Finding a gas leak?

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Our recently acquired Moody S31 has a gas leak, when the Alde bubble tester is used, after a short delay, we get a bubble every couple of seconds, not serious but it needs to be eliminated, the gas line runs by a well hidden route from the tester in the gas locker to a gas cock behind the Plastimo Atlantic cooker passing through two bulkhead fittings on the way. Strangely, despite the gas locker being in the cockpit the pipe emerges from the bottom of the bulkhead surrounding the moulded fridge in front of the cooker with no obvious means of access. The leak is detected even when the cock behind the cooker is shut so I presume the leak is in one of the bulkhead joints, only one side of which I can get at for soapy water testing. It is a tiny leak, there is no detectable smell of gas, we keep the gas off at the cylinder when not using it and ventilate the cabin but it needs to be sorted. Other than running a new copper gas line without joints by an accessible route, (probably have to be the bilges, which with a saildrive are dry) is there any other possible solution. I am not prepared to cut the fridge moulding out or to remove the nicely finished bulkhead in the aft cabin.
Marine Projects like most boat builders seem to have installed the plumbing at a very early stage of the fit out, with zero thought of future maintenance.
 
I think you have asked and answered your own question. If you cannot get at the fittings to leak test then running a new solid gas pipe is your only option.
 
Freebee said:
I think you have asked and answered your own question. If you cannot get at the fittings to leak test then running a new solid gas pipe is your only option.
Click to expand...

Humm, plus 1, its likely going to be another run of pipe. Remember that gas sinks, so even if you can't smell it, beware it gathering in your bilges...

We have a gas detection wand we used when fitting the gas out - the best method was still leak detection fluid we found (be careful with soapy water as it can corrode the pipe/joint). See section 3 of the below.

http://www.albinballad.co.uk/how-tos/fit-out-your-gas/
 
Gas is a quite low pressure so if you could use a small tyre compressor to increase the test pressure after disconnecting the LPG cylinder and regulator you might hear a hiss and find the general position of the leak.

If you can separate the pipe feed into sections at the one side of the bulkhead fitting you can get to you can test each section separately.

A 12vdc car tyre pump can get you to 30 psi. I have used my SCUBA cylinder some times to do tests like this of to clear blockages in pipes.
 
Ok, to really find a tiny leak, this is how one does it:

Close the valve at the appliance. Atatch a vacuum pump at the supply end, complete with a mass spectrometer in the vacuum system. Evacuate to about 10-7 torr, and set the mass-spec to charge/mass = 1/3. Get a small cannister of Helium 3 and squirt it very carefully over each joint while looking at the current from the mass-spec's detector. Shouldn't cost you more than £10k or so.

Alternatively you can renew the pipe. I'd go flexible myself, supporting it rather often and making sure it complies with ISO 10239.
 
I would spray all visible joints and especially the cooker isolation valve with leak detection spray if not already done to eliminate them.
 
No, the gas is only on when we are cooking and we are using an electric kettle when we have shorepower, the breeze is whistling through the boat and we are freezing but the gas detector has yet to chirp. It is a very slow leak but I am not prepared to live with it forever. I had been hoping another S31 owner might tell me how the old pipe is routed, but no luck, and then I had the maths genius.
If I replace the line with new copper inside plastic hose, using grommets instead of bulkhead compression joints and put in a new stop valve behind the cooker I expect it to remain a mystery. Not going to be straightforward, the shorepower dist. box is on the other side of the gas locker enclosure where the pipes emerge.
 
One of the registered gas fitters who works the Argyll area suggested to me a few weeks ago that the plastic coated copper pipe can be used instead of copper pipe pushed through a plastic sleeve. Apparently it is what he uses. Likely you will be using 8mm, unlike me who used 10mm, remarkable increase in stiffness at 10mm, hence more compression fittings.
 
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