Connecting a third LPG tank

[Jamie Taylor]

Hi All,

I hope you are well.

I wonder if someone can help me with something?

I have a Ford Econoline with an LPG conversion. It is a first generation system which runs a V8 engine. It has three tanks, two of which supply the engine with LPG, the third was connected to a now defunct domestic LPG system. I want to 'plumb' the third tank into the fuel system.

My questions relate to:
I was going to use a one way t-valve to connect the system after the previous t-connection between the first and second tanks. I understand there is some debate about expansion of LPG in the pipes, so is that the best thing to do?

I also wanted to check if the solenoid and manual valves will stop the gas from being vented when the fuel pipes are opened?

Finally, I guess I just wire the solenoid of the third tank into the same circuit for the other two tanks, so they all open at the same time?

Thanks in advance

Jamie

[Brian_H]

You might want to have a look at the valve on the tank first. A domestic LPG system will usually run off vapour rather than liquid (tanks for engine use would have a pickup off the bottom of the tank). You might need to swap the valve to actually use it for propulsion use.

You may be better to wire via a relay to energise the solenoid depending on whats switching it in the first place, you haven't mentioned if its a single point or sequential type system, so it might help to confirm that as well? I'm guessing being an Econoline that you may also not be in the UK?

The manual valve should stop the gas flowing as should the solenoid, provided they work. Suggest best to shut them off, then cautiously open the pipework and let the pressure out, once you are happy its stopped continue undoing it.

As far as one way valves go, you want to avoid filling tanks via the outlet valve through the pipework. There is a risk of overfilling tanks otherwise. Thats what your aiming for with the one way valves. the filling side would have the valve in each tank and the one in the filler point, you shouldn't need any more on that side as far as I know.

If you are located outside the UK, some of the regulations and requirements may be different. Particually if you are in the USA, the tanks are different as well (not sure if the differences matter for what your looking to do).

[Jamie Taylor]

Hi Brian,

Thanks for getting back to me, and thank you for your help.

I am in the UK. We were crazy enough to buy a US import...

Should have said the 'domestic' LPG tank and solenoid is the same as one of the auto LPG tanks. i.e., It is an autogas tank. Sorry.

The other two tanks are wired into one another, so I figure that I could connect all the solenoids up to the same relay so they all open up at the same time.

It is a single point system. The LPG feeds a 7.5l V8 carburettor engine through a ring. An ECU would be nice

Ah, the joys of buying a second-hand truck... I am pretty sure the third 'domestic' tank is full of LPG, although it may not be if the gauge is kaput: But I nearly had a heart-attack when I spotted the out pipe was not capped... Then I realised the solenoid and the manual screw were keeping the gas in. Phew! It looks like it was decommissioned at some point in the past. Actually, the whole thing is like some house, that various crazy people have put together... I am trying to make a 'user manual' so if and when we sell it, the next people have some clue what is going on. I reckon I could get a few bob from weighing in the copper piping and wiring which is defunct.lol.

Then again, I love tinkering,,,

Jamie

[LPGC]

A single hole (multivalve) tank can be purposed for vapour take-off by fitting a purpose designed vapour take-off multivalve. Vapour take-off (to connect to a regulator to fuel cookers etc) multivalves can look very similar to liquid take-off (to fuel an engine) multivalves but if the tank has a vapour take-off multivalve you would have to swap it to a liquid take-off multivalve to run the engine (and then it wouldn't be able to connect to a regulator to supply domestic appliances).

On 4 hole tanks the liquid pickup pipe (on liquid take-off tanks designed to fuel) is part of the tank itself (as opposed to being part of the tank valve). You can effectively convert a 4 hole liquid take-off tank from liquid take-off to vapour take-off by removing the gas outlet valve/solenoid and drilling a hole through the side of the tank's liquid pick-up tube. You cannot easily convert a 4 hole vapour take-off tank to liquid take-off because there'd be no way to connect a liquid pick-up tube (inside the already welded closed tank).

If the LPG system was fitted in the US the tanks will likely be 4 or even 5 hole designs, as opposed to multivalve designs.

