1894
THE NEW ZEALAND GAZETTE.
No. 63

it completely fills the pipe from J to K. The steam
from K down to the level of the water in the glass is
thereby trapped, and as condensation proceeds leads
to a reduction of pressure in the pipe below that of
the boiler and an equivalent rise of the water in the
bend and also in the gauge-glass. When the vessel
is quiescent the water in the gauge-glass increases
in height until cock E is opened, or until the pressure
in the boiler is so much in excess of that in the lower
part of pipe I as to cause the water in the bend to be
blown into the gauge-glass. In either case instan-
taneous change of water-level ensues.

In the ordinary course of working the phenomenon
described above is more or less modified by the pre-
sence of air in the upper part of the gauge, and by the
rise and fall of the water in the boiler and gauge-glass
arising from the rolling or pitching motions of the
vessel.

Other Special Points to be noted.

When the cocks A and C are omitted, as in Fig. 2,
it is owing to the bore of the standpipe being
sufficiently large to enable it to be regarded as part
of the boiler. Such pipes require, however, to be
examined and cleared at intervals by passing a rod
through the holes provided for the purpose at P P
and Q Q.

Cocks at A and C are not necessary for the testing
of gauges arranged as shown in Figs. 4 and 5. Ex-
aminers ought, however, to make sure that candidates
are aware of the impossibility of testing the reliability
of the indications of water-gauges arranged as in
Fig. 3 when the cocks A and C are absent, and of
the effect which the choking of cock A or C, or pipe
H or I, has on the indications of the test-cocks T T T
attached to column Y.

Probably more than half the steamers afloat are
fitted with water-gauges as shown in Figs. 3 and 4,
and it is therefore specially important that engineer
candidates should thoroughly understand their con-
struction, the principle on which they act, and the
steps which must be taken to keep them in an efficient
condition.

When fitting a gauge-glass into its place it is spe-
cially important that it should not be placed so high
as to prevent a clearing-rod being inserted at G, Figs 1,
2, 3, 4, and 5. This defect, especially if it occurs
in a water-gauge attached to a boiler subject to
priming, permits a rapid accumulation of scum around
the top of the glass, and results in the choking of the
orifice leading from cock B to the gauge-glass in each
of the figures.

When a gauge-glass is too short, or is placed either
too high or too low in the fittings, it is also liable to
become choked by the packing-material being forced
over its ends by the glands whilst being screwed up.

The use of unsuitable or insecure internal pipes in
connection with either the ordinary glass gauge-
cocks of the description shown in Fig. 1, or with
test-cocks which are jointed to the boiler itself, should
also be carefully guarded against.

Boiler casualties have resulted from the cocks B
and D having the working-parts wrongly placed, as
shown in Fig. 6, Plate II. In one case of that
kind, which forms the subject of Report No. 208
under the Boiler Explosions Acts, the engineer in
testing the water-gauge omitted to see that the pas-
sages in the cocks B and D were clear when the handles
were in their proper working-position. This defect
could easily have been discovered if proper attention
had been paid to the condition of the cocks. A defect
of this nature may be due to faulty construction
originally, or to the handle of the cock having been
overstrained and the neck twisted. Whether the
passages in the plugs are fair and clear can, however,
be verified in a few minutes. As an illustration, the
water-cock D, Fig. 6, Plate II, can be verified by
blowing through E with B shut, and then removing
the handle of D to one side until it is just closed, and
then to the other side until it is again just closed. The
proper working-position of the handle is about equally
distant from each of the above positions. The other
cocks can be verified in the same manner..

Another serious casualty occurred through the
handle of the cock A, Fig. 3, having been twisted
from its original position relatively to the orifice of
the cock, resulting in the cock being shut when appa-
rently open.

When a water-gauge that is clear in all its parts has
been thoroughly blown through, the water in the
glass rises above the level at which it formerly stood
immediately the drain-cock E is closed, but if left un-
disturbed for a time it gradually falls to its former
position. The amount of rise which occurs on these
occasions depends chiefly on the temperature of the
contents of the boiler and on the length of the pipes
by which column Y is connected top and bottom to
the boiler; but in cases where the gauge is of the
description illustrated in Figs. 3, 4, and 5 it amounts
in high-pressure boilers to about 4 in., while the time
occupied by the water in returning to its former level
ranges from thirty to forty minutes. The cause of
this rise is two-fold—namely, (a) the displacement of
the comparatively cold water in pipe H by hotter and
proportionately lighter water from the boiler, and (b)
a slight condensation of the steam and a corresponding
fractional reduction of pressure in pipe I. The cause
of the gradual subsidence of the water in the glass to
its former level is also of a dual character—namely,
(a) the cooling of the water in pipe H, and (b) the
diminution in the condensation of steam in pipe I
owing to the collection therein of air released from the
steam condensed.

These results will, however, be somewhat modified
if the water in the boiler is of higher density than in
pipe H, and this will nearly always be the case owing
to the condensation of the steam in the glass and upper
fittings of the water-gauge causing the water in the
lower part to be fresher than that in the boiler.

The Examiner should impress upon candidates the
necessity for periodically blowing through the water-
gauge on each boiler (no matter what the form may
be) in a systematic and thorough manner, and in cases
where a boiler is fitted with two water-gauges of keep-
ing both in constant use. Finally, he should further
impress upon them the necessity for keeping the water-
gauges well lighted, clean, and in all respects efficient.

———

APPENDIX E.

———

EXAMINATION OF MASTERS AND MATES IN STEAM.

THESE examinations are provided for the purpose of
giving masters and mates who are possessed of certi-
ficates of competency an opportunity of undergoing
a voluntary examination as to their practical know-
ledge of the use and working of the steam-engine.
The Examiners are selected by the Marine Depart-
ment from the Engineer Surveyors appointed under
“The Shipping and Seamen Act, 1903.”

The examination is open to any person who holds a
certificate of any grade in the foreign or home trade,
or as master of his own pleasure-yacht. Candidates
should fill up the form of application (form Exn. 2) at