View Full Version : Threaded PVC Fittings

10-21-2005, 06:52 AM
I replaced galvanized nipples at toilet and cold lavatory supply valves with gray PVC nipples. What would be wrong with using them for the hot supplies as well?

10-21-2005, 06:58 AM
OTher than the fact that they can, and often will, crack at the threads, even on the cold water side, and that the hot water will soften them, I guess nothing. It is your house and you can flood it if you want to.

10-21-2005, 07:03 AM
Are these a pvc nipple or a nylon nipple? If grey pvc then are they SCH 80? Please explain whey these nipples will crack and break. This is something i was unaware of.


10-21-2005, 07:42 AM
PVC is not allowed within a dwelling by any code. Plastic nipples do have a tendency to crack at the root of the threads. In CPVC work, I do not know if nipples are used. I would prefer a glued stub-out.

10-21-2005, 08:37 AM
For what it is worth, they are SCHD 80. Sounds like a bad idea though.

10-21-2005, 09:27 AM
For sure....

Bob NH
10-22-2005, 12:22 PM
PVC is weak when hot; therefore not suitable for hot water even where permitted by code. CPVC is ok for hot water but may be expensive.

10-22-2005, 01:04 PM
Is there somthing other than hot water in homes that makes PVC a particularily bad choice? What makes PVC fail at the threads? Does the size or sch of PVC make a difference?

10-22-2005, 01:29 PM
What makes PVC fail at the threads? :::: It's plastic for gosh sake!

Does the size or sch of PVC make a difference? ::::: size always matters.

10-22-2005, 02:30 PM
I have seen every size of PVC break at the threads. It is a rigid material that has absolutely no tolerance for lateral stress. Especially after a lot of material is removed to thread it. If you move/bend the PVC sideways at a thread it will crack.

10-24-2005, 01:38 PM
How about useing brass nipples. Install today and they'll be good as new when all of us are worm food.

10-25-2005, 08:15 PM
Are we talking pressure PVC or dwv?

I have seen municipal pump houses, well pits, stock water pipelines, and other work done with all PVC fittings. I will concede that often when the pipe is four, maybe three, inches or larger flanges are often use; however small pipes are pretty much put together with threaded pvc. I do notice that many buried PVC fittings in engineered jobs are pack joint type fittings. Also, pvc water well drop pipe is threaded pvc, but that doesn't have lateral stress.

Is there more movement in a household plumbing that causes the threads to fail? Is there something else?

This is all really interesting. Thanks for the information.

Gary Slusser
10-25-2005, 08:44 PM
I think it's LASCO that says the primary cause of PVC and other plastic females failing is overtightening them; in essence, not following the instructions.

I've used many of all types over many years without failure. I also use plastic males with the same results.

Quality Water Associates