2.6
DUCTWORK COMPONENTS
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NOTE: Provide duct access doors at regular
intervals to facilitate the cleaning of duct systems
for applications requiring clean air supplies, such
as hospitals, laboratories, electronics servicing
and similar activities.
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2.6.1
General
Duct shall be constructed of [galvanized] [stainless steel] sheets of the
minimum gauge thickness for ducts as required in [SMACNA Rectangle Duct
Const] [SMACNA Rnd Duct Const]. Ducts shall be constructed and sealed in
accordance with [SMACNA Rectangle Duct Const] [SMACNA Rnd Duct Const] for a
negative pressure of [_____] Pa inch water gauge static pressure. Ducts,
unless otherwise approved, shall be round with longitudinal lock seam and
conform to the dimensions indicated. Ducts shall be straight and smooth on
the inside with airtight joints. Where ducts with crimped ends are used to
make up joints, the joints shall have crimp and bead. The bead shall
provide a rigid stop for the mating open end to seat against. Steel spiral
wound duct is not acceptable.
2.6.2
Fittings
Reducing fittings shall have a minimum of 1 mm increase in diameter per 8
mm 1 inch increase in diameter per 8 inches in length. Elbows shall have a
centerline radius of not less than 1-1/2 times the diameter. Branches
shall stub into mains at main expansion points at an angle of not more than
30 degrees with the centerline of the main duct in the direction of air
flow, unless otherwise indicated or approved. Where riser ducts with
single or multiple inlets are indicated, the riser duct shall connect into
the bottom of the main duct at an angle as specified for branches. Where
flexible connections connect to the main duct, the duct branch takeoff or
stub shall be braced with approved metal straps or members.
2.6.3
Cleanout
Cleanout shall be provided on the end of the main ductwork opposite the end
of the fan suction connection. The cleanout opening shall be sized to the
approximate inside area of the duct. Removable airtight caps or flange
type covers of minimum gauge thickness as the main duct shall be provided.
Other cleanout openings shall be provided where indicated.
2.6.4
Apparatus Connections
Where sheet metal connections are made to fan suction and discharge, or
where ducts of dissimilar metals are connected, an approved noncombustible
flexible connection approximately 150 mm 6 inches wide shall be installed
and securely fastened by zinc-coated steel clinch-type draw bands for round
ducts. For rectangular ducts the flexible connections locked to metal
collars shall be installed using normal duct construction methods.
2.6.5
Duct Test Holes
Test holes with covers shall be provided where indicated, directed, or
where necessary in ducts and plenums for using Pitot tubes for taking air
measurements to balance the air systems.
SECTION 15940A
Page 10
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