Where do you find 7 inch PVC pipe?

[Joe Koren]

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

[Jim O'Dell]

4" and bigger only comes in 2" increments from what I've seen. To use 7" pipe, you'll probably have to go to steel. Jim.

[Lopaka Garcia]

Did you see if they make a reducer for the 8" pipe?

[Ted Jay]

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
Your not going to find 7" pvc pipe. If you do it would have been special order for something and it will be "mucho" expensive!!!!!
Herre is link for pvc online, make you ductwork out of clear pvc so you can watch your "shavings go bye":D
http://www.savko.com/portal/clearpvc.asp

later,
Ted

[Alan Schaffter]

Your not going to find 7" pvc pipe. If you do it would have been special order for something and it will be "mucho" expensive!!!!!
Herre is link for pvc online, make you ductwork out of clear pvc so you can watch your "shavings go bye":D
http://www.savko.com/portal/clearpvc.asp

later,
Ted

Gee, lets see, clear 6" is sold in 5' increments and goes for $21.95 a foot- hmmm:confused: Yikes!!!!!:eek: :eek: :eek:

[Greg Koch]

Over $100 for a 5' piece of plastic pipe?.... Come on...who's gonna buy that?

[Lee DeRaud]

Over $100 for a 5' piece of plastic pipe?.... Come on...who's gonna buy that?The specs for it talk about resistance to chemicals and biological contamination: I'm guessing "dust collector piping" was not high on the list of intended applications.:p

[Greg Koch]

I'm guessing "dust collector piping" was not high on the list of intended applications.:p

I think that's a fair statement!

ROF ROF ROF

[Kyle Kraft]

5 foot length of clear pipe...$100

Watching the blur of your sawdust being whisked away...priceless!

[Bob Deroeck]

Hi,

When calculating pressure drop in the ducting it's important to recognize two factors.

The first is that pressure drop is a function of the duct ID to the 5th power (per Darcy Formula) . This means that a 6" ID piece of duct will have 2.1 times the pressure drop of a 7" ID piece of duct of the same length for the same flow rate. A 4" ID piece of duct will have 7.6 times the pressure drop as the same length of 6" pipe for the same flow rate. There is a good reason that so many members are recommending carrying 6" pipe all the way to the machine instead of using a relatively short length of 4" pipe for the connection to the machine.

The second is that the fittings have a major impact on the pressure drop relative to the straight duct in the system. For example for 6" duct a 45 degree elbow is the equivalent of 8' of straight duct. By comparison a 6" standard 90 degree elbow is 16 equivalent feet (E') and a 6" long radius 90 degree elbow is 11 E'.

What does this all means in practice?

If the longest run in the shop is 40 linear feet, 6" duct is used all the way to the machine and there are two 45 degree branches and two 90 degree short radius elbows, the total E' is 40 + 2 x 8 +2 x 16 +88 E'. In this case over half of the pressure drop is in the fittings. If there is no reduction in duct size from cyclone to machine, the pressure drop of 6" duct would be 2.1 times that of 7" duct.

But this assumes you can get 7" duct and 7" fittings. My understanding is that steel duct is available in 7" size, but PVC is only available in 6" or 8" size. If this is correct, then there is a fairly large incentive to use 7" steel duct instead of 6" PVC duct to reduce the pressure drop in the ducting. In reality you won't see at 52% reduction in pressure drop if using 6" PVC, because the higher pressure drop in the 6" PVC will result in a lower CFM of air flow as you ride down the fan curve. And, as the CFM goes down the pressure drop in the duct does down. The effect of flow rate on pressure drop is significant but far less so than that of duct ID. According to the Darcy formula, the pressure drop is a function of the flow rate squared. But, the net effect of using 6" duct instead of 7" duct is a significant reduction in CFM at the machine. Since a "target" CFM at the machine is the starting point of any dust collection system design, you don't want to fall short of this target because of ducting that is either too small in diameter or has too many fitting.

I also want to emphasize the importance of the type of 90 degree elbow that you use. Try to use long radius 90 degree elbows, instead of standard elbows, if a 45 degree elbow or Y fitting cannot be used.

I'm still in the process of designing a dust collector system for my shop. I prefer plastic over steel for ducting, but don't like the high pressure drop of 6" PVC. I'm toying with the idea of making my own 7" duct out of fiberglass. And, fiberglass fittings could be made in any size and shape. For example a 90 degree elbow could be made in a very long radius (say a 3-to-1 sweep) resulting in a pressure drop lower than a standard 45 degree elbow. I guess it all comes down to how much do I want to work on my shop vs how much I want to do woodworking in my shop.

Bob

[Larry Edgerton]

Hi,

[SIZE=3][FONT=Times New Roman] For example a 90 degree elbow could be made in a very long radius (say a 3-to-1 sweep) resulting in a pressure drop lower than a standard 45 degree elbow. I guess it all comes down to how much do I want to work on my shop vs how much I want to do woodworking in my shop. T]


You can make your own sweeps with PVC by using a sandbox heater.

I have never seen 7" PVC, not saying it doesn't exist, but in 35 years of construction I have not run across it. Does 8" slow down the air too much for your setup?

[johnny means]

Over $100 for a 5' piece of plastic pipe?.... Come on...who's gonna buy that?

label it Festool, stand back, and rake in the dough.:D

[Alan Lightstone]

Bob, how does the pressure drop of two 45degree elbows compare to 1 standard 90 degree elbow?

[Larry Edgerton]

Bob, how does the pressure drop of two 45degree elbows compare to 1 standard 90 degree elbow?

Rule of thumb when plumbing is that 2 45's have half the restriction of one 90. It costs more so you don't often see two 45's used but it is the mark of a good plumber.

[Joe Angrisani]

label it Festool, stand back, and rake in the dough.:D

Amen, brother.....

[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/darcy-weisbach-equation-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.