Boiler copper tube flaring - dos and don'ts

Old 01-25-18, 09:58 AM
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Boiler copper tube flaring - dos and don'ts

Hello from Europe all,
Am living in the Benelux region (Luxembourg, Germany, Netherlands) having bought a small, old home, and am trying to survive given the high $$$$ of everything.

Have a German Weishaupt boiler, which runs great, proving water heat (which does house heat, all water radiators, and our bathing water). It is a two-line oil burner system, installed 20 yrs ago on this old house, where the boiler and the outside underground tank are basically level with each other. The suction and return lines are about a 20' run from boiler to this undergound 3000L tank.

Have been suffering nozzle after-drip on the Weishaupt, have replaced all the usual stuff, finally got around to running some vacuum tests. I did the vacuum test by installing a vacuum gauge on the Danfoss fuel pump (afaik, all Danfoss pumps here have ports for both pressure vacuum testing)...anyhow, did the vacuum test at the fuel pump, and also with the vacuum gauge placed between the incoming suction line as it leaves the Afriso oil filter unit---this hangs on the side of the boiler---and heads to the Danfoss pump. I then attached a clear line hose from the vacuum gauge over to the Danfoss pump, started a run a cycle, and sure enough, sat there and watched as little bubbles ran down into the Danfoss.

So, I'm getting air in somewhere, or possibly I've been told "cavitation" is happening in the underground tank.

Either way, I bought a Afriso Tigerloop fuel Filter Unit device, that I am going to install in the same as the old Afriso unit (once I remove it). It will convert my two-line system to a one line (as I leave the returning line alone, other than plugging it so it doesn't stink up the utility/basement room.

My question is this: is or are there any rule about flaring on copper tube that is 20 yrs old? I mean, should it be done and/or not done? I cannot install a new line to the outside underground tank until summer hits, it just is not possible now. Unbelievably, Germans/French/Dutch still spec a compression-like fitting for the lines coming into the house that go into the Afriso 3/8" filter port. Below are pics of these fittings plus the exact type of oil lines I have currently installed in my system---though please know this is a new pic of these lines, and my lines are 20 yrs old, with a bit of discolorization in them (no more bright, shiny copper).

Thus, if I install this new Afriso Tigerloop fuel filter device, I am going to use a flared fitting on the existing suction copper line (12mm) coming into the house from the underground tank. I don't want to use the compression-like fittings Afriso shows in the box of the new device. I do not like compression at all, for anything, but especially for fuel and/or oil But my worry is, I've never flared old copper pipe.

So, are there do and don't rules concerning flaring old, existing copper pipe? Like maybe never flare any of it since it is old and possibly prone to fail and/or split or...? ....?

Thank you for any advice, help and/or hints
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Last edited by belham; 01-25-18 at 10:06 AM. Reason: spelling errors
Old 01-25-18, 08:32 PM
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Welcome to the forums.

I'm not the oil burner pro but I've made plenty of flared fittings on old copper line and have never had a problem. It needs to be soft copper.... the rolled type not like what is used for water lines.

Definitely a good idea to use flare fittings in the oil lines as the compression type are very hard to get a seal.
Old 01-26-18, 02:18 AM
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I agree.
The age of the copper does not alter it in any way.
Just make sure it is soft copper meant to be flared.
It will split if it is hard copper or you use the flaring tool incorrectly.

If you do not have soft copper it is very easy to anneal it for flaring or bending.
Old 01-27-18, 07:21 AM
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There are several “washer” type items to help seal or deal with leaking flare fittings. See links:

Bought some in local burner supply place.

Last edited by doughess; 01-27-18 at 08:00 AM.
Old 01-28-18, 09:59 AM
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Flare slowly & lubricate the conical end of the flaring tool with a small amount of motor oil.

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