Hi,

I did practice as everybody suggested and failed again. I used a copper
pipe about a feet and had it cleaned, so did brass valve with wire
brush and both of them were shiny. I applied flux to both pipe and
valve. Then I heated it. I noticed that a smoke came off from the othe
end of pipe and the edge of joint turned black and I kept heating until
the solder melt, but still it did not flow into the joint. I have
removed the shut-off part of valve due to that there is rubber on it. I
am wondering whether the flux is no good since after failure, I remove
the joint, both surfaces of valve and pipe are black with some kind of
oxidized stuff. I believe that those black stuff may prevents solder
from working. But I just don't know why. The big problem for me is that
I don't know when to apply solder. When solder starts melting at the
edge of the joint, is it the right time or not? Since the smoke and
black thingy formed during the heating, I don't know what is going on
there.
thx