Gas Bottle Contents

[Mel E]

There have been many threads about this over the months and years.

 

How do you know how much gas you have left? There are only three ways:

 

1. Weigh the bottle and deduct the net weight - far too complicated to keep taking it out, so forget that one.

 

2. With an ultrasound device such as Truma introduced a couple of years back - it senses the level of liquid gas in the bottle. But it was expensive and is no longer listed by Truma, so has it disappeared?

 

3. With a float guage just like a petrol tank. But this has to be built into the gas tank and the only ones I know of that have this device fitted as standard are the MTH Stako refillable bottles. However, we find a single such bottle fine, because we always know how much is in there and can refill as frequently as possible at any gas station - so you save money on a second, unnecessary bottle and all that automatic changeover equipment.

 

WHY IS A PRESSURE GAUGE USELESS?

 

HERE IS THE DEFINITIVE ANSWER: Gas is stored as liquid in the tank and while there is liquid in there, then the pressure will always be constant. You open a gas tap thereby reducing the pressure, some of the liquid turns to gas, and you use some. You close the tap and the pressure comes up to standard until no more gas can form. So the pressure inside the tank is self-regulating.

 

For any given temperature, there is a pressure (called the partial pressure) at which liquid turns to gas and gas back into liquid, For water at atmospheric pressure that is 100 degrees Celcius at sea level. For Butane and Propane it's a much lower temperature. Boil water at 100 and it turns to vapour, reduce the temperature or pressure and it instantly turns back to water (seen as steam).

 

So while there is any liquid gas in the cylinder the pressure gauge will always show a constant reading (subject only to temperature or altitude variations). It will ONLY show you running short when all the liquid is used up and you are reduced to a cylinder of gaseous gas which will last you a few minutes!

 

Hope that helps!

 

Mel E

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[david lloyd]

Hi Mel E

 

We tend to use the fourth (and arguably most accurate) way of telling how much is left - wait till it runs out!

 

Seriously though, with two 11kg Gaslow refillable bottles we use one until it is empty then know we have to fill up again before the second one runs out- it has worked so far but we have never been away for longer than four weeks yet.

 

Regards, David

[michele]

Mel ,

Thank you for that very very good informative peice.

[crinklystarfish]

Very good summary.

The only think I would add is that a second (or more) bottles do let you go further / longer into the true wilds, and that you don't have to faff about with changeovers if you don't want to. The system after the take-off valves can be as simple as a single pigtail; or single 30-37mbar regulator that you manually change over when one bottle start to run low. Simple is often the best solution.

[pete lambert]

There is another way.....I have seen magnetic strips of heat sensitive material similar to the Thermometers that you place on the forehead. If you stick one on the side of the gas bottle, the level will be shown as a temerature difference and colour change. This is due to the temp gradient as the liquified gas turns back to a gas form as it is used. It will only work while you are using gas though.

[Guest caraprof]

pete lambert - 2007-07-24 9:18 PM There is another way.....I have seen magnetic strips of heat sensitive material similar to the Thermometers that you place on the forehead. If you stick one on the side of the gas bottle, the level will be shown as a temerature difference and colour change. This is due to the temp gradient as the liquified gas turns back to a gas form as it is used. It will only work while you are using gas though.

Before I put in my Gaslow system, which solves all of these problems by the way, I tried one of these stick on strips and it was rubbish.

If you're in the U.K the simplest method as mentioned by others is to open just one cylinder and wait until it runs out. You've then got ages to replace it whilst you carry on with the second cylinder.

If you're going abroad buy a regulator for Camping Gaz and if you look as though you're running out buy one of these.

[Clive]

My gas tank has a float gague inside that moves via a magnet an external gague that has inside a potentiometer that feeds a digital display inside the motorhome. Sounds complicated but it aint.

 

[Mel E]

I agree that two bottles solve the problem. BUT - and it's a big but - that means you are hauling around about 25 Kgs of cylinder and gas you don't really need.

 

That's 25 Kgs off your load capacity and 25 Kgs to increase your fuel consumption. We managed North Cape last year when it was very cold, filling up with gas just once in Tromso. Only one cylinder, but we planned the refill (Norway has limited sites) as the bottle dropped below half full.

 

Clive, is the system you fitted available as an retro-fit kit, or does the cylinder already have to contain the float part?

 

Mel E

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[Brian Kirby]

Mel

I think the answer on the Truma Sonatic ultrasonic level monitoring system, is they it is fine in Germany, but not elsewhere.  It is geared to 10Kg or 5Kg cylinders.  I once asked Truma tech whether it would work on 13Kg or 7Kg cylinders, and their answer was that it would not.  Why then was it in the UK Truma catalogue?  Because that was merely a translation from the German.

[Philman]

I usually go abroad for 2 months at a time and always weigh the bottle before I go. It is not that inconvenient and is a fairly accurate method of measuring the amount I have left. My bottle is a 15kg, so weighs about 30kg when full. When I first started motorhoming I carried a spare bottle on my trip to Spain, I kept it in the toilet compartment but it was so annoying and inconvenient that I never did it again.

Phil.

[Clive]

Hi Mel,

"Clive, is the system you fitted available as an retro-fit kit, or does the cylinder already have to contain the float part?

"

The tank already has a float type fuel gague. The external part of this gauge is replaced with one which includes the potentiometer. Just 2 screws.

 

 

[Mel E]

Clive,

 

Same as mine then - but I haven't bothered with the "2 screws"!

 

Mel E

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[Derek Uzzell]

Brian:

 

A good tale, but your Truma technician contact was either misinformed about Sonatic or having a laugh.

 

The 'basic' product was marketed to measure the contents of German-norm gas bottles with capacities of 5kg or 11kg. However, there was a Sonatic variant targeting this country that (as the GB-specific instruction leaflet states) measured "the contents of conventional commercial 6kg propane or 7kg butane gas cylinders". GB Sonatic had a mounting-base designed to fit our 6kg/7kg bottles and English-language markings on its display-panel.

 

For corroborative evidence refer to:

 

http://www.truma.com/_anweisungen/Truma-Katalog/gb/gasvers_freizeit/sonatic.html

 

I suspect Sonatic was a poor seller in the UK. It wasn't particularly cheap, wasn't very intuitive to operate (as you like to say, you needed to RTM) and, being bottle-size particular, had no interest for UK motorcaravanners able to carry our 13kg/15kg gas cylinders or for caravanners using our 3.9kg/4.5kg containers or Campingaz. I do know that at least one 'GB Sonatic' was sold here as I recall seeing its display-panel languishing on a shelf at a Pontypool caravan breaker's yard. Unfortunately the wiring to it had been cut off short and there was no sign of the mounting-base, so it didn't cause me to open my wallet even though I was then using 6kg Calor bottles and liked the Sonatic idea. Nowadays, with Truma(UK)'s heavy involvement with 'visible gas level' BP Gas Light containers, the company may well consider Sonatic an anachronism for this country, or even contradictory to its UK marketing plans.

[Brian Kirby]

Hello Derek

Maybe he was, but the item is still listed in Truma's current catalogue at £89.96, which seems daft for something not generally suitable for UK cylinders!  (Just for 11Kg and 5Kg, as you say) 

I originally asked about use with 13Kg cylinders, which is where the comment about unsuitability came from.  I wasn't interested in 7Kg cylinders, so must have wrongly concluded that the comment was equally applicable to these.

Still, it's worth pointing out it may not work before folks get their hopes up, especially at nearly £100 a throw.  Hope that wasn't the reason for your Pontypool orphan!