compression joints

[andrewpreece]

compression

Compression joints are invaluable where it is wished to disassemble a system ( for whatever reason - but for example, where a solder joint has not been made properly ). This allows you to get things right or work on the system in future with minimum fuss. A pipe run completely made with solder joints is often impossible to disassemble without using a hacksaw as the merest drop of water trapped in the pipe renders it very difficult to desolder. The occasional compression joint in the right place allows draining.

Andy.

Andy.

[Popeye]

Simple one I hope.

Need to reroute a radiator pipe, going to use compression fitting as the pipes will be boxed in, the question is how tight do I do the compression joint, every where I look says don't do it too tight , but no hint about what is tight enough?

Any suggestions

Thanks

[Dave Plowman]

With ordinary spanners - say about 1ft long, you'll not be able to tighten it too much. A lick of Fernox sealing compound wouldn't go amiss - although purists would be right in saying a well made compression fitting will work ok 'dry'.

However, a solder joint is far less likely to leak if it's made properly, and it isn't difficult provided you have a decent blowlamp.

[Andy Hall]

Tighten until the nuts split, and then back off by half a turn.

Seriously though, you don't need to use compression fittings unless you are not confident about soldering.

If you are going to usde compression, if you stick with wrenches no longer than about 200-250mm, unless you are Superman you can tighten them quite hard without fear of breaking. If you are straining really hard, then that is too hard and you should not need to be that tough.

.andy

To email, substitute .nospam with .gl

[BigWallop]

If the pipes are going to take hot water around the system, then drain it down as much as possible so you can install a soldered joint. Compression fittings work themselves loose under heating and cooling situations, so for the savings in the price of the fittings, and the safer environment it causes, it's best to fit soldered fittings in the heating system.

[Set Square]

What units do you understand? If a torque were specified, it would be difficult to implement - because torque wrenches and open-ended spanners don't mix very readily.

It's largely a matter of feel. At a certain point, you can feel the olive being crimped onto the pipe. This is point at which to stop. If you do it up beyond what is necessary, you'll start to "neck" the pipe - and will have a less good seal than when it is just right.

Buy a few spare olives, and practice on a few bits of scrap pipe. Take the joints apart and check that the olives are tight on the pipe without any necking. Then make a mental note of what it felt like as you tightened it.

An alternative is to use metal push-fits . You just push the (well cleaned) pipe into the fitting - and Bob's the proverbial! Very handy in confined spaces where there's not much spanner access.

[Dave Liquorice]

Tight enough so it doesn't weep, but not so tight that the pipe is distorted...

A decent rule of thumb is around 1 1/2 turns from finger tight. A little bit of sealing compound, potable if necessary, helps to make things slide better but isn't required to make the joint water tight.

[nightjar]

It is usually specified as hand tight plus half a turn with a spanner. However, I've always wondered how that works with different people having different hand strengths. Personally, I would trust a solder joint more. Just don't box it in until you are sure it won't leak.

Colin Bignell

[Ed Sirett]

If the joint is in alignment and clean there is a very definate point at which the nut begins to bite. I'd reckon on 4 flats (2/3 turn) from that point. That would be around the same as 1/2 turn from hand tight as you say.

[Popeye]

Thanks for the tips, one further questions, I'm sure your right that compression joints loosen under the constant temperature change which makes sense, then why are all valves either compression (or push fit), and none soldered, don't these work loose as well ?

compression

[David]

In article , BigWallop writes

That's a bit of a wild statement that I don't think is true, there is no reason for expansion and contraction to affect the performance of a properly assembled compression joint

[Andy Hall]

It's a pretty unusual occurence for compression fittings on heating systems to leak, and some are useful to facilitate removal of pieces of the system.

However, they are not used universally for cost reasons as well.

With respect to valves, they are on show and any leaks normally become obvious. For radiator valves, the most common leak is around the spindle, though. TRVs can tend to stick after a while, especially if the system has not been maintained with inhibitor.

.andy

To email, substitute .nospam with .gl

[Elessar]

I'd always assumed it was because the heat of soldering could damage the rubber washer or whatever seals the gland. (Actually I'm not sure if there

*is* a rubber washer in gate valves or stopcocks).

[Andy Jeffries]

From the Collins DIY manual (which seems very good from tradespeople I've spoken to) you should do it hand tight, then one full turn. Use a pencil/marker to mark a line on the nut and centre line to help you line up one full turn.

IANAP

[Lobster]

Would that be *before* or *after* you've eaten your spinach?

David