gauge of fittings

[kayak]

I have read that 26 gauge is the minimum to use for ductwork.  Does that apply to fittings as well, elbows, wyes, and laterals, or does their construction make them sturdy enough at 30 gauge?  Has anyone here ever experience a 30 gauge fitting collapsing under vacuum?

[bbain]

I fired up my blower tonight to do some testing, I have 2 30Ga. elbows and a ~20" section of 30Ga. pipe between the blower and my in-progress separator.  I blocked the inlet and the plastic pail started to crush, but the pipe didn't move a bit.  This setup is extremely leaky at the moment though, everything was just dry fit, no tape on the pipe joints, and the tophat is just held together with gravity (and suction with the blower on) at the moment.  With a tightly sealed system, and a rigid container, I would guess the 30Ga. pipe may implode, but not sure about the elbows, they are quite a bit stiffer because they are only short sections and the ridges in them increase the stiffness.

[retired2]

I suspect what is behind your question is another question, i.e. "Can I safely use 30 ga pipe and components for my DC plumbing?"  The answer is "It depends!"

It depends largely on whether you are using a shop vac or dust collector for the blower.  It depends on whether you are using a typical 1-1/2hp dust collector or a 5hp behemoth.  And it depends on the size of the pipe.

Shop vacs are high SP, low volume devices and are capable of flattening pipe that a DC might not.  On the other hand a high hp DC could also flatten pipe.  And of course it is a lot easier to flatten an 8" pipe than a 4" pipe.

I have a 1-1/2hp Delta dust collector.  In comparison testing, it ranks among the best DC's in this size range.  However, under deadheaded conditions it has never collapsed the plastic Brute waste drum I use.  Yes, the sides flex a little and that might produce small leaks around the top seal that keep it from collapsing, but I don't believe that is the case.

My plumbing is all 5" 26 ga.  It is very stiff, and I can't imagine collapsing it with DC I could get into my shop.  I often wished I had just used 30 ga to save money and weight.  It is also a lot easier to cut, trim, and crimp lighter ga pipe.

[kayak]

The hidden agenda behind my question is regarding the wye's and elbows only, not the pipes (6" mains and 4" drops).  I am content with getting 26 gauge pipes from a local HVAC fabricator.

I will be using a Harbor Freight 2HP (optimistically) dust collector with the impeller replaced with a Rikon impeller, and a Wynn filter replacing the top bag.  I am planning on a double height (12") tophat over a 32 gallon Brute can.  The longest run in the shop would probably be to the bottom side of the table saw, about 12 feet of 6" with one elbow, and 15 feet of 4" with two elbows (approximate lengths).

BTW, I have a 6" bellmouth waiting in the wings for the outlet of the tophat (purchased from Spiral Mfg.).  The outside diameter of the flange on the bellmouth is out of round.  The pipe portion is perfectly round.  Should I try to grind the flange to round, or will it matter? 
Also, the diameter of the pipe on the bellmouth is exactly the same as the 6" duct pipe.  Instead of trying to crimp the bellmouth, I am thinking about making a 9" long, three vane air straightener to insert into the outlet, and use it as a "splint" to tie the bellmouth and the pipe together, using foil tape to seal the seam. Thoughts?

[retired2]

The hidden agenda behind my question is regarding the wye's and elbows only, not the pipes (6" mains and 4" drops).  I am content with getting 26 gauge pipes from a local HVAC fabricator.

I will be using a Harbor Freight 2HP (optimistically) dust collector with the impeller replaced with a Rikon impeller, and a Wynn filter replacing the top bag.  I am planning on a double height (12") tophat over a 32 gallon Brute can.  The longest run in the shop would probably be to the bottom side of the table saw, about 12 feet of 6" with one elbow, and 15 feet of 4" with two elbows (approximate lengths).

BTW, I have a 6" bellmouth waiting in the wings for the outlet of the tophat (purchased from Spiral Mfg.).  The outside diameter of the flange on the bellmouth is out of round.  The pipe portion is perfectly round.  Should I try to grind the flange to round, or will it matter? 
Also, the diameter of the pipe on the bellmouth is exactly the same as the 6" duct pipe.  Instead of trying to crimp the bellmouth, I am thinking about making a 9" long, three vane air straightener to insert into the outlet, and use it as a "splint" to tie the bellmouth and the pipe together, using foil tape to seal the seam. Thoughts?

You are far less likely to collapse fittings than straight pipe, so I don't think the 30 ga fittings would be a problem.  The easiest way to find out is buy just one, hook it to the blower intake with a short piece of pipe, cap the end, and fire up the HF to see what happens.  However, my recollections are that the 30 ga. fittings looked flimsy and poorly constructed compared to the 26 ga.  Also, I don't think the 30 ga. elbows are available in 5 segment.  I am a strong advocate of these longer radius fittings due to the much lower line losses.  Yes, you can put two three segment elbows together and get close to the same thing, but now you have another crimped joint, more work, greater potential for leaks, and less cost benefit.

