Hi Geoff....interestingly, quite a few French model steamers are using butane in the
liquid form at the same burners most use
The commercial manufacturers of refillable gas tanks provide explanatory detail as to the ~~75% fill, then vent process etc.....
We read of UK or European steam modelers being concerned with low ambient temperatures, in OZ we can see a 30 degree C rise from dawn to mean lunchtime temperatures of gas tanks in open boats
Australia has an established set of Standards [copy below] which include the construction and use of Model Gas Tanks........
So quote the extract......
"
4.4 This Code of Practice applies to a Butane Gas only firing system supplied from a separate gas container at the vapour pressure normally between 140 to 180 KPa at 25°C. 4.5 The pressures contained within the butane container are directly related to temperature. This Code uses 50°C as the container temperature to determine the pressure and thus structural requirements of the container'----------------
I hold an Authorised reporting capacity role within our AALS - AMBSC [Australian Model Boiler Steam Safety Committee]
Derek