The whistles are the largest ever made. Each set consists of three bell domes grouped together with a suitable branch plate, as shown in Fig. 71.
Probably the least observant person who has been to sea on a steamship under conditions in which the steam-whistle has been used, either as a signal or as a warning, has noticed what a long time elapses after the steam is turned on before the whistle can make its voice properly heard. There is first a deluge of water over the deck from the pipe, then a lot of sputterings, followed by a series of more or less spasmodic false notes, which as they come are choked in a gradually decreasing degree until at last the steam-pipe is blown clear of condensed water, and the true sound of the whistle is heard. All this is a serious drawback, particularly when signals have to be given by the whistle at stated definite intervals, for it is not always easy to get the whistle to speak properly at the exact times required, owing to the rapidity with which the condensed water forms, especially in a cold atmosphere. It is no uncommon thing for as much as 30 seconds to elapse between the turning on of the steam and the true note of the whistle being heard. This is a matter of increasing importance because, owing to the fact that the speeds of vessels at sea have so greatly advanced during late years, and are still advancing, the effective working of the whistle has become very closely associated with the safety of the ship. Vessels approach one another so rapidly now that the distance between them may be sometimes reduced by as much as three-quarters of a mile per minute. It will thus readily be seen that this accumulation of water in the steam-pipe is not only an inconvenience, but may be a distinct danger, particularly in cold weather, when the water is liable entirely to be frozen, and the whistle rendered inoperative.
In order in some way to obviate this trouble, the whistle-pipe is sometimes provided with drain-pipes for dealing with the water of condensation; but these are frequently of little use, because they cannot deal with the water in the pipe at the moment the lanyard is pulled, nor with the water that is formed by rapid condensation of the steam that passes upwards to the whistle. It is evident, therefore, that the only satisfactory way to cure the evil is to supply dry steam directly to the whistle by withdrawing all the condensed water that comes along before it can do any harm. With this object in view the Crosby Steam-Gage and Valve Company, 147, Queen Victoria-street, London, E. C., have brought out and patented the apparatus shown in the accompanying illustration.
It is made in sizes suitable for whistle-pipes of 1 in. in diameter and upwards. It consists of three concentric cylinders, made of cast iron, the outer cylinder being lagged with silicate cotton, and covered with planished sheet steel. The arrangement of the inner cylinders is such as to provide a reservoir for dry steam, from which the whistle is supplied the moment the valve opens. An inspection of the figure will, however, give a clear idea of actual construction. It is a vertical section of the apparatus through the centre.
The three concentrically-placed cylinders previously mentioned are shown at A, B, and C, the outer one of which forms a closed vessel provided at the bottom with a steam inlet D, by means of which it is fitted on the end of the steam-pipe. The vessel B is provided at, or near, its upper end with openings E, which allow the steam to pass through from the outer vessel A. In the centre of the bottom of the intermediate vessel B there is a cone-piece F, which projects upwards under the centre of the bell-mouthed part of C. This latter part has a steam outlet at the top, to which the whistle is secured. It will be seen that the vessel B is provided with pipes G, which are intended to convey away the separated water from the vessel B to the lower part of the vessel A, whence it is carried away to a trap by means of the outlet H. As an alternative to the steam-trap the makers can supply a special ball check-valve for returning the condensed water to the boiler, which can be fitted if desired.
When the steam is admitted at D it strikes against the
bottom of the vessel B, and is turned out of its course by the special
form of the bottom. This throws down some of the water it contains.
It then passes up the annular space between A and B, enters the slots E,
and strikes the surface of the inner vessel C. Passing down this vessel
it is thrown outwards against the inside of the vessel B by the flared-out
bottom part of C. Rebounding from the surface of B, it strikes the cone
F, and is directed upwards through the inside of C, and passes to the whistle
free from water, and without any eddying or irregular flow.