Small Calor Gas bottles to be discontinued

[Fazerloz]

Refilling a small bottle from a big one is very easy but potentially very very dangerous. The issue is the ullage space. It is vital that you leave it empty, so you must NEVER fill past 80% full.

The reason for this is that LPG expands a huge amount as it warms, so if you get a sunny day and a full bottle, the pressure can easily exceed 1000psi and be enough for the bottle to burst.

The temptation is to overfill. That's why it's illegal and dangerous to refill bottles yourself. I have had a job doing it, but we always weighed the bottles to make sure we weren't overfilling. DIY refillers tend not to.

An exploding full bottle will spoil several people's day.

Do you have a link to confirm your statements about the amount of pressures that can be generated in a propane cylinder by the expansion of the Propane.

As all propane cylinders have to have a built in relief valve by law.Common usage Calor cylinders are Propane 26bar Butane 21bar I would think it highly unlikely for your scenario to ever happen.
I am not condoning the self filling of bottles but see these types of claims as scare mongering.

 

[GeoffL]

Do you have a link to confirm your statements about the amount of pressures that can be generated in a propane cylinder by the expansion of the Propane.

Whether or not @Geek has a link to confirm his statement, I've found several to suggest that the relief valve on most propane cylinders is set to between 25 and 26 bar, which concurs with your point. Also, the pressure at 70°C (way past what it would be on a 'sunny day') is ~ 24.8 bar (360 psi).

Gas Regulator Pressure: LPG Pressure Regulator | LPG Gas Pressure Regulator

Everything about LPG pressure. Pressure in the gas bottle, in the valve, vapour pressure, boiling point and more.

www.elgas.com.au

1.3.2 Cylinders/Tanks - Canadian Roofing Contractors Association

Propane is liquefied by compressing and/or cooling propane gas and placing it in metal cylinders or tanks designed for that purpose. The compression rate of one litre of liquid propane produces approximately 270 litres of propane gas. This explains why so much energy (BTU’s) can be contained in...

roofingcanada.com

GIYF for many, many more such links...

 

[Fazerloz]

Whether or not @Geek has a link to confirm his statement, I've found several to suggest that the relief valve on most propane cylinders is set to between 25 and 26 bar, which concurs with your point. Also, the pressure at 70°C (way past what it would be on a 'sunny day') is ~ 24.8 bar (360 psi).

Gas Regulator Pressure: LPG Pressure Regulator | LPG Gas Pressure Regulator

Everything about LPG pressure. Pressure in the gas bottle, in the valve, vapour pressure, boiling point and more.

www.elgas.com.au

1.3.2 Cylinders/Tanks - Canadian Roofing Contractors Association

Propane is liquefied by compressing and/or cooling propane gas and placing it in metal cylinders or tanks designed for that purpose. The compression rate of one litre of liquid propane produces approximately 270 litres of propane gas. This explains why so much energy (BTU’s) can be contained in...

roofingcanada.com

GIYF for many, many more such links...

Did a quick search also for the bursting test pressure on propane cylinders and there were not many results but one was from a University in Iran. we're propane cylinders are in common use in kitchens for cooking.. Anyway the result was 102 to 104 bar the difference due to the + - tolerances of the thickness of the steel used in construction.
Nearer home though. According to BPEC they have a design bursting pressure of 96 bar.

 

[Geek]

No, I don't have a link to confirm what I stated. That's because it is something I know, not something I happened to read on the web.

Yes, gas cylinders do indeed have safety valves. Untested safety valves, which may or may not work. How lucky do you feel?

A value of 24 bar at an unlikely 70 degrees C is the vapour pressure. That's not a problem. That's why you have a 20% ullage space at normal temperature.

However, if you fill the bottle up completely, it isn't vapour pressure you are worrying about. The liquid propane expands and takes up all the gas space. At that point, incompressible liquid meets inelastic steel cylinder.

1000 psi at hot weather temperatures is entirely feasible, although the safety valve should have sprayed liquid LPG all over the place before then.

 

[Pudsey Bear]

Oh, if you know it then it must be right then.

Sorry, but if you know then you must have got this questionable information from somewhere.

LPG expands at 1.5% for every 5.56°C (10°F). LPG at 1 atm of pressure and 20°C is a gas that is about 1.55 (propane) to 2.08 (butane) times heavier than air. LPG is liquefied under modest vapour pressure of 1,220 kPa (177 psi) at 37.8°C (100°F).

