Sneezing LPG tanks - no idea where to begin!

[Bigwilly1]

1st off all, been around on here for a while and its a great site so keep up the good work. Anyway, for the 1st time, i'm completely stuck on this problem.

Car set up
The car is a '95 range rover classic V8. Due to an offroad incident my car ended up sat under water for about 15mins (seemed alot longer at the time). It has 5 LPG tanks. 2 underboot floor replacing orginal tank, 2 torpedo and one in the boot and its running an Emmegas single point system. Shortly after the swim one of the solenoid/coil/relay things gave up the ghost on top of the vapourizer so that is currently removed. The other one the filter still works.. Through out syntoms below ive tried the switch unit unplugged and with the remaining working solenoid disconnected


Syntoms.
My LPG tanks occasionally sneezes. By sneeze i mean they randomly seem to discharge themselves and the sounds seems to localise itself to one of the tanks at different times. It only seems to happen when the cars warm and there is a slight tendacy to be on a bumpy road or braking but that isnt 100%. The guage is definatley dropping sneeze by sneeze but it always did gradually drop but seems to be dropping quicker. It only seems to have started doing this since i removed the broken relay. there is a definate smell of gas also if its sneeze and i then get out of the car

has anyone got ANY ideas! Like i say, - i have NO idea where to begin. Ive managed to sort most things without clogging up forums but this one has me stumped!

Thanks in advanced!

PS il put the youtube link of my car swimming up soon!

[classicswede]

I take it from what you are saying that the pressure relief valve is letting gas out? you will need to work out which tank is doing it and then replace the valve.

If the tanks are over filling then the PRV is only likely to open when the tanks are full.

[Tubbs]

I would also doubt that you have any non return tees in the lines. So one tank can overfill more than the other. And the prv will 'sneeze' to release the pressure build up.

[Bigwilly1]

Hi Guys, Thanks for the replys!

I agree with you to one respect - however there was only £40 worth of LPG put in about 2 weeks ago which has sneezed its way out. The analogue guage on the tank in the boot says just over empty?

Presumably/hopefully only one PRV has broken - why does the sound seem to come from different tanks or is that just cars for u?

Also, they are only 1 hole tanks (rather than 4 hole) - do single holes still have PRVs?

[Tubbs]

All automotive lpg tanks be it single or 4 hole have prv's. Could be a knackered spring on the valve.

[rossko]

I would really think more about cross feeding than duff PRV - though they can seep, I've never seen one lift without just cause. You could test for a weaky one simply by attempting a fill I suppose - forecourt pump will deliver at around 15 bar.

After it's all sorted you will need to see that the PRVs have plastic bungs or suchlike to replace the lost one(s), to keep road dirt out.

[SimonHobson]

On my 110, if I don't do anything about it, the rear tank will cross fill from the front tank while I'm driving - more so in warm weather.

In miles worth, I get about 160 from the rear and 80 from the front. I can get enough crossfeed in 40 miles to fill the rear tank before the front one is empty. If the timing is "wrong", then I'll complete theta process during a journey from cold, and then park up while day warms up. So when I come to drive off, the rear tank has pressurised until the PRV is slowly "hissing" the gas away - this one dribbles rather than sneezing. The pressure is such that the solenoid valve can't lift against it - and so I end up out of gas while carrying a full tank which is "rather annoying" (more so if, like now, I have no petrol tank installed).

The Emer valves are supposed to have all the requisite non-return valves, but having taken one apart, it's possible to fill from the outlet pipe if the flow rate is low enough to avoid tripping the fill shutoff - the inlet and outlet are joined together internally.

So I manually shut the valve on the front tank until the rear is nearly empty to prevent the crossfeeding.

So one potential process is that the internal tank runs a bit warmer and crossfeeds to the external tanks (which are also lower). On a drive from cold, this is OK - the four tanks just fill up. If things warm up while not running, then the tanks "lock" their solenoids - and with a bit of warmth, and a jolt, they sneeze out some excess. Then the next morning, everything is cold, and you repeat the process - running down the inboard tank.

One suggestion is to run on gas until the inboard tank is completely empty, and see what happens.

Also, it's worth checking that all your tanks have working outlet valves. If the coil (or wiring) fails then that tank will fail to empty - so you can be lulled into a sense of it being empty when it's actually full.

[Bigwilly1]

Hi Guys,

1st off sorry for late reply. Had fun and games with a starter motor not doing what it should then a battery issue so the sneezing LPG tanks werent a problem as it wasnt going anywhere. Ive read all your replys and now im even further away from under standing how this all works lol.

