Results 1 to 13 of 13

Thread: What is ideal Air to cloth ratio for woodworking dust collectors ?

  1. #1
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162

    What is ideal Air to cloth ratio for woodworking dust collectors ?

    I am in the middle of trying to figure out filter options for my cyclone. I have figured out the original air to cloth ratio for my Grizzly GO442 as 9.60/1 from dividing 2184 cfm by 226 sq feet of filter. This is the easy part. What is a good ratio ? Google from several sources has me from 3.5/1 all the way to 10/1. At least four or five other sources talk of the importance of getting this ratio right without telling you how to get it right. I have deduced this is a moving target because of all the variables in collection. How does one proceed to figure out a suitable ratio ? I would like a better idea before talking to sales guys who will tell me they have exactly what I need.

  2. #2
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    10,009
    The higher the filtration the higher the back pressure and the higher the need for more area of filtering media to reduce back pressure. If you use a cloth bag it will need more area then a cylinder of chicken wire.
    Bill D
    Last edited by Bill Dufour; 06-11-2020 at 7:14 PM.

  3. #3
    Mike, I'm in the process of designing my own dust collector, so have been researching this exact topic...

    Bill Pentz's website says: "With typical 0.5-micron all polyester filters used for indoor air filtering we need about one square foot of filter area for every 4 CFM of dirty air. This means our 800CFM needed for good fine dust collection at our larger tools requires 200square feet of fine all poly filtering material"

    That would be a 4:1 ratio.

    Al-Ko makes some models that are highly-regarded (and highly-priced), and they publish specs on their max airflow, nominal airflow, and filter area (and I believe they use 0.5micron filter fabric, making this a good apples-to-apple comparison with Bill Pentz's data). Their models use 8 or 9:1, if you use "nominal" CFM (measured at 10" static pressure), or 13 or 14:1 if you use "max" CFM.

    I found a presentation by an industrial baghouse manufacturer (https://www.iaom.info/wp-content/uploads/04kicefc18.pdf) that says:
    7-10:1 General Suction
    7:1 Secondary Collector
    5:1 Centro-vac system

    So, I'm designing mine for around 8:1, but I primarily decided that based on the physical size I want the filters to take up.

  4. #4
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    Quote Originally Posted by Bill Dufour View Post
    The higher the filtration the higher the back pressure and the higher the need for more area of filtering media to reduce back pressure. If you use a cloth bag it will need more area then a cylinder of chicken wire.
    Bill D
    O Bill....

  5. #5
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    So Dan ,what are you using for filters ?

  6. #6
    Join Date
    Dec 2008
    Location
    Ouray Colorado
    Posts
    1,404
    Mike, my Belfab bag house is about 6 to 1. A lot of variables here though. When I bought it they asked a lot of questions about ratio of coarse to fine material and hrs of usage. They then determined the correct number of filters.
    It is important to get it right, we had a Murphy Rodgers 15 hp baghouse that the fan came apart and replaced it with a higher output fan and motor hoping it would keep up with the moulder better. It had better suction but the bags clogged quickly and the performance was worse till you spent some time cleaning the bags.
    i would suggest trying to find a engineer that could help with this.

  7. #7
    Join Date
    Mar 2006
    Location
    SoCal
    Posts
    22,513
    Blog Entries
    1
    From American Fabric Filters: "Ideally, total CFM rating of the bag should be 50-100% larger than the rated air output of the unit." This is the bag on my old 600 CFM bagger which is a bit undersized due to my space restrictions at that time.

    DC Bag Cleaned.JPG

    Every 6 months or so I would turn it inside out and vacuum it with a soft brush head. The giveaway for when it needed cleaning is when the bag starts to look like a balloon when running versus this pic which is running right after cleaning. IIRC this bag is about 4 times the size of the factory bag. I ran a solid plastic bag inside the lower bag which used to breathe. This made this collector actually usable without blowing fine dust all over everything.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  8. #8
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    Glen I was just on their site looking at the chart for sizing bags. I noticed they had a different value for commercial applications. I will be contacting them tomorrow to see what they think. There is also a picture of a Grizzly cyclone before and after a conversion to bags.Thanks for the performance review on AFF 's bag filter.

  9. #9
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    Joe thanks for the reply. So you used to have a Murphy collector,I think they are made in Ontario. I will get help/research this more before buying anything.

  10. #10
    Quote Originally Posted by Mike Kees View Post
    So Dan ,what are you using for filters ?
    I'm planning to do something crazy (a homebrew pulse-jet system), so I was looking for bag-type filters with internal cages.

    I found a vendor that sells 0.5-micron PTFE-coated nonwoven fabric, ostensibly for filtering biodiesel, but I can't imagine why this wouldn't work equally well for air?
    https://www.dudadiesel.com/search.ph...%2Bbag+%2BPTFE


    Regarding sizing: unless I'm misunderstanding, there's nothing wrong with having "too much" filter, right? You could go with a 3:1 ratio, if you wanted - it would just cost more and be bigger? Presumably the performance is best with minimum restriction, so if cost/size were no object, go big?
    Last edited by Dan Friedrichs; 06-11-2020 at 9:16 PM.

  11. #11
    Join Date
    Dec 2008
    Location
    Ouray Colorado
    Posts
    1,404
    Quote Originally Posted by Mike Kees View Post
    Joe thanks for the reply. So you used to have a Murphy collector,I think they are made in Ontario. I will get help/research this more before buying anything.
    Mike, not sure it’s the same company. Murphy Rodgers was in California.they went out of business a few years ago. Another company in the US still has some parts for them. Wynn Enviromental.

  12. #12
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    I contacted AFF and have a quote coming on three different scenarios. After my conversation I ran through all three to figure out the square footage of cloth. All were smaller than the pleated filters already on my machine.Grizzly started at 226 sq.ft. Option #1 was tall 36" tapered bag ,135.59 sq.ft. Option#2 four 24"diameter x72" tubes for a baghouse 150.72 sq.ft. Option#3 two 24" diameter x14' high bags 181.25 sq.ft. My thinking at this point is the bigger the better,but I am disappointed that all three options have less air surface than where I started. I would like to increase my area and move the surface to air ratio down from 9.6/1 to 4-5/1 or so. I also looked at Wynn's website ,their filters look promising. I can get two filters that stack together and are rated for 230 sq,.feet each,so 460sq.ft. of filter area total. I guess my biggest question/dilemma is if you are cramming dust laden air into a tube 8"-10 "ID with all those little pleats is that really just like 460 sq.ft. of cloth filter ? I see a bag as being way less likely to plug up if of suitable size,but do not have half a shop to use for a big baghouse. What say you ?

  13. #13
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    I also found a section on Oniedas website on how to check your cyclone for air leaks with an incense stick. I am going to be doing that today. Apparently even a very small leak really messes up separation ability in a cyclone resulting in way more fine dust ending up in your filters.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •