shall conform with ASTM C 1071, Type I or II. Provide suitable
duct-transition sections for connection to ductwork.
2.2.6.1
Net Noise Reduction Values
Conform with the following:
Sound Pressure Level dB
(Reference Sound Power at 10-12 Watts)
Octave Pass Band
2
3
4
5
6
7
125
250
500
1000
2000
4000
Noise Reduction (dB)
11
16
19
30
40
32
2.2.6.2
Factory-Fabricated Sound Attenuators (Traps)
Provide sound attenuators constructed of galvanized sheet steel casing and
sound absorbing material covered with an internal perforated zinc-coated
metal liner. Sound absorbing materials shall be faced with glass fiber
cloth and hold in compression to prevent settling. The internal perforated
metal liner shall be not less than 24 gage, with perforations not larger
than 4 mm 5/32 inch in diameter providing a net open area not less than 22
percent of the surface. Attenuators shall be insulated to prevent
sweating. Attenuators shall be acoustically tested with metal duct inlet
and outlet sections while under the rated air flow conditions. Noise
reduction data shall include effects of flanking paths and vibration
transmission.
2.2.6.3
Factory-Fabricated Sound-Attenuator Ducts
Sound-attenuator ducts may be provided in lieu of sound attenuators
(traps). Comply with requirements specified herein for sound attenuators.
Construct each double-walled duct and fitting of an outer zinc-coated metal
pressure shell with 25 mm one inch thick acoustical blanket insulation and
an internal perforated zinc-coated metal liner. Install sufficient length
certification from manufacturer stating that the sound reduction value
specified will be obtained within the length of duct run provided. The
internal perforated zinc-coated metal liner shall be not less than 24 gage,
unless ribbed, then not less than 28 gage for the duct liner and not less
than 26 gage for the fitting liner with perforations not larger than 2.40 mm
3/32 inch diameter. Seal joints as specified in paragraph entitled "Round
and Oval Ducts." [Rigid molded fiber-glass inserts with the air side
surface [PVC] [neoprene]-coated, when complying with requirements specified
herein, may be used in lieu of internal perforated zinc-coated metal liner.]
2.2.7
Valve shall be
the standard product of duct and fitting manufacturer.
2.2.8
Air Valves
Provide [manual] [or] [normally open, automatic] air valves for pressure
reducing or volume control on single duct systems. [Provide manufacturer's
standard linkage and motor mounted platform to accommodate pneumatic
actuators.] Construct valves of corrosion-resistant materials. Frame,
links, and levers may be of zinc-coated steel. Vanes, pivots, hinges or
SECTION 15810N
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