Industrial Scale Dust Collection #3: Just what exactly is a "bag house"

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Blog entry by Mainiac Matt posted 08-07-2015 04:03 PM 2287 reads 0 times favorited 5 comments Add to Favorites Watch
« Part 2: Rules and Regs.... how to stay out of trouble. Part 3 of Industrial Scale Dust Collection series Part 4: Houston, the Eagle has landed... »

Though you see mostly pleated canister filters on the newer small DC systems and a lot of guys upgrade their bag systems with filters from the likes of Wynn Environmental, I found 100% agreement from everyone I talked to… bag house dust collectors are recommended for industrial scale wood operations.

So what’s a bag house?

and here’s a picture of the “belly of the beast”

You’ll often hear the filter guys rate their systems for what % of dust at a particular size (usually measured in micons) the filter will catch. And while pleated filters will catch more fine stuff than felt bags, as the bags get caked with dust they are “seasoned” and the dust actually aids the filtering process. Our old Torit system was a cartridge system, and when we started pushing large chips and wood shards from our pallet notcher (a 9” wide x 2” deep dado cut made in one pass), we wound up damaging the pleated filters, which are quite pricey to replace.

In larger systems, you’re actually specifying the system capacity as follows:

1. Each machine will have a designated cfm requirement to remove it’s waste. In a busy industrial shop, you want the DC system sized so that you can run all of your equipment at the same time, and though you install blast gates, they should normally all be open, as shutting a blast gate here and there, will unbalance the design air flow.

2. The type of waste you are transporting will determine the air speed in the ductwork required to keep the debris suspended in the air stream and avoid deposition in the headers.

We’ve had two fires in the ductwork of our old system over the years, and discovered that the main headers were 1/3 full of wood waste. The root problem was that we had moved, added and removed machines to the system so many times that the system was no longer properly sized or balanced. After the fire fighters pull the access port covers and dowse the pipes, your left with quite the mess to clean up.

3. The air flow requirements from 1 & 2 will lead to a duct design, from which you can determine your system losses (both to friction, and bends in the pipe).

4. Now you look for a blower with a fan curve, such that you can overcome your losses and provide the airflow requirements. Here’s a typical curve from the net.

Since our intern just finished his Fluid Dynamics class I made him crunch the numbers using Bernoulli’s Equation, but we’re not really launching the space shuttle here and there are some nifty cheat sheets out there that simplify matters. Here’s the geeky slide rule one of our vendors hooked us up with…. It was very reassuring to see that the calculations we ran, were almost spot on with the slide rule.

5. Once you have your blower selected, you have to find a bag house that has enough filter area to get the desired 10:1 (or better) ratio between the total area of the filter bags and the system cfm. The system we’ve purchased second hand, has 124 bags (more like socks) that are each 10’ long.

So your really specifying and buying three systems. Ductwork, a blower, and a bag house.

And now you know…. the rest of the story….

-- Matt -- I yam what I yam and that's all what I yam

5 comments so far

View stefang's profile


17040 posts in 4391 days

#1 posted 08-07-2015 05:00 PM

This looks like dust removal of epic proportions, so my question is: would it be possible to locate my entire shop inside one of these?

-- Mike, an American living in Norway.

View Don Broussard's profile

Don Broussard

4015 posts in 3309 days

#2 posted 08-07-2015 05:12 PM

That’s going to be a heckuva system when it’s done, Matt! We used a similar system in our water treatment plant operation to catch lime dust from transferring and feed silos. Ours looked similar to what you’re calling the bag house, but ours was quite a bit smaller. I think our bag house has 12 cloth socks at about 8’ long.

-- People say I hammer like lightning. It's not that I'm fast -- it's that I never hit the same place twice!

View Mainiac Matt 's profile

Mainiac Matt

9862 posts in 3386 days

#3 posted 08-07-2015 05:29 PM

I just learned that this system was used to collect rock dust from some sort of crushing operation….

I sure hope that this isn’t a problem…

I don’t think it will be, but I’ve got a couple of maintenance guys who are going to curse my name if they have to replace 124 bags.

-- Matt -- I yam what I yam and that's all what I yam

View DIYaholic's profile


19921 posts in 3732 days

#4 posted 08-07-2015 11:07 PM

Thanks for the update & edjumacation….

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

View Bluepine38's profile


3390 posts in 4142 days

#5 posted 08-09-2015 03:25 PM

When you said the material was damaging the pleated filters, my first thought was that it would be easier
to place a cyclone or Thien top hat type separator in line to collect the big pieces and most of the small
ones. The filters would only have to stop the smaller particles and would last longer. Just wondering.
I just went back and read the first post, and I can see that building a pre separator for that size of an
operation would be way above my skill level. I hope your version works for you.

-- As ever, Gus-the 80 yr young apprentice carpenter

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