dust collection gripe

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Once again I'm fitting another device for dust collection. And once again I'm irritated by the fact that nothing fits without an adaptor. Seems to me all that should be needed is:
4" male connection 4" female connection 2.5" male connection 2.5" female connection
All hoses should come with female on one end and male on the other.
All dust collection devices should accept a male connector.
All dust producing devices should accept a female connector.
Add the following adapters:
2.5" male to 4" male adapter 2.5" male to 4" female adapter 2.5" female to 4" male adapter 2.5" female to 4" female adapter 4 more adapters, but elbows instead of straight.
Wouldn't that make life a lot simpler?
Maybe I'll send this post to a couple of the woodworking magazines :-).
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On Sun, 28 Feb 2016 01:10:50 +0000 (UTC), Larry Blanchard

I'd be really happy if all 4" male pieces even fit 4" female pieces. I'd give big bonus points if they'd fit 4" PVC pieces.
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On 02/27/2016 9:30 PM, krw wrote:

...

Then you'd have the same problem when using (better if more expensive) metal ducting.
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How is it better than PVC?
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On 02/28/2016 4:10 PM, krw wrote: ...

Lower friction, no static buildup...
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Do you have a reference for friction? Not doubting you but I'd like to understand how big an issue it is. I've never worried much about static (in the woodworking context).
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On 02/28/2016 7:17 PM, krw wrote:

Hadn't seen the reply, sorry...
Not huge altho my experience has been that the static buildup tends to cause small stuff to stick to the surface which can't help.
The static buildup in small shop settings at least is mostly just a nuisance factor that I dislike simply for the effect. It is virtually impossible to ignite a wood dust cloud with it as the ignition source; while pretty high voltage and zap when you're the target, it has very low actual energy. After the other thread I did a little looking but wasn't able to find in a short period the paper I'd seen a number of years ago where a guy at T A&M did some discharge measurements, unfortunately.
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No problem. It's not like it's an emergency. ;-)

I was wondering more about the airflow resistance increase, though I can see where dust sticking to joints wouldn't help. Is there a significant air resistance difference between "clean" metal and "clean" PVC?

Yeah, though others may disagree, I think this horse has been beaten near enough to death.
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On 02/29/2016 7:25 PM, krw wrote: ...

For straight pipe, no. Where I was headed was that the fittings (el's, wye's, etc.) associated with PVC are much tighter radius (even "long" el's) than those used in "proper" dust collection and handling systems and a single elbow is some 5X the dP of 100 ft of straight pipe whereas for the metal ducting with 1.5 radius it's more like 1.5-2.0X. That differential will more than make up for whatever minor improvement the straight PVC might have over the galvanized.
I've got quite a bit of data and design stuff from various sources but haven't ever actually put it all together as a easy-to-use pattern w/o being intimate w/ the details of what the various pieces mean -- stuff like which friction-factor formulation goes with which pressure drop correlation, etc., etc., ...
Since I'm in the process of setting up a new area in the barn and will have to do at least a modicum of this shortly, maybe this will be the impetus to try to consolidate some of that to a more "handbooky" kind of process...
The upshot is, however, that you need to keep the sizes such that for whatever CFM you have the linear velocity for branch lines of roughly 4000 fpm and 3500 fpm or so for main ducts. This will ensure won't have issues w/ drop out and so on. If the chip sizes are small or dust like a sander, you can get by w/ somewhat less; the above are targets for that include planers, shapers, routers, etc., that make a fair-sized chip.
Just for info, though, the difference in cfm required for 3500 fpm is
3" 170 4" 300 5" 475 6" 600
As you note, it goes up by the ratio of cross-section areas, obviously. The fortunate thing is, of course that the percentage increase in area decreases from step to step in uniform diameter increments so the biggest jump is from 3" to 4"; 4" to 5" isn't quite as painful.
Hopefully that helps..
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This link might save you some time and trouble. http://hhrwoodworkingclub.org/Dust%20Collection%20System%20Design%2010%20April%2009.pdf
One thing you did not mention was the inches of water column necessary for the flow. This will help you with the sizing of the DC needed, or if done in reverse what you can due with what you have.
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On 03/02/2016 7:52 PM, OFWW wrote:

Just didn't seem pertinent to the question asked...
Static Head ("in H20) for given diameter at linear flow velocity...
Diam 3500 4500 3″ 7.5 10.0 4″ 5.5 7.0 5″ 4.2 5.5 6″ 3.5 4.5 7″ 2.8 3.8 8″ 2.4 3.2
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To me it does, for how else can you determine the flow in a given size of pipe? If the DC is undersized then the negative static pressure will be less as will the CFM and FPM. I was hoping that the pdf I linked to would help you both. It also confirmed some of what you were saying.
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On 03/02/2016 10:15 PM, OFWW wrote: ...

Of course, but KRW wasn't trying to do a size computation per se, wo was simply pointing out that he does, for the DC he has, need to look at what the effect of his thought of using a given size of ductwork would do to the resulting linear velocity. Have insufficient data available to do anything more.
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On 03/03/2016 12:14 AM, dpb wrote:

Or, for his DC rated CFM where in the table does he fall as a starter? If free air is insufficient volumetric flow, then it's clear it won't with added restrictions.
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On 03/02/2016 7:52 PM, OFWW wrote: ...

...
Oh, I see that's the technical data from Air Handling Systems; that's one of the many pieces and does walk thru a process...being an engineer, I'd intended to automate it and use the actual correlations behind their tables instead...I get fixated on the details _behind_ the big picture. :)
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That helps a lot. Thanks guys. I'll have to digest this some more. Maybe I don't have the problem I thought I did and can use a longer run (with blast gates). Do you happen to know of an easy way to measure the flow rate?
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You can make a U-Tube Manometer. It is the cheapest way I know of, otherwise you can buy one, at an HVAC supply house or WW Graingers.
Measure the inches of water negative pressure, take the inside diameter of the pipe you measured and compare it to a FPM chart on one of the links I provided. It will require that you drill a hole to connect the U-tube to, with no leakage while connected. I can find you a how to on it if desired.
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Sure, I'd appreciate any help here (thank you, again). I probably won't get to the DC system for some time so there is no rush.
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On 03/05/2016 8:54 AM, krw wrote: ...

Easy in theory, the effort to measure it well enough to be meaningful isn't trivial...doable, yes, but must be done w/ care. If you're serious, read Bill Pentz's stuff...
<http://billpentz.com/woodworking/cyclone/Measurement.cfm#Testing%20Setup
Generally you can get satisfactory results by the methods outlined earlier to estimate pressure losses _providing_ the manufacturer of the DC gives realistic data. That may or may not be a reasonable assumption unfortunately.
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On 03/06/2016 12:19 AM, dpb wrote: ...

That is, computing pressure drops is pretty basic and reasonably accurate from which the requirements can be estimated. Then you're relying on the stated capacity of the chosen DC to actually match what it performs at--if they'll supply an actual head curve other than just total no resistance CFM you've got better chances the data are valid.
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