Copper Pushfit - Not for use with gas

[Chris Cowley]

I had to cap off the hot and cold pipes to my kitchen sink last week while I'm re-plumbing the kitchen. All Wickes had in stock was copper push-fit end-caps, which did the job a treat, but I noticed that the packet says "not for use with gas" (or similar words to that effect).

Just out of idle curiosity, why is that? I would have thought that, if they're good enough to form an air-tight seal to withhold mains water at, say, 5 bar then they would comfortably cope with gas at 20-odd millibars or whatever it is. Obviously, there must be a reason, but what is it?

I happened to notice that the bloke who installed our new combi last year used a plastic push-fit end-cap to cap off the gas supply (probably for all of about 2 or 3 hours while he plumbed in the new boiler). Was that, strictly speaking, a bit "iffy" (even though the supply would have been off at the meter, and presumably disced-off or disconnected from the meter too) or is there something about the plastic end-caps that make them suitable for gas?

Also, on a similar tack, why is there a separate (thicker?) type of PTFE tape for gas? Again, if the standard PTFE tape for use with water is good enough at typical mains water pressures, why is it no good for gas at a fraction of the pressure?

Enquiring minds, etc. etc.

[Grunff]

It'll seal OK, but is not regs compliant. This is for the same reason plastic pipe isn't allowed for use with gas - in the even of a local fire, it will give way very quickly.

This is common practice, but I don't know if it is strictly speaking incorrect. It poses no danger if it's just a temporary measure for a couple of hours while working on the system.

This one I never figured out.

[Andy Hall]

I think that that is probably part of the clue.

The metal teeth in the fitting dig into the pipe as one attempts to pull it or with pressure from the water - the greater, the more.

Since gas is at a tiny fraction of that pressure, this effect doesn't happen. Whether that would lead to a leak is another thing, but the manufacturers certify their products for an application.

For example, I have some John Guest nylon airline and the push fit fittings to go with that. They are good for so many bar of compressed air. The fittings are slightly different to the water ones.

It's a requirement for a fitter to cap the supply if he is going to leave it unattended. I suppose that by the book, it should be a fitting rated for gas use.

I had always understood it to be because taper threads are typically used meaning greater gaps to seal and the gas tape is thicker.

[Roger Mills (aka Set Square)]

Unless it happens to be a gas *main*!

[Grumble]

Maybe it has something to do with the size of the molecules as much as the pressure.

Grumble

[Dave Fawthrop]

|> Also, on a similar tack, why is there a separate (thicker?) type of PTFE |> tape for gas? Again, if the standard PTFE tape for use with water is |> good enough at typical mains water pressures, why is it no good for gas |> at a fraction of the pressure? |>

|> Enquiring minds, etc. etc. |> -- |> Chris Cowley | |Maybe it has something to do with the size of the molecules as much as the |pressure.

Also the risk. Water leak, things get wet. Gas leak, you may get an explosion.

[Chris Cowley]

Ah, that makes perfect sense. I had a poke about with one of the copper fittings before I used it and they seem to have a rubber O-ring that compresses around the circumference of the pipe to make the seal. I don't suppose that would last too long in a fire.

Actually, thinking about it, I'm not sure I'd like to use push-fit connectors at all for anything long-term - the compressed O-ring will perish at some point, maybe a few years down the line, but even so someone would get wet feet at some point. There's something slightly bodgy about them IMHO.

[Andy Hall]

The manufacturers are giving 50 year guarantees, so they feel pretty confident and the O-rings are not conventional rubber.

The main point is to cut the tube squarely and cleanly with the proper cutter when assembling

[Chris Cowley]

Well, that's certainly a possibility I suppose. It would be nice to know for sure though. Maybe the gas PTFE tape is somehow denser than the standard stuff?

[Russel Sprout]

So far two materials which were "guaranteed for 50 years" that I have used have failed before 10 years. Specifically, plasic push-fit plumbing (now replaced with soldered copper) and a putty substitute (now replaced with proper putty). There seems to be a pattern! Anyway, how do they know these _new_ materials will last 50 years? I increasingly find myself going towards traditional methods/materials.

[Chris Cowley]

Well, a 50 year guarantee does sound mighty impressive I must say, but even so, I'm going to remain with the flat-earthers on this one and stick to my olde fashionde solder and compression fittings, I think!

I wonder what those O-rings are made of that will not crack or perish under compression for 50 years?

[Grunff]

O rings have been used in industry for a very long time, and the aging characteristics of the rubbers used (mostly EPDM) are very well understood. As long as the installation is carried out correctly in the first place, the service life will be 30+ years, more likely 50+ years. This is plenty for domestic use.

[Tony Bryer]

They 'know' by accelerated testing. But when you look back there are more than a few cases where adopting new materials proved to be a bad idea - high alumina cement for example - but plenty more where the new has proved to be much more durable that what it replaced - concrete roof tiles, PVC cable, copper tube for starters.

[Dave Plowman (News)]

Concrete roof tiles more durable than clay or slate? Not my experience.

[Doctor Drivel]

Some fittings will hold water but not gas. A copper pushfit on copper pipe is not a fire hazard it itself. Plastic pushfits would be. Restrictor elbows on gas fires have neoprene washers in them.

It is in effect illegal, but he is there and temporary, so not dangerous.

Some threads are course and the thicker tape fills in the gaps. Also it supposed to have a mix that is more suitable for gas. No many pros do not it preferring the tried and tested jointing compound which is also quicker to apply.

[Doctor Drivel]

In which we used rubber bungs as temporary solution.

[Doctor Drivel]

Pushfit fittings should be avoided. Many pro avoid them like then plague. They can hold for weeks then fail either in the O ring or the grab ring. You can use brass compression fitting on plastic with the olive wrapped in PTFE. Cheap and better and easily demountable. Hep2O and Polyplumb fitting have been known to have the nuts work loose.

[Doctor Drivel]

Soldered copper is by far ten best pipe system.

[Doctor Drivel]

..and movement with expansion and contraction.

[Chris Cowley]

Oh gawd! Perhaps I should've kept my big gob shut...