Boiler Accessories Furnaces

This is done by means of the hollow arch. One of these arches of the "Wade-Nicholson" type, installed on a locomotive, is illustrated in Fig. 15, the method of operation being clearly indicated. The device may be installed at both back and front ends of the firebox.

The hollow passage through the arch leads directly through suitable openings in the firebox sheets, from the outer air to the combustion chamber, being deflected downward toward the fire at the inner end. The walls of the arch, being highly heated, impart their heat to the current of air, which, as it emerges into the firebox, is practically at the temperature of ignition. There mingling directly with the combustible gases, an approximately perfect combustion is established. The resulting economy in fuel is estimated to average a saving of at least 8 per cent.

The Chicago & Northwestern Railway, has, after severe test, adopted arches of the above type on over 200 of its locomotives; and its example has been followed on many of the locomotives of the Santa Fe, the Chicago, Milwaukee & St. Paul, the Pere Marquette, the Duluth & Iron Range, and other important railroads in this country. In addition to the saving in fuel, the following advantages are claimed for the hollow arch: Being air-cooled, its life is two to three times that of the ordinary solid brick arch.

It does away with the smoke nuisance.

The air, being heated before striking the combustible gases, unites with them instantly, giving a brighter, cleaner, more intense fire, and resulting in a better steaming engine.

The back arch acts as a baffle-sheet, protecting the crown sheet and upper flues, and gives a more uniform distribution of heat throughout, resulting in less leaky flues and a saving in boiler repairs.

The arch can be used either with or without water-filled circulating arch tubes as supports.

Arches can readily be removed and reset., in wholeor in part, without damage, to give access to flues when repairs are needed.

Fuel Economizers. Many devices have been employed whereby a portion of the heat may be extracted from the gases as they pass from the boiler to the uptake. Most of these consist of a tubular arrangement through which the hot gases pass; but, as these are soon covered with a thick deposit of soot, they quickly become inoperative.

The "Green" economizer (Fig. 16) solves this difficulty by means of small scrapers which work up and down between the tubes. These scrapers are operated by a small engine, and keep the tubes free from soot. The feed-water is pumped through these tubes on its way to the boiler, and is thoroughly heated. An economizer of this sort will extract 40 per cent or more of the heat from the waste gases; but by reducing the temperature of these gases, the draft is somewhat reduced, and either the chimney must be built higher, or a blower must be used.

Mechanical Stokers. The mechanical stoker, which feeds coal and tends fires by machinery, is coming more and more into general use. With a good mechanical stoker, one man can tend several furnaces with little labor. There are several different types, and in most of them the coal is fed into a hopper of such size that it need not be often filled. Some stokers work continuously; others, only when thrown into gear by the fireman. In the "Roney" stoker (Fig. 17), the grate-bars extend across the furnace, and form a series of steps down which the fuel moves. Each grate bar is hung on pivots at the ends, and is operated by a rocker-bar. This rocker-bar is driven by a small steam engine, with a slow, regular reciprocation which causes the grate-bars to tip so that the coal of its own weight slides from one grate-bar to the next. Coal from a hopper falls onto a zontal plate, and is fed into the top of the grate by a pusher. The rapidity with which the fuel can be fed, is regulated by changing the stroke of the pusher and by governing the speed of the engine. Ashes and clinkers collect on the dumping-grate at the end of the grate-bars, whence they can be dumped into the ash-pit.

This type of grate is well adapted for smoke prevention, for the fresh fuel fed in at the top is rapidly coked, and the volatile gases are easily consumed. The rapidity of feed should be so regulated that no unburned fuel gets past the dump-grate. If the fire becomes too thin, there will be a loss of efficiency due to the excess of air which passes through the burning fuel. It is easy to detect the loss from too much fuel, but not so easy if there is too little fuel.