I've noticed that in a properly (I assume) crimped Pex connection the tubing will rotate around the fitting it is crimped to - so that you have, in effect, a union.

So, I'm wondering:

  • Is that how it should be? And,
  • Can the connection be treated as a union? In other words, can you use the rotating property to use, say, make a PEX to NPT transition which might have to come apart without needing to install a union?

Copper pipe union

  • There are some crimped connections at my house that rotate, and never have leaked. How do you mean treated like a union?
    – freshop
    Feb 13 '18 at 21:50
  • To allow a connection to be disassembled when you can't unthread the connector (in hard pipe this happens when the other end is threaded into another fitting or in some other way is prevented from rotating). I added an image to the question.
    – dlu
    Feb 14 '18 at 1:45
  • Oh okay. You can't disassemble the crimpled connection its not like a union. Have to cut it out and recrimp.
    – freshop
    Feb 14 '18 at 18:18
  • @freshop - Didn't explain it too well - what I was wondering about was using, for example, a pex-to-pipe adapter in a location where, with hard pipe, you would need a union and taking advantage of the rotation in the pex connection to avoid a union.
    – dlu
    Feb 15 '18 at 5:32

Should PEX connections rotate?

Yes, this is normal, and true of both crimp and cinch style connectors. It's also a useful property of PEX during installation, as it makes it even easier to dry-fit and pre-assemble sections and then fit them into place.

Can the connection be used as a union?

A union is designed to come apart, and in copper or PVC plumbing are typically used in two situations:

  1. To make a part accessible for removal for servicing/replacement (such as an in-line filter)
  2. In a tricky installation where there's no other option for the final connection to be made

In the first case, a simple PEX connection obviously doesn't satisfy the need since it doesn't come apart, and so you'll need an actual union.

In the second case, the flexibility of PEX and fact that the connections can rotate does allow installations that aren't possible with copper or PVC. I've installed dozens of water treatment systems (typically involving complex turns and tight spaces) and cannot think of a situation where an actual union was needed because of the install. But if this is what you mean, then I'd say yes, you can avoid using a union and just rotate the PEX.

Rotary union

If you are trying to do something that involves regular rotation, where you'd normally use a rotary union, I'd say no -- you should just use a rotary union. The fittings aren't designed with rotation in mind, it's just a property of the style of connection. I'd expect if used this way, it's going to wear out the pipe and/or connector itself and the connection will eventually fail.

  • I was thinking of the first case, where you need (or anticipate a possible need) to remove a component for servicing.
    – dlu
    Dec 6 '20 at 21:34

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