Most affordable SDR-35 6" fittings?

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ryanjg117

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I'm about ready to finally install my CV1800 and, since I have a fairly long run, I want to be sure to use 6" pipe pretty much everywhere. I'll be using ASTM-2729 sewer pipe for the runs, and while the pipe doesn't cost and arm and a leg, the fittings certainly do. I'm located near Seattle and we do have a Ferguson nearby, but I was wondering if that's the best/cheapest place to purchase these fittings or if there is a better alternative? Also, are SDR-35 fittings the best option (e.g. the cheapest) or are there other fitting alternatives? Thanks.

EDIT: I just re-read Bill's Duct Design page and realized he mentioned HVAC fittings as being fairly compatible with S&D pipe. I also noticed they're WAY cheaper than SDR-35 fittings. Anyone have experience retrofitting these fittings onto S&D pipe? Thanks.
 
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Unfortunately, you'll pay $20-22 for 6" wyes, but 6" couplings and 6" 45* elbows (and 22-1/2* if you need them) are pretty cheap. Just bite the bullet and you won't regret staying with PVC. By the way, most S&D fittings are compatible with D-2729 or SDR-35 pipe since they have the same outside diameter (many are marked for both). Do not use 90* elbows as they are usually short radius and reduce flow (use two 45's and a short section of straight pipe). Considering the investment you've already made, the ductwork cost is not all that bad. I would recommend that you look at Home Depot, Menards or Lowe's -- if unsuccessful there, try farm supply or irrigation suppliers.
 
Robert I see people advising to use two 45's and a short straight section as being better than a 90* elbow. On another forum that was challenged by the information in this pfd.

http://www.lorencook.com/PDFs/Catalogs/Cookbook_Catalog.pdf

On page 54 it shows the losses of elbows in equivalent lengths of straight pipe. The loss of a 3 piece 90* (close to what you describe) is 3 times that of a short radius smooth 90* elbow. Even if you take the 45* elbow numbers they are approximately the same as the short radius 90* and worse if the 90* has a bigger radius. So from that it would appear that using the 90* isn't going to harm the performance of the system.

To double check I played with this duct friction loss calculator and came to the same conclusion.

http://www.freecalc.com/ductloss.htm

Using 6" round duct, 40' long and an airflow of 1500 and stamped elbows as they are closest to PVC. With 6 elbows of 90* with .75R it shows a loss of 13.3 inches of water. The same with only changing to 12 elbows of 45* gave the same loss of 13.3 inches of water. The loss ratios stay the same no matter the number of fittings if the radii are the same.

So has anyone done any actual tests of the losses of two 45* elbows with straight section against a 90* elbow to see if it is the better arrangement or is just an assumption that has become an internet fact? I'm not trying to infer that you are mistaken, just want to understand better.

Pete
 
McRabbet, where are you buying your fittings? This is the best quote I could get from Ferguson, with a contractor discount to boot. Fittings are more like $37 apiece.
 

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Check Menards and Lowe's. Not all Lowe's carry the 6" drain fittings but you may get lucky. Menards has a good selection and priced reasonably even with the shipping. Pipe, McMaster-Carr. I was fortunate that there is one locally and I did not have to contend with shipping. They also have fittings.
 
Hcollado, good call on McMaster-Carr. Certainly the best price for fittings that I've seen so far - about $26 for a 6" wye. My only concern with McMaster-Carr is that they don't provide you an estimate on shipping charges before you place the order...
 
Curly1,

I question the values in the document you cited when applied to dust collection where velocities are much higher in the ductwork as compared to HVAC ducts. According to Bill Pentz' description of 45* elbows versus 90* elbows, he states in his StaticCalc spreadsheet (lines 41 and 42):
Enter the number of pipe 90's. Count 0.5 for each 45 degree bend and 1.0 for each full 90.
R/D is the ratio of the bend's centerline radius divided by the pipe diameter.

I have had very good results using a pair of 45's separated by 18" to 24" of straight S&D pipe. Typical 90* elbows I have found have a short and tight bend, which renders them unusable for dust collection -- McMaster Carr has both short and long radius 90* elbows and has good drawings to show their dimensions -- see
https://www.mcmaster.com/9102k123 for short radius and https://www.mcmaster.com/9102k116 for their long radius. Despite their name, the long radius elbows are still fairly tight for our dust collection.
 
Thanks. I'll look into this further but because of the high cost of PVC here ($10 - $16 per foot for 6" and $16 - $24 per foot for 8", you don't want to know about fittings) and spiral-lok being a little less, I'll be making mine out of plywood. The losses for rectangular and being able to make long radii of 3xD or better should minimize the losses with the CV-Max. Shop is 23.5' x 27' inside. Shipping stuff like that across the line is too expensive even without factoring exchange and taxes. Different if I lived close to the border but I'm over 6 hours North.
Pete
 
What I've discovered is that McMaster is far and away the best option for 6" SDR-35 fittings, while my local plumbing supply (Ferguson) is by far the best pricing on actual pipe (about $1.80 per foot).
 
McRabbet said:
Curly1,

I question the values in the document you cited when applied to dust collection where velocities are much higher in the ductwork as compared to HVAC ducts. According to Bill Pentz' description of 45* elbows versus 90* elbows, he states in his StaticCalc spreadsheet (lines 41 and 42):
Enter the number of pipe 90's. Count 0.5 for each 45 degree bend and 1.0 for each full 90.
R/D is the ratio of the bend's centerline radius divided by the pipe diameter.

I have had very good results using a pair of 45's separated by 18" to 24" of straight S&D pipe. Typical 90* elbows I have found have a short and tight bend, which renders them unusable for dust collection -- McMaster Carr has both short and long radius 90* elbows and has good drawings to show their dimensions -- see
https://www.mcmaster.com/9102k123 for short radius and https://www.mcmaster.com/9102k116 for their long radius. Despite their name, the long radius elbows are still fairly tight for our dust collection.
Click to expand...

I am in the process of setting up my first CV1800 system and as such am reading as much of this forum as I can. I do find this discussion interesting however. I went through the bulk of the Bill Pentz spreadsheet and don’t see anywhere where he indicates that 2 x 45 deg fittings is any more efficient than one 90. As McRabbet points out, he uses 0.5 units for each 45 and 1.0 for each 90 indicating that two 45s is equal in loss to one 90. In his example he states 2 90s and one 45 would equal 2.5 90s. So, I’m starting to believe the 2 x 45s is better than a 90 is lore of some sorts. Not saying it won’t work, just saying it might cost more for no real benefit. And, a sweeping 90 might be even less loss and thereby a better choice. Only jumped in because after reading the spreadsheet it looked to me as if Curly1 might be onto something here.

Thanks to all that have posted on here. I am learning a ton of awesome info and will have a much better DC system in the end because of you guys and gals.
 
I have found that the 90 degree elbows found at plumbing supply houses or the big box stores have tight turns (usually 1-1/2 radius) so they have higher turbulence and static pressure loss when compared to longer sweep 90's (3 x radius) or the combination of two 45's connected by a short straight section. In addition, the strategy of creating a drop from a horizontal pipe is best done using a wye with the 45 part facing down, a short straight section and a second 45 to the down pipe to a blast gate. This works well when the horizontal pipe needs to continue along the ceiling. By the way, most of the manufacturers label the fittings with both D2729 and 3034 (the latter corresponds to SDR-35 pipe, which is lime green and has the same outside diameter as D2729 but has thicker walls). McMaster Carr carries the sweep 90's and yes, one is cheaper than two 45's.
 
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