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Thread: Should I keep this DC or go Cyclone?

  1. #31
    I also use a PT separator and vent outside. Living in a very-close-packed suburban neighborhood, I can't just blow all the sawdust outside. So I catch nearly all of it with the PT separator, then blow just the very fine stuff outside. There is absolutely no dust visible outside.

  2. #32
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    Quote Originally Posted by George Bregar View Post
    The PT separator, like a cyclone, removes much of the fine dust, but not all. My point was to your comment of your "neighbors window"...there is an inconsequential amount of fines to worry about
    Fair enough. My point was that if the remaining dust was truly inconsequential (of no consenquence), then there would be no need to exhaust outside. I live in the country, and could exhaust outside with no separation, but chose not to do so due to the heat loss issue. However, I'm sure there are those around in subdivisions where houses are close enough that even a separated exhaust would be an issue with a picky housewife doing her dishes while looking out the open kitchen window.

    And while it is true that both restrict flow, you can upgrade a single stage DC with a PT and get better performance for much less money. A Grizz 2HP cyclone is a grand, a 3HP single stage is $400.
    Agreed. That's why I recommended to the OP that he not upgrade until he considers options 1-3. I guess now he also has options 2+3 combined to considered, given your comments.

    My woodshop is actually in Northern WI at my lake home. I plan on exhausting outside for most of the year but using a filter in the winter for the very reason (heat loss) that you bring up. The PT will reduce the fines getting to the filter, and eliminate the hassle of emptying bags.
    Are you exhausting outside to improve air flow in your shop? If the PT design had been around when I was looking at DC for my shop in '05, I probably would have considered using the PT with good canister filters after it. I looked at either direct exhaust or building my own cyclone (seemed like a lot of work, but I didn't want to lose shop heat which is precious during the time of year when I have the most time to do woodworking). Then, I found a good deal on a used cyclone and jumped on it (same price as a Grizzly 1 stage).

    Going the extra step of creating some diverter system to vent outside and inside to filters just seems like a lot of trouble to me, and I don't see the extra upside . . . other than perhaps reducing the number of times you have to clean the filters. Then again, I don't like to make things any more complicated than they absolutely have to be. Your solution does sound interesting. Good luck with planning and implementing it, and enjoy the time at the lake house!
    Last edited by Homer Faucett; 01-21-2011 at 4:39 PM.

  3. #33
    The reasons to vent outside are:

    1) better performance because you're removing restriction
    2) HEPA filters are expensive so you want them to last forever if you can manage it. They certainly don't last forever.

  4. #34
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    LA & SC neither one is Cali
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    I once had a thought about using a canister filter DC and attaching PVC to the top center with a true union ball valve then venting outside. With the twist of a valve one could convert, not the best solution for a convertible system but easy and cheap.

  5. #35
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    Quote Originally Posted by Homer Faucett View Post
    Fair enough. My point was that if the remaining dust was truly inconsequential (of no consenquence), then there would be no need to exhaust outside. I live in the country, and could exhaust outside with no separation, but chose not to do so due to the heat loss issue. However, I'm sure there are those around in subdivisions where houses are close enough that even a separated exhaust would be an issue with a picky housewife doing her dishes while looking out the open kitchen window.
    I could exhaust outside w/o separation my shop has woods behind it but will probably keep the PT because of ease of emptying...I'm doing a 55 gallon drum conversion...and to accommodate winter when I will be going thru a filter.

    Quote Originally Posted by Homer Faucett View Post
    Are you exhausting outside to improve air flow in your shop? If the PT design had been around when I was looking at DC for my shop in '05, I probably would have considered using the PT with good canister filters after it. I looked at either direct exhaust or building my own cyclone (seemed like a lot of work, but I didn't want to lose shop heat which is precious during the time of year when I have the most time to do woodworking). Then, I found a good deal on a used cyclone and jumped on it (same price as a Grizzly 1 stage).
    No, to save wear and tear on and cleaning the the filter

    Quote Originally Posted by Homer Faucett View Post
    Going the extra step of creating some diverter system to vent outside and inside to filters just seems like a lot of trouble to me, and I don't see the extra upside . . . other than perhaps reducing the number of times you have to clean the filters. Then again, I don't like to make things any more complicated than they absolutely have to be. Your solution does sound interesting. Good luck with planning and implementing it, and enjoy the time at the lake house!
    I was thinking of doing a diverter but will probably remove the "duct" on the DC and run my own ducting outside in the summer, reinstall in the winter. Can't take more than five minutes. Worth it not to have to clean filters for nine months. My BIL will fab up the "square to round" transition. He works with metal.