Ive done a picture of how i think my set up is. Are there more selnoids than that or any more 1 way vales i should no about?



Also does anyone have a piccie of a PRV on the tanks? Looked at the one in the boot and cant see anything but a sender? Ive just been to fill up, only £40s worth and seems fine, is there any other way to test a PRV?

There are 2 screw type valves on the boot tank, presumably they should both be open.

Another thing is the cars not running now - replaced the solenoid valve but still dies. various loud clicks when it makes the jump but nothing happens. Shortly after its swimming lesson, she was running on LPG nicely!

[rossko]

There should be a solenoid on or close to each tank. Running five tank solenoids off a switch intended for one or two could fry it. If the installer planned ahead, there could be an external relay to handle the load.

What makes you think there are one-way valves at the tank outlets?

Maybe there's\no gas in it now, if its been emptying itself.

[Gilbertd]

Take a photo of the gubbins on one of the tanks, at least someone will be able to identify what bit is what. There should, unless very old tanks, be a solenoid on each one but there wouldn't normally be a one way valve, they should be in the T pieces.

[Bigwilly1]

Right- im way out of my depth now with a dangerous substance so i need to go back to basics again and see what ive missed. I know alot about the construction of compressed air systems and know about fueling systems and safe practices accossiated with each so im confident enough to get it fixed myself but im going to be very careful so be prepared for lots and lots of qus.

Theres definatley no solenoid on the boot tank - 2 thin wires to the sender and what im presuming is a neg. Just crawled under a sill tank and there is a solenoid on that one but there is also a hiss.

http://www.autogasshop.co.uk/lpg-tank-p ... -637-p.asp ...... Is a PRV like that maybe 10mm in diameter - if so it is that that is leaking!!!

I know the legal issues of LPG in cars are sketchy at the moment but i read somewhere tanks shouldnt be above a certain age - if i send my car to a proffesional - are they going to charge me hell + high water before i get my car back replacing all the tanks etc etc?

[Bigwilly1]

T peices look like standard plumming items to me - no none return valves.

Can someone clalify with me....The drawing ive done - There is an in and an out on each tank yer? NOT like the image ive done below.

[Gilbertd]

It's definitely not like that latest diagram. Assuming you have single hole tanks, you will have what is known as a multivalve which is where the in, out, PRV and gauge sender live (see http://www.tinleytech.co.uk/acatalog/Ta ... Boxes.html for pictures of different sorts). The input must have a non-return valve so that you don't empty the tank if the hose to the filler, or the filler itself, gets damaged. The outputs will not have a one-way valve but will be open. Modern multivalves will have a solenoid valve on the output but older ones didn't. In a multi tank installation, the filler pipe uses standard T pieces to fill all tanks but the output should use T pieces that incorporate one way valves so gas can flow out of the tank but not in (have a look about 1/3rd the way down this page http://www.tinleytech.co.uk/acatalog/Pipes_and.html). If it is done properly, if one tank was holed it would empty that tank and the contents of the pipe from the filler to all the tanks (as there is a one way valve inside the filler), the other tanks would remain filled. It sounds like you have no one way valves so the tanks can cross fill and a faulty PRV so the gas you put into any tank will end up leaking out.

Tanks should be less than 10 years old and in sound condition. It would be a particularly picky installer who insisted that you replace the tanks if they are 11 years old on an 11 year old installation unless they are badly rusted and look unsafe. However, most installers wouldn't take kindly to the use of non-LPG T pieces and no one way valves.

[rossko]

...but there is also a hiss.

Bear in mind that could represent a perfectly healthy PRV - that is dribble venting because the tank has overfilled via crossfeeding.
Or it could indeed be stuffed; either simple old age, or its just lifted once too often to seat properly again - in the ideal world a PRV never lifts at all, its not really intended for repeat operation.
Going to be difficult sorting root cause from effect.

Or it could be some other joint or seal altogether thats leaking.

You'll probably have to decide what standards you want to reach, the rules have changed over a decade.
If you need any form of certification, it would have to meet present day standards.
If you don't change anything, you have to accept lower standards; example you describe the internal tank as having no solenoid, so there's an opportunity for a split/damaged pipe to dump the entire tank content unexpectedly. (There may actually be a seperate solenoid under the car)

You might simplify the problem by abandoning some tanks

[Bigwilly1]

HI guys, Making abit more sense now. Will have to do some research.

The hiss i describe is coming from a PRV, providing the PRVs look like the one in my link and are about 10mm. theres definately a red plastic disc and the note of the hiss changes as i rub it . Im pretty sure it wasnt crossfeeding as the car had been parked for a few hours before i went out and checked and the tanks were only a 1/4 full so wouldnt be enough to blow.

