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[tonyH]

Hello all!
I've been used to silver soldering all the steam connections but I'm stuck with a short (35mm) connector piece of gas piping from a new Clevedon gas tank to a servo cut-out valve. The coupling to the tank should be the knurled knob type but that has a rubber "O" ring while the other could be either a flat ring or a conical one. Am I just making life difficult for myself by even considering silver in a lpg connection?
 

[Treble]

 Suggest you try having a look at a product called La-Co Cool Gel . I have used a similar American product to great effect.

[Mege66]

Definitely silver soldering - it doesn‘t take much more time to silver solder the joints, but the mechanical strength is significantly better. A LPG leak in a model steam boat equals a Vicing burial and is the last thing I would risk to safe a little bit of time.

[Bunkerbarge]

The knurled connection with the 'O' ring on the tank is designed to be easily dismantled in case you want to remove the tank for filling.  Every time you connect or disconnect this fitting you will induce stresses and strains along the piece of pipe, which will then be transmitted into the soft solder joint at the other end.  Soft solder is just as good at sealing as silver solder but its main weakness is its inability to resist movement.  Frequent playing around at the tank end of the pipe could well lead to the soft solder joint failing, possibly by a hardly detectable crack which could then leak.  If both ends of the pipe were to be permanently fixed then it might be more justifiable but having the other end easily dismountable would suggest silver solder is the best option.

[tonyH]

Right then, silver solder it is and this leads me to another couple of questions if OK with you. Firstly, which type of coupling, flat ring or conical, is preferred and secondly, since any seepage of gas is, unlike steam, invisible is it worth putting a smear  of plumbing sealant on the mating face of the coupling?
  Tony

[Mark T]

Hi Tony I have used both flat and conical couplings and both are good.  I have never used any kind of lubricant or sealant on the joints either.  If you want to know if they are gas tight just turn the gas on and hold a flame by the joints - it will be pretty obvious if there is a leak or not.

[Bunkerbarge]

I have always used conical as I believe they have a better chance of sealing.  If the faces are clean, they match, the pipework is square and the nut is correctly tightened you should not require any sealant. 


I would not recommend using a flame to test for gas, there are far too many potential hazards, the best option has always been to first remove the nozzle and replace it with a plug, open the gas valve, then simply paint the pipework and fittings with a soapy water solution.  A leak will make very obvious bubbles.

[Geoff]

Whilst I would tend to agree silver soldering is better, if you don't have the facilities, I have used soft solder by using a brass sleeve to overlap the pipework by about 8mm each side then when soft soldered this gives a perfect seal and the sleeve provides significant support.


Cheers


Geoff

[tonyH]

Many thanks all for the input. I've managed to make the section, silver and cones, all 35mm of it, with both ends apparently stuck so bench test with loads of bubbles  or not  tomorrow!

Cheers
Tony