Overfilling Gas Bottles.

[sailaboutvic]

Here another question , how many people turn the gas off at the bottle every time they not in use ?

 

[Daydream believer]

It cost more money to fill the bottle completely

 

[vyv_cox]

It cost more money to fill the bottle completely

I did a bit of a search yesterday to try to learn some background to the question. Gaslow say just the opposite, claiming that filling to 80% is harder on the equipment and thus costs the supplier more in the long term.

I did not find a definitive answer to the question but the most likely one, reading between the lines on largely USA websites, is that streams of liquid hydrocarbons may well exit over-full bottles, with evident risks of uncontrollable flames. I suspect that even with filling to well under 100% there is an increased risk of some liquid carryover.

 

[charles_reed]

When we had a calor gas concession in our family business, we were told that under no circumstances should a cylinder be used other than in a vertical position. I have seen cylinders stored on their sides in boats.

Stored, may be, used never.

 

[charles_reed]

This is undoubtedly true, but is also true of wine bottles. So for me the real question is not "why are gas bottles not filled brim-full?", but "why are gas bottles only filled to 80% [rather than 83, or 91 or...]?".

It can't be that liquid expansion would burst the bottle if filled to more than 80%, that would only require a tiny free space as in a wine bottle, and besides the coefficient of expansion of the liquid gas and that of the metal bottle will largely cancel out.

It can't be due to vapour pressure should the temperature rise as the vapour pressure is the same whether filled to 90% or 0.9%, ie as long as there's any liquid at all.

It might be to reduce splashes of liquid entering the regulator or hose to regulator - the gas can be used in moving appliances such as boats - or maybe to give some tolerance to heel.

It might be to allow a margin of error when filling. The point being that the gas bottle is opaque, so the only way to know how much gas is in there is by weight. But the gas bottle is heavy compared to the re-fill, so one is subtracting large numbers to arrive at the 'fullness' of the cylinder, and this is renowned as a recipe for poor accuracy, especially as the scales are not the same and will have calibration errors in addition to random ones. Suppose it gives a standard deviation of 4% of fill, then to ensure that the bottle is filled to 100% in fewer than 1 in 1 million (say) cases one has to be approximately 5 sigma away. Thus the max safe nominal fill is 100% - 5 x 4% = 80%.

My bet is that it's the last reason, with a few extra margins added on for good measure.

I've found wide variations in the 907Gaz form cylinder, from about 65% to nigh 100%. I think it's down to operator error (or cupldity) and leakage whilst stored. For that latter reason (and because it costs far less) I prefer having my bottles refilled rather than exchanged.

 

[NickRobinson]

I've found wide variations in the 907Gaz form cylinder, from about 65% to nigh 100%. I think it's down to operator error (or cupldity) and leakage whilst stored. For that latter reason (and because it costs far less) I prefer having my bottles refilled rather than exchanged.

I use something like this to check gas remaining- http://www.ebay.co.uk/itm/50kg-10g-..._Measurement_Equipment_ET&hash=item5afe32b92e

 

[Mark-1]

This still only gives about 5%, depending on assumed max temperature allowed (and isn't that far from petrol anyway), but is undoubtedly a significant contribution.

I may have my sums wrong but I reckon if you take (say Butane rather than Propane) with a coefficient of expansion of 0.0023 from -20deg to +100 you'd expand the fluid by about 27%. (Say 270ml per litre.)

I'm sure someone will be along shortly to explain why that's wrong. If it is right, the whole of the suggested 20% under-fill could be explained by catering for the thermal expansion of the liquid in the likely range of temperatures the canisters might experience.

 

[paul-essex]

also you have to consider unless you want to compress the liquid ( witch would require compressor pumps ) the empty volume of the tank has to have a area to compress into as you dont vent off when refilling gas

 

[charles_reed]

I use something like this to check gas remaining- http://www.ebay.co.uk/itm/50kg-10g-..._Measurement_Equipment_ET&hash=item5afe32b92e

I got one on Amazon UK £3.29, from 50mg up to 44kg, load cell and digital read-out, battery operated - Xpect it one of the Li ones.
Up till now I've used a spring-load handheld.

 

[charles_reed]

also you have to consider unless you want to compress the liquid ( witch would require compressor pumps ) the empty volume of the tank has to have a area to compress into as you dont vent off when refilling gas

The twice I've seen it done, from a large cylinder, - in out of the way places - they've vented twice, usually I've had about 2.8kg of lpg. Much better than the 2.4kg offered by Camping Gaz.

 

[RichardS]

iN
In post #2 Why did you seemingly misquote the original post.....changing liquid to gas?

I didn't change anything. Mark-1 seems to have changed his post #1 after I quoted his original wording.

Richard

 

[Trundlebug]

I may have my sums wrong but I reckon if you take (say Butane rather than Propane) with a coefficient of expansion of 0.0023 from -20deg to +100 you'd expand the fluid by about 27%. (Say 270ml per litre.)

I'm sure someone will be along shortly to explain why that's wrong. If it is right, the whole of the suggested 20% under-fill could be explained by catering for the thermal expansion of the liquid in the likely range of temperatures the canisters might experience.

Yes you have it right.

Cylinders in the UK are filled to about 80% to allow for thermal expansion of the liquid.
They're OK up about 50degrees IIRC (I may be wrong on this, it was a long time ago so please don't rely on that temp figure as gospel) beyond that they are at risk of hydraulically bursting the cylinder.

In hotter countries the cylinders are filled less (not sure on the % figure) to allow more ullage and expansion room.

Realistically the only time you are likely to be at risk is if full cylinders are stored in direct sunlight - something that should never be done, and not worth chancing.

I can't quite follow how this thread has gone but I hope I'm wrong in thinking some people seem to be refilling / transfilling cylinders themselves.
There have been some horrendous accidents involving attempts at home cylinder filling. It's a crazy thing to do, even if you really understand it.
Cylinder filling of any gas apart from maybe scuba gear is high pressure, high stored energy and high consequence stuff.
Add in flammability (with LPG) and you have an extremely dangerous process which is heavily regulated and capital intensive.
You're not being jipped if you can hear the liquid sloshing around in a nominally full cylinder. That gas portion is there for your safety.

Think about it, even a bottle of milk, pop or washing up liquid has some ullage.
Leave it alone and don't mess!

 

[Steve_N]

Realistically the only time you are likely to be at risk is if full cylinders are stored in direct sunlight - something that should never be done, and not worth chancing.

I trying to think of a local Calor stockist where the cylinders in their outside compound are NOT stored in direct sunlight, but no, none come to mind.
Now while the sun may not be cracking the slabs here at 53 degrees north, there are racks of full gas cylinders outside French and Spanish supermarkets under the Mediterranean sun..