
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Directional anchor
A directional anchor, 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 considered. When designed for the purpose, a directional anchor may also function as a pipe guide. When designing a directional anchor, an effort should be made to minimise the friction between its moving or sliding parts, since this will reduce the loading on the pipe and equipment and ensure correct functioning of the anchor.
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Directional pipe guide
A directional pipe guide is a pipe alignment guide designed to permit the pipeline to move freely in one plane with a limited movement, movement in another plane. This type of guide is used in applications involving movements in more than one plane as in a 3 pin piping configuration.
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Extenal shroud
A device used to protect the external surface of the bellows from damage by foreign objects or mechanical damage.
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Flanged ends
The ends of a bellows unit with flanges for the purpose of booting the unit to the mating flanges of adjacent piping or equipment.
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Free length
The natural length of the assembly without cold pull or lateral offset.
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Hinge restraints
Fabricated assembly on single and double hinged or gimbal bellows unit which allows the bellows to angulate and containing the effect of pressure within the unit.
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Intermediate anchor
An intermediate anchor is one which divides a pipeline into individual expanding pipe sections. Such an anchor must be designed to withstand the forces and moments imposed upon it by each of the pipe sections to which it is attached. In the case of a pipe section containing a bellows these will consist of the forces and/or moments required to deflect the bellows unit plus the friction forces due to the pipe moving over its guides. The pressure thrust is absorbed by the main anchors or devices on the bellows unit such as limit rods, tie rods, hinge restraints, gimbal restraints etc.
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Internal sleeve
A device which minimises the detrimental effect of media flow through the bellows expansion joint.
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Lateral offset
Is the lateral, or shear, pre-setting of one connection to the other to enable the maximum movemnet to be obtained from the bellows unit.
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Limit stops or rods
Devices used to restrict the range of movement of bellows unit or its component parts. Various designs such as rods, bars or sliding stops may be used. It should be noted that to function properly aslimit stops these devices must be designed for full pressure loading, unless the load is absorbed by other structural devices.
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Main anchor
A main anchor is one installed at any of the following locations in a pipe system containing one or more bellows:
1. At a change in direction of flow
2. Between two bellows units of different size
3. At the entrance of a side branch into the main line if this branch contains a bellows
4. Where a shut-off or pressure-reducing valve is installed in a pipe run between two bellows units.
5. At a blind end of pipe
A main anchor must be designed to withstand the forces and moments imposed upon it by each of pipe sections to which it is attached. In case of pipe section containing an unrestrained bellows these will consist of the thrust due to pressure, the force required to deflect the bellows unit and the frictional force due to the pipe moving over its guides. Where a main anchor is installed at a change of direction of flow, the effect at the bend of the centrifugal thrust due to flow must be considered.
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Movement
Axial compression. The dimensional shortening of a bellows unit parallel to its longitudinal axis.
Axial extansion. The dimensional lengthening of a bellows unit parallel to its longitudinal axis.
Lateral deflection. The relative displacement of the two ends of a bellows unit perpendicular to its longitudinal axis. this is sometimes referred to as lateral off-set, lateral movements, parallel misalignment, direct shear, etc.
Angular rotation. The angular displacement of one bellows connecting face relative to the other from its straight line position. this is, not to be confused with torsional rotation about the longitudinal axis which must be avoided. Sometimes known as rotational or radial movement.
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Multyply
A bellows constructed from a multiple of tubes fitting closely inside each other.
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Pipe alingment guide
A pipe alignment guide ai a form of sleeve or framework attached to some rigid part ofthe installation which permits the pipeline to move freely in only one direction, i.e. along the axis of the pipe. Pipes alignment guides are designed primarily for use in applications involving axial movement only.
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Pressure thrust or end load
The force due to internal or external pressure acting on the bellows trying to extend or compress the bellows.
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Restraing ring
A device which fits closely into the crest or root of a convolution to reinforce the bellows against the effects of either internal or external pressure. Restraining rings are manufactured from solid round bar or heavy gauge tube in stainless steel or other suitable alloys.
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Spring rate
The force required to extend or compress the bellows unit length.
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Stability
The ability of a bellows to withstand internal pressure without distortion of the convolutions. This is sometimes known as squirm and can be compared with stru instability of long thin columns.
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The rods
Rods or bars for the purpose of restraining the bellows unit from the pressure thrust due to internal applied forces. Tie rods may also act s limit stops when provided with the necessary stops.
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Weld ends
The ends of a bellows unit equipped with pipe suitably bevelled for welding to adjacent piping or equipment.
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