It is of the first importance that those in charge of a boiler shall
know with certainty the position of the water level within the boiler.
[Illustration: Fig. 85.]
These attachments, also called Try cocks, are usually placed in a
conspicuous and accessible position on the front of boilers. They are
so arranged that one will blow only steam, one at the working level of
the water, and the third at the lowest water level or say three inches
above the highest point of the fire line of the boiler. The cut, Fig.
85, exhibits them as commonly arranged.
It is not essentially requisite, that the cocks themselves should be
placed at the point indicated, so long as they have pipes projecting
internally into the boiler, with their ends corresponding to the height
of water above mentioned. In order that these cocks may readily be
cleaned out, a plug is usually fitted into bit of cock opposite the
port or opening of the plug, upon removing which a pricker can be
readily inserted.
The gauge or cocks should be tested many times each day, and when
opened the top one should always give _steam_ and the bottom one
_water_. They should be allowed to remain open long enough to make sure
whether steam or water is issuing from the cock. This is a matter of
instruction, but the beginner with a little experience can detect the
difference by the sound.
In so universal an appliance as this there are very many forms and
arrangements, but they all work upon the same principle as stated
above.