These are the second and auxiliary arrangements for ascertaining
the water line. Nearly all boilers are supplied with both try cocks
and glass gauges, and so important is it considered to be correctly
informed as to the water line that a third method consisting of a float
which is carried on the water surface, is sometimes added to the two
named.
[Illustration: Fig. 86.]
The glass water gauge _column_ consists of an upright casting bolted to
the front of the boiler, in which are fixed two cocks having stuffing
boxes for receiving the gauge glass. The lower of these cocks is also
fitted with a drain cock for blowing out the glass.
The try cocks are frequently placed on the above-mentioned standard or
column.
The action of the gauge glass is to show the level of the water in the
boiler by natural gravitation and the best position for it is in view
of the engine room, as close to the boiler as possible and preferably
in the middle line of its diameter, at such height that its lowest
portion is about two inches above the highest part of the fire line of
the boiler, and its centre, nine inches above that, making the total
visible portion of glass eighteen inches long.
Glass water gauges sometimes have pipe connections top and bottom. The
object of this arrangement is to have an undisturbed water level in
the glass by carrying one pipe to the steam dome and the other near to
the bottom of the boiler; the one position not being so liable to be
affected by foaming and the other by the boiling of the water. Cocks
should always be fitted to the boiler ends of these pipes, in order
that in case of accident to the pipes, steam and water may be shut off.
The glasses are liable to burst and become choked up with dirt.
The former defect is easily repaired by shutting off the cocks in
connection with the boiler and putting in a new glass. The mud or
sediment is cleaned out by opening the above-mentioned drain or
blow-out cock and allowing the steam or water, or both, to rush through
the glass, which will effectually blow out all sediment and leave the
glass in good condition again to show the height of the water in the
boiler.
In opening the cocks connected with the glasses, it should be done
cautiously, as the glass is liable to burst.
A strip of white running the whole length of the glass on the side
toward the boiler is a great help in observing the variations of the
water line in the tube.
It is not needed to remove the gauge glasses to clean them. There are
good fixtures in the market that by taking out the plug in the top,
the glass may be cleaned with a bit of wicking on the end of a stick.
A slight scratch will break the glass, hence do not use wire. Use soft
rubber gaskets when setting the glass, screw up until all leaking
stops. Don’t let the glass come in contact with the metal _anywhere_.
Don’t try to reset the glass with an old hard gasket. Two glasses from
the same bundle will not act alike.
The glasses used to show the water line are made of a soft glass known
as “lead glass,” and are easily cut, or broken square across. Most
of them can be broken by filing a notch at the point at which it is
necessary to break them. After filing the notch, place the thumbs as
if you would break the glass; it will crack easily, and the fracture
be straight and clean. If the tube be brittle, as some are, to avoid
cutting the hands wrap two pieces of paper around the glass, each side
of the notch. If the ends are rough or uneven, they can be made smooth
by filing or by the grindstone.
The Manchester, Eng., Boiler Association attribute more accidents to
inattention to water gauges than to all other causes put together. It
is, therefore, of much importance that these glasses should be kept
clean. It is not an uncommon thing to go into a boiler room and find
that a leaky stuffing box has allowed the steam or water to blow out,
and, by running down the outside of the glass, leave a deposit of lime
scale. After this deposit has been formed, it is sometimes difficult
to remove—and more than a few glasses have been broken by the engineer
attempting to remove the scale. After this scale has once been formed,
unless it is soft enough to be wiped off with a piece of waste, it
is best to take the glass out and soak or wash it in a solution of
one-half muriatic acid and one-half water until it is clean or the
scale so softened that it may be readily wiped off. To prevent the
scale from again forming and hardening, the glass should be dipped in
glycerine before replacing.