Gas....

Discussion in 'American RV's' started by Dodgey, Nov 12, 2008.

  1. Dodgey

    Dodgey Funster

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    Hi all, a question if I may?

    LPG tanks, now there's a gauge on ours and bearing in mind these things are not known for accuracy I always guess amount to put in rather than 'fill 'er up'. Stems from a gassed Ranger we had a while back were the seller advised if we filled up full, gas wouldn't flow with the solution being belt tank with a hammer:Eeek:
    Needless to say I didn't and actually removed system, which was good as it was about to have a major leek!!!!

    Back to the point, filling the tank what governs full? Is it the pump or to do with the tank?
    Tank in question is an old Manchester tank on a '77 Brougham (Dodge).

    Cheers, Si.
     
  2. American Dream

    American Dream Read Only Funster

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    Hi Si,

    There should always be a valve that actuates at the 80% full mark and evacuates the extra gas when filling.That's the reason all horizontal tanks are mounted with the valves at the recommended angle at installation.

    This should give you the indication to stop filling.

    As you know 80% is the maximum fill point for a LPG tank allowing safety margins.

    Like Yours, My Gauge is very unreliable.

    Steve.

    Welcome to another Dodge Owner.:thumb:
     
    Last edited: Nov 12, 2008
  3. walburga

    walburga Funster

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    Mine must be auto 'cause it stops itself. I then look at the gauge, which must be accurate, 'cause it reads approx 80 %. The sector between 80 & 100 is coloured red.
    As an aside (observation ?) when I hook up the gas gun in uk it always seems floppy until I pull the 'trigger' , then all firms up, I then press (lean on) the gas delivery button 'till it stops automatically at 80 % !
    I have had probs with autogas not flowing at sub zero temps. This summer I lagged the regulator & pipes from the bulk tank to where they enter the van. Not been cold enough yet to test.
    regards
    Allen
     
  4. scotjimland

    scotjimland Funster Life Member

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    Hi Allen

    If it's too cold for the LPG to evaporate in the tank, lagging the pipes and regulator will be of no benefit, nor indeed would lagging the tank help unless it was heat traced, lagging keeps the chill in.
    The chilling effect can be seen on bottles as condensation or frost when they are in use.

    Jim
     
  5. Dodgey

    Dodgey Funster

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    Thanks for the responces....

    Yup, I know the 80% bit and I suppose that's what worries, ie if there is any function of the tank that affects this. I would guess it's all down to back pressure on the pump but it's a confidence thing. When topping up the other day I guessed a quantity which didn't cause the pump to stop but put the gauge way past the 80% point....!

    Cheers, Si.

    PS Steve, there's something about the old Dodge one's it has to be said! Well we love ours, even if she is a bit tired round the edges:Smile:
     
  6. American Dream

    American Dream Read Only Funster

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    We love out Old 'Un too.She's got a few more years in her yet with the TLC She's getting.:thumb:

    It's like stepping back in time.That's why I'm replacing as much as humanly possible with original parts.New-style stuff just wouldn't look right.Call me a purist or what!!!!:Rofl1:

    I'm frankly, very surprised what I can source from the USA.They seem to stock, or be able to supply, virtualy everything.Just need the £-$ ratio to go in our favour again.:BigGrin:

    Steve.
     
  7. walburga

    walburga Funster

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    Hi Scotjimland
    I lagged the pipes & regulator after reading of a similar incident on the motorhomelist. The member there said it cured the problem. Possibly moisture in the system ?
    I wouldn't lag the bulk tank.
    When the system wouldn't gas off (-10 c outside, effectively were the bulk tank lives) I switched to my 6 kg propane, which is inside the insulated gas locker, and that worked as it should.
    Now, does the autogas have too much (any) butane in it ? Is there a 'waxy' by product of the gas thats clogging up the system, or might there be moisture present ? Just waiting for a really cold spell then I can test it.
    regards
    Allen
     
  8. olley

    olley Funster

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    Hi all LPG tanks should be fitted with an 80% cut off valve, usually similar to the float valve in your toilet cistern. Its possible for this to stick, mine did soon after installation, but in the "up" position meaning I couldn't fill the tank. :Sad:

    As I understand it, Autogas in the UK is about 100% propane, but abroad it can be up to 40% butane or more. A 50% mix will I believe give you a vapourising temperature half way between Propane and Butane, around -30C??

    Olley
     
  9. damondunc

    damondunc Funster

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    lpg tanks

    American lpg bulk tanks as fitted to RV's prior to 1996 did not have to have auto stop filler valves fitted, after 1996 it was and is a legal requirement to have an auto stop filler valve(in the USA). The valve is similar to a ballcock in a cistern if it has been fitted correctly it should stop the pump from filling the tank to over 80% full.

