30 Gauge Ductwork

[William C Rogers]

I NOW know that 26ga is the rule for dust collection ductwork. Not knowing much of anything about ductwork the 6" pipe I bought at Menards was called "Std Gauge". I thought this is what was used. After reading the thread on the aluminum duct I can see that is not the case. What I have is 30ga. Searching the forums some have not had a problem and some have had no problems with 30ga. I feel if one gate is always open it would not be a problem. This would mean I would need to be sure a gate was open anytime I ran the DC. But if for some reason I could clog the system with my J/P then I would be at risk for collapse of the pipe. So my choices are 1) do nothing and make sure one gate is open, 2) junk the 30ga and buy 26 ga, 3) install a vacuum relief in the system (saw in one post).
I don't like 1, and 2 would be expensive, so 3 seems to be my choice. Has anyone done this and how? Secondly I was thinking of running the pipe above my 12' drop ceiling, but now have second thoughts on this. Opinions?

Bill

[Ole Anderson]

Menards won't take it back for a refund? IMHO #2 is the right choice. A vacuum relief (or leaving one gate open) is contradictory to wanting a good suction on a DC system. And if you forget to leave a gate open, splat goes all of your duct and you start over. Personally I would run the pipe below the ceiling, especially a 12' high one. 30 ga pipe will dent easily from a lumber bump, and a dent will compromise the ring strength needed to keep the pipe from collapsing. 26 ga is much more difficult to dent, and if you do, you still have plenty of strength left. Don't use 30 ga pipe. Go to post 43 of the following thread.

http://www.sawmillcreek.org/showthread.php?79131-And-the-fun-begins-yet-another-DC-project!/page3

[Jamie Buxton]

My duct is the standard 6" stuff Home Depot sells, and it hasn't collapsed in ten years of use. Perhaps the reason is that it is impossible to completely close off my ductwork. Right at the entrance to my cyclone, I have a suck-switch. It is a single shop-built unit which is essentially two standard blast gates mechanically hooked together so that if one is closed, the other is open. One of the duct lines from this switch goes to the tablesaw. The other goes to a flex duct which I plug on the bandsaw or the jointer/planer in either of its two configurations.

[William C Rogers]

Ole, Menards would take it back, however it would be an additional $400 to change the pipe and not sure how much additional cost for fittings. That would be the best choice, however I have already sank a fortune into this shop with 1/2 bath, in floor heat, etc. I need to try and save some money as I am already over budget. I think I will take your advice and run the ductwork below. What I have is a 3hp Jet 1900 DC. Impeller is 14" in diameter. I will be using the eBay cyclone. I intend to install a tee in the long run using the outlet for some type of spring loaded plunger that would open when a 6" blast gate is about 90% closed.
Indid see that post of the collapsed pipe. It appears to be 8-10' long section. Mine will only be 5' long sections.

Jamie, good idea. I might be able to incorporate something like that.

[Mark Bolton]

Unless you've got a massive dc and your ductwork uses a lot of large diameter pipe and is dead tight you'll never have an issue with 30ga.

[Jim Andrew]

The 8" elbows I picked up at Menards were 26 gauge. Otherwise, the cheapest place locally is the Ace hardware. They stock 26 gauge pipe and fittings.

[Michael W. Clark]

There are a couple of options if you are concerned about the 30ga.

Someone on here posted pictures of stiffening rings they used made from plywood. Those same stiffeners could be made with a flat side to accommodate supporting the duct from the wall. If you run it below the drop ceiling, I would not support it from the grid. I don't see any harm in running it above the ceiling (done all the time and a good place to hide balance gates from operators) except that you need to look up there every now and then for a general inspection. If something major happens above the ceiling, you will know because you will loose flow at the tool.

The simplest and most used style of "vacuum break" is a gravity damper. It is a butterfly damper with a threaded rod attached perpendicular to the shaft. Install weights and nuts on the threaded rod. Adjust the opening point by moving the weights back and forth, automatic, no wires, and fully adjustable. Install it at the end of your longest run and set it to open when all gates are closed.

Mike

[Sam Layton]

Hi William,

I have a 3 hp cyclone dust collector. I used the 30 gauge snap lock hvac ducting from Home Depot. I ran some of it through the attic to get to the other side of the shop. After purchasing the ducting, I realized that I should have purchased 26 gauge. However, I did not. I got the 30 gauge at a really good price.

So, on all of my straight ducting I doubled it. I snap locked the first duct, then placed another one over that, and used several layers of aluminum duct tape to tape the seams together. Then connecting my ducts for the runs, I used plywood rings to hang and support the ducts. Blast gates were placed at each machine.

