LOCOMOTIVE ENGINE.
419
Gauges.—L L, (Plates XC. and XCII.,) is a glass gauge for show- fig. 8.
ing the height of the water in the boiler ; it is shewn detached in
fig. 8, which is a section through the centre of it to a scale of Sc
inches to a foot, or three times the size of the engraving. The
gauge consists of a strong glass tube, A, fig. 8, about three quarters
of an inch diameter outside, fitted into a brass socket, B B, at top
and bottom, the joints being made steam-tight by hemp packing,
put round the glass, and compressed against it by the glands C C,
which are screwed in round the glass. From each of the socket-
pieces B, a tube, D, proceeds with a cock in it and a screw on
the end for fixing it into the fire-box ; and the piece E, containing
another cock, is screwed into the lower piece, and the plug F into
the upper piece, affording the means of putting the glass tube down
into its place. When the two cocks in D D are opened, the water
of the boiler rises in the glass tube to the same height that it is in
the boiler, the upper part of the glass being filled with steam,
the height of the water in it shewing always the level of the
water in the boiler ; the cocks are for the purpose of stopping
the communication, when required, from the gauge being out
of order or otherwise. The cock in the piece D is for the purpose of clearing
out the gauge, by allowing a stream of water to run through it ; and it is often
necessary to open it when examining the gauge, in order to get rid of the bubbles
of steam formed by the rapid ebullition of the water, which sometimes render it
difficult to ascertain the precise height of the water. The difficulty is also in
creased by the motion of the engine producing oscillation in the water ; but the
disturbing effect is much diminished by choking the tube, or making the communica
tion with the boiler through the tube D very small, so as to impede the motion of
the water in the tubes. A small plug, G, is screwed in opposite each tube, B, to
afford the means of clearing out the tubes D, by passing a wire through them when
the plugs G are taken out.
To afford an additional means of ascertaining the height of the water in the
boiler, two gauge cocks, M M, are fixed in the side of the fire-box, one being four
inches above the other, and the lower one, one inch above the top of the internal
firebox. The boiler is generally filled at starting, until the water runs out at the
upper cock ; and during working the water level is kept between the two cocks,
and often up to the upper one. The cocks are opened occasionally to try the level,
and if steam should ever be found to blow out at the lower cock, showing that there
is not more than one inch of water over the roof of the internal fire-box, instant
attention has to be paid to the feed-pumps, and the fire damped if necessary, to