How are shops cutting Taps into Double Wall Spiral Pipe?
We’ve introduced the Trumpf Profile Nibbler as a means of cutting the taps in Double Wall Spiral Pipe. At D&N Ductworks in Miami, they offer up another means of doing this: with a Hand Held Plasma Torch.
Footnote: Miami Dade Codes are, along with City of Los Ángeles, among the most particular in the country. Double Wall with Solid Inner Wall is a required specification for Schools and Hospitals. While this does not improve the Acoustical value, it does improve the Thermal Values dramatically and that’s their intention.
David Frias, the owner at D&N Duct, allowed us to find out more about how they do this.
First step is running Spiral Pipe to the Double Wall diameter requested. Keep in mind it’s based on airflow. That means that the fabrication of 16” Double Wall Spiral begins with running a 5.394” into a 16” diameter single wall Spiral.
After that is where the fun starts…
- Liner wrapped around perforated inner wall, held together with aluminum tape
- Wrapped with insulation before sliding into the solid section to the right of it
Double Wall Spiral will have two diameters—the larger of the two diameters will be the “outer wall” and the one that’s visible. The smaller of the two diameters is the Inner Wall. This inner wall is then wrapped with a 1” Insulation, often Unfaced Duct Liner like the popular JM 1” x 60” x 100 ft 1.5 lb Spin Glas.
Perforated
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- If the engineer is specifying Double Wall for Acoustics, the spec is to use a Perf Inner wall
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- Section of Double Wall Spiral Duct with unfaced liner insulation, 5.394″ perforated inner wall and AccuFlange double wall connection
Solid
- If the engineer is specifying for Thermals, they might choose solid inner wall
Code requires a Mylar film to be wrapped around the Perforated spiral before the Insulation is wrapped around it. This is to keep the fibers from poking thru the 3/32” round holes and into the Airstream.
Step 1. Cut Outer Wall (exterior wall) of Spiral Pipe and peel away the Spin Glas
Step 2. Cut Inner Wall of spiral Pipe but leave a skeleton to retain the structural integrity
- Solid Inner Wall
Step 3. Using Duct Butter or Duct Sealant, paint the edges so that the Spin Glas around Inner wall does not work it’s way down into airstream
- D&N uses Ductmate’s EVERseal, a gray colored fiber free water based duct sealant
Step 4. D&N attaches the ECONOflange / AccuFlange double wall connections so that the contractor can easily hang the duct in the air. D&N happens to make their own Flanges; other shops buy these out from Ductmate or Spinfinity
