A productive Sunday afternoon.....

[Master-of-none]

Just a passing comment on the use of PTFE tape with compression fittings:
it should not be needed as the seal should be between the pipe and olive, and olive to fitting. Tape or compound sealant can be used around the olive but tape on the threads is the wrong place and should have no positive effect.

 

[Porschemaniac]

Thanks for all of the replies. I must admit that having read some of these, I do now have a few concerns about the compression fittings.

When I checked out the Conex website, it seemed to initmate that the fittings were good for 10 Bar, or so, up to 95 degrees C, where the rating drops to 7 Bar.

The two compressors, both cut off at 8 Bar, which would put them about 15 PSI beyond this rated 'safe' 7 Bar limit.

Has anyone else used these fittings (Malcolm, the fittings in your photographs look like standard compression fittings).

Naturally, I don't want a sudden release of 74 Litres of high-pressure air (and that's no comment on my diet!!) so, with this in mind, is there another type of compression fitting that I can use, or should I go the fully soldered route?

Thanks again,

Ian.

 

[malcolm]

Looks like you are right there. All of the compression fittings I can find seem to be made to "BS 864 part 2" and the specs look copied directly from there as different manufacturers seem to give the same specs (though it's impossible to read standards without paying for them which seems very silly). Airline Pneumatics sell compression fittings, presumably for use in airlines, but there's no data on that site about ratings.

Interested to know myself. I accidentally didn't tighten one and it hissed but didn't pop off, and the whole system has been in service for a year without problems, so I'm not too worried about mine, but it would be good to find out how to make them standards compliant. Should imagine it's down to safety factors if the same 15mm connection is rated 25 bar for water, 7 bar for compressed air and 1 bar for natural gas.

PS - will move this into the compressor section - useful info in this thread.

 

[Porschemaniac]

Thanks Malcolm. Guess I'll make sure I've got full safety gear on when I take it to full pressure the first time around

 

[madkayaker]

Spoke to the plumbers at work who have experience of compressed air systems. There view was that standard compression fittings shouldn't be use but there is fitting that you flare the pipe after putting the nut and olive over so that if the olive failed it can't fly apart as the pipe is flared.

 

[madkayaker]

http://www.bes.co.uk/ Quick google found these under air con section

 

[gavuk]

I worked in factory that used abs pipe for air,not pvc which is no good,easy to join glue together,scared the hell out of me(being used to galv steel pipe).not sure i would want splatter landing on it tho......

 

[eil]

All air con / refrigeration pipework is either silver solderd, or solderd with a copper to copper rod such as silweld 2, and flared connections, also the copper used are in imperial. But on another note if you look at the clarke compressors most have the discharge pipe in copper with compression fittings on them the same can be said about my broomwade so ??, a good tip to help seal compression fittings is to just use oil on the pipe and olive when tightening up.

 

[aero]

They seem to use standard plumbing compression fittings on the compressors themselves to connect the pump to the reciever.

Going back to an earlier question---does it make a difference if its water or air.

Yes it does, a huge difference. But only in a failure situation. If a pipe fails with 10 bar of water pressure it will just go 'phut' and the water come rushing out. Not very exciting as water is not compressable.

If it goes bang with 10 bar of air presure, it will go bang, VERY loudly and possibly with shrapnel as with air you get an explosive decompression...air is compressable and expands rapidly.

Hence insurance companies get so twitchy about compressed air systems.

The copper system was probably only condemed as steel pipe is more damage tolerent then copper.

 

[eil]

Not quite shure about steel being more tolerant to damage as opposed to copper after reading about this unfortunate engineer
http://news.bbc.co.uk/1/hi/england/beds/bucks/herts/4242264.stm

 

[Paul.]

Compression fittings for air are different to plumbing fittings although they may look similar, and they are normally designed for steel tube (bundy). or plastic pipes with the correct olives, enots and norgren, both have a full range.

 

[Davidss]

Not quite shure about steel being more tolerant to damage as opposed to copper after reading about this unfortunate engineer
http://news.bbc.co.uk/1/hi/england/beds/bucks/herts/4242264.stm

Yes OK, a disastrous result which could put Customers off their sandwiches, BUT ....

the Health & Safety Executive engineer told the hearing that too much pressure had caused part of the compressor to fly off and smash into Mr Ferreira's head.

So that's a mechanical compressor failure, not a steel pipe failure.

.... The hearing was told that the valve from an old cylinder had been used on the new nitrogen gas supply and its gauge showed a reading of 79 bar when the recommended pressure was 19 bar.

The man who died had asked his apprentice to increase the pressure; 79 bar instead of 19 is surely outside any built in safety factor. Was it wise to rely on an apprentice? (There is no information in the report to say how much experience the apprentice had).

I know we can't totally rely on media reports, but this does seem a bit like looking for a leak of inflammable gas with a lighted match!

 

[eil]

Point taken david, what the media report dident say is they had a 100bar reg on the bottle. also the copper pipe expanded with the sudden inrush of pressure but the 3mm steel compressor exploded or blew apart however you might like to describe it, care must then be taken with bottled gases/reguators/fittings and their pressures was the point I was trying to get across.

 

[Davidss]

... care must then be taken with bottled gases/reguators/fittings and their pressures was the point I was trying to get across.

OK, 'care required - don't just open the tap', certainly came across to me.

Cheers.