 

[mariesnowgoose]

All I know is a that a (swapsie) 6kg Propane Calor Gas cylinder cost me £36 this afternoon...

 

[GeoffL]

No, I don't have a link to confirm what I stated. That's because it is something I know, not something I happened to read on the web.

Yes, gas cylinders do indeed have safety valves. Untested safety valves, which may or may not work. How lucky do you feel?

A value of 24 bar at an unlikely 70 degrees C is the vapour pressure. That's not a problem. That's why you have a 20% ullage space at normal temperature.

However, if you fill the bottle up completely, it isn't vapour pressure you are worrying about. The liquid propane expands and takes up all the gas space. At that point, incompressible liquid meets inelastic steel cylinder.

1000 psi at hot weather temperatures is entirely feasible, although the safety valve should have sprayed liquid LPG all over the place before then.

This seems to me to be something that might be heard from a 'bloke down the pub' -- an urban legend that 'everyone knows is right'. However, without references, that's is just argument by assertion. As @Fazerloz noted, bursting pressure of propane cylinders is circa 96 bar (i.e. well over 1,300 psi). Also safety valves are routinely tested and inspected (clicky link to BCGA info). Further, when that safety valve lifts (or bursting disc bursts), the liquid gas starts to very quickly evaporate and a liquid/vapour interface forms inside the cylinder, at which point the latent heat of vapourisation is extracted from the cylinder and liquid, rapidly cooling it down and so reducing the pressure inside the cylinder.

 

[Fazerloz]

Assuming we believe what we read on forums.
According to the physics forums the pressure would reach 1000psi 69Bar at 35C in a completely full bottle. I am sure there will be a graph for this somewhere if anyone can be arsed searching it out.
In the real world though the chances of someone with a filling adaptor filling a bottle so full and that bottle just happens to have a non working safety valve and the bottle getting up to such a temperature that the bottle fails.
What are the odds on that happening.
Pretty remote I would think.
But it is possible. As are a lot of things.

 

[mariesnowgoose]

Anyone for solar?

 

[GeoffL]

Quick thought experiment ...

Assume that one propane cylinder is be filled from another and both are initially at the same temperature. As propane transfers:

• The amount of liquid in the source cylinder reduces and the amount of vapour increases. This can only occur if some of the liquid vapourises and hence extracts latent heat of vapourisation from the cylinder and the remainder of the liquid and/or the vapour expands in accordance with the gas laws. In either case, the temperature of the source cylinder must reduce.
• Since the vapour pressure depends upon temperature, the pressure in the source cylinder must reduce.
• The amount of liquid in the receiving cylinder increases and the amount of vapour reduces. This can only occur if some of the vapour condenses and hence gives up latent heat of vapourisation to the cylinder and the remainder of the liquid and/or the vapour is compressed in accordance with the gas laws. In either case, the temperature of the receiving cylinder must increase.
• Since the vapour pressure depends upon temperature, the pressure in the receiving cylinder must increase.

So, provided the cylinders start at the same temperature, the pressure in the receiving cylinder soon exceeds that of the source cylinder, making further transfer impossible until the temperatures have equalised and hence it's difficult to completely fill the receiving cylinder. My experience with filling butane gas lighters and my butane soldering iron add weight to this, as I usually need to cool down the equipment to be filled (10 minutes in the freezer) and I can feel the source gas canister getting cold as the equipment fills.

According to the physics forums the pressure would reach 1000psi 69Bar at 35C in a completely full bottle.

If there is any vapour at all in the bottle, the pressure would be the temperature-dependent vapour pressure, which at 35°C is < 170psi (clicky link). Once the bottle is completely full, any further temperature increase will expand the liquid in line with its coefficient of thermal expansion and the cylinder rupture once stretched beyond its limit of elasticity. The pressure in a completely full bottle is hence variable and depends upon both the current temperature, the temperature at which the last bit of vapour condensed, and the elasticity of the bottle... at least, that's what my understanding of the underlying physics suggests!

 

[Pudsey Bear]

My head hurts, Cheers Geoff.

 

[REC]

we found a shop where his dealer gets gas from flogas as well as calor, he is happy to exchange the small calor bottle for a small flogas at no extra charge. Smith's timber merchants in lowestoft . Our small bottles last for a year and we have a full spare but we will exchange when we have an empty.