Compression Fittings, "The Knack"

[mickeymouse]

OK, I am still a newbie Plumber. But I have put together about 20 of these sort of joins now on radiators, isolation valves and other things, I do not use PTFE tape or jointing compound and not a single one of my compression joins has leaked, bar the second, which only leaked because I did it up weakly on purpose to see how much further I had to tighten it to stop it leaking.

So, I've seen it written on here that there is a knack to doing up compression joints. Since "a knack" doesn't help anyone, this is how I do them up. Of course I am still a newbie so would appreciate comments from experienced plumbers on if this is any good or not because you will either save me future leaks or help out future newbies

First, I do the nut up finger tight, I do not strain in any way, as soon as it doesn't turn anymore, holding it with two fingers and not applying anymore effort than before it reached the olive, it is done up finger tight.

Secondly, I grip whatever I am trying to attach to the pipe, (fixing, valve, etc) to stop it and the pipe moving then twist the compression nut until the force required to twist the nut increases. I only apply enough force to twist the nut until it moves slowly (not that slowly, it takes maybe 3-4 seconds to complete half a turn) so that when the force required increases, the nut stops turning.

Three, I turn the water on, it never leaks.

Tools used:

Tough Fittings: Mole Grips or Water Pump Pliers to grip fixing, Spanner (Normally 24) to twist compression nut.

Chrome Fittings: Two soft-jaw (plastic inserts) water pump pliers. You have to squeeze these hard, I would be surprised if lady plumbers found these tools adequate, it's just what I use.

 

[seco services]

sounds ok useally half a turn with an adjustable after finger tight is enough.

 

[AfterburN003]

Asa rule of thumb that is correct. Its impossible to explain how tight u actually have to do it. Too tight is often as bad as not tight enough. It is one of these things that comes with experience but as u are not having any leaks i think u are doing fine

 

[mickeymouse]

Ah, well I'm trying to explain "the knack" because, well the olives are all much of a much, pipes are of the same thickness, it should be a science not an art. I'm sure you're right you need to do it to know how to do it, but this is the series of instructions I follow for myself and it seems to work every time so far. I'll put it on the wiki after a while if nobody thinks it's nonsense!

This method does end up turning it about half a turn most of the time, it seems though that when it becomes harder to turn a second time it's likely cause the pipe would distort, so you can treat it like a science as well as a knack.

 

[Whitespirit66]

Smear of Boss White on olive, finger tight with the nut, then half a turn with the spanner.

If it weeps, nip it up a little bit more.

 

[TicklyT]

...... because, well the olives are all much of a much, pipes are of the same thickness, it should be a science not an art....

There are too many other variables, including:-
The hardness of the pipe,
The material of the olive,
The dimensions of the individual olive.
The hardness of the olive,
The angle of the olive seat in the fitting,
The angle of the seat in the nut,
The finish of the olive seat,
The pitch of the thread,
The accuracy of the thread,
The finish of the thread,
etc,
etc.

To make it a science, you could accurately measure every possible variable for every possible combination of components, and tabulate the results, or, more likely, just develop a 'feel' for how far you need to tweak each individual joint.

Some will seal when they are finger tight, others need winding up untill they scream, and just occasionally, you come across an unfortunate combination of components that just won't work together, despite each individual part being within the manufacturer's normal specs.

 

[Onetap]

http://www.ibpconex.co.uk/pdf/compression_technical.pdf

Just follow the manufacturer's instructions. There's a video on that site too somewhere. You will eventually just do it so it feels right.

Swage-lok (US made stuff, very expensive, used mostly on hydraulics, I think) do Go/No-Go gauges for quality control inspectors to check the nut has been tightened to within the specified tolerances. I don't think you need to go to that extreme.

Tough Fittings: Mole Grips or Water Pump Pliers to grip fixing, Spanner (Normally 24) to twist compression nut.
.

Mole grips? Water pump pliers?
They always chew the fitting &/or nut up. Use a good adjustable wrench, Bahco or similar.

 

[Whitespirit66]

,

and just occasionally, you come across an unfortunate combination of components that just won't work together, despite each individual part being within the manufacturer's normal specs.

Had to seal a Danfoss 10mm TRV onto a towel rail and 10mm barrier pipe the other day. Had those funny grooved olives that split when tightened.

Couldn't for the life of me get it to stop weeping. If I'd have tightened it any more, I would have broken something.

Only way was to smother the olive in LSX. Yes, I know, but sometimes it gets you out of a hole!