Solder on an all-metal
cycle valve, "inflate" the boiler to a considerable pressure, and submerge
it in a tub of water. The slightest leak will be betrayed by a string of
bubbles coming directly from the point of leakage. Mark any leaks by plain
scratches, solder them up, and test again.
[Illustration: FIG. 94.--Benzoline lamp for model central-flue boiler.]
The boiler should then be quite filled with cold water, and heated
gradually until the pressure gauge has risen to over the working pressure.
There is no risk of an explosion, as the volume of the water is increased
but slightly.
The third test is the most important and most risky of all-namely, that
conducted under steam to a pressure well above the working pressure.
In order to carry out the test without risk, one needs to be able to watch
the steam-gauge from a considerable distance, and to have the fire under
control. My own method is to set the boiler out in the open, screw down the
safety-valve so that it cannot lift, and raise steam with the help of a
blow-lamp, to which a string is attached wherewith to pull it backwards
along a board.
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