In article .com, " wrote:
Thanks everybody for taking time to answer my question.
Here is how I did it:
First I used torch to heat the copper pipe and tried to remove residue
of remaining solder with a clean sock(as damp cloth), then I used emery
cloth and the other tool(cleaning tool with wire in it) to clean the
pipe joint. I can tell that the copper pipe is shiny after cleaning. I
am not sure whether I need to clean the fitting of newly bought brass
valve or not, should I?

Clean it. It may not be necessary, but it takes only about ten seconds. No
point whatever in not doing it.

Next I applied the flux only to the copper pipe
source, then placed the brass valve.

Flux both the pipe and the valve.

I don't have MAPP gas, only the
propane gas.

That's not helping you. You can solder valves with propane, but it's a *lot*
easier with MAPP. It takes a *long* time to get a valve hot enough with
propane.

I heated the fitting until I can hear the sizzling sound,
then I applied the solder.

You didn't apply nearly enough heat to the valve. With a propane torch, it can
take several minutes to get a valve body hot enough to solder, *long* past the
point at which the flux begins to boil.

If I use propane torch, how can I tell that time is right to apply
solder or in other word, when the fitting is hot enough to apply solder
using propane torch?

It's real simple: when the fitting is hot enough to melt solder, then it's hot
enough to make the joint.

Can propane torch generate enough heat for
solering brass valve?

Yes, but you need to be more patient. It takes a *lot* longer to heat up a
valve body with propane than it does to heat up a coupling or elbow.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.