You would help your system a lot by eliminating as much of that 4" pipe as possible (to the table saw)

My 5" bellmouth slipped easily into the end of snaplock 26 ga. pipe.  Not sure why yours doesn't, but I like your idea of a butt joint with a three vane air straightener as the spline.  For my joints, I used the foil duct tape with the black adhesive mastic on the back side.  Your HVAC supply house will have it.  It's not cheap, but you will never have an air leak with that stuff.  And don't tape any joints with it that you expect to take apart.  It is like trying to remove old bubble gum, and I have not found a solvent that works on it.  I tried, alcohol, acetone, and paint thinner.

I would recommend grinding the flange on your bellmouth for a reason other than concentricity.  There is a chart I've posted several times showing the benefits of various style pipe ends for inlet ports.  For sure the bellmouth is the best, but many of the other variations, some pretty basic such as a flat flange, capture a large part of the performance improvement.  I have also come to the conclusion that the flange diameter of bellmouths may lead to additional waste bypass.  The reason I suspect this is most of us have separators that are around 20" in diameter.  The large flange diameter on the bellmouth, especially a 6", results in air being picked up closer to the separator walls and consequently some by-pass.  I have no sound proof of this theory especially since the increase, if it exists at all, is very small.  Sure, if you were to put a large bellmouth in a very small diameter separator, then you might be able to suck in a lot of extra waste.  In your case, there is little to be lost in efficiency by grinding off some of the flange, and possibly something to be gained by less by-pass. 

[kayak]

R2, thank you for your reply.

[kayak]

<snip>

You would help your system a lot by eliminating as much of that 4" pipe as possible (to the table saw)

<end snip>

I will have a lateral directly above the table saw blade with a 4 inch diameter drop to an overhead blade guard.  I have been advised by one person to also drop the horizontal that will eventually end up at the under saw collection to 4 inch at that lateral.  Another person advised that even if I kept the horizontal at 6 inch, to reduce it to 4 inch for the vertical drop to the saw cabinet to keep up air velocity. And yet another person advised keeping it 6 inch all the way to the saw cabinet.  I'm so confused...

[retired2]

<snip>

You would help your system a lot by eliminating as much of that 4" pipe as possible (to the table saw)

<end snip>

I will have a lateral directly above the table saw blade with a 4 inch diameter drop to an overhead blade guard.  I have been advised by one person to also drop the horizontal that will eventually end up at the under saw collection to 4 inch at that lateral.  Another person advised that even if I kept the horizontal at 6 inch, to reduce it to 4 inch for the vertical drop to the saw cabinet to keep up air velocity. And yet another person advised keeping it 6 inch all the way to the saw cabinet.  I'm so confused...

There have been some articles written that say 5" is the sweetspot for plumbing 1-1/2 hp dust collectors.  In formal testing many 1-1/2 HP DC's cannot support 6" piping, and I believe the HF unit may be questionable.  I don't know how much better it will perform with the Rikon impeller, it would be nice if someone who has done this mod and has the test equipment, would run some tests to quantify it.

Now, if the HF is on the ragged edge of being able to provide velocities high enough to convey waste in a 6' pipe, then a table saw with a 6" dust port and a 4" dust port that are open simultaneously is going to be disappointing at best, and possibly not work at all.  In fact, I'm betting you are not going to be pleased with two 4" ports.  I say that because of my experience with two ports on my bandsaw. ( http://www.jpthien.com/smf/index.php?topic=537.msg2846#msg2846 )   The post does not describe my final change, but I am going to update the thread so that it does.  The short version is I blocked off the second pickup port to give the primary connection all the air.  In the end that worked best.  It is worth noting that my  bandsaw is the tool farthest from my DC, so it has the highest line losses.

How far is the lateral for you table saw from your DC? 

[kayak]

How far is the lateral for you table saw from your DC?

The lateral should end up about two feet up, an elbow, and six foot across from the dust collector.

[retired2]

How far is the lateral for you table saw from your DC?

The lateral should end up about two feet up, an elbow, and six foot across from the dust collector.

That's very close and it will make your situation a lot better than my bandsaw example.  You may have to experiment with the line sizes you use for the two saw ports, but I don't think a 6" and  4" is going to be the best combination.

[kayak]

Keep in mind, that is a 4 inch coming out of the side of the lateral to the overhead blade guard, AND a 4 inch coming out of the end of the lateral to the underside of the table saw.

[retired2]

Keep in mind, that is a 4 inch coming out of the side of the lateral to the overhead blade guard, AND a 4 inch coming out of the end of the lateral to the underside of the table saw.

That's a good reason to start  out with 4" runs to both ports of the table saw.  However, you should be aware that you can buy laterals with three different sized legs.  In fact, the one on my bandsaw has three different connection sizes, and the 3" leg has a reducer inserted into it to take it to 2-1/2".  So, you have a lot of options to try if things don't work out.

[kayak]

On the lateral, the dust collector side of the lateral would be 6 inch, the overhead blade guard side would be 4 inch, and the table saw cabinet side would be 4 inch.  As you said, I can reduce the blade guard port down to a smaller size if wanted/needed.  I am going to talk to my local HVAC fabricator to check a cost comparison of 26 gauge elbows vs. big box store 30 gauge elbows.