Where do you find 7 inch PVC pipe?

[Aaron Rowland]

Nice. D'Arcy- Weisbach surface roughness effect. The friction coefficient of PVC is .0015-.007 compared to galvanized steel at .15 . I did some numbers at one time but not sure what the effect of all the seams ,especially spiral wound are. If you have two ducts 6" in diameter, one PVC, one spiral gal steel at a velocity of lets say about 3500 FPM what would be the CFM difference between the two. Not stated properly but I think you can figure out what I'm trying to obtain.

[Dan West02]

Hi,

I have had a problem finding 7 inch PVC pipe for ducting. I have found 6 inch and 8 inch but no 7 inch. I have tried 3 irrigation supply places. Any ideas?

Thanks,
Joe

In my previous life (before retirement) I spent many years designing extrusion tooling for PVC pipe. The company I worked for is one of the largest in the US. I designed tooling for pipe as small as 1/2" (nominal) up to 32" (used for sewer mains). As others have said, 7" is just not made in PVC.

[Dan Hintz]

Nice. D'Arcy- Weisbach surface roughness effect. The friction coefficient of PVC is .0015-.007 compared to galvanized steel at .15 .

<chuckle> The boundary conditions for a 6" pipe are so tichy comparing PVC to galvanized steel it's not even worth mentioning. Here's a convenient little calculator... do a 20' run at 6" with steel and it barely regsters to 3 sig figs:
http://www.engineeringtoolbox.com/da...ion-d_646.html

I'd essentially ignore seams, too... not worth the extra paper to calculate the extremely minor reduction. Spiral wound is more of a problem...

[David Hostetler]

Simply put, you don't. The only realistic option in 7" is steel duct.

[Ole Anderson]

I am having trouble understanding the facination with using PVC for duct when galvanized is the norm in the industry and is economical and easily available in any size and configuration you need.

[Ole Anderson]

Now having thought about it more, could be that woodworkers are comfortable working with PVC as it cuts and glues like wood.