6" Galvanized Pipe for DC System?

[Dan McCallum]

I am considering using 6" galvanized pipe rather than 6" PVC for my DC system for several reasons.

I see that the borg sells only 30 gauge. Is that going to be strong enough for a Clearvue cyclone with 1800 CFM of suction?

Dan

[Quesne Ouaques]

I use the 6" snap-lock, and I would highly recommend going with 26 gauge at a minimum. It's available through Penn State Industries ($15 for a 5' length), though I got mine for less through a local HVAC supplier ($10 for a 5' length).

Sandor Nagyszalanczy discusses this in his excellent book, and says that 28 gauge pipe or thinner can collapse under the suction of even some small cyclones, particularly if you make the mistake of turning on the blower with no blast gates open! It is especially true for 5" and greater diameter, but even your 4" drops in 30 gauge could be at risk with a strong cyclone. The 26 gauge, however, is strong enough.

[Jamie Buxton]

I have borg-supplied 6" round duct on my cyclone. It hasn't collapsed.

[Chris Padilla]

There is much debate about the gauge or wall-thickness of metal duct. As Jamie indicates, his #30 is fine (I assume his is #30?) whereas you'll find others claiming to have issues.

The big variable here is that there are A LOT of variables involved and so it is hard to make a blanket statement and paint it across all systems. I think with some certainty, the larger the gauge (wall-thickness of the metal duct), the better the odds it WILL NOT collapse.

Dig into the vendors that supply metal duct for dust collection and see what gauge metal they are using for their pipes and that might help you out.

Certainly, HVAC duct was not designed for dust collection (high volume, debris laden air movement) but that doesn't mean it won't work just fine.

[Jim Becker]

My entire system is 26 gage snap-lock with laterals, etc., from Oneida. Joints are all sealed/reinforced with heavy HVAC foil tape and those in high stress areas have 2-4 pop rivets to secure them.

[Eric Gustafson]

I am considering using 6" galvanized pipe rather than 6" PVC for my DC system for several reasons.

I see that the borg sells only 30 gauge. Is that going to be strong enough for a Clearvue cyclone with 1800 CFM of suction?

Dan

If you are using the longest runs of the 30 gauge snap lock it is not likely to resist collapsing. Shorter sections, and the adjustable elbows are no problem. I have a cleavue and am using thinwall S&D pipe. The DC lifts the metal 30 gal garbage can into the air! I did see somebody on this forum who used 30 gauge snap lock successfully by re-enforcing with rings on the outside of the pipe. I thought that is a good idea. I just went with the S&D pipe cause it is cheaper and easier to work with.

[Greg Funk]

Here is a graph from Spiral pipe manufacturing showing the collapse pressure for spiral pipe. The thickness of 30 gauge pipe is .0157" and the ratio T/D for 6" pipe is .0026 which would indicate you would need more than 2psi to collapse the pipe. Spiral Pipe Collapse Pressure.jpg

I think normal dust collectors don't generate more than 15" of static pressure which is less than 1psi so I would say it's unlikely the pipe would collapse. Spiral pipe is likely stronger but it seems that for 6" pipe there is quite a bit of margin available.

If you want the spiral pipe www.eccomfg.com makes it locally.

Greg

[Dan McCallum]

Thanks guys. Checking a different local borg today revealed that they carry 26 and 28 gauge as well (with less selection), so if I do go that route it looks like the heavier gauges are available if I want to use it. I'm also going to check a couple local HVAC shops.

Greg, thanks for the table. Looks like it shows 30 gauge may be plenty sufficient.

Dan

[Joe Chritz]

Since the fittings are normally heavier than 30 GA anyway and the pipe is a very low portion of the total cost it makes sense to go with the thicker pipe and avoid even the possibility of problems.

I have many time more in my fittings and gates than straight pipe.

Joe

[Mike Cutler]

It should be fine.
If collapsing the suction piping becomes a concern. A Magnahelic vacum switch can be installed on the suction side and set for a very low inhg value to trip the cyclone off.

[Robert Payne]

Thanks guys. Checking a different local borg today revealed that they carry 26 and 28 gauge as well (with less selection), so if I do go that route it looks like the heavier gauges are available if I want to use it. I'm also going to check a couple local HVAC shops.

Greg, thanks for the table. Looks like it shows 30 gauge may be plenty sufficient.

Dan

I am using 6" PVC (D2729 S&D) and associated fittings for my ClearVue CV1800 -- I found 10' lengths at $15.90 and all of the necessary fittings at a plumbing supplier at prices well below the BORG's. In your initial post, you say you want to use galvanized versus PVC "for several reasons" and then express strong concerns over the strength of the very lightweight galvanized duct. I don't know what your reasons are, but I know the PVC won't collapse, it is smoother on the interior, allows more flexibility for inevitable changes in layout and won't cut you to ribbons during the install! If your concerns are the static charge that can occur with PVC, read this article. I've dissapated any static on my system by grounding the metal wire in my flexible duct sections to their machines and I never get zapped. Just my .02