No air leak, but fuel leaks after repair?

I experienced more than once this last year that after soldering a part or area, then dunking in water to check for air leaks, the area will then leak kero when I fire the stove up. Any explanation? Sure frustrating thinking you fixed a leak. I eventually get it.
Duane

 

Hi, an operating stove is probably working at a tank pressure of up to 2 bar or 28psi. Some people, when leak-testing with air, rely on self pressurisation of the tank by just increasing the pressure of the enclosed air by raising the temperture of a chilled tank.
A more realistic leak test would be to use the pump to duplicate operating pressure (28 psi) before immersion or applying soap solution to joints.
Best Regards,
Kerophile.

 

I had a Preston Loop on a Petromax lantern that only leaked when very hot. I then determined I had small cracks from the heat and quench I did.

 

I've pumped up the stove at two levels. Maybe 20 pumps on a 96 or similar size.
Duane

 

Another possibility, as @snwcmpr , has suggested is thermal expansion of a crack or gap, due to the heat of an operating stove. This might be enough to open a leak path which is tight at near room temperature.

Best Regards,
Kerophile.

 

I know that when industrial pressure vessels are tested they are not tested with air.
They always use a pressured liquid, usually water, because a vessel that can pass a pressure test with air can fail when tested with water.

 

I was thinking that my dunk in cold water shrinks the fix, heat from soldering expands metal. Maybe like other metal fixes, especially aluminum, I need to heat a larger area. A fix on a 1915 96 around the air screw keep needing to be redone, was thinking metal was contracting too much away from where I was soldering. That crack kept moving around the part.
Duane

 

Are you soldering or brazing?
Low temp or high temp?

 

Soldering, can't get a stove area hot enough to flow silver solder.
Duane

 

Ok.
You did not say where.