Some of the US design vapour take-off tanks feature a 'tell port/valve' which is like a little bleed screw on the tank. During filling you're supposed to have the tell-port open a little bit, gas vapour escapes during filling and you know when to stop filling (when the tank gets to 80% of full) because liquid gas instead of vapour comes out of the tell port.

[Jamie Taylor]

Hi LPGC,

Thank you for that! I will go and take a look and see what I can see, before I do anything I may not even do it myself, but I do want to try and understand what is going on either way.

The tanks are defo a UK system, they were installed long after the vehicle was imported here.



Jamie

[Jamie Taylor]

Hi,

I have taken a look.

The multivalve on the 'domestic' LPG tank is a Tomasetto AT02, which is the same as the valve on one of the autogas tanks. The solenoids are both the same. Is the model AT02 indicative of it being a liquid take-off, or is there more?

Cheers

Jamie

[LPGC]

AT02 is Tomasetto's generic tank valve... The float mechanism, liquid pickup pipe and vent pipe design differs between cylinder and toroidal tanks (and tank height or diameter) but the design is much the same regardless of those aspects, the intended fitting (0 degree for full toroidal external toroidal tanks, 30 degree for cylinder tanks, 30 degree internal for internal toroidal tanks) and height/diameter are stamped onto the valve body.

I'm not entirely sure if the vapour take-off variant(s) are still labelled AT02... But it would be possible to adapt (say) a 30 degree or 90 degree cylinder variant to pickup vapour instead of picking up liquid... all you'd do is adjust the pickup pipe (or remove the pickup pipe entirely in case of 90 degree as 90deg valves mount of top of a cylinder where the headroom/vapour is anyway).

Usually valves use on vapour take-offs don't have the electronic shut off solenoid (or at least the solenoid is disabled by removing the plunger from the solenoid post)... If the valve for a vapour take-off still had a working electronic solenoid it obviously wouldn't allow gas to be drawn from the tank unless the solenoid coil was powered up (which might lead to flat battery etc on a camper van if powering say a gas fridge long term).

Begs the question if your tank valve has a liquid pickup pipe, or was a factory modified vapour take-off valve, or was modified by the installer to pick up vapour instead of liquid. If it picks up liquid it could explain why it isn't connected to run your gas appliances... gas appliance regulators need a vapour supply not liquid, it wouldn't have worked with a liquid feed, maybe it was disconnected when someone found it couldn't be used to run gas appliances.

If it is a factory design vapour take-off valve we would expect the stamping on the brass body to reflect that.

Mick at Fox Vehicles / LPG Auto Supplies will be able to fill in any blanks / answer any questions on this.

[Jamie Taylor]

'Begs the question if your tank valve has a liquid pickup pipe, or was a factory modified vapour take-off valve, or was modified by the installer to pick up vapour instead of liquid. If it picks up liquid it could explain why it isn't connected to run your gas appliances... gas appliance regulators need a vapour supply not liquid, it wouldn't have worked with a liquid feed, maybe it was disconnected when someone found it couldn't be used to run gas appliances. '

That is what I reckoned as well... There is a side box under the truck with a ventilated cover, and the remains of pipe work. I reckon there were some propane tanks in there; and yes someone ran a pipe before realising that it would not work.

Thanks again for taking the time to reply!

It would be good to get it to someone, but we are up in Glasgow and there appears to be a dearth of garages to do the work

[LPGC]

For your intended modification --- converting the tank that was supposedly set up to supply just a regulator to run gas appliances from to become an extra tank to fuel the engine --- you might hope that someone made the mistake of fitting a standard liquid take-off valve. In that case you could simply plumb it's outlet to connect to the pipe that feeds the engine and your modification would be complete (assuming the tank is connected to a/the filler and it's solenoid is wired in parallel with the other 2 tanks solenoids).

There are too many dodgy installers but I would have given almost all installers the benefit of the doubt regards being aware that a regulator that feeds appliances needs a vapour outlet from it's feed tank. It would be interesting to find out if the valve on this 'domestic gas' tank is a standard (liquid take off), factory vapour take off, or any attempt to modify a liquid take-off valve to vapour take-off has been made. But before that question - was it professionally fitted or did a previous owner fit it.

