Is it really possible to weld/solder copper pipe to these valves? The heat is not going to destroy them?
Small valves get “sweated” (soldered) into copper piping systems all the time. With old style globe valves where rubber washers were used - if you were concerned about heat damaging the internals you could loosen the bonnet and remove the valve stem. With a gate valve or ball valve - where the internals are all metallic - there is less propensity for heat damage. Remember that you are just heating the pipe/valve connection hot enough to melt the solder not to melt/weld the pipe/valve
I have not seen any Ball Valve here in the UK which is made for soldering, all are compression and they have some plastic or rubber pieces in (as much as I remember), I have seen these just online form Chinese or US website(?) We had a case of leak with a compression valve and that made me think of this type of valve and I started to google it. Have you used them in US in your projects?
Yes - many - over may years in the plumbing business.
I found a video - you might watch:
Thanks Fred, that was a good video, I was thinking of a wet cloth keeping it cooler but I thought it might not let it to get enough hot for soldering. I don’t think they use these valves in UK at all.