# 2 dust collection questions



## mike65072 (Apr 13, 2008)

This is probably over kill...I tend to over think thhings like this, but

Question 1 (easy...just not for me) - For optimum air flow where do you place the blast gates, closest to the tool or closest to the duct collector?

Question 2 (harder) - My new DC has a 5" opening, but I'm going to use all my 4" lines and fittings since I already have them. I've read that doing this will hurt my air flow, but that I can partially open a blast gate to improve the overall air flow. Which blast gate, closest to the DC or one farther away and should it be opened all the way or just partially (if partially, how much...half way open, 1/3rd etc)??

Thanks,
Mike


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## Fred Hargis (Apr 28, 2012)

#1, you can probably prove the difference in a laboratory, but as you said...you're overthinking the blast gate placement. Place them where they will be most convenient _for you_. In my case, that next to the machine.

#2, nothing you can do will increase the air flow in a 4" duct past maybe 400 CFM or so. So opening that extra blast gate may well (and likely will) reduce your collection at the machine in operation. If you only get about 400 CFM, you don't want any of it coming from somewhere else.


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## Dave Paine (May 30, 2012)

#1. All tools and components of the dust collector result in some pressure drop.

I think that in theory you want to reduce the pressure drop in the line, so technically the blast gate at the end may give slightly better performance, but as Fred said, this may not be detectable in real world situations.

Most people put blast gates at the tools for convenience. This is how my system is set up.

#2. I do not know who advocates opening a second blast gate, but this is not going to help. It will hurt.

As Fred said, you can only get so much airflow through a 4in duct. Opening a second blast gate will reduce overall static pressure in the line and that means lower airflow at the main tool. Lower airflow means less dust being pulled at the main tool.


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## JoeNY (May 8, 2012)

Dave Paine said:


> #2. I do not know who advocates opening a second blast gate, but this is not going to help. It will hurt.


Depends upon set-up. I run 6" main lines on my system, but some of my smaller tools, like the Delta 12" disc sander, Jet Oscillating spindle sander and my mortiser use 2.5" ports, so opening a second gate partially or a 4" gate fully further downstream of that branch helps to keep the flow in that 6" line up to where it should be.


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## rrbrown (Feb 15, 2009)

I agree with all three post. :thumbsup:


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