Self cutting taps

[Theo]

I want to add some tees to my heating pipes, but I don't want to drain the system down. There are things like:

but I wondered about them. In particular, apparently they cut a flap of copper pipe where the tee goes in - does this restrict the flow in the original pipe?

I'm also wondering what happens if that flap detaches: since it's copper I'm not sure my magnetic filter is going to catch it, so it could get lodged somewhere.

Any opinions as to whether they're a good idea?

Thanks Theo

[John Rumm]

There are plenty of ways of working on CH pipework without a full drain down. Perhaps we should do a wiki page on the various techniques?

Yes.

There is a type that compresses the slug of copper it takes out and pushes it out the back into a small reservoir in the back of the fitting. These don't restrict the flow.

They are normally only available as isolators, so you would need a suitable branch of pipe to fit them to:

They cut bit tends to stay put.

However the linked above is designed for connecting washing machine hoses, not additional fixed pipe. Something like:

Is intended for pipe extensions.

IMHO, the self cutting tap type are a bit of a bodge really. The Aladdin ones do have a real cost benefit advantage in in some circumstances though.

For mods to a typical domestic system it is little extra work to do the job without needing them.

[alan_m]

What size hole does it cut in the pipe? It could be a lot less than the bore of the pipe you are cutting in to.

Someone removing a washing machine self cutting tap fitting.

[John J]

It's entirely possible to introduce a compression tee into copper pipework in an undrained system without draining down. If open vented use rubber plugs in both feed and vent pipes (these are sold as "no drain" kits). If it's a sealed system depressurize and close any auto air vents. Protect the area you are working in with a poly sheet and a highly absorbent cloth or towel. Clean up the pipe you intend to cut, use a pipeslice to cut the pipe with a suitable end to slide easily into the compression tee which has a smear of boss white in the olive and work quickly.

[Robert]

And a Wet & Dry Vacuum does wonders in sucking the water up !

[RJH]

And close the valves on all the radiators. There was barely any pressure/water loss when I replaced a ground floor valve recently.

[Theo]

That would be most useful - I think there's various tricks you can do that I'm not really familiar with. Pointers to videos are also handy.

(in this case, the reason for not draining down is the system contains about

75 litres of glycol mix - so it's expensive to do a complete refill, and you can't use pipe freezing. It's a pressurised sealed system)

I was also looking at that one, but it sticks out quite a lot. Also the tiny isolation screw isn't the nicest UI for turning the extension off. (which might be an every-few-months thing, not once-a-decade)

That was my feeling. If I can do it without having to drain or get water everywhere, I'm happy with that option.

Agreed.

Thanks Theo

[Andrew]

Must have been sealed system then. If you have an open header tank then I would have expected a gush of slimy black water.

There is always the "carrot in the header tank outlet connection" trick or use a proper concentric-stepped rubber bung.

[Andrew]

and also fit some full-bore 'lever' valves in strategic places too.

[Andy Burns]

I though that was mentioned in a diywiki article, but search didn't find it earlier.

[RJH]

Yep.

[RJH]

Is it? ISTR a discussion on this NG that settled on the notion that refilling introduces more oxygen into the system, increasing the liklihood of corrosion (or something, forget the exact details).

[Clive Arthur]

It was a long time ago, probably 35 years, but I remember a former colleague telling me he'd used one of these. He went on to discover that an emergency plumber on christmas day was not cheap.

[Theo]

As a counterexample, our dishwasher is plumbed with one of these. The dishwasher is about 15 years old, so I assume there has not been a problem since then (otherwise it would have been replaced with something better)

Maybe those 35 years ago weren't as good?

Theo

[Tim+]

If you depressurise (and turn off all the radiators as someone else suggested) you really will lose very little water. It’s one of the big advantages of a pressurised system.

Have a towel and/or wet & dry vacuum cleaner handy but I think you’ll find that you’ll only see a bit of a dribble.

Tim

[The Natural Philosopher]

+1 Very informative

[John Rumm]

ok here is a start on the words (not proofed yet!)

I will find some pictures to add.

Some others may want to add more.

[John Rumm]

That is part of the job of corrosion inhibitor - it has an oxygen scavenger designed to mop up any dissolved oxygen.

However the point stands, that if the water is keep clean (filters / inhibitors), then there is no need for a routine drain that often on a sealed system since there ought not be much corrosion.

[John Rumm]

They work well enough, at least for a washing machine hose anyway. They do occlude the pipe they are fixed to a bit though.

The main risk is probably cocking up the fitting and getting a leak then.

[Theo]

Thanks, that's really useful :-)

Theo