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Thread: Should I keep this DC or go Cyclone?

  1. #1

    Should I keep this DC or go Cyclone?

    I am finally getting ready to pipe my DC and tools in the shop. I will have a Tablesaw, Jointer, Planer, Bandsaw, Router, Belt Sander.

    I am going to run 6" PVC and drop to 4" right before the tools.

    I currently have a Powermatic PM1900 dust collector. The specs on it are 3HP, Static Pressure 11.31" of water, velocity at 4" 5200 fpm, air flow at 4" 234 cu. ft/min, air flow at 8" 1754 cu. ft./min.

    This DC should be big enough to get the job done. I have had it for a couple of years and have been just connecting to tools as needed. Now that it is getting down to plumbing time, I am wondering if I should consider selling it and buying a cyclone. My only reason for thinking this is because emptying the bags can be a pain in the butt.

    I bought the thing for a good price and would not loose any money on it, but would need to put quite a bit with it to get a cyclone.

    Is their any reason for me to consider a cyclone instead of this dust collector other than the ease of dumping a drum rather than emptying the bags?

  2. #2
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    Well, you're either going to empty the bags in your existing DC, or you're going to empty the bin from under a cyclone. That's pretty much a wash, isn't it? Where the cyclone has an advantage is that less dust gets to the filter, so you don't have to clean it as often.

  3. #3
    Consider spending some more time reading about the design of good dust collection ductwork, first. Your idea of running 6" duct and reducing to 4" is very, very bad - the 4" restriction will essentially make the entire system perform as though it was plumbed entirely with 4". It's kind of like hooking a fire hose up to a garden hose. If you run 6" ducts, you really need 6" ALL THE WAY to the tool to get the full benefit (and that may mean hacking a larger, 6", dust port into tools which don't have 6" dust ports already).

    That DC is plenty powerful for a 1-man shop. If all you want is ease-of-emptying, consider a pre-separator (a la Phil Thien)

  4. #4
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    Quote Originally Posted by Dan Friedrichs View Post
    . Your idea of running 6" duct and reducing to 4" is very, very bad - the 4" restriction will essentially make the entire system perform as though it was plumbed entirely with 4".
    Not true. Have you ever seen a real shop with a full professionally designed dust collection system? All sorts of duct sizes including 4" short end runs and drops for some of the smaller tools. The closer you are to the cyclone, or bag unit the bigger the pipe. As one example, if you go to the Oneida site, they start with a 7" main collector pipe, go to 6", then go to 5" and end up attaching to a machine with a 4" port. I don't agree with their maximum length on 7" and 6" pipe, but you get the idea.

    http://www.oneida-air.com/files/Duct...er%2010-06.pdf

    One reason to go to a cyclone/filter system is that you can generally get a filter that is able to get the fine dust below 1 micron, whereas the bags stop at 1 micron if you are lucky and have the 1 micron bags. The specs on the Powermatic 3 hp unit look good, presuming you dropped a decimal on the air flow at 4" of suction. Plenty of performance for a shop operating one tool at a time.
    Last edited by Ole Anderson; 01-17-2011 at 12:08 AM.

  5. #5
    Quote Originally Posted by Ole Anderson View Post
    Not true. Have you ever seen a real shop with a full professionally designed dust collection system?
    The design of ductwork for a commercial shop is entirely different than a 1-man shop, because there is a possibility of having more than one machine running at a time. Not true of a 1-man shop, so it's best to a have a single diameter of ductwork all the way from the blower to the tool.

    The disadvantage of reducing duct size is that the airflow decreases. At the relatively low static pressures produced by this type of blower, air does not readily compress, so even a short section of smaller ductwork absolutely limits the airflow of the rest of the system.

    I also wouldn't trust that file from Oneida you linked to. The first thing it says is that PVC is bad for ductwork because of dust explosion risks (a myth that has been debunked many times over).

  6. #6
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    I recently installed an Oneida cyclone and ran it to my bigger tools. I kept my bag type Penn State DC and use it on the 12" disc sander, and band saw. I also bought a floor sweep tool from Rockler and use the DC to vac the shop floor. With the DC specs asking to not turn on the cyclone over 6 times in one hour, I thought tools like the disc sander would be better off, using the smaller bag type DC.

  7. #7
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    Darrell,

    Your 3 hp DC will likely perform as well a larger cyclone and better than many home size cyclones. A 3 hp DC doesn't have to pull air through a cylone body, so doesn't have nearly as much friction to overcome. If you check some of the WW mag articles on dust collection design, you'll see this confirmed. The downside with a DC is they also aren't nearly as good at separating fine dust, so the filters clog more easily.

    I'm using a 3hp DC with Thien separators inside the separator body as well as cartridge filters. They generally work well, although I have clogged them after a day of using a drum sander. I view that as a tolerable tradeoff, since that is a grand or two that I don't have to spend (yet).

    For the lower bags, you can get nifty quick release bands from Grizzly for pretty cheap. They are giant hose clamps with a knuckle that you lock down after you've taken up the slack by hand. Quick and easy to use.

    BTW, you should at least run 6" to your tablesaw. There is just no way to get enough airflow through 4" ducting to do the job. Consider that 6" will allow more than twice the airflow as 4". The difference is very noticeable and worth the effort.
    Last edited by david brum; 01-17-2011 at 11:26 AM.