Gilbert, thats for the links. I will get some piccies of the kit i have and get back to u so we can work out whats going on with it all.

From what ive seen today, i think the tanks were fitted at different stages of my cars life. Rossko, abonding tanks isnt an option. I potentially have a 90mile a day commute at least 5 times a week but potentially 7 days a week. The nearest LPG station is 7 mile away in the opposite direction to the one im in . i get 350+ miles to a tank and im not prepared to begin filling more than twice a week lol! Spending more time at Lymm services than with my girlfriend wouldnt go down well haha

[minormatt]

I fill my diesel at least twice a week...

I work 270 miles from home...

[rossko]

providing the PRVs look like the one in my link

That's the kind of PRV you'd find on a 4-hole tank, where various fittings are seperate.

Typical multivalve
http://www.acntest.com/products/convers ... ical-tanks
the integral PRV here is the brass post surmounted by a red plastic disc with writing on.

theres definately a red plastic disc and the note of the hiss changes as i rub it

Sounds like a PRV right enough.

Im pretty sure it wasnt crossfeeding as the car had been parked for a few hours

Ideal conditions to generate a temperature difference between internal and underslung tanks, no proof there.
Don't forget the PRV may have been worn out by repeated crossfeeding. Fit a new multivalve, and it might stop the seeping ... for a while ... but not the "sneezing"

before i went out and checked and the tanks were only a 1/4 full

Which ones? There is nothing to guarantee tank levels are at all similar. Is there a mechanical gauge on your suspect tank?

[Bigwilly1]

The leaking tanks doesnt have the mechanical guage on - the boot one has the guage on it!

Right lots to check there and things to do and ill get back to you!


On a seperate note,
Im thinking about ripping the whole lot out and refitting it all and getting it properly cert'd! Whats involved? Can do a good job of waterproof wiring being a marine engineer and have access to wires etc but what do i need to re plumb in all the tanks? Is it expensive? I mean i have all the tanks + mounting brackets etc i just plan to replace the odd multivalve/PRV and the hoses

[SimonHobson]

... but the output should use T pieces that incorporate one way valves so gas can flow out of the tank but not in (have a look about 1/3rd the way down this page http://www.tinleytech.co.uk/acatalog/Pipes_and.html).

Those valve are as much use as a chocolate tea pot - they will not in any way even slow down cross feeding. All there is is a loose ball which can roll to one end or the other of the head of the tee. So in theory, if a pipe burst then the ball would be pushed to that end and would "more or less" close the hole (there's no soft seat to seal against) - but without that sort of pressure differential the ball will just roll around and do nothing.
The non-return valves they sell do have a spring loaded plunger with proper resilient seat.

Im thinking about ripping the whole lot out and refitting it all and getting it properly cert'd! Whats involved? Can do a good job of waterproof wiring being a marine engineer and have access to wires etc but what do i need to re plumb in all the tanks? Is it expensive? I mean i have all the tanks + mounting brackets etc i just plan to replace the odd multivalve/PRV and the hoses

Have a look around the articles on my website (see signature below) - that should give you some idea.
It's not hard or even complicated, it's just that there used to be (and still are) a lot of vested interests that want consumer to think that it is, and there are a lot of mechanics who think it is and spread their ignorance as "facts".


Back to the non-return valves, while I've only seen a small number of makes/types, my experience is that the 4 hole tanks don't even pretend to have a non-return valve in the outlet (it's just a solenoid), and the Emer multivalve (single hole tanks) sort of has one but it's ineffective.

So you've 5 tanks, at different heights, and different temperatures (= different pressures) - I'd say it would be a miracle if you don't have cross-filling.
When you looks underneath and one of your PRVs was hissing, was this by any chance later in the day on a nice day when the temperature had risen a little since your last drive ?

And just had a thought ...
The tank in your boot has no solenoid (unless there's one in the pipework underneath) - so it's contents are always open to the outlet pipe. The solenoid valves on the other tanks will act as non-return valves when off and allow gas into the tank when the pressure is high enough. I don't know if (say) having the internal tank in the sun on a sunny day would lift the temperature (and pressure) enough to cause cross feeding even when the vehicle isn't running.

[Bigwilly1]

Hi Guys, Had customers over from Holland recently so havnt been near my car.

Can anyone help we work out why the LPGs not working. Is it a case of check theres 12v at each solenoid and see if theres gas in the tank? Or taking hoses off and working my way back untill i find where the gas isnt getting through? Is there anyway to check the solenoids are working.