Sealing a fabric duct

[kapo84]

I am testing a 150'long 4" dia fabric duct carrying air which enters the duct at ~ 5 psi. Due to the seam along the hose and the losses between duct connections (one every 50 ft) I am losing an incredible amount of pressure and airflow.

I have recently ordered some "Vyna Bond" to seal the seam on the duct. I will try and tape the hose connections as well.

Has anyone had experience sealing a seam? Any other suggestions on how to seal the duct? Any long term suggestions on fabricating a duct which is lightweight and flexible (preferably fabric) yet well sealed?

Thanks in advance.

 

[RossABQ]

Is this really 4-inch diameter? It is customarily much larger in HVAC applications.

Is pressure really 5 psi? or is it 5 inches w.c.? 5 psi is way past the rated pressure of any of the fabric ducts I am familiar with for HVAC purposes.

 

[kapo84]

We aren't your standard HVAC company -- For this specific application a 4" duct is ideal -- and yes we're pushing 5 psi (~ 140 inches w.c.). The duct was built specifically for this purpose --

Thanks.

 

[RossABQ]

Wouldn't fire hose be the way to go?? ;-) It's seamless... Seriously, I'd check with those kinds of folks, I have seen lightweight hoses that can be rolled up very compactly that are rated for typical 50 - 75 psi without any (water) leakage. Are there many outlets required along the length?

 

[Compositepro]

"Fabric" is very permeable unless it is coated with something. The seam will be the least of your problems. So what are you actually using? The seam seal has to be compatible with the fabric coating, not the fabric.

 

[kapo84]

RossABQ -- I had never thought of fire hose... why not? It may be a little heavy but we'll see. We are simply using the hose to transport the air so there is only one outlet.

Compositepro -- I agree that the seam will be a portion of the problem. I guess the Vyna Bond will help me seal off the seam so I can go to the next major problem (Good thing I bought 5 gallons right?).

To be honest I don't know if it is coated or not. Similar ducts are PVC coated. This particular duct has a layer or two of insulation between the air and the outer duct layer.

 

[berkshire]

Check with aircraft ground support companies for preconditioned air hoses.
Or is this what you are building?

B.E.

 

[kapo84]

I have checked with a number of aircraft ground support companies. They have a number of "welded" hoses but their weight is more than I'd like. Their fabric hoses have the same leakage problem as this one does.

I may be asking for too much -- Regardless, it has been helpful to hear other's ideas.

Thanks!