  8. #8
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    I am not concerned with the explosion hazard of static electricity, but the startling shock factor when working with rapidly spinning sharp tools, which is also appropriately listed by Oneida as a plus for metal ductwork. I don't wonder why the NFPA requires metal in commercial shops. I am not saying PVC is not an appropriate material for home shops, I just prefer steel, and that was after considerable deliberation. And it helped that I get a huge discount from my son who manages a HVAC supply shop. My shop has the TS closest to the DC, needing 600-900 cfm for top and bottom suction, therefore I am running 7" from the my 2 hp Oneida upstream past the TS to the next big split, where I start reducing the pipe size in accordance with the flow requirements of each tool, 7" to 6" to 5" to 4" hose for tools like my drill press and BS for which 350-400 cfm is adequate. No hard pipe smaller than 5". To occasionally flush out my 7" I just open several upstream blast gates. Oversize your pipes for small flow tools and you will build up material in the pipes due to inadequate air velocity. Unfortunately, sometimes you need to oversize your very long pipes to minimize pipe friction losses. Now if your big tools are at the end of the run, yes you would hold the diameter constant. Bottom line, there is no simple answer to correct pipe sizing, it depends on your shop layout, your DC capability, your tool requirements and your preferences and capabilities.

  9. #9
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    The disadvantage of reducing duct size is that the airflow decreases. At the relatively low static pressures produced by this type of blower, air does not readily compress, so even a short section of smaller ductwork absolutely limits the airflow of the rest of the system.

    That is very good advice.

    I'd modify your machines if possible to accept a 6" fitting. The increased airflow will also do a much better job of reducing the fine dust....and that IMO is the most important part of dust collection.

  10. #10
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    Quote Originally Posted by Ole Anderson View Post
    Not true. Have you ever seen a real shop with a full professionally designed dust collection system? All sorts of duct sizes including 4" short end runs and drops for some of the smaller tools. The closer you are to the cyclone, or bag unit the bigger the pipe. As one example, if you go to the Oneida site, they start with a 7" main collector pipe, go to 6", then go to 5" and end up attaching to a machine with a 4" port. I don't agree with their maximum length on 7" and 6" pipe, but you get the idea.

    http://www.oneida-air.com/files/Duct...er%2010-06.pdf
    That is the proper design in the case that you are collecting from more than one tool at a time (and have the horsepower to do that). The reason for combining multiple smaller branches into a larger one is to keep the velocity in the main pipes within a reasonable range (fast enough to keep the dust suspended, not so fast that you create too much drag which limits the volume of air you can move). It is not the correct design for cases where you are only collecting from one tool at a time.

    mark
    Last edited by Mark Beall; 01-17-2011 at 8:08 PM.

  11. #11
    Quote Originally Posted by Dan Friedrichs View Post
    The design of ductwork for a commercial shop is entirely different than a 1-man shop, because there is a possibility of having more than one machine running at a time. Not true of a 1-man shop, so it's best to a have a single diameter of ductwork all the way from the blower to the tool.
    I'm not sure how that would make a difference when reducing the duct size at the machine.

    If people want a more thorough explanation of cyclones, ducting, etc. then check out Bill Penz's site here ... http://billpentz.com/woodworking/cyclone/ducting.cfm

  12. #12
    All you have to do is run a 6" duct, stick your hand in it, and then put a 4" reducer on it and do the same thing. The difference is dramatic, I don't care what any dust collection experts design. This is shouldn't be in question. The questions are:

    1) will the reduction in airflow be enough to prevent effective movement of dust through the ductwork, i.e. will the dust simply fall out and collect in the ducts....if so then you need to add more inlets to keep the airflow up.

    2) will the airflow at whatever inlet or inlets you select adequately collect the dust you wish to collect. That depends on your tool design, not just the dust collector.

    Generally, it's a good idea to take the largest size duct right to the tool, and then if you need to reduce it, reduce it there. That minimizes friction losses, and also gives you the option of upgrading later when you find that airflow to be inadequate.

  13. #13
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    Why not do both, keep your current unit and just add a cyclone body to it in conjunction with the current system.
    Richard Poitras
    Central, Michigan....
    01-02-2006


  14. #14
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    Why not do both, keep your current unit and just add a cyclone body to it in conjunction with the current system.
    Because a 3hp DC relies on it's inherent efficiency to perform well. A 3hp unit has a roughly a 12" impeller. This works great if you're just emptying into a filter or bag. If you add a cyclone body however, the added friction will reduce the airflow significantly. For instance, you might get 1800 cfm in the stock configuration. With a cyclone attached, you might get 1000 cfm (a guess based on a quick look at the 12 1/2" impeller on Grizzly's 1.5hp cyclone). Could be less.

    Even then, you can't just use any cyclone body. Unless the body has correctly placed ramps, neutral vane, etc, it won't work any better than a Thien separator. I figure if you're gonna get a decent cyclone body, you would need a bigger impeller, bigger impeller housing, appropriate filters, etc. to make it work properly. All that can be shop built or purchased in the case of an impeller, but it takes some serious shop time and effort. I think the Thien separator/Wynn filter setup works great for minimal effort.

  15. #15
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    Jamie answered your question. When I went to a cyclone, it was because I was running my thickness sander a lot and I got tired of the cfm loss I experienced with my jet 1100 can unit. If I had your unit, I wouldn't have made the change.

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