Softus said:
Chris, if the pipe can move into the fitting after installation then it hasn't been fully inserted.
Wrong.
Firstly, that statement of mine was in the context of full or partial insertion at the time of installation, so I believe it to be correct in that context.
You push the pipe in until it stops. Force not specified. So if you pushed harder, the materials would elastically deform more and you'd have the pipe in a bit further.
I agree with that theory. However, the additional force needed to compress the pipe longitudinally is far beyond anything I could apply with my hands, and if I tried then I would squash the pipe with my grip before it moved further into the fitting.
Note the importance of cutting the pipe squarely - if you don't, then less of the pipe is retained laterally, and more movement will result. Also, with a high insertion momentum, the lip of the insert could be deformed at its reduced area of contact with the end of the pipe, equating to partial insertion. Note also the importance of not deforming the pipe radially - if you do, then you could expect more lateral movement during temperature and pressure changes.
Then you do the unspecified "tug". That moves the pipe out of the fitting, some distance or other. At some unspecified point the grab ring does its thing and moves with the pipe, digging in to it. Your tugging elastically deforms the materials, so when you let go, things move back.
That would be my view of what happens too. You can hear the result of a similar, if not identical, effect of this by livening the supply to installation at a reasonably high pressure, say at 10 bar. The assembly creaks as the water forces the grab wedge into the taper of the capnut, with the result that it grips harder onto the pipe.
So now you have a pipe in a fitting which can move. It can't move much, but it can move. (This is the point Speedfit addressed with the twist-lock).
Then the temperature cycles, and the water pressure cycles, and the different materials move in relation to each other. The metal in the grab ring will move in relation to the grab ring it sits in, the grab ring in relation to the pipe, and so on.
I don't disagree that movement is possible, but determining whether the pipe is moving through the grab wedge, or whether the pair of them are moving together, is something that needs more data anyone who's posted here so far claims to have.
It could be argued that, if Speedfit grips the pipe more effectively that Hep2o, the stresses that result from temperature and pressure changes are not dissipated as effectively. I don't know the answer to that one. I don't know if Speedfit is better, or has fewer instances of failure, than Hep2o.
There aren't many installation variables. The pipe could have axial or radial tension, but Hep should have tried all ranges of those.
The method relies on the friction between the pipe and the grab ring being sufficient to make the grab ring move with the pipe when it's pulled outwards from the fitting. If thr pipe can move at all without the grab ring, EVER, it'll come out.
I don't have enough information to agree or disagree with that. However, if a product design is such that the failure rate is acceptably low, then that design can be deemed to have been successful. I don't know what the rate of failure is, and every attempt I've made on the forum to solicit information from people who report failures is met with the now commonplace derision aimed at people who don't pledge lifelong allegiance to copper.
An analogy might be the number of complaints that the general public makes about the police force. There are lots of outraged forum members when things go bad for the police, but very few of those (only one, AFAIK) postulates that the very existence of the police force, in its current form, is A Bad Thing.
So I would say it's a Fitting design error, damaged component, or manufacturing fault.
That's a valid list, but incomplete. It could also have been installation error.
I don't know where to find the statistics that would show a comparison between longevity of push-fit fittings compared to soldered fittings. I don't believe that Hep2o O rings will last forever, but I
know that copper doesn't.
Another factor that could be theorised about, without any hard data (but that's never stopped us), is the general stigma about the use of plastic pipe and plastic push-fit fittings. In my experience, long-term users of copper and solder tend to favour its continued use over newer materials, and I have no problem with people feeling more comfortable with what they know best, because all learning carries a risk of an increased rate of mistakes. But the result of this is that push-fit tends to be used by many people who don't care about the stigma because either (a) they don't care about their work, or (b) because they're not the person making the decision about the materials. In either of those cases the rate of installation error is, IMHO, likely to be higher than it would be in the hands of more experienced, or caring, installers. This skews the statistics in the direction of a higher failure rate.
Plenty of builders still use solder, and enough of them do such a poor job that I still go to at least one job a week where the copper has corroded right through as a result of all the flux, copper shards and iron filings that remain inside the pipework through sheer laziness or incompetence.
_________________
Someone who considers himself to be a guru said:
Yet again Hepworth proves itself to be a flawed system.
It's frequently stated on the forum that no properly trained, competent, professional plumber (or heating engineer, or whatever) would ever use push-fit. If this is true, then it's easily argued that the
only people using it are improperly trained, or incompetent, or unprofessional, or any permutation of those.
And if that really is the case, then I would expect the failure rate of a poorly designed and manufactured product to be failing in most installations. So if
that's true, then it's testimony to the design and manufacture that such a system can be fitted, badly, by idiots, with what nobody has shown to be more than a fraction of a percentage of failures.
If you're going to hoist a petard, you should retire to a safe distance.
And then said:
One day insurance companies will see sense and refuse to offer cover on these carp systems.
Those dratted insurance companies - they just won't see sense, will they! If only they would ignore the industry statistics and instead listen to a bunch of narrow-minded bigots, everything would be OK.