Thread: PVC duct minimum wall thickness..?

Originally Posted by GreggMacPherson

Hello from NZ.
You have a great forum here. Lots of interesting ideas about dust extraction..

Not just "ideas" but tested ideas.

[QUOTE]I'm hoping that someone can unstick me on a couple of questions...These are all theoretical sofar. I have no existing system yet, or test gear...Assume a common 2HP fan, 300mm impeller, with the inlet and outlet size optimised.

- There is some 125mm OD by 3.2mm WT PVC for sale here and I wondered if it was stiff enough to handle the max possible negative pressure...?
- What's the worst load case scenario...? Closing the gate while the fan is running?
- What is the maximum negative pressure the fan can pull? Can we convert that to PSI..?
- Do I have it right that 1" water on the manometer is 1/28 PSI..? I'm trying to get a feel for just how small these pressure differences are...

The pressures a very small, a 2HP DC generates at most ~8" of water column (WC), this is equal to about 1/4 of a PSI.
The pipes a made to handle water (1000 denser than air) so have no trouble handling less air with a bit of dust in it. Also they are even stronger under negative pressure (compression) than when they are carrying water (Expasion

There is also some 125mm ODx5mm WT and 160mm OD x 5mm WT Polyethylene, quite cheap, fits PVC fittings.
- Would this be a suitable duct material..

Bigger is FAAAAAR better.
At about 8" of WC 125 mm will draw about a max of 780 CFM, 150mm will draw about 1250 CFM PROVIDED the DC is up to the task - even a modified 2HP runs out of puff and cannot reach 1250 CFM AND when it is back pressured it drops off quite badly.

Thanks Bob. I'm probably constrained to a small scale experiment with a used 2HP fan. I'm going to look at a Trupro one (motor plate Nov/2004) with a 150mm inlet and an outlet that's easy to modify. The Trupro current specs...impeller diam=12"...flow rate= 1600CFM without the bag and max static pressure =11" H2O.

Do you think their specs are a bit optimistic? Is there much difference in the performance of fans with nominally the same specs but differences in the impeller design or fan body design? Are all these 2HP fans made in the same factory in China or Taiwan. Or using the same impellers and fan bodies...?

I had some ideas towards an epoxy/glass cyclone...removing the corners and inadvertent turbulence from the upper body. Started with the forms but then life got busy. Pics on the Canadian forum, but they may be having tech problems, a lot of the text has disappeared. If I get going again I will start a separate thread...
Cheers,
Gregg.

Did I forget the link to the cyclone pics...? My last post is not visible yet.
Making an epoxy/glass fibre cyclone -

Canadian Woodworking and Home Improvement Forum.

Originally Posted by GreggMacPherson

Thanks Bob. I'm probably constrained to a small scale experiment with a used 2HP fan. I'm going to look at a Trupro one (motor plate Nov/2004) with a 150mm inlet and an outlet that's easy to modify. The Trupro current specs...impeller diam=12"...flow rate= 1600CFM without the bag and max static pressure =11" H2O.

Do you think their specs are a bit optimistic? Is there much difference in the performance of fans with nominally the same specs but differences in the impeller design or fan body design? Are all these 2HP fans made in the same factory in China or Taiwan. Or using the same impellers and fan bodies...?

The tests are made using an incorrect testing standard - this has been know for years.
I have tested a few 2HP DCs and they have been pretty much all the same.