Replies

1. 
   Quickstep | Jun 04, 2007 05:29am | #1

   Wondering if you've considered an Oneida cyclone. It sounds like you're into doing the math, but Oneida offers a design service.

1. 
   brucet99 | Jun 04, 2007 09:41am | #2

   "Wondering if you've considered an Oneida cyclone."I'm more interested in a Grizzly, especially after seeing their performance data from side-by-side comparisons with Oneida and the extra features they include.Oneida's design service is available only after you agree to buy their machine. Seems like there'd be an incentive to steer the customer into a bigger, more expensive unit.

1. 
   PlaneAround | Jun 09, 2007 07:46am | #14

   I ended out purchasing an Oneida Pro 1500 3HP cyclone 6 months ago, after looking long and hard at the competition - and haven't regretted my decision for one second. Their 5 year guarantee on the Pro series can't be beat... although the quality of the unit makes me believe I will likely never have to use it. As regards your comment about their duct design service, I found them to be very customer-oriented. I never felt they were trying to sell me anything while they walked me through the process. Remember: a dust collection system is like any woodworking tool: you will eventually need the manufacturer's support, even if it is to get some spare parts from them, many years down the road. Oneida's sole product is dust collection and they're set up to ensure availability of spare parts and advice for many years to come. I'm not sure that the same can be said of the other companies - who sell every piece of woodworking equipment under the sun. Incidentally, I don't have any affiliation with Oneida, other than having purchased a unit from them.Marty

2. 
   Cowsine | Jun 04, 2007 06:58pm | #3

   Are the values given for the same airflow or the same airspeed? In my diagrams the resistance/drop in pressure is higher in smaller diameter elbows for the same flow, as you believe it should. Unfortunately my values are metric.

1. 
   brucet99 | Jun 05, 2007 09:20am | #6

   "Are the values given for the same airflow or the same airspeed?"Same velocity - 4000 FPM."In my diagrams the resistance/drop in pressure is higher in smaller diameter elbows for the same flow, as you believe it should. Unfortunately my values are metric."Metric units are convertible. Can you share your values for similar-sized ducts? 10cm, 12.5cm, 15cm, 18cm at perhaps 1000m/minute or 1250 m/min? 90 deg elbows at center radius = 1.5x diameter and 2.5x diameter.

1. 
   Cowsine | Jun 05, 2007 01:02pm | #7

   "Metric units are convertible"Yes, they are, but when one ventures into the realms of pressure and flow it's just not fun anymore. :-) Sure has confused better engineers than me http://www.cnn.com/TECH/space/9911/10/orbiter.02/I started reading diagrams but got bored so I googled some instead, and found: http://www.spiralmfg.com/downloads/elbows_engineering.pdfChart and table 51-1 is probably the ones of interest. The equivalent length of straight pipe is found at the last page and I assume it is possible that errors may have come from using similar aproximated values to calculate the resistance at an elbow. I'm not sure how much dust and debris affects the values, but I have a very vague recollection of typical woodworking applications beeing almost equal to air, but I could be wrong.

1. 
   brucet99 | Jun 06, 2007 06:52am | #8

   Thanks for finding that Spiral Manufacturing site. Within that engineering document there is a chart showing 90-degree elbow resistance values at 4000 FPM in linear progression from about 0.12"wg for 7" diameter elbow, to 0.3"wg for 3" diameter.There is also a table giving the same nonsensical "equivalent feet of straight pipe" values that the how-to books use where 3" elbow causes less flow resistance than a 6" elbow but more resistance than a 4" elbow.In your earlier post you said you had metric numbers that gave elbow resistance in linear progression in metric units. Are those static pressure values that could be compared to straight pipe values in similar sizes to 4",5" and 6" pipes?

   Edited 6/6/2007 2:20 am ET by brucet99

1. 
   Cowsine | Jun 06, 2007 06:52pm | #9

   "Within that engineering document there is a chart showing 90-degree elbow resistance values at 4000 FPM in linear progression from about 0.12"wg for 7" diameter elbow, to 0.3"wg for 3" diameter."Yes, chart 51-1, about equal to mine. "In your earlier post you said you had metric numbers that gave elbow resistance in linear progression in metric units. Are those static pressure values that could be compared to straight pipe values in similar sizes to 4",5" and 6" pipes?"I found the equivalent chart on page 7 (56) of this more complete document: http://www.spiralmfg.com/downloads/engineering_data.pdf
   Just find the relevant intersection of the red and blue lines and read the SP loss at top or bottom. (The "equivalent length" table is roughly based on this chart and the 51-1 chart)"There is also a table giving the same nonsensical "equivalent feet of straight pipe" values that the how-to books use where 3" elbow causes less flow resistance than a 6" elbow but more resistance than a 4" elbow."It's just meant to be used for a very rough estimate with too few significant figures for calculations. Unfortunately they haven't got a chart for CLR 2.5, only the "Quick Reference Chart". As they say themselves, even this document presents a very simplified method but it is probably quite adequate (not including the "nonsensical" parts :-))for a smaller system.I also found: http://www.spiralmfg.com/downloads/dust_collection.pdf
   But for a small shop you would probably choose you dust collection unit first based on your budget and try to design your ducts around it (could require the units fan curve).To get the most from the fan unit the trick is probably to avoid elbows and tees at just about any cost, :-) since they really reduce the possible length of the system at larger diameters. PVC has definitely got an advantage here since it is possible to shape ducts to a very large CLR, thus reducing the SP loss. It's obvious, but I'll mention it anyway, flex ducts have a higher SP per feet than typical metal/PVC ducts but should probably be considered at times.To really reduce the tees and elbows I guess one could construct a system inspired by railroad switches and using large CLRs where possible. Don't know if it would be worth the effort but it is an alternative...In the end it's "just" a matter of summing up the SP losses in ducts, tees, machines, filters and bends, trying to hit the sweet spot of the fan unit. :-)

3. 
   DanG | Jun 05, 2007 01:13am | #4

   What reference books did those numbers come from? If you go to

   http://www.woodworkingtools.com/Editorials/february.html

   in Step 3 the static pressure loss for 90 degree elbows is given in terms of equivalent feet of straight duct.

