90), to protect the latter
from the direct action of the steam. Water condenses in the siphon, and
does not become very hot.
[Illustration: FIG. 91.-Water gauge.]
Water Gauges should have three taps (Fig. 91), two between glass and
boiler, to cut off the water if the glass should burst, and one for blowing
off through. Very small gauges are a mistake, as the water jumps about in a
small tube. When fitting a gauge, put packings between the bushes and the
glass-holders, substitute a piece of metal rod for the glass tube, and pack
the rod tightly. If the bushes are now sweated into the boiler end while
thus directed, the gauge must be in line for the glass. This method is
advisable in all cases, and is necessary if the boiler end is not perfectly
flat.
Pumps.--Where a pump is used, the supply should enter the boiler below
low-water level through a non-return valve fitted with a tap, so that water
can be prevented from blowing back through the pump. As regards the
construction of pumps, the reader is referred to p. 164 and to Chapter
XXII.
Filling Caps.--The filling cap should be large enough to take the nozzle
of a good-sized funnel with some room to spare.
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