Is the pressure in Butane cylinder (13kgs size) less than a Propane one of similar size? Tried a Propane burner torch on a Butane cylinder and the flame was rather pathetic to say the least. It is probably two thirds full.
Wikipedia says that the pressure required to liquify these gases is "approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) for pure propane at 55 °C (131 °F)."
I can't remember if Butane is stored as liquid in the cylinder or not, but I think propane is.
Im sure this is a path trod by many caravanners in the past, and lots of people on camping forums have said just to swap the bottle. Having done that on our static and been driven mad by a flame faliure device which didnt operate correctly on the lower bottle pressure and the hob gently broiling everything, I did a little reading round of actual specs too and as you found out, you cant just swap between the two and get the same results. It *almost* works, but the end result is pathetic.
Hiya Steve202
I think you will find its the weather, ie temperature being a caravaner you can only use butane (blue) in the summer as it will not gas at less than five degrees thats why you will see caravaners switching over to propane (red) bottles during winter as this gasses right down to minus forty degress
Hope this helps as i often swap the bottles over for this reason and there is absolutely no difference in performance