Bending strength of PB vs PEx pipe

[Steve S.]

Hello All,

I haven't posted in awhile...but I do lurk on occasion...still one of the best websites out there! I have a question concerning polybutylene pipe for all of you plumbing experts. What is the maximum amount of bend that PB can withstand w/o damage or potential failure? I know that bending ability of plastic pipe is one of the advantages over copper since fewer fittings are required. When I had my bathroom floor torn out (the result of an acetyl fitting failing at water heater) I noticed that some of the 1/2" PB supply lines were bent and twisting all over the place...the supply to the toilet was in an S-curve(and could have been routed with less curve if the t-fitting had just been reversed). None of my PB pipes have failed yet (knock on wood) mostly just leaks at corroded AL crimp rings and that one elbow fitting failure. I suppose PEx has even less ability to bend since the walls are thicker...but I would think that 90* would be the maximum for any plastic pipe. Maybe the experts will prove me wrong. I have entertained the thought of replacing all my PB with PEx...perhaps this summer. I've always been one that adheres to the old adage, "if it ain't broke, don't fix it"...but knowing that a potential disaster is just one failed Qest fitting away, makes me nervous.

[JD]

Hi Steve,

The bending limitation for both PB and PEx is measured in Radius. From what i remember, PEx has a 4" minimum radius, which could make an 8" ID circle. Proper clamping to structure would be needed to anchor the pipe secure. From personal experience, PB will not turn nearly as tight. PEx can turn within a 2x4 wall, where as PB cannot. it has been over 20 years since i heard this, but I remember it as PB has a turning radius of 10 times its OD measurement. This would give 1/2" pipe about an 8" turning radius.

I have no engineering skills, so consider all of the above just an opinion. Maybe someone with more verifiable info will pipe in.

The supply line to the toilet would be easy enough to rectify. You could cut the PB above the floor and install a PB to PEx coupler. Then a short piece of PEx pipe to a PEx shut-off, or to a 1/2" thread fitting, to a standard shut-off valve like the BrassCraft brand at home Depot. Then add your flex supply line. Or you can go to a SharkBite fitting.

You may be able to eliminate the PEx altogether by cutting the PB above the floor and using a BrassCraft PushFit Shut-Off valve. I just found these at Home Depot a several months ago and have used them several times. Basically, it is a 1/4 turn brass valve with the SharkBite incorprated into it. But just as with SharkBite, GatorBite and the rest of the push fitting products, they are not approved for Polybutylene pipe use. It is not that they won't work. We all know that they do work. But PB is not an approved residential plumbing anymore. Well, not here anyways. I use these push fit valves on copper pipe stub outs and they are great.

JMO
JD
Not a plumbing "expert"

[Steve S.]

Thanks JD, I feel better about the bends in my PB pipe under the floor as most don't even come close to resembling an 8" circle. On second thought, after you proposed my above floor toilet supply line fix(which I need to do anyhow because of an inoperative Qest shut-off valve), maybe the pipe was configured in an s-curve to provide more length of pipe to pull up through the floor in case of a future repair. Hard to believe that MH construction plans would put any thought into future problems though, like using particle board for flooring in a bathroom! And my bathroom floor WAS carpeted as well...crazy.
-Steve

[Lorne]

I know I'm a little late, but I saw these brackets a while back for bending PEX to a large radius 90 Degree angle.
http://www.pexsupply.com/PEX-Bend-Supports-719000
I couldn't find them locally and work around my problem. I didn't want to bend my 22 year old PB too much. Hope this helps someone.

[JD]

Thanks for the link Lorne. Never used those before but they look like a good idea. They are very cheap, so I will be picking up a couple of boxes.

JD