I have a panal van based DIY campervan conversion, which I would like to fit a fixed underfloor gas tank to. I have a spare torpedo tank from a Discovery that I converted a few years ago which is still in good condition. My plan is to replace the liquid take off multivalve with a vapour take off, and then run the pipe to a regulator to give the correct pressure for the cooker, fridge etc.
But then I had a couple of (possibly daft!) ideas that I thought would be a good idea to get advice about before taking things any further. My first idea was wondering aabout running the liquid pipe to a standard vaporiser unit, which, as the amount of gas being used is small, may be OK without freezing up? Anybody know whether this is the case?
The second idea was even simpler - just remove the multivalve and cut off the pipe to the bottom of the tank, thereby converting it to a vapour take off. Is it really that simple?

The last thing I want to do is put anyone's life at risk, so I would welcome any advice on this, even if it is "Don't do it because...."

Taking vapour through parts designed for liquid will result in much reduced capacity at the end ; although it might well be enough. Obviously you need a regulator to drop full tank pressure to 'domestic' pressure. An old autogas unit will not do - wrong pressure, and almost certainly won't meet BS.whatever is needed.

Can't recommend modifying things ; not least because anyone 'inspecting' the setup and seeing an apparently standard liquid valve feeding a domestic supply will have kittens, again it won't be to BS.something. Bear in mind if you fit/modify use non-standard equipment it would almost certainly invalidate any insurance. Might struggle to find a proper vapour multivalve (with no electric shutuff) most vapour tanks seem to be 4-hole.

I believe there is a convention to paint vapour tanks red, but thats easy to arrange!

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www.blazegas.com

The regulator bit is fairly easy to deal with - the standard setup these days is for a remote regulator with high-pressure hoses to the cylinder(s). But as Rossko says, you really don't want to start modifying stuff.

I'd suggest the easiest way to deal with it would be to install a purpose designed tank/cylinder and tee it's fill line into the fill line for the main tanks - that way your domestic gas supply will be filled up every time you fill the engine fuel tanks. Doesn't let you use your current cylinder though.

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Land Rover 110 V8 LPG
Land Rover 90 petrol (no longer diseasel :D), still awaiting V8 & LPG
http://www.diy-lpg.co.uk

Ah. I didn't explain this very well...

It is a diesel (shhhh ) campervan so no current onboard tank. The gas locker takes 2 3.9kg propane cylinders, and it would be useful to have the extra space for other stuff, plus at about £15 for an exchange cylinder, a cost saving too.

When I was musing about an autogas regulator, I was meaning to take a 6mm liquid pipe to it to vapourise the liquid (assuming the small flow would be enough not to cause a freeze up), THEN take the vapour to a standard domestic regulator to get the pressure correct. I haven't yet got to the stage of looking for parts, I wanted to bounce the idea around to check I wasn't doing anything stupid...

Agreed, modifying the multivalve is probably not the best idea I've had! I am trying to do this on a limited budget, but not at the expense of safety. If I did need to buy another tank as well, I'd probably knock the idea on the head for now.

Ahh, now it's clearer.

Pity your tank isn't a 4-hole tank since there are outlets for those for vapour takeoff - ie you'd just need to buy the vapour take-off outlet as you'd already have the filler, gauge etc.

There are refillable cylinders designed for these applications - ie use you existing regulator etc and plumb in a fill line. They are quite pricey though.

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Land Rover 110 V8 LPG
Land Rover 90 petrol (no longer diseasel :D), still awaiting V8 & LPG
http://www.diy-lpg.co.uk

Or just buy a purpose made refillable system especially designed for motorhomes,

http://www.autogasshop.co.uk/lightweight-refillable-lpg-cylinder-with-guage-26-p.asp

Dunno if Im allowed to do that !! not promoting anyone as such, but I knew where to find it seems the best answer for you if it needs a cert after.

Cheers guys for the suggestions. However the problem is I'm limited for space as it is - I wouldn't be able to fit the larger refillable cylinders in the gas locker, and the idea of mounting a tank (that I already have!) underneath is quite appealing. I also like the idea of wiring up the solenoid on the tank to the ignition circuit, so it would be impossible to drive away with the gas supply still turned on (at present I have to remember to turn off the bottles before I drive anywhere).

Regarding the legalities - I've not been able to establish what is actually legally required before taking it on the road. Before I go ahead with any mods I think I'll do a spot of phoning around to see whether anyone is able/willing to check it out.

I do not think you'd be able to set up an automotive vaporiser to deliver "standard domestic" 30mbar or whatever it is, although its not impossible. The idle bleed would need to be sealed off permanently, and it may not regulate low demands very well at all ; I can imagine pilot lights getting snuffed out etc.

