Designing a dust collection system

[Don1357]

I recently picked a used Grizzly 2hp dust collector, which should be a great starting point for making a two stage cyclone dust collector. Currently it has a 5" intake, I plan on opening it up to 6" so I can have 6" - 5" - 4" metal ducts working their way down to the machines. On them the focus is best dust capture, so there is less **** in the air to content with.

For the dust filtration itself, I was thinking about using the usual round canisters, but looking up I have a loooong channel between floor joists. To save space I'm going to seal a length of that space and mount flat filters on it. I have enough space that with pleated filters I can exceed the surface area of most two canister setups.

The first question is this: What MERV rating should my filters be? The recommendations seem to run from 12 to 16, with 12 sounding too low and 16 a bit too much? There are some great prices at MERV 13, and MERV 15 gets to be pricey...

 

[Don1357]

Really? Nobody around here are into putting together dust collector systems?

I'm currently digesting cyclone separator principles and designs. For starters I'm scaling down the size of my cyclone; Originally I was planning on building a unit around 8" inlet but tradeoffs between collection volume and collection efficiency made me decide to scale things down to 7" or even 6". Long story short a larger cyclone can process a higher CFM, but a smaller one can be more efficient around 10 micron particles. If I can live without the higher CFM (single user shop, one machine used at a time) I reap the benefits of less stuff going past the first stage.

 

[knobby]

Its a tricky question the proper amount of filter restriction would depend upon the static pressure that the blower is meant to handle as well as the amount of duct used with that loss added on.
FWIW I would start with a lower number first to see how well the filtration/air flow presents and work from there.

 

[Don1357]

Yeah.

Currently I have a 2hp oldie Grizzly motor/blower to start with. Once I have it hooked up I can hook up a (homemade) manometer to see what I got where. Without doing that everything is just guess work on my part. The cool thing is that then I can measure the effect of different components: The piping going downrange no filter, the filter, no piping going down range, etc.

Then at that point I can measure my intake velocity under working conditions, which to a large degree defines efficiency on either volume or particle removal. Once I get to this point I should be able to tell whether the size is ideal, too big, or too small.

Another thing is that most cyclone design papers I have been finding suggest a cone three times the diameter of the cyclone. I don't know if this is ideal for the sort of material I'm trying to process (woodworking sawdust). I'm not seeing a single dust collector being sold to the home workshop market following this design so I'm trying to figure out if this is significant for the task at hand.

 

[Don1357]

Has anybody seen a study on particle size generated by a given woodworking process? table sawing vs. planing vs. joining vs router, so on so forth? I'm thinking of building a gate bypass to outside vent on demand. I figure there may be certain processes I would rather vent outside than send to the filers, winter or no winter going on.