My blast gates are 6" and 4". When I use the 6", only one gate is open. When I use the 4", I make sure another 6" gate is open. My system has been up and running for years, and never a problem, works great. Doubling the sections of ducting, and the plywood rings really make it strong. Anyway, not the best way of doing it, but I could not spend thousands on my dust collection ducting.

[Wade Lippman]

Right at the entrance to my cyclone, I have a suck-switch. It is a single shop-built unit which is essentially two standard blast gates mechanically hooked together so that if one is closed, the other is open.

Can you share a photo of this switch? I could use something like that.
But DO NOT google on suck-switch. I don't know what it is, and really don't want to.

[John McClanahan]

I have seen pictures on the internet of 30 ga. ducting collapsing when all blast gates were closed.


John

[Jamie Buxton]

Can you share a photo of this switch? I could use something like that.
But DO NOT google on suck-switch. I don't know what it is, and really don't want to.

I could post a photo, but it doesn't tell you much -- just a plywood boxy thingy with ducts attached. I can describe it better with words.

The usual blast gate has a sliding piece of wood or metal. The slider has a hole in it that is about the same size as the duct. If the slider is slid to one end of its travel, the hole is in line with the ducts, and air goes through the blast gate. When the slider is slid to the other end of its travel, the non-hole end of the slider blocks the ducts, so no air passes through. So far, so good? If not, google up a picture of a blast gate.

My switch has the same slider with a hole in it. When it is slid to one end of its travel, the hole is in line with one of the switched ducts, and the non-hole end of the slider blocks the other switched duct. When the slider is slid to the other end of its travel, the hole moves to the duct that had previously been blocked, and the non-hole part of the slider blocks the duct that had been previously open.

[Peter Aeschliman]

No experience from me, but in concept, it seems to me that the stiffening rings that both Michael and Sam referred to would work, if spaced closely together (say, every 18"?). In order for the duct to collapse in one dimension, it needs to widen in another dimension. The goal is to keep the duct round. One way to do this is to buy thicker duct material, and another way is to use stiffeners on thinner material.

Heck, you could maybe even buy a bunch of metal duct clamps and fasten them on the duct in sections where there's a long span of straight duct.

So I don't think all is lost, although it's not ideal.

[Ole Anderson]

Ole, Menards would take it back, however it would be an additional $400 to change the pipe and not sure how much additional cost for fittings. That would be the best choice, however I have already sank a fortune into this shop with 1/2 bath, in floor heat, etc. I need to try and save some money as I am already over budget. I think I will take your advice and run the ductwork below. What I have is a 3hp Jet 1900 DC. Impeller is 14" in diameter. I will be using the eBay cyclone. I intend to install a tee in the long run using the outlet for some type of spring loaded plunger that would open when a 6" blast gate is about 90% closed.
Indid see that post of the collapsed pipe. It appears to be 8-10' long section. Mine will only be 5' long sections.

Jamie, good idea. I might be able to incorporate something like that.

Wow, a $400 upcharge to go from 30 ga to 26 ga? You must be putting in a heck of a lot of pipe.

[William C Rogers]

Wow, a $400 upcharge to go from 30 ga to 26 ga? You must be putting in a heck of a lot of pipe.

My mistake, it is about $200 more. For some reason I doubled it, not intentionally. I think I have a solution I'll post later using the 30 ga.

[Brian W Smith]

Am not advocating one gauge over another....just sayin.

You need to look at how long each section is.There's a noticeable difference in the stiffness of a 5'....uninterrupted section,and one half that length.Now throw a fitting or a joint into the equation.....you are effectively doubling the thickness.Will leave "spiraling" alone at this point because it's a deep subject.But will say that you can really boost your stiffness with the hangars.We use gage metal,run through a sliproll,and used in compression on the duct.......one side is longer and is easily bent to attach to ?.Think of them as shrink fit sleeves,that just happen to act as hangars.The point being if you support a pce of tubing like this(and think "where" it'll do the most good(as a stiffener) within the length of that section)it goes a long way in stabilizing that section.Further,having "stiffeners"(in whatever fashion) isn't always about collapses.....DC ducts have been known to take a "hit" with material.

As a side benny to our style hangars......the same process is used when making removable sections of duct.They're(compression sleeves)also used in certain cases where we have flex hose connecting to a machine or other duct where speed is involved.They work great with quick/flip style fasteners(we use them on cartridge filter connections).

[William C Rogers]

Brian, when you say "hanger" are you talking about the perforated 3/4" steel strap? I was thinking of putting that around the pipe.

