My dust collection system is already up and running. I am about to add a new toy to the mix and started looking at my whole collection system again with a critical eye.

Currently, I have a 1.5 HP dust collector attached to a trash can separator and then to a series of ducts, blast gates, etc. After reading some dark web blog posts I decided to vent the dust directly outside, thus avoiding those pesky filter bags altogether.

So now I am thinking about avoiding the separator as well. And maybe instead of blowing the dust outside, I started to wonder:

Why couldn't I just blow everything - fine dust, wood shavings, loose change, whatever - directly into a sealed container? That is, what is the purpose of the filter bag in the first place?

It seems to me that the whole point of the separator is to preserve the life of the filter (less stuff reaching it so less stuff clogging it up). But I don't even have a filter to preserve. I've also heard conflicting info about separators:

  1. They will drastically reduce your airflow
  2. It's a closed system so it won't matter

If airflow is indeed being compromised by the separator, then my thought is remove it and convert it into a sealed container that collects everything that goes through the system, without worrying about how many microns it is.

Am I missing something elementary here?

Original poster here...

Thanks jdv! (And Graphus & blacksmith37)...

OK, a few clarifications. Regarding the physics of creating a negative-pressure scenario, my shop is in Hawaii and only has three walls and windows that are permanently open. Air flow is not a problem. Rust, on the other hand... But that is a different topic. Also, this is a hobby shop. I putz around in there as much as I can, but it is definitely not a commercial shop. I don't create enough sawdust to be "that guy". The annoying noise of the woodshop is most certainly a bigger nuisance to my neighbors than the dust. But I live in an upscale redneck neighborhood so we're all good. :)

I still have bad memories of being the low person on the totem pole awhile ago at a shop I worked at. I was the newbie who had to clean out the filter bag. It always struck me as odd that so much effort was put into carefully collecting the dust in the shop only to dive headfirst into the filter bag and make a huge messy dust cloud. I like the idea of those pleated filter bags that have the butter-churning-type cleaner, but honestly this stuff gets expensive! Once I built my shop and started designing the dust collection system, I was determined to make it work well and be as hassle-free as possible. The idea of venting directly outside appealed to me. My shop is built on a deck that is about two feet above the ground and the dust is vented underneath the deck. I have one plank that is not screwed down so I can monitor the end of the hose and make sure nothing weird is happening beneath my feet. The shop itself has almost constant trade winds but under the floor is still air due to the fact that the shop is built alongside a rock wall that blocks the prevailing winds. So in other words, the fine dust that doesn't end up in the separator doesn't really blow around, it just kinda settles onto the gravel below my shop, virtually undetectable to the eye (well, so far).

I guess the only reason I was thinking of removing the trash can separator from the system was to recapture as many CFMs as possible. And my follow-up thought was, if I remove the separator, then I will end up blowing a lot more dust under the deck (rather than just the finest particles) which could in fact become a problem. Which led me back to contemplating a more proper collection system whilst avoiding the hassle of the filter bag.

I think what I will do is temporarily bypass the separator and do some sort of makeshift test to see if I do actually get more suction without it. Maybe I am trying to solve a problem that doesn't exist.

Thanks again! I appreciate everyone's thoughts... Aloha!

  • 8
    You can't vent the system into a sealed container — it's a sealed container. Regardless of separation the air has to go somewhere. Perhaps you could give a clearer indication of what you're envisaging?
    – Graphus
    Dec 12 '20 at 9:32
  • I am sure discharge of dust to the atmosphere violates some EPA rule on the US. Dec 12 '20 at 16:55
  • If not EPA, @blacksmith37, certainly some Prop 65 rule in CA... :(
    – FreeMan
    Dec 14 '20 at 17:50

There are probably no regulations for this in a home shop. For a commercial shop, you would not be able to exhaust dust to the outside without collecting it. There are a pile of rules about environmentals and fire safety and so on that will almost certainly restrict you doing this commercially. Check your local statutes just to be sure.

But in the 70s and 80s central vacuums that exhausted to an attached garage that was technically outside the main building were common. So a system that mimics this would be fine.

In fact, many shops exhaust to the outside anyway, because it can actually lead to overall healthier internal air quality (when done right). But, there are considerations and caveats.

When you vent outside, you are creating negative pressure that may need to be offset with a heat/air exchanger of some sort. Again, this may just be for commercial systems that move lots of CFMs, but it really depends on your shop. How much air are you removing from the space, and what (furnaces, spray rooms, other vented equipment) will be affected?

(Example: For my shop, which is essentially unheated and leaky as hell, I could do this. But I'd also be sucking out the small amount of heat my radiant system makes to the cold Canadian outside. This is not a win for me without also coming up with a heat exchanger, which makes no sense given how the rest of the shop is right now.)

So, do your homework and make sure you understand the physics. As pointed out, you cannot exhaust into a sealed container. Also, please don't be That Guy in your neighbourhood that blows raw sawdust into the air around your house. But, with a little consideration you should be able to make a separator and a collection system that vents outside correctly.

But it'll be more work than you think (because of the airflow and exhaust and maybe legal considerations), and you already have a perfectly working collection system. Why mess with that when you could be creating sawdust?


Can you create one? Yes.

Will it be effective? No.

If your final receptacle is sealed, dust and air will leak through any small opening in the system because it will be pressurized. You can observe this happening as the filter in a "regular" dust collection system gets clogged and it's easier for air to escape through small leaks than it is for it to get through the caked filter. That's how you know when it's time to clean/replace the filter/bag.

Even if your dust collector has enough oomph to push the dust into a sealed container, you're going to have a pressurized container full of saw dust. As soon as you turn off the collector, the pressure in the container will blow at least some of the dust right back out.

You put a one-way flap on the container so it can't blow back out when you turn the collector off. At some point, your container will be so full that your dust collector cannot force any more air or dust into it and you're going to have to empty it. Opening that container is going to give you a dust explosion that will make you wish you'd spent the last 6 months beating out filters.

You'll end up cleaning the mess up with your shop-vac and/or dust collector and cleaning filters as necessary anyway. The good news is that since you're in Hawaii and your shop is open, your friends and family will get a good kick out of watching the explosion from a distance. Maybe you'll keep your neighbors as friends if the trade winds are blowing the right direction on explosion day.

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