I am having a problem sweating a quarter turn shut-off valve for a
bathroom sink. It seems that since the valve is such a large chunk of
brass it takes a lot of heat to get it hot enough to melt the solder.
The valve gets damaged from the heat and then leaks. Since this is a
ball valve there is nothing I can take apart before I heat it. Thanks
for any advice you can give me. Jim
That is why I use compression fittings on shutoff valves.
Easy to install, years of service, and when they finally fail,
you can just loosen the nut and screw another valve onto it.
But, to your question. Get a small towel soaking wet, open
the ball valve and then wrap the part of the valve that is
away from the solder socket with the wet towel. Make sure you
use Mapp gas for soldering and apply heat to just the end of
the socket (where the tubing enters).
Mapp gas is not that different from propane other than it
burns hotter, allowing you to heat up the valve faster. They
mean that you should not use an oxygen acetylene torch. As
for heating the pipe, I started to mention that before, but
didn't want you to get the wrong idea. Usually I will heat
only the valve and let the transferred heat warm up the pipe,
since the copper will heat up faster. In this case, I do heat
the pipe, but only in addition to the valve. I point my torch
at the point where the pipe and valve intersect in an attempt
to get both pipe and valve heated quickly. The pipe being
heated will transfer the heat to the inside surface of the
valve socket (copper being a great conductor of heat). Apply
the solder and remove the heat as fast as possible. This is
where experience really comes into play. Heat it up just
enough for the solder to flow, but not enough to damage the
valve. It is tricky.
In my experience overheating causes more soldering problems than anything
except lack of cleanliness. For successful soldering: clean both surfaces
thoroughly, flux, heat rapidly just until solder melts thoroughly, apply
solder, cool. A torch flame can easily overheat part of the joint without
the rest being hot enough and practice helps a lot. A good job is usually a
The discoloration is harmless oxidation. The colors result
not from actual color change to the metal, but from light
being bent within the thickness of the oxide layer.
To avoid burning metal when soldering, speed is of the essence.
Use the hottest flame practicable -- here, meaning your trusty MAPP
torch -- on CLEAN metal. I've used these to silver solder (jeweler's
silver/copper) bottle bosses onto heavy gauge Schwinn-quality steel
bike frames. Takes about a minute to heat the joint glowing red hot,
hot enough to make the silver flow.
Practice is the whole secret.
Crack a valve somewhere along the line to vent expanding
hot air somewhere _other_ than the joint at hand. Make
sure the pipe end being sweated is drained, or you'll never
get the joint above 212F.
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