RECOMMENDED SPECIFICATIONS FOR SPIRAL DUCT AND FITTINGS IN LOW PRESSURE SYSTEMS SEMCO PRODUCT DESIGNATIONS: SL95P AND SL95N
I. GENERAL
All round and/or flat oval spiral duct and fittings shall be manufactured by a company whose primary business is the manufacture of spiral duct and fittings and who has been in business for at least ten (10) years. All spiral duct and fittings shall be manufactured by the same firm and shall be as shown on the contract drawings.
All spiral duct and fittings shall be manufactured from G-60 galvanized steel meeting ASTM A924 and A653 requirements.
II. CONSTRUCTION
A. Branch connections shall be made with 90º conical and 45º straight taps as shown on the drawings. All branch connections shall be made as a separate fitting. Factory or field installation of taps into spiral duct shall not be allowed without written approval of the engineer. Manufacturers published individual fitting performances shall be on file with the design engineer ten (10) days prior to bid.
B. 90º and 45º elbows in diameters 3" round through 12" round shall be stamped or pleated elbows. All other elbows shall be of the gored type, fabricated in accordance with the following:
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CENTERLINE RADIUS |
ELBOWS |
< 30º |
37º - 71º |
72º - 90º |
< 1000 fpm |
1.0 x diameter |
2 gores |
2 gores |
3 gores |
1001-1500 fpm |
1.0 x diameter |
2 gores |
3 gores |
4 gores |
> 1500 fpm |
1.5 x diameter |
2 gores |
3 gores |
5 gores |
Where it is necessary to use two-piece mitered elbows, they shall have a minimum number of vanes in accordance with the following:
| DUCT DIAMETER |
NUMBER OF VANES |
| 3" thru 9" |
2 |
| 10" thru 20" |
3 |
| 21" and up |
5 |
C. Circumferential and longitudinal seams of all fittings shall be a continuous weld or spot welded and sealed with mastic. All welds shall be painted to prevent corrosion.
D. All field joints for round duct up to and including 36" diameter and oval duct up to and including 41” major axis shall be made with a 2" slip-fit or slip coupling. Diameters 38" round and larger shall be provided with AccuFlange, or equal, flanged connections. AccuFlange, or equal, flanged connections may also be used in lieu of slip connections on smaller sizes.
Access doors shall be supplied by the duct manufacturer at all fire and/or smoke dampers.
All flanges and access doors shall be factory installed. Shipments of loose flanges, access doors, or taps for field installation into spiral duct will not be allowed.
III. DOUBLE WALL DUCT
Where indicated on the drawings, double wall, acoustically insulated round duct shall be supplied.
Double wall duct shall be constructed of an outer shell, a 1" thick layer of fiberglass insulation and an inner metal liner. Insulation shall have a thermal conductivity "K" factor of .26 BTU/hr/sq. ft./ºF or less.
The inner metal liner for all spiral and longitudinal seam duct shall be perforated metal. All fittings from fan discharge to a point where 35 lineal feet of spiral duct has been used shall have a perforated metal liner. All other fittings shall have a solid metal liner, which may be one even gauge lighter than that shown for perforated liners.
IV. METAL GAUGES
A. Metal gauges for single wall round duct shall be as follows:
1. Round Duct with Maximum 2" W.G. Positive Static Pressure
DIAMETER |
SPIRAL DUCT |
LONGITUDINAL SEAM DUCT |
3" thru 26" |
26 |
24 |
28" thru 36" |
24 |
22 |
38" thru 50" |
22 |
20 |
52" thru 60" |
20 |
18 |
62" thru 78" |
18 |
16 |
DIAMETER |
SPIRAL DUCT |
LONGITUDINAL SEAM DUCT |
3" thru 17" |
26 |
24 |
18" thru 20" |
24 |
22 |
21" thru 22" |
24 |
20 |
24" thru 26" |
22 |
20 |
28" thru 30" |
22 |
18 |
32" thru 34" |
20 |
18 |
36" thru 42" |
20 |
16 |
44" thru 48" |
20 |
18 |
50" thru 60" |
18 |
18 |
- Reinforce with 1¼" x 1¼" x 3/16" girth rings every 4 ft.
- When companion flange joints are used as reinforcement,
- 44" to 48" diameter shall be 2" x 2" x 3/16"
- 50" to 60" diameter shall be 2½ x 2½ x 3/16"
2. Round Duct with Maximum -2" W.G. Negative Static Pressure
B. Metal gauges for dual wall round duct shall be as follows:
1. Round Duct with Maximum 2" W.G. Positive Static Pressure
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SPIRAL DUCT |
LONGITUDINAL SEAM DUCT |
DIAMETER |
SHELL |
PERFORATED LINER |
SHELL |
PERFORATED LINER |
3" thru 8" |
26 |
26(non-ribbed) |
24 |
24 |
9" thru 24" |
26 |
26(ribbed) |
24 |
24 |
26" thru 34" |
24 |
26(ribbed) |
22 |
24 |
36" thru 48" |
22 |
26(ribbed) |
20 |
22 |
50" thru 58" |
20 |
26(ribbed) |
18 |
22 |
60" thru 62" |
18 |
26(ribbed) |
16 |
22 |
62" thru 76" |
18 |
22(non-ribbed) |
16 |
22 |
2. Round Duct with Maximum -2" W.G. Negative Static Pressure
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SPIRAL DUCT |
LONGITUDINAL SEAM DUCT |
DIAMETER |
SHELL |
PERFORATED LINER |
SHELL |
PERFORATED LINER |
3" thru 8" |
26 |
26(non-ribbed) |
24 |
24 |
9" thru 15" |
26 |
26(ribbed) |
24 |
24 |
16" thru 20" |
24 |
26(ribbed) |
22 |
24 |
22" thru 24" |
22 |
26(ribbed) |
20 |
24 |
26"thru 28" |
22 |
26(ribbed) |
18 |
24 |
30" thru 32" |
20 |
26(ribbed) |
18 |
24 |
34" thru 40" |
20 |
22(ribbed) |
16 |
22 |
42" thru 46" |
20 |
22(non-ribbed) |
18 |
22 |
48" thru 58" |
18 |
22(non-ribbed) |
18 |
22 |
- Reinforce with 1" x 1" x 1/8" girth rings every 6 ft.
- When companion flange joints are used as reinforcement,
- 44" to 48" diameter shall be 2" x 2" x 3/16"
- 50" to 60" diameter shall be 2½ x 2½ x 3/16"
V. MANUFACTURERS
All spiral duct and fittings shall be as manufactured by SEMCO Incorporated or approved equal.
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