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