A. Gas Seal Membrane
The gas seal membrane is intended to withstand system pressure and be resistant to chemical attack from the interior and the exterior. The gas seal must also have the flexibility to absorb thermal movements. Depending on system temperature, it may require additional thermal protection.
B. Insulating Layers
The insulating layers provide a thermal barrier to ensure that the inside surface temperature of the gas seal membrane does not exceed its maximum service temperature. The insulating layer can also reduce condensation caused by the gas stream coming in contact with the "cool" surface of an uninsulated gas seal membrane.
C. Insulating Retainer Layer
This layer is provided to keep the insulating layers in place in order to maintain thermal integrity. The retaining layer must be capable of withstanding gas stream temperatures and must be chemically compatible with system media.
D. Back up Bars
Back up bars, positioned at the flange attachment, use clamping pressure to create the fabric-to-duct seal and restrain the fabric when it is subjected to the system pressure. The thickness and width of the back up bars should be sufficient to perform this function with the bolt spacing being used. The edges of the back up bars should have a radius to preclude cutting of the fabric.
E. Metal Liner or Baffle
A liner is designed to protect the gas seal membrane and insulating layers of the flexible element from abrasive particles which may be present in the gas stream. A liner is also used to reduce flutter of the fabric element caused by turbulence, to help control the accumulation of dust or ash in the expansion joint cavity, and to reduce the temperature of the flexible element.
F. Accumulation Bag
An accumulation bag is intended to deter flyash from building up in the expansion joint cavity. It is typically used, in conjunction with a liner, in duct runs from boilers to air clean-up equipment such as precipitators, scrubbers and bag houses, or whenever high amounts of dust or ash are present in the gas. A flyash barrier must be capable of retaining its strength and flexibility while being exposed to maximum system temperatures and media.
G. Fabric Attachment Flanges
Fabric attachment flanges are required to connect the flexible element to the ductwork. Properly designed, they can be attached directly to the duct work and thus eliminate the necessity for an adjoining duct flange. Flanges can be designed with a "landing bar" duct attachment which allows some installation misalignment without affecting the flexible element. The flanges establish the stand off height of the fabric, which is necessary to achieve thermal integrity during all movement conditions. The edges of the flanges in contact with the gas seal membrane should also have a radius to prevent damage.
H. Gasket
Single ply fluoroplastic and fluoroelastoplastic belt designs such as Ultrachem materials require flexible chemically inert gaskets.
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The system thermal expansions are the differential expansion/contraction of operating and/or excursion temperatures and the minimum ambient temperature during installation and shutdowns. The expansion joint engineer uses these movements and temperatures to select the proper material and design for each expansion joint. Senior Flexonics Pathway's nonmetallic expansion joints frequently can handle combined axial, lateral, angular and torsional movements in a single assembly.
The expansion joint locations can often be optimized, reducing the total number required. Consideration should be given for accessibility and belt replacement, for new ducting systems, it may be more economical for the duct fabricator to provide a portion of the expansion joint frame.
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Lateral Movement - The amount of duct movement occurring in either or both of the two perpendicular planes to the longitudinal axis of the duct, which moves the expansion joint flanges out of alignment.
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Axial Compression/Extension - The dimensional shortening (compression) or lengthening (extension) of the expansion joint face-to-face dimension parallel to it's longitudinal axis.
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Torsional Deflection - The amount of twisting movement (in degrees) occurring in the perpendicular planes to the longitudinal axis of the duct system.
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Angular Deflection - The amount of rotation (in degrees) of the duct system which flexes the expansion joint flanges out of parallel position with each other.
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Typical Movement Capabilities
| Single Layer |
Axial Compression |
2" (51mm) |
3" (76mm) |
4" (102mm) |
| Fabric Element |
Axial Extension |
1/2" (13mm) |
1/2" (13mm) |
1/2" (13mm) |
| (Non-concurrent) |
Lateral |
1" (25mm) |
1 1/2" (38mm) |
2" (51mm) |
| Composite Belt |
Axial Compression |
1" (25mm) |
1 1/2" (38mm) |
2" (51mm) |
| Axial Extension |
1/4" (6mm) |
1/4" (6mm) |
1/4" (6mm) |
| (Concurrent) |
Lateral |
1/2" (13mm) |
3/4" (19mm) |
1" (25mm) |
| Integrally Flanged |
Axial Compression |
2" (51mm) |
3" (76mm) |
4" (102mm) |
| Single Layer |
Axial Extension |
1/2" (13mm) |
1/2" (13mm) |
1/2" (13mm) |
| (Concurrent) |
Lateral |
1" (25mm) |
1 1/2" (38mm) |
2" (51mm) |
Notes:
1. Special considerations must be made when movements exceed those listed above or differ from nonconcurrent or concurrent ratings. Consult with factory for these applications.
2. Breaching tolerances: Axial extension 1/4" (6mm), axial compression 1/2" (13mm), lateral + 1/4" (6mm). Exceeding these tolerances will affect movement capabilities.
3. Lateral movement exceeding 3" (76mm) should utilize cold lateral offset (preset) to reduce the relative belt movement.
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Breach Opening Face-To_Face
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