Comparison with locomotive type.
As regards the use of those varieties of water-tube boilers which give the
greatest power for their weight and the space occupied, a very considerable extension
took place in Great Britain in 1893 by the demand for the class of small
vessels of great speed known as 'torpedo-boat destroyers.' Many varieties have
since that date been fitted and tried in such vessels with satisfactory
results, and they have now entirely superseded the locomotive type, which had
previously been mostly used for such purposes.
An example of the results obtained in sister vessels with locomotive and
water-tube boilers may be given in the trials of 'Havock' and 'Hornet,' both built
and engined by Messrs. Yarrow & Co., the ' Havock ' with locomotive boilers
having copper fire-boxes similar to that illustrated in Fig. 44, and the
'Hornet' with water-tube boilers similar to Figs. 65 and 66.
|
|
|
Having now briefly descrlbed the history of the revival of water-tube boilers
in recent years, we will proceed to the detailed consideration of these boilers,
their advantages lying in their lightness for the power generated, the capacity
of raising steam quickly owing to the small quantity of water carried, and
their comparative freedom from leaky tubes, the joints being more protected
from the direct impact of flame.
The Belleville boiler.
This type of water-tube boiler is shown in Figs. 49 and 50, and is of more
extensive use on board large ships than any other. It consists
essentially of a top steam cylinder and a lower water chamber, with a series of
straight zigzagged tubes of comparatively large diameter connecting them. There
is an external return water pipe on each side, connecting the ends of the top
steam chamber with the lower water chamber. The zigzag generating tubes are
inclosed in a sheet-iron or steel casing, which confines the flame and gases
generated from the combustion of the coal on the fire-bars. ..........
