Pex, fittings, and low ph water
dfvellone
| Posted in General Questions on
I’m moving on to plumbing in my house project and to begin the research into the world of pex (I’m a copper guy who’s soon heading back to square one.) I currently know nothing about the different fittings options.
My well water has a ph of 6.24 and my question is if that factors into any decisions on which way to go with fittings, if that even makes a difference.
Thank you, Daniel
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Replies
That's not that low, in my home state of Massachusetts when they talk about low pH they mean something with a four in front of it.
I think PEX with brass will do better than copper in low pH.
After plumbing my entire house with Uponor expansion PEX and fittings, I cannot imagine using any other PEX system. The productivity of the system is astounding.
PEX is crosslinked polyethylene -- a VERY stable material. PEX will be fine with 6.24 ph. That's not really that acidic anyway, I don't think you're likely to have any real problems regardless. I woud try to stick with the compression type PEX connectors that use a metal crimp ring though. I'm not a fan of any of the push to connect type fittings for permanent installations.
Bill
My concern is the fitttings, which I don't know much about yet, and if any part is metal that comes in contact with the water. I've had issues here with copper and the waters ph. Aside from having to flush the system anytime the water's not been run for over 30 minutes to get the copper taste out, I've gone through two heat exchangers in 15 years that had corroded from the inside out.
Most of the good fittings are brass, but there are poly ones too. The poly fittings won't have any problems with the pH level of your water. The brass fittings are not recommended (below 6.5, which you have, is too acidic), but there will be a relatively small amount of them compared to the amount of PEX in the system so you shouldn't notice any taste the way you did wit hcopper pipes. With copper piping, there is a LOT of copper in contact with the water, but with PEX, only the small amount of metal in the fittings would be in contact with the water.
Overall, PEX is going to be better for you here.
Note there are also thermally fused fittings (such as in the Aquatherm system), but I'm not sure if anyone makes anything like that for the small fittings typically used on residential water systems.
Bill
I haven’t seen anyone mention it but you should also be aware that there’s Pex-A and Pex-B. Generally speaking, anything that you find at the big box stores is Pex-B and is going to use clamp, cinch, or push to connect fittings. These fitting types reduce the ID at each connection point. Pex-A on the other hand uses cold expansion fittings and actually better maintains the ID of the pipe at the connection point. Pex-A also has better flex than B. If you’re doing a small remodel the B stuff is probably fine but anything major and A would be recommended. Biggest downside is that the expansion tools can be quite pricey compared to their clamp/cinch counterparts for pex-B
Zach,
I'm not convinced the difference is significant enough to worry about. Pex B with compression fittings has been used in almost every residential project here in BC for the last 20+ years. I don't find the reduction of volume at fittings is significant enough to need compensating for - remembering that the end fittings (faucets, hose-bibs, etc.) all have small apertures anyway.
It isn't worth worrying about in any normal residential systems. The slightly reduced ID of the fitting is typically less restrictive to flow than the run of the pipe. You do get an "equivalent head", so a fitting might count as 5 feet of pipe or so, but it's not worth worrying about.
Unless you're running really high pressures, slight restriction of pipe fittings is only very, very rarely something to be concerned with. I suppose on the flip side, with very low pressures (natural gas systems), you have to worry more about pressure drop, but you just use the "equivalent feet of pipe" method for all the fittings, so it's not a big deal there either -- just add up all the feet of pipe, equivalent feet of pipe of the fittings included, then check against the tables for allowable flow rate for a given size pipe run of that length.
In all of the many, many chilled water systems I've been involved with at work (the largest of which had 42" diameter main pipes!), There are only TWO locations where the fitting diameter matters: one is in the inlet and outlets to pumps (where turbulent water flow can be a problem for the impellers in the pump, which increases wear and reduces life of the pump), and near venturi fittings (flow meters that use certain effects of turbulent flow to measure flow rate through a reduced aperature of known area that is made in a certain shape).
Note that common theme of "turbulent flow" here. That's what's important in my designs, not the flow reduction of the fitting itself. Everywhere else in the system I just use whatever fitting is needed for the size of pipe I'm running and I don't worry about it. Even the big victaulic fittings on 8" (and other sizes) of steel pipe reduce the inside diameter of the pipe a bit during the grooving process that makes the grove in the pipe that the fitting clamps onto. No one worries about it. I've had some systems running for over 20 years in 24x7 service too, and we don't have any abrasion issues in the fittings, so don't let anyone tell you that's a problem either.
The bigger question for me is why does an electrical engineer (me) get stuck doing so much mechanical engineering (pipe sizing and flow rates) work at work? Hmmm.
Bill
"Why does an electrical engineer (me) get stuck doing so much mechanical engineering (pipe sizing and flow rates) work at work?"
Only you can answer that one Bill :)