Under pressure ...

[Phil Pascoe]

My friend has just bought a Sievert torch from Cooksongold and they advised her that she needs at least an 11kg propane cylinder as a smaller one won't have enough pressure for that torch. Surely the pressure isn't decided by the size of the cylinder? I have a torch that's probably larger than that one and it runs perfectly well on a 6kg cylinder.

 

[Fitzroy]

Pressure is a misnomer I expect, the pressure is dictated by the temperature. As the propane is in liquid form the tank pressure is equal to the vapour pressure of the propane at it's current temperature.

In operation the propane tank needs to take energy (heat) from the environment to allow the propane to boil into gas and feed the appliance. If insufficient heat can flow to the cylinder then the propane temperature will drop and the pressure will also drop, reducing the maximum supply rate. The benefit of a larger tank is that the amount of propane in the tank is greater and it will take longer to cooldown during use.

Possibly the supplier has found that people using smaller tanks have seeing performance issues, they may or may not understood the fairly complicated thermodynamics and trying to explain these to the general public they've simplified it to saying it's a pressure issue.

 

[Spectric]

If your bottle is to small and you try and draw too much then you will see it icing up.

 

[ChaiLatte]

If the demand (draw off rate) does prove too large for the smaller bottle, an option is to manifold two bottles together. In some circumstances, that might be preferable to changing to a larger bottle.

 

[Ozi]

If the demand (draw off rate) does prove too large for the smaller bottle, an option is to manifold two bottles together. In some circumstances, that might be preferable to changing to a larger bottle.

Or sit on the bottle to warm it

 

[Fitzroy]

Or sit on the bottle to warm it

The viscous circle of trying to warm the gas bottle to your camping stove with your cold hands because the stove can't boil the kettle that you want to warm your cold hands after a day hiking in the snow! Been many years since I've been in that position, 'type 2 fun'.