   For 4", 5", and 6" elbows, the equivalents are given as 6 feet, 9 feet, and 12 feet, respectively. The static pressure loss per foot of straight duct for those sizes is given as 0.055, 0.042, and 0.035 in/ft, so if you multiply the inches per foot loss by the number of feet, the static pressure losses for the elbows work out to 4" = 0.330 in, 5" = 0.378, and 6" = 0.420 in.

   Those losses do increase with duct size, like the numbers you cited. However, the corresponding CFM numbers are given in Step 2, i.e., 4" = 400, 5" = 650, and 6" = 800. It is not the same CFM for all sizes.

   The information on the site above is courtesy of JET Equipment, so I would expect that the CFM numbers in Step 2 are their recommended maximum flow rates for those particular duct sizes. In turbulent flow, pressure loss is a function of the flow rate squared, so based on the numbers above, the losses you cited would correspond to flow rates more like 450, 750, and 950 CFM. It may be that the numbers you found are based on recommended maximum flow rates from some other supplier. In any case it seems certain they are not based on having the same flow rate for each size.

   Dan

1. 
   brucet99 | Jun 05, 2007 09:10am | #5

   "What reference books did those numbers come from?""Controlling Dust in the Workshop", Rick Peters; "Dust Collection Basics", Woodstock International. I got Taunton's "Woodshop Dust Control" today and found the same "equivalent feet of straight pipe" numbers as Rick Peters' book and yours. They all seem to have gotten their info from the same source. "Those losses do increase with duct size, like the numbers you cited. However, the corresponding CFM numbers are given in Step 2, i.e., 4" = 400, 5" = 650, and 6" = 800. It is not the same CFM for all sizes."CFM differs with size, but all are at the same velocity (FPM). Your numbers are for 3500 FPM, mine were at 4000FPM needed in branches, but the anomalies are still there. "In turbulent flow, pressure loss is a function of the flow rate squared"
   Well, flow rate is assumed to be the same in all of the charted "equivalent length" values (either 3500 or 4000 FPM) so why would a 6" duct cause way more resistance than in a 4"? Is there some resonance factor with diameters between 4" and 7", or is everyone publishing data from the same flawed test?

1. 
   DanG | Jun 07, 2007 12:59am | #10

   I did some Googling last night and found the same Spiral Manufacturing site that Cowsine did, as well as a few others. They seemed to pretty much agree regarding equivalent straight pipe, but there were some small differences in pressure loss, e.g., between Spiral's Table 55-2 and Chart 2 athttp://www.airhand.com/designing_charts.asp#chart3Judging from the fractional exponents in the equation at 55-2 there was some heavy curve fitting going on, so differences of opinion there shouldn't be too surprising, especially if the others were simply eyeballing charts.I wasn't able to find anything that referred back to an original source for the data, and don't have either of the books you mentioned, so I don't know if they do. In any case, I would think that as a Knots member and a bona fide Taunton customer of Sandor Nagyszalanczy's book, your best approach would be to email Matt Berger and see if he can forward your question to Sandor Nagyszalanczy. Much better to Ask the Expert, especially since it's all within the same Taunton family.And when you find out, please let us know.Dan

1. 
   brucet99 | Jun 07, 2007 07:12am | #11

   "Much better to Ask the Expert, especially since it's all within the same Taunton family.And when you find out, please let us know."Thanks, I did just that but so far got only an auto-reply from Taunton.I e-mailed Spiral about the fact that two of their charts/tables disagree with one another. Got a quick response saying, "You are right, we are working on this and I will get back to you just as soon as I receive the updated information."I'll keep you all posted.

4. 
   PADDYDAHAT | Jun 07, 2007 09:09pm | #12

   Bruce, don't beat your self to death squeezing all those numbers. As far as I know, there is no penalty only better performance for having too much air flow. Just buy the most air flow that you can afford and still fit in your space and consider the size of the removable cans/bags, their costs and the reputation and tactics of the vendor.

   A blast gate ( a quality one-not the plastic junk) at each primary machine and or  leg of the system and the absolute least amount of flex hose that you can get away with even if it's a PITA to fit the pipe as close as ya can.

   There are certain tools or equipment that require the most or strongest you can do to be very effective like; pressure water cleaners, hammer drills, sawzalls, chain saws, and DC Cyclones etc. They will work better, faster, live longer and you really only want to only do it once. Makes sense to me. Good luck, Paddy

1. 
   brucet99 | Jun 08, 2007 05:09pm | #13

   Thanks for your comments, Paddy.I do in fact have a space problem that may limit me to a 1 1/2 hp cyclone and it would have to be set up in the opposite corner of my garage from the tools, thus requiring long duct runs and some elbows in the main line as well as comparatively long flex hose sections to enable pulling the table saw out from the wall during use and a ceiling drop for the miter saw. I also wanted to try to build in as much capacity as possible to handle future addition of a planer that would require more air flow. All of these factors bring the calculations close to the rated capacity of the cyclones I am looking at.

1. 
   PADDYDAHAT | Jun 09, 2007 08:22pm | #15

   Bruce, I too had a space problem so I did a JDS cyclone (JDSTOOLS.COM ) to fit my 7'10" overhead in the shop. BTW, your email dosen't work ya better check your profile. Paddy