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Motorhome LPG installation

Posted: Tue Jan 08, 2019 1:45 pm
by Ian_Fearn

I'm in the process of installing a domestic LPG tank on my campervan (not bottles).

Can anybody tell me if PTFE tape should be used on the threads for the pipe from the external fill valve to the tank and likewise from the tank valve to the regulator?

As far as I knew, its not required but i've seen lots of pictures where people have used it.

Many thanks, Ian

Re: Motorhome LPG installation

Posted: Tue Jan 08, 2019 3:01 pm
by Gilbertd
The Code of Practice says:

"Every joint or connecting fitting should be of metal and of a type suitable for service with
LPG at the operating pressure. This does not preclude the use of suitable non-metallic
seals within the fitting, complying with BS EN 549. Jointing compound for screw
threads should be suitable for use with LPG and comply with BS EN 751."

Assuming PTFE tape complies with BS EN 751 (which I would assume it does as it is also used on domestic gas installations) it should be OK. It may not be needed but it's probably better to use it than not.

Re: Motorhome LPG installation

Posted: Tue Jan 08, 2019 7:40 pm
If it's a JIC filler hose the seal is made between the male cupped shape of the filler point / tank port mating surface and the female cupped shape at the ends of the JIC pipe. The threads only serve to keep those cupped shapes tightly together, even with those threads fairly tight (not tightened right up) the JIC pipe can still rotate independently of it's nuts.. If gas gets past the cup to cup contact then even if you make a gas tight seal on the threads by using ptfe tape the fitting is still likely to leak because there is no proper seal between the pipe nuts and the pipe that runs between them.. so I don't use PTFE or other means of sealing joints on JIC hose connections.

If M12 threaded fittings and you're using 8mm copper fill pipe it will involve olive connections, again it is the olive that makes the seal not the threads, again if the olive leaks even if you've sealed the threads gas will leak from between the pipe fitting's hole and the pipe that runs through the pipe fitting, so again I don't use ptfe or similar on olive joints.

If it's an M12 threaded fitting (designed for use with 8mm copper pipe) and I'm screwing Faro type fittings directly into the M12 thread instead of using copper pipe (usual these days) then I sometimes use a bit of LPG compatible gas paste (most is compatible with LPG) on the threads if the connection will be difficult to access later.

Might as well mention flanged fittings... Same again, if gas gets past the curved joint of the flange it will get between the pipe and the pipe nut even if it can't get past the threads, so I don't use sealant on threads on flanged joints either. Jic curved end connections could be considered just pre-formed large diameter flange fittings.

I use ptfe tape on tapered threads such as wide diameter 4 hole tank fittings and on various fittings / adaptors that are solid (i.e. doesn't have pipe nuts, the whole units spins to screw up to counterpart's threads). The latter are usually none metric fittings used on gas outlet side of vapour take-off installs.

Re: Motorhome LPG installation

Posted: Tue Jan 08, 2019 9:13 pm
by hitman
Its banned offshore on all oil and gas joints
But I'd still use it at home tbh

Re: Motorhome LPG installation

Posted: Wed Jan 09, 2019 9:25 am
by Ian_Fearn
Thank you for your advice. Yes, its a JIC filler from Tinley Tech.

I've made hundreds of threaded and compression joints for water and never used PTFE so I think i'll go without it initially.

For the first fill and leak check, would people recommend just putting a couple of litres in or do I need to put much more in to get the tank pressure high enough?

Many thanks, Ian

Re: Motorhome LPG installation

Posted: Wed Jan 09, 2019 9:34 am
by Gilbertd
Tank pressure is relative to temperature rather than volume so the pressure will be the same whether it is full or has only a dribble in it.

Re: Motorhome LPG installation

Posted: Wed Jan 09, 2019 9:38 am
If I were you I'd put just a bit i first, leak test, if OK fill up.
if the tank contained only LPG it's pressure would be the same from a small amount of liquid gas to almost full... That's the usual way it's thought about but I raised the point on another thread about tanks containing air which compresses above the rising level of liquid gas. ... &start=260