"Leo Lichtman" wrote in
There are some subtleties to hydrostatic testing.
The actual test is something like:
fill tank with water and measure volume.
Increase pressure to 5/3 working pressure. The steel tank WILL
expand so an additional volume of water must be added to the tank
to reach this pressure.
Release pressure and measure NEW volume of tank.
To pass the test the new volume must be no more than 110% of the
A problem arises when a tank has been handled roughly. It is
possible for the tank to be dented. The pressure from the test
may push out the dent and increase the final volume beyond the
limit. But the tank may then pass a second test.
This problem was initially encountered with SCUBA tanks. They are
made as light as possible and are more easily dented than
If you like you might want to select a "failed" tank that is fairly
new and have it tested. It just may pass.