Edited To Add:

The main thing I am asking here is whether it is beneficial to have blast gates that close off as much of the unused dust collection branches as possible. I will already have blast gates closed at the tools at the end of every branch. Is it beneficial to also have a blast gate that closes off an entire unused branch at the point it branches? I'd be closing off about 20 feet of 4" PVC duct. If it will improve performance of the dust collector, is it something where I'll really see a noticeable improvement in dust collection at the tool being used, or is it just a few percent that I probably won't really notice?

Original question:

I built some blast gates to put on the main branches of my dust collection system. My goal was to close off the entire volume of that branch so the dust collector doesn't have to evacuate its air when I'm trying to use a tool on a different branch. However, I've run into a problem. Long story short, at the location I'd intended to install at one of the blast gates, there is a conduit blocking the path of the gate. I wouldn't be able to close it.

I have some ideas on how I might fix this. I can use a different style of blast gate, or I might be able to scoot the whole main branch over. However, before I go to that trouble, I'm wondering how important these gates actually are. My dust collection has three main branches (simplified for the purpose of this question): the Radial Arm Saw Branch, the Planer Branch, and the duct to the dust collector. My plan was to be able to close off the entire Radial Arm Saw Branch and the entire Planer Branch when those branches aren't in use. One way to fix this is, instead of closing off the entire branch, I could put the gates at the tools themselves.

My gut tells me it won't work as well. If I close off the entire branch, it will be a smaller volume of space for the dust collector to evacuate. But I'm not sure about this. Maybe if the tools on that branch are closed off, it won't really be much more work because no air will be moving along that duct?

Will closing off as much of the unused branches as possible make the dust collector do its job better and collect more dust from the tool that is open? If so, will it be by a noticeable amount? Or will it mostly not matter as long as the branch is closed off at the end?

Here's a diagram of my duct and where I planned on putting the gates. Instead of putting them here, I could just move them closer to the tools.

The three main branches of my dust collection duct

The self-cleaning style blast gates I built. Note that when closed, half of the sliding gate will be above the duct:

Self-cleaning style blast gates

But that won't work as-is, because there is conduit above the duct:

Conduit blocking the gate

(For the record, I did check for obstructions before I started hanging duct... but I checked at the other end, which is perfectly clear. I didn't check exactly where I wanted the gates. Whoops.)

  • "Ididn't check..." That's NEVER happened to me :)
    – Ashlar
    Feb 12, 2018 at 15:54
  • Fortunately, I hung the duct in a way that makes it easy to move if I need to. :) Feb 12, 2018 at 16:34
  • 1
    Why don't you just move the gates from left to right instead of up and down? It looks like there's plenty of room to either side of the duct. Worst case you might have to notch out the gate's frame, but I think it would still work properly. Feb 12, 2018 at 21:48
  • 1
    Support joists are overrated! This is dust collection we're talking about.
    – Ashlar
    Feb 13, 2018 at 1:28
  • 1
    You could build a blast gate with a double length frame where just the "solid" portion slides back and forth in the frame (like a sliding door). (This is actually how most blast gates are built.) Then you would only need clearance on one side of the duct. Feb 13, 2018 at 21:59

2 Answers 2


There is no benefit to reducing the "dead" pipe lengths. That has no impact on the available airflow and pressure drop. The only time this would be a concern is if the branch exited the bottom of the duct and over time dust could settle in this pipe. Then when you opened that blast gate, a slug of material would be sent to the dust collector.

  • I was able to test it this weekend, and as @ChuckS said, it appears to give no benefit. Thanks for your help! Feb 20, 2018 at 22:36

Also, the use of PVC pipe for dust collection is specifically prohibited by NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities due to the build up of static electricity.

  • Can you edit into your answer some information about inexpensive, easy-DIY materials that are not prohibited and would be a better solution than PVC?
    – Rob
    Jan 18, 2021 at 17:37
  • I believe this is false, for a multitude of reasons: it is out-of-scope, the specific language was removed from the draft, and the standard is now being consolidated into another document. Can you provide a link demonstrating otherwise?
    – aghast
    Jan 19, 2021 at 0:04
  • Even if this were current (it appears it isn't but I don't know) the operative part is "in Wood Processing and Woodworking Facilities" .....and not to point out the obvious but a home workshop is not a wood processing facility.
    – Graphus
    Jan 19, 2021 at 6:26

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