  6. #36
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    Quote Originally Posted by John Coloccia View Post
    I disagree that you maintain the same flow when you transition to 4".
    That was never stated...at least by me. Please re-read my earlier response.

    The statement that I was responding to was that "adding a 4" duct at the end of a 6" run makes the run behaves like it is all made up of 4". That is simply not the case whether calculated or properly measured. Rather, it makes the run behave less than an entire 6" duct run but more than an entire 4" duct run.

    By the way, air is indeed an ideal gas (PV=nRT), but that's irrelevant in the discussion here. That's because there are no density changes at these low pressure differentials (i.e., systems typically operate with a differential pressure of less than 1 psi) and are therefore considered an incompressible gas at these low pressures (i.e., P & V remain constant). Also, the temperature (T) doesn't change significantly from start to finish. So, nothing changes in the ideal gas equation of PV=nRT and it can be ignored.

    Jeff
    Last edited by Jeffrey Makiel; 01-22-2011 at 6:17 PM. Reason: Gramma'
    Thank goodness for SMC and wood dough.

  7. #37
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    bags on most dc's really block a lot of airflow. I had a jet 2hp dc and put the impeller and motor on a clearview and I saw a good increase in airflow. for the most part most dc's don't have enough bag area to really get the airflow they are rated for. my clearview got upgraded to to the 5hp setup and I went with huge bags. I have 5 30"x8' bags and they never fully inflate when in use so they don't restrict airflow. it makes a big difference.
    Steve knight
    cnc routing

  8. #38
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    Quote Originally Posted by Dan Friedrichs View Post
    Jeff, I don't know enough about fluid dynamics to argue this point with you convincingly, but I do disagree with you, because based on my extensive reading on dust collection, I know that what you're saying is contrary to what nearly everyone else has concluded. Bill Pentz's website explicitly says:
    "Even reducing ducting size right at the machine for the shortest possible distance to a small 4" port will still kill system performance. The smaller ducting, flex hose, and small ports limit the maximum airflow..."

    I think your mistake is, as John says, assuming ideal compressible gases. As such low pressures, you will not compress air.

    I disagree with your static pressure numbers. Bill Pentz has a static pressure calculator on his website. Using it, I find that in order to get the 2" of water you spec'd, you'd need 47' of 6" ducting. 47' of 4" ducting will only produce (according to the calculator) 3.3" H20, not the 8" you specified. Clearly you are making some simplifying assumption about fluid flow that is incorrect in this application.
    Dan...we are talking about one 4" fitting right at the machine. I'm assuming this was done to accommodate a 4" port on the machine itself. The example you provided from the website talks about including additional 4" fittings along with 4" flex duct, which has a very high loss factor due to its roughness and bends. This is more than just one fitting as the OP discussed.

    As for the ideal gas thing... I agree... Ideal gas laws are irrelevant here. I'm not sure how it entered into our discussion. Please see my post directly above this.

    Regarding the Bill Pentz calculator, I suspect that your design flow in the 4" duct was less than the 6" duct. Please check to see if the flow thru the 4" duct is less than the 6" duct. This appears to be a neat calculator that includes fan response as well as duct design.

    However, I did find one qualitative statement on the Excel calculator chart that helps assert my point: "Pipe loss factor based on 4000 FPM. This loss factor increases rapidly as the airspeed increases." Boy...is that true and possibly understated!

    Perhaps my earlier post was overly worded, my apologies. But, if you try to push the same design air volume (in CFM) thru a 4" duct as a 6" duct to satisfy the needs of the machine, the velocity will double and the pressure loss will increase four fold. That's Mother Nature, not theory. In response, the dust collector blower will see the increased pressure and therefore reduce its output until a happy medium between pressure loss and flow capability are met. In the end, the flow thru the 4" duct is reduced. This all happens because of pressure loss, and is worsened because pressure increases as a square of velocity. That's why we get a big bang for the buck when going with a 6" duct vs. a 4" duct when operating a 2 or 3 hp dust collector.

    To summarize, a 2" pressure loss thru a length a 6" duct at XX CFM will equate to an 8" loss thru a 4" duct of similar length at the same XX CFM. Therefore, flow must be reduced (high flow at 8" vs. less flow at 3.3") unless you get a much, much bigger dust collector blower to supply 8" at the desired high flow. Sorry, no other way around it!

    Jeff
    Last edited by Jeffrey Makiel; 01-22-2011 at 6:34 PM.
    Thank goodness for SMC and wood dough.

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