    USA tanks after 1996 have three ways of telling if a tank is 80% full:
    (1) the auto stop filler valve.
    (2) the guage with the red needle(the F mark is 80% full) watch this guage when filling or get someone to watch it, never let the needle go above the F mark.
    (3) the small brass valve adjacent to the filler valve (The 80% valve)which is at the same height as the filler valve. When filling open this valve very slightly you will hear a small hiss of gas vapour as the tank level reaches 80% the vapour will turn from a vapour jet to a white jet of liquid gas stop filling and use gloves to close the valve(obviously be very wary about using this one on a petrol station forecourt as lpg is heavier than air and will form a pool of vapour on the ground)

    The correct way to fill the tank is to use AT LEAST two of the above never rely on one method only.

    Prior to 1996 do not assume that the tank has an auto stop filler valve, the tank should be marked with a lable next to the filler if it has.

    One very important fact is that some electric pumps at filling stations have sufficiently powerful pumps that will overcome the float on an auto stop filler valve.

    The reason that it is so important not to overfill a lpg tank is that liquid lpg expands at a rapid rate with a small rise in temperature. You can compress a gas but not a liquid, if the tank has no expansion gap above the liquid where is going to go?
    If the tank pressure goes over a preset amount the safety valve in the bottom of the tank will leak lpg onto the ground. The greatest danger however is that if the tank is filled to the brim it is possible to get liquid lpg into the vapour takeoff to the regulator and get liquid lpg into the appliances and you really don't want this to happen it will turn your cooker into a flame thrower!
    If you follow the rules lpg is a very versatile fuel, if in doubt ask! most Rv'ers are more than happy to help if asked.
    Dunc.
     
    Last edited: Nov 13, 2008
  10. Tony Lee

    Tony Lee Read Only Funster

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    Vapor pressure - Wikipedia, the free encyclopedia has some semi-technical info on what happens with a mixture of propane and butane.

    There is a graph and the lines of interest are the purple line - propane, and the lime-green line - butane.

    One complication is that the left hand scale is pressure in absolute terms - so that the 1 atm line represents no positive pressure ie it is the same as normal atmospheric pressure. At zero degrees C, the pressure of butane is zero psi (1 atmosphere absolute) so you won't get any butane gas off below zero.

    There is also an article on Relative volatility that is relevant and what we do when using a tank of autogas with both propane and butane in it is very like putting fermented mash into a still and heating it to somewhere between the boiling points of water and alcohol to give us a higher proportion of alcohol out the top while leaving most of the water behind in the still. In the autogas case, if the temperature of the tank is below 0 C, you will get mostly propane out as a vapour and the butane will mostly be left behind. The lower the temperature, the worse the problem will be. Once the propane is all gone, the liquid butane will not evaporate.
    It is a bit simplistic, but close enough.

    Note - in an autogas powered car, it is liquid that is drawn off and this is either direct injected into the cylinder, or evaporated using hot coolant so relative volitility isn't a problem unless the temperature is low and the tank is full of butane when the tank would need heating as well.
     
  11. Dodgey

    Dodgey Funster

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    Duncan, many thanks.

    I will now continue with my paranoid approach!

    I know the little valve your discribing as we have one but as you say bleeding LPG on a petrol station forecourt:Eeek:

    Si.
     
  12. PeteH

    PeteH Funster

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    Lpg.

    Hi

    I have some sympathy, with this thread, as it can be a real pain getting a reliable reading of current gas (sorry LPG) level. I rely entirely on the "vapour vent" valve when filling, Its mechanical AND simple, no relying on gauges which are notorious for being in-accurate, and the flammabilty danger is no greater than that of "petrol" fumes during re-fueling. (In industry Gauges are checked for accuracy at regular periods, and the gauges that check the gauges are certified regularlly too!!!! and stored in foam lined boxes when not in use!!)
    The auto fill cutoff device current is prone to jambing, and there was a thread on one forum about someone who actually had an OVERFILLED the tank, I think at Americana? or one of the shows, and had to be put in "quarantine" whilst it was dealt with.!! with emergency services in attendance ETC (bet that was not "claimable" on insurance!!) so be warned!!

    p.s. There are two "limits" outside of which vapour will not ignite ie too Much Oxygen (upper explosive limit) and too little oxygen (lower explosive limit) Only within those bands will vapour ignite. So "smelling" gas does not actually indicate and explosive mix. The "stench" is actually put into the gas, as natural LPG has no odour. An empty tank even when "gas freed" still stinks, and the smell lingers on your clothing even after washing!!! (the Mrs used to make me get undressed in the porch after I`d done a "Calor" tank internal examination, `cos she did`nt want the stink in the house!!!)


    Pete
     

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