The biggest problem with sweating joints is not having sufficient heat.
I don't mean flame temperature I mean heat (energy.) The thermal mass
of a goods sized ball valve is substantial and a small propane torch is
not going to be able to raise the temperature of the valve quickly
enough to avoid also overheating and damaging the ball seals. A good
MAPP torch is the minimum I'd use. Most times I reach for my acetylene
torch for ball valves.

RB

William Brown wrote:
I am going to replace the gate valves in my home the ball valves, so I
have been reading up on sweating joints. Briefly, the advice is to heat
the valve, then heat the line, then heat the valve while applying the
solder, then wipe the joint with a wet rag. My question is, since there
will be two joints at each valve, should I solder both before wiping
with the rag, or should I complete one, and then do the other. I am a
bit concerned that if I fully complete one, I may undo it while doing
the second, while if I wait to wipe until I have done both, the first
will have cooled to where the wiping will be ineffective.