8" Ts, or 6" Wyes"... Put in Ts for future machines?

[Wade Lippman]

I am considering two options:

1) Using 6" PVC with Wyes and double 45 elbows. The pipe is cheap, but the fittings are expensive.
2) Using 8" steel for most of the system (dropping to PVC for individual machines), using Ts and 90 elbows. The pipe is expensive, but the fittings are cheap.

Seems to me, based on those engineering courses I vaguely remember taking 40 years ago, that an 8" T should be as good as a 6" Wye. Anyone strongly agree or disagree with that? Sure, 8" Wyes would be optimal, but they aren't available here, would be harder to lay out, and geez, how good does a system have to be to run single machines off 3hp?
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Second question is whether I put in a T (or a Wye) where I think I might need one for future machines, or do I rebuild everything when it comes to that?

[Michael W. Clark]

Wade,
With a 3HP machine, you may not generate enough air speed in the 8" to keep the dust suspended.

Use a long radius 90 instead of the double 45s. You are not really gaining much (if anything) with the two 45s vs the 90.

As a general rule, wyes (or laterals) are better than tees from a pressure loss standpoint for the same duct size. If you oversize the tee, you have more fittings, and a place for dust to drop out.

You can add branches for future expansion easily with a system that only runs one machine at a time. Just put in a wye and blank it off for future use (end cap or blast gate). Adding future branches requires some thought if you have a tapered duct system with multiple machines operating at the same time.

Mike

[Wade Lippman]

Wade,
With a 3HP machine, you may not generate enough air speed in the 8" to keep the dust suspended.

Grizzly's manual says to use 8" for the main line, but what you said make sense. So I called Griz and asked.
He said that with one blast gate open there might not be enough airflow and the suction will be reduced. However, it is proper to partly open a second blast gate to increase the air. That will give better performance than using a smaller main line.
This is counterintuitive but I guess it makes sense.

[David Kumm]

If you are talking about Grizzly's new 3 hp cyclone look at the motor rating and impeller size. I think it is closed to an actual 5 hp system so it could benefit from the 7 or 8" mains. I would not put a T on any DC system period. I had them on my first system to be cheap and they cost lots or cfm and dust collected in the fittings. turbulence in the airflow doesn't improve your life or your lungs. If you were closeer I'd sell you some used ones but you can find them on CL or ebay if the cost is a problem. Used go pretty cheap if you watch. Dave

[Alan Melbourne]

my system is done with 2 45 degree fitings and a 8"pipe fetween them
i coulnt get long radiused 90s anywhere without getting them made up adn costing 60 euro each. a 45degree is only 5 euro each.

it works good enough for me.


dont use Ts no matter what. they are a total distroyer of cfm. you should be ably to get Y fittings .
i had to get mine in the uk and ship to ireland. it was still a lot cheaper than buying them here.

[Michael W. Clark]

Alan,
Absolutely it is better to have the LR 45s than a SR 90 in terms of pressure loss. I was commenting based on the elbows being the same radius.

I often see claims that two 45s are less loss than a 90 of the same radius and it is simply not true. The only reason for less loss would be if you are cutting the corner with the 45s, shortening the duct run (i.e. the shortest distance between two points is a straight line). If you put them back to back, I don't think you would be able to measure the benefit in reduced static pressure unless you had a meter that read to 3 or 4 decimal places. If a piece of wood is big enough to plug a 90, it will likely not go through the 45s back to back either.

Mike

[Ole Anderson]

If I were installing a 3 hp DC I would go with 7" horizontal mains, they are the optimal size for 800-1200 cfm. 6" on verticals. Of course, that means steel. But you should find that 26 ga snaplock is in the same price range as thin PVC. I presume you have been through the current steel vs PVC thread/poll.

[Wade Lippman]

The local HVAC supplier can order wyes for a reasonable price, so I am okay there.

Thanks all.

[Jim Andrew]

Would your local HVAC guy tell what company he is ordering reasonably priced fittings from?

[Ole Anderson]

Grizzly's manual says to use 8" for the main line, but what you said make sense. So I called Griz and asked.
He said that with one blast gate open there might not be enough airflow and the suction will be reduced. However, it is proper to partly open a second blast gate to increase the air. That will give better performance than using a smaller main line.
This is counterintuitive but I guess it makes sense.

Unless you are doing a ton of heavy planing which generates lots of material, often with just a 4" port, I would not leave another gate open just to get the velocity in the main. By doing so, you are reducing the flow in the active machine port and thereby reducing the collection at that machine. To get a feel for it, just listen to the velocity (suction) at the machine with a second port open and again with just the machine port open. If you can't hear the difference, you are OK to leave another port open. I have the same comment when designing a router table to dump lots of air into the box, when you do that you loose flow at the tool and that is what dust collection is all about. Now when you are done using that tool, then open up another gate upstream briefly to clear the pipe of any built up material, which should be minimal. There have been plenty of discussions on the concept that a pipe will not fully plug.

"with one blast gate open there might not be enough suction and airflow will be reduced" Yes that is not only counter intuitive is is totally wrong. The more gates you have open, the higher the airflow and the lower the suction (in inches of water column). You may have misunderstood him on that point.

[David Kumm]

The whole opening the second gate is self defeating until you get to at least a 5 hp 15-16" impeller system. Some chips left in the horizontal is less dangerous than reducing the flow at the machine and allowing more dust to escape to your lungs. If the gates is necked down to 4" right at the machine you can still get 6000-8000 fpm through it rather than the 4000-5000 you might acheive with the second gate open. Depends on the system but the key is velocity into the machine. Any stray chips in the main- assuming it isn't grossly oversized- will clear out when another gate is opened. If the ducts have sweep ells and wyes there is little for the chips to cling to. Dave

[Wade Lippman]

Would your local HVAC guy tell what company he is ordering reasonably priced fittings from?

Probably not...
When I say reasonable, a 8" T or a 8-6-6 wye is $15. He would have to call to get a price on the special order 8" wye, but is sure it will be less than $20. Penn State doesn't have one that large, but their 7" is $55, so I figure $20 is reasonable.

[Wade Lippman]

"with one blast gate open there might not be enough suction and airflow will be reduced" Yes that is not only counter intuitive is is totally wrong. The more gates you have open, the higher the airflow and the lower the suction (in inches of water column). You may have misunderstood him on that point.

It might not be right, but I understood him correctly. He says that if inadequate air is getting to the impeller it reduces the output of the motor and will actually draw less air through the machine in use. He said it is not like a vacuum cleaner, where a leak ruins suction at the tool; here a leak can actually improve air draw at the tool.

[David Kumm]

It might not be right, but I understood him correctly. He says that if inadequate air is getting to the impeller it reduces the output of the motor and will actually draw less air through the machine in use. He said it is not like a vacuum cleaner, where a leak ruins suction at the tool; here a leak can actually improve air draw at the tool.

Opening a second gate can not add cfm or suction to a gate, only reduce it or leave it the same. The second gate allows more airflow in the main which helps the chip flow and keeps them from accumulating in the horizontal. It won't aid the collection at the machine. Dave