the_anomaly wrote ...

Well, at least according to your profile, you are located in the UK. In the US, acetylene is everywhere. Every auto shop has a torch setup. I have one although I don't keep tanks around unless I absolutely have a project due to safety fear.

When brazing HVAC connections, manufacturers put the valves near (~2") to the tubing connection such that you have to wrap the valve with a wet cloth and keep it wet so it doesn't burn during the brazing. The connections/tubing are made of brass/copper. So you have to get the joint 'hot' all the while heat is being wicked away by the high thermal conductivity of the metal. Time is of the essence, the less time you spend heating the joint the lower the chance of damaging the valves. This is an instance where it makes sense to use oxy-acetylene. That extra bump in temp gets the local joint hot before the valve is overheated. It can be done with oxy-propane too but its more difficult.

Conundrum, no matter what you do, follow manufacturers guidelines. Double check if the system you purchase has flashback arrestors.