Dust Collector Duct Work Question

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Forum topic by flyingoak posted 04-19-2011 08:56 PM 1862 views 0 times favorited 12 replies Add to Favorites Watch
View flyingoak's profile


68 posts in 3130 days

04-19-2011 08:56 PM

Topic tags/keywords: question

I am about to re-do my dust collection system. My current collector only has a 4” port but i intend on upgrading when $$$$$. I was thinking about installin 6” piping for future expansion and use. i know you should use the largest duct work possible to minimize friction.

QUEstion: do you see any problem with using 6” ductwork as a main line when the collector has only a 4” intake?

Thanks in advance,

-- where is the duct tape.....

12 replies so far

View Steven H's profile

Steven H

1117 posts in 3082 days

#1 posted 04-19-2011 09:05 PM

IT depends of how much HP of collector you have,

View ClayandNancy's profile


519 posts in 3037 days

#2 posted 04-19-2011 09:27 PM

The intake on your DC needs to be at least the same size as your main line otherwise you create a restriction at the intake opening and you also hinder the air flow to keep the dust suspended in the air stream.

View Lee Barker's profile

Lee Barker

2170 posts in 2872 days

#3 posted 04-19-2011 09:32 PM

Unless you’ve got some machines that really crank out the waste, 6” seems awfully big.

The river analogy works well here. Where the river gets wider, the current slows down. If you bump to 6”, you’ll lose velocity in a big mathematical way.

In my professional shop, when there were two of us in there really cranking, 4” pipe did the job and never clogged and never backed up and never failed. 2hp Murphy Rogers was under the hood.

My $.02!



-- " his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View Viktor's profile


464 posts in 3441 days

#4 posted 04-19-2011 09:33 PM

No problem. Friction losses are additive. All 6” duct is better than 6”+4”, and the latter is better than all 4”. Improvement will be smaller (but still noticeable) for low CFM collector and greater for high CFM unit.

View flyingoak's profile


68 posts in 3130 days

#5 posted 04-19-2011 09:35 PM

MY DC is actually two 1 HP collectors mated into one line.

Clay,—I agree but is there a problem if the ductwork is LARGER than the intak opening


-- where is the duct tape.....

View ClayandNancy's profile


519 posts in 3037 days

#6 posted 04-19-2011 09:49 PM

I don’t think 2 DC’s pulling from one line really work that well. I would think they would be kind of fighting each other for the dust. For now can you do two separate lines each pulling from their own respective machines and stay with the 4”? If not I would get one 2hp DC like a Grizzly that has a 6” then go to 6” ducts.

View dbhost's profile


5723 posts in 3254 days

#7 posted 04-19-2011 09:52 PM

Yes, If the intake is smaller than the ductwork, then the velocity of the air / dust moving through the duct will tend to slow down, and drop the dust load in the pipe instead of the collector. For what it’s worth though, lots of folks report good results upsizing the intake port on the HF 2 HP DC. Since you are pulling with 2 1HP collectors, you should go with a 6×4x4 wye like what ships on some dust collectors… You are just reversing the directions… That should be okay. Not great, but okay…

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View Viktor's profile


464 posts in 3441 days

#8 posted 04-19-2011 10:04 PM

No, there is no problem with increasing the main while keeping intake the same. It will be an improvement (although ideally you would want to increase the intake also).
Two DC’s pulling from the same line is no problem either. They have to be matched (which they are in your case) – have similar static pressure and turn on simultaneously. DC’s in parallel configuration are commonly used. They can also be connected sequentially if you need to fight particularly high friction in the system.

View ClayandNancy's profile


519 posts in 3037 days

#9 posted 04-19-2011 10:12 PM

Viktor With 2 DC’s pulling on one line is there a problem with balance as the filters start to collect dust (one plugging faster then the other).

View Viktor's profile


464 posts in 3441 days

#10 posted 04-19-2011 10:25 PM

Clay, I can imagine this happening (no two DC’s will be absolutely identical). However, if one filter gets more clogged it will slow down the air flow, then the second DC/filter will start getting a greater share of the flow (and dust). This is until the second one becomes more clogged and so on. The system will equilibrate itself.

View TheWoodNerd's profile


291 posts in 3214 days

#11 posted 04-19-2011 10:35 PM

It depends on the air volume your DC(s) are pulling. A 6” line is more than twice as large as a 4”, the velocity of the air will drop by 55%. A general rule of thumb is that you need the air moving at 4000 feet per minute to keep things moving. To make this work, your system needs to be pulling air at 9000 fpm (102 mph) through that 4” inlet or 800 cfm minimum and more likely at least 1000 cfm. Offhand, I think it’s unlikely that your system can move that volume of air though such a small opening.

A much better solution, I think, would be to use a Y-connection with a 6” inlet and two 4” outlets, connecting to your collectors. Not ideal, but I think it’s more likely to work. When you upgrade one day, just pull out the Y and hook right up!

-- The Wood Nerd --

View ScottN's profile


261 posts in 2701 days

#12 posted 04-20-2011 01:56 PM

Your putting the cart before the horse.

You need to get a bigger dust collector first, then install bigger pipe.

If you install the 6” main you wont have enough cfm to move the saw dust through the pipe and could plug up.

-- New Auburn,WI

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