-––
[
FUNCTION OF FABRIC EXPANSION
JOINT COMPONENTS]
–-–
A
D
B
C
H
G
F
E
A. GAS SEAL MEMBRANE
particles which may be present in the gas stream. A liner is
The gas seal membrane is intended to withstand system
also used to reduce flutter of the fabric element caused by
pressure and be resistant to chemical attack from the
turbulence, to help control the accumulation of dust or ash
interior and the exterior. The gas seal must also have the
in the expansion joint cavity, and to reduce the
flexibility to absorb thermal movements. Depending on
temperature of the flexible element.
system temperature, it may require additional thermal
protection.
F. ACCUMULATION BAG
An accumulation bag is intended to deter flyash from
B. INSULATING LAYERS
building up in the expansion joint cavity. It is typically
The insulating layers provide a thermal barrier to ensure that
used, in conjunction with a liner, in duct runs from boilers
the inside surface temperature of the gas seal membrane
to air clean-up equipment such as precipitators, scrubbers
does not exceed its maximum service temperature. The
and bag houses, or whenever high amounts of dust or ash
insulating layer can also reduce condensation caused by the
are present in the gas. A flyash barrier must be capable of
gas stream coming in contact with the “cool” surface of an
retaining its strength and flexibility while being exposed to
uninsulated gas seal membrane.
maximum system temperatures and media.
C. INSULATING RETAINER LAYER
G. FABRIC ATTACHMENT FLANGES
This layer is provided to keep the insulating layers in place
Fabric attachment flanges are required to connect the
in order to maintain thermal integrity. The retaining layer
must be capable of withstanding gas stream temperatures
flexible element to the ductwork. Properly designed,
and must be chemically compatible with system media.
they can be attached directly to the duct work and thus
eliminate the necessity for an adjoining duct flange.
D. BACK UP BARS
Flanges can be designed with a “landing bar” duct
Back up bars, positioned at the flange attachment, use
attachment which allows some installation misalignment
clamping pressure to create the fabric-to-duct seal and
without affecting the flexible element. The flanges establish
restrain the fabric when it is subjected to the system
the stand off height of the fabric, which is necessary to
pressure. The thickness and width of the back up bars
achieve thermal integrity during all movement conditions.
should be sufficient to perform this function with the bolt
The edges of the flanges in contact with the gas seal
spacing being used. The edges of the back up bars should
membrane should also have a radius to prevent damage.
have a radius to preclude cutting of the fabric.
H. GASKET
E. METAL LINER OR BAFFLE Single ply fluoroplastic and fluoroelastoplastic belt designs
A liner is designed to protect the gas seal membrane and such as Ultrachem materials require flexible chemically
insulating layers of the flexible element from abrasive inert gaskets.
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