Here is what else I plan on doing. I am going to try to add a vacuum relief valve. Looked at a couple of damper style images, however cleaning a few things saw I had a left over gutter pop up. It seems to be a solution if I can get the right spring pressure balance. Nice thing is the shaft is a taper making it self center. I needed to drill a hole in the shaft for a longer screw and added spring length. Hopefully I can find the right spring balance. It fits just inside a 6" pipe.
This is the modifications I made. Won't know what spring rate until I get the system running.


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[Rick Potter]

I wonder what you have against having one gate open all the time? I have done that on two different shops with no problem. On my shop with the 1 1/2 Onieda, I left a 2 1/2" open with no gate, on the RAS. Never a problem. This was with 30 gage.

On my current shop with the 3 HP Onieda, I did the same, but usually have two 4" gates open at a time ( it works just fine), unless running the drum sander which takes a 6" drop. With your 3 HP DC, you could probably do the same, without worry, especially with 5' sections. Matter of fact, it is common for me to have the cabinet saw, 8" jointer, and RAS gates open all at the same time, not to mention that 2 1/2" open line to the RAS blade cover.

Note: I have spiral in the current shop. I give this example to show that an extra gate open should not kill your 3 HP DC. I will soon be adding a 20', 4" extension using 30 gage to my router tables.

YMMV

[Ryan Baker]

It depends on so many factors, it is hard to say what will happen. You can probably run a long time with the 30ga if you keep one gate (per branch) open all the time. It is pretty easy to get it to suck down though if you have a good collector.

With my old, small collector, there is no way I could ever suck down the 30ga pipe. There was nowhere near enough suck and way too much leaking. My cyclone could suck that down in a heartbeat and probably then pull it right through the collector. :) When I put in the cyclone, I rebuilt everything with spiral pipe. That's a whole other world.

[Ole Anderson]

Brian, when you say "hanger" are you talking about the perforated 3/4" steel strap? I was thinking of putting that around the pipe.

Here is what else I plan on doing. I am going to try to add a vacuum relief valve. Looked at a couple of damper style images, however cleaning a few things saw I had a left over gutter pop up. It seems to be a solution if I can get the right spring pressure balance. Nice thing is the shaft is a taper making it self center. I needed to drill a hole in the shaft for a longer screw and added spring length. Hopefully I can find the right spring balance. It fits just inside a 6" pipe.
This is the modifications I made. Won't know what spring rate until I get the system running.



And if you get the wrong spring balance and you collapse all of that 30 gauge stuff, what then? For $200 do it right the first time. Just go up from 30 ga snap lock to 26 ga snap lock, no need to go Cadillac style with spiral duct if money is the issue. No damper, no ugly rings and no diminished suction. Your dust collection system is the most important tool in your shop. Would you buy a great cabinet saw and run a cheap 24 tooth no-name blade on it? I hope not.

[Brian W Smith]

William,no on the perforated.

In HVAC world there is a name for this part......I've tried googling it several times and it just isn't coming up?Imagine two pcs of pipe/tubing that are the same diam,how can we connect them.The part is a sleeve,make it as long as you need......we use 3 and 4".The HVAC part is generally used to connect "boots" to straight tube(and that is really overslimplifying)where for a variety of reasons you can't or don't want to use a more conventional approach.

The sleeve is sized to go all the way 'round the joint,it has it's ends broke at a 90 to form flanges.It's through these flanges that we bolt this thing around the tube.Obviously everything is based on your accuracy/fit....but its pretty easy.What we do on hangars,instead of both flanges being 1/2" or so......one is left long.We still bolt it together just like the others......but this long leg serves as the standoff for that particular pce of tubing.The neat part is that it dosen't really matter which way we orient the duct....meaning,it works as well hanging from ceiling or mounted vertically.It also adapts readily when hanging at any angle to joists or whatever(you can break the long leg at the correct angle).

So,they act as connectors,they act as hangars,the side benny is they also stiffen.Not saying you should run 30g.......heck,you could "sleeve" two pcs of plastic SD together.And you can also sleeve the inside(no flanges,duh....).

*As a note,the original HVAC specs for these are quite a bit longer,guessing would say 1 1/2 X tube diam

[William C Rogers]

William,no on the perforated.

In HVAC world there is a name for this part......I've tried googling it several times and it just isn't coming up?Imagine two pcs of pipe/tubing that are the same diam,how can we connect them.The part is a sleeve,make it as long as you need......we use 3 and 4".The HVAC part is generally used to connect "boots" to straight tube(and that is really overslimplifying)where for a variety of reasons you can't or don't want to use a more conventional approach.