I'm going to speak to Mick tomorrow anyway (on other matters) and will mention this thread, so he might reply. As far as I know he might say that Tomasetto didn't make any (AT02) vapour take-off valves, might say that he'd have advised (say) an Emer (make) valve for a vapour take-off multivalve setup. It he says Tomasetto didn't make an AT02 variant that was dedicated to vapour take-off it still wouldn't rule out an installer or owner modifying an AT02 to make a vapour take-off valve but would seem to add extra weight to the theory/speculation that it was once connected to a regulator but didn't work to supply the regulator because it is a liquid take-off valve.

[Jamie Taylor]

Hi LPGC,

Thanks!

[LPGC]

I did speak to Mick today, he says Tomasetto don't make a vapour take-off valve.

As said above this doesn't mean that someone couldn't adapt one to be vapour take-off by adjusting (particularly) the pickup pipe... If the pickup is rotated so the entry point is at the top of the tank (and the valve is already mounted at the usual 30degrees above horizontal, or higher, then it would pick up vapour instead of liquid.

But it does seem odds-on that yours is a standard valve fitted in the standard way, in which case it will pickup liquid.

[Jamie Taylor]

Hi LPGC,

Thank you for that, I really appreciate it. I guess the only real thing to do is to test it and find out.

I think I will activate the solenoid and loosen the knurl off to see if anything comes out. If it does, connect it into the system and see if the engine will run.

I will let you know when I find out.

Jamie

[Jamie Taylor]

So, there is gas... But what sort of gas???

To be continued...

[LPGC]

There's excess flow prevention built into the outlet port of the valve... Especially in warmer weather this means that you might only see vapour come out of the tank (even if the valve is liquid take-off) because you can't get gas to flow quickly enough out of the tank for it not to vaporise on it's way out before the excess flow valve severely restricts the flow (unless you set the thumb screw so gas comes out as quickly as possible before the excess flow valve cuts in and leave it flowing until the tank valve gets very cold). In this situation it would be liquid in the pipes all the way up to the engine bay pressure reducer because the pipe itself would be at tank pressure.

[Jamie Taylor]

Hi LPGC

Thanks.

I had a poke around the truck the other day and realised there is a very good chance that the mystery pipe fed a generator. Which I imagine means it was a liquid take-off. Fingers crossed.

Thanks for the latest advice as well.

Jamie

[LPGC]

Small engines and generators are often converted using vapour fed reducers so are run from a vapour take-off, especially if the engine is air cooled. If the reducer has to turn liquid gas to vapour it usually has to be heated by engine coolant but there are ways of heating liquid LPG before it gets to the reducer... Effectively a length of LPG feed pipe (between tank and reducer) is ran along the exhaust. But it's a special exhaust unit in this case and such special unit is only available to fit certain model vehicles such VW's with air-cooled engines.

Doesn't mean someone didn't assume an air cooled generator engine would need a liquid supply (when actually it might need a vapour supply).

[Jamie Taylor]

Hi Simon (just spotted your name)

I guess the only thing I can do is either do the test you suggested above, or just plumb it in and see what happens...

Jamie

[LPGC]

Yes and you might as well plumb it in... But test it during a drive because at idle it might seem to run OK from it even if it's a vapour outlet.

[Jamie Taylor]

Hi Simon,

So finally plumbed it in and went for a drive. It actually worked downhill and on the flat, but did a lovely job of suddenly stalling uphill!!! SO, yes, a vapour take-off. I thought it was when I saw the difference between the gas coming out of the other tanks and that one. So, I guess it was installed for the domestic stuff.

Thanks for your help!

Jamie

[LPGC]

Did you plumb only to that one tank (other tanks disconnected)?

It does seem most likely that it is a vapour take-off... But if the other tanks are still plumbed in and empty (and there isn't a one way T or inline valves fitted) there can be a situation where gas goes from one tank to another so there isn't as much pressure to push gas to the front end.