1892
THE NEW ZEALAND GAZETTE.
[No. 53

In one case two furnace-crowns came down in a steamer that was just starting on a voyage. The engineers were satisfied that there was plenty of water in the boiler, because the water-gauge showed full glass, and they called the attention of a Board of Trade Surveyor to this fact as being conclusive evidence that the casualty could not have resulted from shortness of water. On examination of the fittings, however, it was found that the cock between the boiler and the steam-pipe leading to the gauge was shut, having been carelessly left in that position on the previous day, when the mountings were overhauled for survey. Directly the cock was opened the water disappeared from the gauge-glass, and the second engineer admitted that he had blown down the boiler in order to lower the water-level, as the glass was full.

Many steamers have had their furnaces brought down at sea in a similar manner to the above through what the engineers of the watch have called “false water in the glass,” and which, on examination, has been found to result from the top communication being choked.

These casualties resulted from what, to say the least, was bad management, not false water.

Unless a candidate under examination is able to prove that he understands how to verify the indications of the water-gauge, he should not be passed in practical knowledge; and, as failure in practical knowledge involves the candidate going to sea for another three months before being eligible for re-examination, the Examiner should explain to such candidate his error, after failing him, in order to prevent further casualties resulting from his want of knowledge on this subject.

The sketches, Figs. 1, 2, 3, 4, and 5, Plate I, represent the usual methods of attaching water-gauge mountings to marine boilers. The important features in each gauge and the method of verifying its indications are dealt with separately in the following remarks.

Referring to Fig. 1 only.

In this case the water-gauge cocks are attached direct to the boiler, and the accuracy of the gauge when the boiler is under steam can be tested as follows:—

First.—Let B remain open, then close cock D and open cock E, and if steam issues it proves that cock B and the passage through the top fitting and gauge-glass are clear. If no steam or water issues, either cock B or the passage through the top fitting and gauge-glass is choked, and the gauge cannot act properly until the obstruction is removed.

Second.—Close cock B and open D and E, and if water issues cock D is clear. If no water or steam issues, either cock D or the passage from the boiler through the lower fitting is choked, and must be cleared before the gauge can act properly.

Referring to Fig. 2 only.

In this case the gauge-cocks are attached to a bent pipe of comparatively large diameter (at least 3 in. in the bore), the upper end of which communicates with the steam-space, and the lower end with the water-space of the boiler. Owing to the bore of the pipe being large it is not liable to become choked or stopped under the ordinary conditions of working. The water-gauge is therefore in practically the same condition as if it were attached direct to the boiler as in Fig. 1.

This gauge, when at work, is tested in precisely the same manner as the one shown in Fig. 1.

Screw-plugs are inserted at P P and Q Q by the removal of which the apertures in the pipe can be cleared, if necessary, by the insertion of a wire or rod when steam is down.

Referring to Fig. 3 only.

In this gauge there is an open communication from A to C through the column Y, and in order to “blow through the glass” it is only necessary to shut cocks D and B alternately, keeping E open. But to “blow through the water-gauge,” including the pipes H and I, it is necessary, after blowing through the glass as described above, to shut A and C alternately, at the same time keeping B, D, and E open for such time as will insure the complete discharge of the contents of the gauge and its connections. When B, D, and C are clear and A choked, the steam lodging in the glass and in the pipe I leading from Y to A becomes condensed, and the water flowing through C to take its place rises in column Y and in the glass to a level above that of the water in the boiler. In other words, the gauge shows a false level. If now E be opened and water is blown out, then on E being again closed the water in the gauge will rise higher than before and be still further misleading. On the other hand, when B, D, and A are clear and C choked, the water (if any) in the glass is trapped, and no longer rises and falls with the water in the boiler or with the motion of the vessel; it, however, slowly rises in the glass owing to condensation of the steam in the upper part of the gauge until such time as E is opened, when the whole of the water in the glass is blown out, and on E being closed the glass does not show any water, notwithstanding that the water in the boiler may be at the proper level. When the test-cocks T T T are attached to column Y, as shown in Fig. 3, they cease to be reliable when either cock A or C or the pipe in connection therewith is choked or nearly choked.

Referring to Fig. 4 only.

Sometimes the water-gauge fittings are arranged as shown in Figs. 4 and 5, with no passage up the column, the central portion (N) of the column being simply a pillar or connecting-piece of any convenient section between the upper and lower portions to which the cocks B and D are attached.

By this arrangement double communications are obviated, and there is no need for what is known as “double shut-off” in testing the accuracy of the gauge. When, however, the gauges are constructed in this manner the cocks B and D are unreliable as test-cocks in the event of there being no water in the gauge. This feature should be carefully noted. Moreover, when in working-condition the reduction of pressure in the glass which arises when E is opened causes the water in pipe H to rise above its normal level. This objectionable feature should also be noted.

Referring to Fig. 5 only.

Sometimes there is a bend (L) in the steampipe (I) leading from cock A to cock B. This has occasionally escaped observation when new boilers have been fitted on board ship. In most cases this bend arises from the pipe being led in an abnormal direction to escape other pipes, beams, or fittings near the smoke-box. With such a bend the condensed steam collects in the pipe and falls to the bottom of the bend, and in time