Icing may or may not be a problem ; the usual vapour arrangement uses the whole tank/cylinder surface to exchange heat with the environment. If you are evaporating in a liquid-fed vaporiser, there is much smaller surface.

I'd still say the complete show-stopper is that any insurance will be invalidated because automotive parts are marked for E-something, which is not the same as E-otherthing for domestics. Technically comparable, no doubt, but insurance assessors would "take steps" ... long ones!

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www.blazegas.com

Hmmm, I think that's made my mind up then! I will enquire about a vapour take off fitting for my tank to replace the multivalve - as far as I can imagine the actual tanks would be the same. Mine is a cylindrical tank therefore can be rotated to position the valve in any position. Or does that have implications for filling?

Re your comments on the icing up - thinking about it I have once seen Calor propane cylinders with frost on the outside when they were feeding a catering van. That would suggest that at high demand levels an unheated autogas vaporiser would not be any use.

Problem is, most vapour take-off tanks are 4-hole fitting ; the idea of a multivalve is almost exclusively automotive. A vapour take-off multivalve is therefore a rare and wonderful thing .... in the UK.
I think what you need is a E-marked vapour multivalve for a scooter, outboard, or tuk-tuk LPG tank. Try suppliers HKL or FES.

Don't even think about a CNG valve ; deals with vapour but is designed to work at ridiculously high pressures - so the inbuilt safety PRV valve would be useless and outright dangerous on an LPG tank.

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www.blazegas.com

The penny has now dropped (eventually), thanks Ross! I will look out for a vapour multivalve, although I suspect they may be even more difficult to come by than a BRC stepper motor...

I did have a search but couldn't find any multivalves, but as far as I can see, a 4-hole vapour tank is the same bit of metal but painted red and with a different outlet fitting.

On the subject of a solenoid valves, bear in mind that these are typically 8 or 12W - so 2/3 to an amp of current. That's a lot to draw continuously and would seriously impact on battery capacity for the other hotel loads. On the other hand, once activated, the solenoid probably only needs a fraction of this to hold it open - so it should be possible to rig up a simple circuit to apply full voltage initially to open the valve, and then cut back to a much reduced current to hold it open.
I'd then extend that to push-button control so you have to press a button to turn the gas on, but it will turn off (and stay off) if you press the off button or (as suggested earlier) turn on the ignition. If you just use a switch, then connecting the battery would turn on the gas if you'd left the switch on.

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Land Rover 110 V8 LPG
Land Rover 90 petrol (no longer diseasel :D), still awaiting V8 & LPG
http://www.diy-lpg.co.uk

Interesting...I hadn't realised they drew that much current. Will give the circuit some thought but I think I have an idea. I had thought about the switch arrangement - as you suggest there would be times when the ignition is off that you wouldn't want the gas on - storage and whilst on a ferry for example. Even just a big warning light on the dash would be a useful reminder which would be easy to add with a valve controlled by electrickery.

No, they are different ; an automotive 4-hole tank has a welded-in downward dipping pick up tube. See halfway down ...
http://www.v8engines.com/Billing_2003a.htm
Even if you mounted the tank upside down, the fillstop float would then be all wrong.
Presumably a red vapour tank has an upward poking tube, never had an opportunity to find out!

Well known brand Tomasetto vapour multivalve
http://www.tomasetto.com/a_ENG_88_1.html
but electric shutoff. UK availability ????
(suprisingly, 6mm outlet pipe is considered big enough up to, I think, 125cc engine - but this pipe is at full tank pressure, to be fed to the regulator)

It would be feasible to remove the innards of a multivalve solenoid shutoff so that it was "always on", so long as there was a manual shutoff instead. That would be the same in practice as a normal calor bottle arrangement. But once again, "disabling an existing safety feature" is handing a cop-out to your insurers on a plate ...

I just can't see this working out in legal terms, short of getting the correct kit.

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www.blazegas.com

Well you learn something every day. I guess that's why they can get away with the price they charge for them.

Well you've a few bar of pressure behind it, and in a typical caravan you might see long runs of fairly small copper pipe running at low pressure to the appliances. I know that my V8 will run on the vapour that will pass along a few metres of 6mm pipe - it only starts loosing power when the last of the liquid has gone, and then I get at best another mile on rapidly reducing power as I use up the pressurised vapour.

Well the multivalve you show would do the job, all that's required is an adapter to the inlet on a bulkhead mounted regulator - as is now standard on new caravans.

And I checked with a friend who's recently bought a new motorhome - you would not believe the price of them He has a 28l tank underneath and a switch inside to turn the gas on/off.
I notice the valve above is specced as having an 11W coil on it - so not far short of an amp to run it, though as I said above, it would probably hold open on considerably less.

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Land Rover 110 V8 LPG
Land Rover 90 petrol (no longer diseasel :D), still awaiting V8 & LPG
http://www.diy-lpg.co.uk