Pressure (Bar) in a propane tank

Here is a photo to describe better what I mean. Are all cylinders of this type filled to a similar pressure, for a given temperature? Why is 15-16 bar considered full is this for a particular type of cylinder? 

Hopefully somebody with better technical knowledge of LPG than myself will comment on your question, however, with my limited knowledge I do know that the pressure varies enormously with temperature so I don’t understand how a pressure gauge would be of any use at all unless all the readings were referred back to the same ambient conditions.

Thanks Hitchglitch, I think that is what is going on here, I just chose a cold day to change my cylinder adding to the confusion! According to the first table here, 5 deg C is ~ 5 bar, roughly what I'm seeing.  So it might be that for a full cylinder you achieve the table values dependent on ambient temperature, and as you exhaust the liquid, the pressure drops of the vapour above the liquid so you see a drop in pressure relative to the ambient full cylinder case.  It's all a bit confusing for a layman :)!

On a side note, the other dodgy thing about the gauge is that I believe if I opened the gas tank on the RHS without the LHS connected to a regulator, the unregulated tank would vent, which seems a bit dangerous!

 

 

  

 

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As good as an ashtray on a motorbike! 🤣🤣🤣