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….
-- Pine is fine, but Oak's no joke!