Hi Joe,
Any more information on the regulator?
I've not seen one like this supplied in a Sievert kit. (But I have been out of the front line for some time now!) Is it a case of buying a Sievert torch (good call!) and then getting a regulator?
What size burner have you got? As Simon says the number is stamped on the side and will determine the necessary pressure..
Not all burners will run at 4 bar. Some are designed to run at 2 bar and trying to run them at the higher pressure is going to be, at best, counterproductive. At worst, the flame will be extinguished and you start to fill your workshop with propane!
Alternatively, trying to reduce the heating by running the burner at too low a pressure, will cause incomplete combustion within the nozzle and block the injector with a carbon deposit.
I am unable to offer any further help and as in all such cases, I would refer you to your regulator supplier.
Your burner selection will depend on what you will be attempting to silver solder, the material, the size and design of the joints, required heating rate and the filler metal being used.
Regards
Keith