Page:EB1911 - Volume 04.djvu/158

 A somewhat similar boiler is made by Messrs. Clarke, Chapman &amp; Co., and is known as the “Woodeson” boiler (fig. 13). It consists of three upper drums placed side by side connected together by numerous short tubes, some above and some below the water-level, and of three smaller lower drums also connected by short cross tubes. The upper and lower drums are connected by numerous nearly vertical straight tubes. The whole is enclosed in firebrick casing. The design permits of the insides of all the tubes being readily inspected, and also of any tube being taken out and renewed without displacing any other part of the boiler.



11.—Babcock & Wilcox Water-tube Boiler fitted with Superheaters.



12.—Stirling Water-tube Boiler.

The earliest form of water-tube boiler which came into general use in the British navy is the Belleville. Two views of this boiler are shown in fig. 14. It is composed of two parts, the boiler proper and the “economizer.” Each of these consists of several sets of elements placed side by side; those of the boiler proper are situated immediately over the fire, and those of the economizer in the uptake above the boiler, the intervening space being designed to act as a combustion chamber. Each element is constructed of a number of straight tubes connected at their ends by means of screwed joints to junction-boxes which are made of malleable cast iron. These are arranged vertically over one another, and except in the case of the upper and lower ones at the front of the boiler, each connects the upper end of one tube with the lower end of the next tube of the element. The boxes at the back of the boiler are all close-ended, but those at the front are provided with a small oval hole, opposite to each tube end, closed by an internal door with bolt and cross-bar; the purpose of these openings is to permit the inside of the tubes to be examined and cleaned. The lower front box of each element of the boiler proper is connected to a horizontal cross-tube of square section, called a “feed-collector,” which extends the whole width of the boiler. When the boiler is not in use, any element can be readily disconnected and a spare one inserted. The lower part of the steam-chest is connected to the feed-collector by vertical pipes at each end of the boiler, and prolongations of these pipes below the level of the feed-collector form closed pockets for the collection of sediment. The tubes are made of seamless steel. They are generally about 4 in. in external diameter: the two lower rows are in. thick, the next two rows and the remainder about  in. The construction of the economizer is similar to that of the boiler proper, but the tubes are shorter and smaller, being generally about 2 in. in diameter. The lower boxes of the economizer elements are connected to a horizontal feed pipe which is kept supplied with water by a feed-pumping engine, and the upper boxes are connected to another horizontal pipe from which the heated feed-water is taken into the steam-chest. Both the boiler proper and the economizer are enclosed in a casing which is formed of two thicknesses of thin iron separated by non-conducting material and lined with firebrick at the part between the fire-bar level and the lower rows of tubes. Along the front of the boiler, above the level of the firing-doors, there is a small tube having several nozzles directed across the fire-grate, and supplied with compressed air at a pressure of about 10 ℔ per sq. in.

13.—Woodeson Boiler (Messrs Clarke, Chapman &; Co.).

In this way not only is additional air supplied, but the gases issuing from the fire are stirred up and mixed, their combustion being thereby facilitated before they pass into the spaces between the tubes. A similar air-tube is provided for the space between the