On 03/01/2016 7:26 PM, krw wrote: ...
It will, but unless the lengths are quite long which is unlikely in most home/small one-man shops, friction loss difference owing to pipe diameter is likely not a big effect.
_BUT_, for those same shops, the cfm to keep the same linear velocity has to go up by >150% which really begins to strain the size of most DC's folks are going to have at that size shop or want to invest the $$ for...
Length in a home shop may not be an issue. I use the clear wire reinforced flex hose, the robust kind, not the flimsy kind. Anyway it is any thing but smooth inside and is 30' long. It leaves the DC, goes straight up to about 7' high, over 8', and back down to the floor, and lots of loops bends and curves, to what ever I choose to hook it up to. No loss of suction at all. This is with an 1100 CFM DC with the pleated top filter.
I have 3, 10' lengths coupled together.
I think the only time length is going to matter is if you have a bunch of leaking blast gates and or leaking fittings. I have none.
Nor do I. And when I use mine it never has to make a vertical lift. It ro lls around on wheels and is about 12" off the ground when in use, just high enough to let the bag inflate and then droop a bit when getting close to f ull. I probably about about 25 - 30 ft on the collector, down from the len gth of the hose I purchased originally at 50'.
When it was still 50', I didn't have any problems with it in the slightest.
Robert
I may have to go a bit further than I'd like to get to all the tools. I may just service a few of them with the DC, though, and use shop vacs elsewhere.
The port on my DC is 6" (with a 2x 4" adapter), so my thought was to just extend this as the main line(s) and split off that to 4". 6" stuff is a PITA to work with so if 4" works, I'm all for it.
Right now I just have 4" flex hose on the floor and connect the tool I'm using but I want to clean that up so it's not a pain to use the tools.
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" 600As 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..
This link might save you some time and trouble.
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.
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
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.
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.
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.
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. :)
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?
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.
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.
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...
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.
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.
Oh, also...as you'll note on the Pentz site, it's pretty concerned about dust as opposed to simply chip collection. If you're after that level, it'll take a _lot_ more CFM than the 350-400 at each tool that has been the norm. That's shown in the tables there. I've not been terribly concerned figuring there's far more grain dust and such from farming that has no chance't of collecting than what I'll ever make from sawdust... :) For others, have to make own decision on how strict to be in comparison to commercial/OSHA/EEU guidelines.
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