I was helping my uncle modify the plumbing in his bathroom yesterday using
>PEX and Qestpex compression fittings when it dawned on me that these
>fittings may not be as reliable as they would appear to be when you first
>look at them. Inside these fittings is a plastic ferrule that forms a water
>tight seal and behind that is a metal grip ring that serves to grab the pipe
>and prevent it from sliding out of the fitting. And, of course, over both is
>the nut that flattens out the grip ring causing it to grab the pipe and, at
>the same time, pushes the ferrule into the fitting forming the water tight >seal.
>
>But what happens if the grip ring grabs the pipe too far back while the nut
>is being tightened? I would think that the pipe would bottom out in the
>fitting and the nut would force the grip ring to snap inside out before it
>seated the ferrule into it's proper place. In such and event, the grip ring
>would be rendered useless because the metal blades on the inside of the ring
>would be pulling away from the pipe as it slides out instead of digging into >it.
>
>Has anybody seen a Qestpex compression fitting blow out for this reason? >
> Robert
>
Most of the Qest compression fittings specifically say they are only to be used in accessible locations, not inside walls. Check the warnings and instructions that came with your fittings.