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Thread: Thoughts on Dust Collection Please

  1. #1
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    Thoughts on Dust Collection Please

    I am currently working on building my shop and have bought a used Grizzly 3 HP Cyclone Dust Collector with a 8" main connector. The main run will be over 40' and figure something like 55' or so total to the machines. It had come with some 6" Northfab piping what I am wondering is should I use 8" as main pipe instead? Either way I will be stuck buying a bunch of piping no matter what. My thought is it would be better to use 8" as the main pipe with 6" pipe used pointing down that I split into 2 4" flex to the machine. Is this the best way to approach it or is there a better way? Thanks.

    -Rob

  2. #2
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    If it has an 8" fitting at the collector, why would you want to hobble the whole system by starting out with 6" pipe?

    I would use 8" mains, with 6" drops. You could also drop to 6" towards the end of the 40', just keep the large cfm machines closer to the collector.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  3. #3
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    Ditto what Rick said, especially if you have to buy pipe any way. I would not use ANY 4" unless you have NO choice, especially if you have an 8" main line.

  4. #4
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    I agree with maintaining max size as long as possible. 4" to machines represents no issue as far as I am concerned. Are there opinions that 4" is not acceptable? Of course there are. These opinions may be a result of a purist approach. If 4" was not acceptable in any way shape or form, I do not believe that the many professionals in the field, such as the Wood Whisperer, would use it. I use it. 6" main until the tool, then reduction to 4" for all tools except my 20" planer, which is hooked up with 5".

  5. #5
    Join Date
    Mar 2012
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    I'm certainly no expert but from all the reading/research prior to beginning my install I would say the biggest issue with reducing to much less than the main (more than one size smaller) is that when the dirty flow gets back to the main it may lose so much velocity that it can no longer carry the debris away and it could settle in the duct. The way to avoid this is to allow more air to enter the flow near the reduction. Maybe by having more than one 4" open on more than one tool, maybe by just letting air enter an unused branch. In the case of an 8" main this would require four 4" openings at once to match (in this case exactly) the area of 8".

    When planning my install I made a simple calculator to help figure out how many of each size was needed to approximate a 6" main. An 8" main opens up many more combinations of sizes than with 6".

    I was going to attach the file but can't seem to figure out how to upload an XLS file (if it's even possible) so if you're interested, just PM me and I'll get it to you.
    Last edited by John Donofrio; 06-10-2015 at 9:49 AM.

  6. #6
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    Quote Originally Posted by John Donofrio View Post
    I'm certainly no expert but from all the reading/research prior to beginning my install I would say the biggest issue with reducing to much less than the main (more than one size smaller) is that when the dirty flow gets back to the main it may lose so much velocity that it can no longer carry the debris away and it could settle in the duct. The way to avoid this is to allow more air to enter the flow near the reduction. Maybe by having more than one 4" open on more than one tool, maybe by just letting air enter an unused branch. In the case of an 8" main this would require four 4" openings at once to match (in this case exactly) the area of 8".

    When planning my install I made a simple calculator to help figure out how many of each size was needed to approximate a 6" main. An 8" main opens up many more combinations of sizes than with 6".

    I was going to attach the file but can't seem to figure out how to upload an XLS file (if it's even possible) so if you're interested, just PM me and I'll get it to you.
    I wouldn't leave four 4" openings just to match areas. To do so would reduce the available suction at the tool being used to the point much of its effectiveness would be lost. Better to just use the one opening, even if it is just 4", and occasionally open up a few gates to clean the duct while not otherwise in use. If you are running a planer generating a ton of tangled shavings off a 4", then you might want to keep one more 4" open upstream. You might be surprised how much air you can suck through a 4" hose with a 3 hp DC.
    NOW you tell me...

  7. #7
    Join Date
    Jan 2013
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    I don't know if it is the answer for your situation, but I have the same Grizzly model. I reduced to 6" immediately and ran 6" pipe to every machine (if possible). If I have a machine with an unalterable 4" opening, I always make sure and open another 4" or 5" somewhere down the line. I get good dust collection and no clogs.

