Brass cutting rings

[Kittyhawk]

Would anyone have experience in using these please?
I have a length of 8mm copper pipe which needs to go into an 8mm brass conector, sealed by a brass cutting ring. I am advised to use a cutting ring as opposed to an olive as there will be a bit of pressure in the line. The cutting ring is quite sloppy on the pipe before tightening with 0.3mm between the pipe diameter and the the cutting ring hole. Will this take up once it's cranked up tight onto the connector? I don't recall olives being so loose.

 

[Nail]

I don’t think I’ve come across them but I’m curious about what pressure level you’re going to be getting that would blow out an olive compression fitting.

 

[Kittyhawk]

I don’t think I’ve come across them but I’m curious about what pressure level you’re going to be getting that would blow out an olive compression fitting.

I'm of the same opinion regarding the olive. It's the termination point of a gas line where it connects to a small Truma water heater. Supply source is bottled gas. I made a mock up joint using a piece of 8mm pipe joined to a connector using an olive. Clamped thr pipe in a vice and no way could I pull the connector off the pipe. The fellow who advised the cutting ring was a hydraulics man and probably thinking of much higher pressures than a gas line will ever have. A cutting ring is likely an overkill?

A cutting ring is like an olive - slightly different shape - and has inside a couple of sharp ridges that bite into copper pipe when it is compressed/tightened up thereby increasing its holding power.

 

[Nail]

I’ve just looked it up and the specs of an olive are way over what would be needed for gas!

From the sound of it the cutting ring will just be what he knows well.

 

[imageel]

From what little I've read it would appear that cutting rings are favoured in some hydraulic applications - I've no idea why - perhaps just an alternative...
A bit like this discussion on how tight to make 'em - thread...

 

[Kittyhawk]

Thanks for the replies.
Forum common sense to the rescue. I'm going to stick with the good old olive for the connection. Will do the soapy water test thing once the connection is installed and working.

 

[Fitzroy]

What an interesting topic, gosh I’m dull. I deal with fluids and gasses in pipes every day and I’d never thought about the design specs for copper pipe work.

Looking at olives it seems max design pressure is c.15barg, and 15mm copper pipe c. 50barg. Brass cut fittings are variable but look to be 70barg and upwards.

LPGs are stored as liquids and the the pressure in the cylinder results from the vapour pressure of what is stored and the ambient temperature. Propane is more volatile and at 40degC has a vapour pressure of c. 12barg. Butane is lower volatility with a VP of 3barg at 40degC.

So you would need an abnormal situation with temperatures above 40degC and be running pure propane cylinders for the olive to experience pressures above design.

I love engineering.

Fitz

 

[Tris]

@Kittyhawk, does the supply come through a bulkhead regulator? If it's anything like ours that should be a 30 mbar supply. Based on @Fitzroy s figure above the olive should be good to 15000 mbar, assuming my maths is working

 

[Kittyhawk]

What an interesting topic, gosh I’m dull.

No you're not!
In my book there is nothing better than an answer to a question that is backed up by facts and figures from a man who knows what he is talking about. I can now go ahead and make the connection with an olive, assured that it is more than adequate for the job, always under the proviso of course that it is done properly.

@Kittyhawk, does the supply come through a bulkhead regulator? If it's anything like ours that should be a 30 mbar supply. Based on @Fitzroy s figure above the olive should be good to 15000 mbar, assuming my maths is working

Yes, delivery is via a standard regulator set at 30mbar.

 

[Lons]

If olives were a problem there are many thousands of campervans, motorhomes and caravans that would have gone up in smoke by now. A large number use propane rather than butane for extended seasonal use.

 

[MorrisWoodman12]

Are you using a sealant in the joint, e.g. white paste, PTFE tape?

 

[Fergie 307]

I run an LPG converted Jeep, and have helped many others with similar. Nothing wrong with regular olives.
Very much frowned upon to use tape or any sort of sealant on an olive. Completely unnecessary anyway. You just need to make sure everything is nice and clean, and don't overtighten them.

 

[MorrisWoodman12]

I run an LPG converted Jeep, and have helped many others with similar. Nothing wrong with regular olives.
Very much frowned upon to use tape or any sort of sealant on an olive. Completely unnecessary anyway. You just need to make sure everything is nice and clean, and don't overtighten them.

I stand corrected - you live and learn until you drop.

 

[cmoops2]

As a (now retired) LPG operative, cutting rings and associated steel fittings are only used on steel / stainless steel pipe. Joints for LPG when using copper pipe are predominently made using brass compression fittings with parallel soft copper olives. All LPG joints are assembled dry - jointing compounds / tapes are only permitted on taper threads.

Thoughout my 18 years in the industry, the majority of my call-outs were to attend LPG escapes relating to poorly made joints. As an example of just how crazy things can get, LPG on boats uses imperial pipe and you'd be amazed at the effort & ingenuity that can be employed to get a gas-tight joint in 3/8" (9.35m) pipe when using 10mm fitting -plumbing (not parallel) olives over other plumbing olives, MILES of PTFE tape to name but two. Getting 10mm pipe into 3/8" fittings is also possible but requires more 'grunt' than ingenuity . For information, the ONLY imperial / metric equivalent recognised by the LPG industry is 8mm to 5/16" (7.937mm).

And, to cap it all, I wish I had a quid for every person who'd told me they has a 'small' gas leak - LPG is heavier than air, and lingers for ages (and that why boats have a ZERO (non-discernable) leak tolerence. If you need to appeciate just how powerful LPG is, (at cylinder pressure) LPG can be, just look at any explosion in an action film or the huge spouts of flame from installations around sports pitches when a goal / try is scored. If you don't know what you are doing - DON'T do it - that's why the gas industry is regulated by the HSE who regularly prosecute the hell out of businesses / individuals who are not "A Class of Person as Approved by the HSE" ...

 

[okeydokey]

If it's all outside probably ok
If it's inside do you need a gasafe person