The sleeve is sized to go all the way 'round the joint,it has it's ends broke at a 90 to form flanges.It's through these flanges that we bolt this thing around the tube.Obviously everything is based on your accuracy/fit....but its pretty easy.What we do on hangars,instead of both flanges being 1/2" or so......one is left long.We still bolt it together just like the others......but this long leg serves as the standoff for that particular pce of tubing.The neat part is that it dosen't really matter which way we orient the duct....meaning,it works as well hanging from ceiling or mounted vertically.It also adapts readily when hanging at any angle to joists or whatever(you can break the long leg at the correct angle).

So,they act as connectors,they act as hangars,the side benny is they also stiffen.Not saying you should run 30g.......heck,you could "sleeve" two pcs of plastic SD together.And you can also sleeve the inside(no flanges,duh....).

*As a note,the original HVAC specs for these are quite a bit longer,guessing would say 1 1/2 X tube diam


Thanks Brian, I will check with my HAVC guy and see what he has. Sounds better than strap.

[Rod Sheridan]

I have seen pictures on the internet of 30 ga. ducting collapsing when all blast gates were closed.


John

And I've run mine for 20 years without issue, all depends upon the installation.

I hung mine with MDF hangers that have a cutout large enough for the pipe to slip through. (Made them on the bandsaw, don't worry about the blade entry cut, use that side on the wall/ceiling part).

The hangers provide reinforcement for the shape.

You won't have a problem with those hangers, use one on every legth of ducting, in the middle if possible. The normal crimping where they fit together provides plenty of strength at each end of the pipe.............Rod.

[John McClanahan]

Its only a work of caution, that it can happen. I don't remember what may have caused the collapse, maybe closing all blast gates while the dust collector is running.(?)

John

[Ole Anderson]

I close all of my blast gates frequently. I make a cut on the MS, close the blast gate and walk over to another part of the shop, open a gate and run the jointer. All without turning off the DC in between. It would be a pain to have to remember to always leave a gate open. Why buy the biggest, baddest DC you can afford, then compromise that DC flow and suction by leaving a gate open to save your piping? I don't get it.

[Alan Bienlein]

I made wooden hangers for mine out of scrap 1/2" plywood I had that the duct work slips thru.
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[Kent A Bathurst]

Why buy the biggest, baddest DC you can afford, then compromise that DC flow and suction by leaving a gate open to save your piping? I don't get it.

I look at it from a different perspective. You can properly design a dust sytem that will pull from multiple machines at the same time. Proper CFM, proper duct sizing from from DC thru all the drops.

In which case, you don't need to close any gates - because the system is designed to operate properly with them all open.

Or, taking one step back, design it with 2 main branches of [roughly] equal volume/flow, and then switch one gate from section A to B, but no gates downstream from there. In which case, a system with, for example, 1500 CFM capacity becomess the equivalent of a system with 3000 CFM capacity. You only need to pay for two blast gates, plus [assuming a top-notch filtration system] you are constantly pulling air from around the shop and filtering it to sub-micron or smaller.

If all you want to do is pull dust from one machine at a time, one 4" or 5" pickup at 400 - 600 CFM +/- will do it. Doesn't need to be big nor bad.

[William C Rogers]

I have read a lot on DC pipe collapse. The only pipes that have experienced collapse are 30ga. Basically (from recent memory) I have found two 8", one 7", and two 6" systems that have experienced this. I really only found the picture of the 6" by the poster on this form. Only one section of that poster's pipe collapsed. That section appears to be longer than 5 foot, but not sure. He had other sections that did not collapse that were 30ga. They were along the wall nested in wood half rings. However I found many instances where there was no problem with 30ga. From everything I have seen, it appears that installation is a key factor. On one of the 8" pipe collapse, it was replaced with the same gage with plywood rings and had no problems. I have concluded as Rod and Alan have done it is installation that is importantwhen using 30ga. With 26 ga not near as important. When the pipe collapses it changes shape and moves slightly at the end connection. It always collapses between the two end points. With a stiffener you prevent the changing of shape and screws at the connection prevent movement. Also it is more difficult to collapse a shorter length of pipe and a stiffener reduces the pipe length IMO. I will add some type of stiffener and will screw all the joints. I will go ahead and install my vacuum relief because it is easy to do. However I don't think I really need it. My system is no Dust Gorilla as my impeller is 14" vs. 15" and a little less CFM. It will cost me about $15 extra for the vacuum set up, but that is still $185 less than switching to 26ga. It will be mid January before I get this installed as I am building a wall in the workshop now. I will post my result. I do appreciate all of the input as it makes me think of different possibilities.