Shop Vac Cyclone

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Forum topic by bradf58 posted 12-03-2012 02:31 AM 1748 views 0 times favorited 4 replies Add to Favorites Watch
View bradf58's profile


4 posts in 3057 days

12-03-2012 02:31 AM

Topic tags/keywords: trash can cyclone shop vac cyclone

Hey all!

I hope I posted this in the right forum.

I’m getting ready to build me a trash can cyclone for my shop vac.

I have the general idea but have one question I hope someone can answer.

I notice on most of these plans they use 4” pvc plumbing parts.
A 90 degree elbow and a straight piece.

The question is, is 4” the magic number/diameter or can you use 2-1/2” elbow and straight piece and accomplish the same. Since I have a craftsman 9 gallon vac with a 2-1/2” hose I figured well why not just make the lid with 2-1/2” parts then I wouldn’t have to go buy adapters to adapter the 4” parts.

My thinking is the 4” would make it more efficient, and maybe the 2-1/2” make it too much of a vacumn and crush the can. I will be using an old 13 gallon oil drum which I’ve been using for a garbage can for some time now.



-- Beginner, Hobbyist, Serious Dust Maker!

4 replies so far

View Kreegan's profile


1452 posts in 3202 days

#1 posted 12-03-2012 03:45 AM

I think the 4” thing is just because that’s the size fitting used by most full fledged dust collection systems. I think you’ll be fine with 2 1/2”. Check out this link for someone who made a cyclone using that size connectors.


View Viktor's profile


473 posts in 4474 days

#2 posted 12-03-2012 08:06 AM

For a shop vac 2.5” is fine. Wider diameter piping has less resistance, but in your case the difference will be negligible. If you use 1.5” or so, pressure loss will become noticeable in comparison to 2.5”. Increase in resistance is nearly exponential. Likewise, for a typical dust collector as a rule of thumb you shouldn’t use pipes smaller than 4”. DCs move more air than vacs, but generate much smaller static pressure and 2.5” fitting will choke it.

View HorizontalMike's profile


7915 posts in 3969 days

#3 posted 12-03-2012 03:52 PM

I use the 2 1/4in hose from my 16gal shopvac and then use 4in-to-2 1/2 reducers at a Grizzly cyclone lid on a 30gal trashcan.

They make different sizes so check what you need.

-- HorizontalMike -- "Woodpeckers understand..."

View ChrisMc45's profile


117 posts in 3915 days

#4 posted 12-31-2012 12:44 PM

Hi Brad;

I have the same Craftsman shop vac, mounted atop a 55-gallon plastic drum on casters. Hose is 2.5”, never a problem. The vacuum really cannot generate enough negative pressure to crush the can, or else our vac canister would often implode. (steel drums “squash” at 3-5 inHg inches of mercury).

FWIW, I did not use a 90-degree turn but instead ran a straight section through the lid at a downward slant. I used a picture of an ellipse to make the oval-shaped cutout, sealed with glue and Dap foam.

Cheers, Chris Mc45

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