  8. #8
    6" will work, 8" will work better. Rick Potter is right.

  9. #9
    when the dirty flow gets back to the main it may lose so much velocity that it can no longer carry the debris away and it could settle in the duct.
    I'm no expert either, so for my own learning is there really any problem with debris settling in the duct (assuming it doesn't reach the point of clogging the duct)? While it may be aesthetically unappealing to have sediment in your DC system, one could make the argument the a layer of debris could actually improve airspeed, by reducing the cross sectional area of the duct!

  10. #10
    If debris were to settle in your main duct, all you would have to do is open another gate to let in more air.

  11. #11
    Join Date
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    One place that I worked had 12" main piping and a 5 hp collector for a roughly 4 car sized shop with 3 men working. We frequently had to run the collector with at least 4 of the the far end gates wide open to clear the pipes. It was a big pain because it was necessary to do this for about 1/2 hour every day. In my opinion, it would be best to carefully size the pipes by the amount of flow that was needed. For a one man shop where only one or two machines are ever run at the same time, I think that a maximum of a 6" trunk is all that is needed with 4 or 6" drops to the machines, and if the shop is less than a 2 car garage, a 3 hp collector is way overkill. A 2 hp would be a much better choice. Bill Pentz website has all the calculations that is needed. http://www.billpentz.com/woodworking...ccalc_faqs.cfm.

    Charley

  12. #12
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    You need to understand the trade off between too large and too small here. A low pressure impeller can only handle so much static pressure. While an 8" main can slow the velocity, a 6" over 40' will also create additional resistance, especially through the fittings and reduce the overall cfm at the machine. With a 3 hp system running that far, machine placement will be important. You won't want the high cfm machines at the end of the run as the impeller will be marginal unless the machine hood is well designed or small. A 13" planer at the end will work, but a 20" will be marginal. Personally I'd go with the 8" and reduce to 7" along the way because I think you will someday go to a 5 hp system. Make the drops come off the main horizontally and then drop vertically so if any chips stay in the main, they don't drop down into other verticals. Measure the impeller. I think the Grizzly runs closer to a 5 hp motor on their 3hp system. A 14" impeller will be marginal but I'd prefer 8 or 7 over all 6" unless you run a radial impeller. Dave

  13. #13
    The Grizzly 3hp cyclone has a 15 1/2" impeller, so it is in the class of a Clearvue.

  14. #14
    Join Date
    Jan 2013
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    Jerico Springs, MO
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    I know this is an old thread, but always pertinent nevertheless. I posted previously here that I had an 8"-capable 3HP Grizzly d.c. and used 6" ducting from start to finish. I recently removed the first 6" section and replaced it with 8" leading to a wye (to two 6" lines). While I haven't noticed any superior dust collection, I'm very impressed with the reduced noise level.

  15. #15
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    Toronto Ontario
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    Quote Originally Posted by Robb White View Post
    I am currently working on building my shop and have bought a used Grizzly 3 HP Cyclone Dust Collector with a 8" main connector. The main run will be over 40' and figure something like 55' or so total to the machines. It had come with some 6" Northfab piping what I am wondering is should I use 8" as main pipe instead? Either way I will be stuck buying a bunch of piping no matter what. My thought is it would be better to use 8" as the main pipe with 6" pipe used pointing down that I split into 2 4" flex to the machine. Is this the best way to approach it or is there a better way? Thanks.

    -Rob
    Hi Rob, you need to actually go through the calculations on the airflow required at each machine, which wll allow you to determine pipe size and airflow and static pressure.

    After that you can determine what size pipe you need and whether your cyclone is capable of that performance.

    You'll need a flow versus static pressure chart from Grizzly for your cyclone. You don't want to start guessing and then have to rip out your piping or scrap your cyclone........Rod.

    Regards, Rod.

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