You say start with a full bottle, I'm saying start with an empty bottle containing say air at atmos. press. then as the pump fills LPG @ say 110psi ie it will be liquid in the bottle as soon as the pressure in the bottle reaches 110psi but the air in the bottle will remain a gas @110psi the pump will then shutoff.
This assumes of course that there is no bleed off, which is why I said "sealed filler"as would be the case at self service fill points,at least I hope so!
I say start with a bottle full of GAS - as in Propane gas - because this is what the normal situation is.
Yes, what you say would apply ONLY for a first fill of a brand-new unpurged tank, but that is a very special case that would give very unpredictable safety margin and it doesn't apply in a general case anyway.
The presence of air in a bottle IS a problem in liquid delivery systems (for LPG powered vehicles) because as you say, it doesn't liquefy and it prevents the bottle from being filled to its proper capacity. Normally, these are purged of air prior to first fill by pulling a vacuum and then filling with LPG. However, for gas delivery systems like we use, there isn't likely to be any air left in the tank after the first fill because it will be bled out the top of the tank as soon as the valve is opened (makes getting a fridge or water heater pilot light to stay lit a very long process). Once the initial volume of air bleeds off first, there will only be propane/butane left in the tank and when the tank is refilled, this will liquefy once the pressure rises above the vapour pressure at whatever the temperature is at the time.
If you are filling the tank with Butane and the temperature is a few degrees below zero, you don't need a pump at all and could theoretically pour it in using a funnel, so completely filling a bottle with liquid isn't just a hypothetical situation - and once it is full, and the valve shut, you then rely on the safety valve if fitted (and even then, while it may prevent the bottle from rupturing, opening the car door on an interior full of a perfect propane-air explosive mixture isn't real safe either. Plumber in Sydney died a few years ago from just this situation.
I'm curious. Am I the only one to admit to being distracted when filling a bucket or fuel can or siphoning fuel into a can or whatever, and having it overflow. Water or petrol on the ground is pretty obvious and you take appropriate precautions, but a hydraulically-full LPG bottle looks no more dangerous than a properly-filled one, but in fact is a bomb waiting to cause major damage or injury.
-------------------------
Someone made the point that anything not specifically prohibited, was therefore permitted - so why would it be illegal to use an adaptor to fill a portable bottle. I don't think this is a true reflection of how our society operates anyway, but my assumption is that gas, like electricity and vehicle components - and even city water supplies, is normally very tightly regulated and only tested and approved appliances, fittings and components may be used - and often, only installed by authorised people. If these refilling adaptors do come under any such regulation then it is a case that anything not specifically approved is prohibited and there may be a further requirement that the operation must only be performed by trained and authorised people.
