A. It will run from that corresponding to 311⁄2 inches of water pressure to 12 or even 13 inches.

Q. What is the relation between the coal consumed per square foot of grate surface per hour and the draft in inches of water in the smoke-box?

A. It is about 0.05; that is, the draft in inches of water is 1/20 the number of pounds of coal consumed per square foot of grate per hour; so that 200 pounds of coal per square foot of grate per hour would call for 10 inches of draft.

Q. What may be said of the quality of the combustion-gases in the smoke-box of a locomotive as compared with that in the power plant stacks?

A. It compares very favorably; the carbonic acid gas averaging between 10 and 13 per cent.

Q. What may be said of the efficiency of a locomotive boiler at minimum and at maximum coal consumption? A. At maximum coal-consumption rate it will run from 39 to 60 per cent; at minimum from 63 to 79; the average being between 55 and 68 per cent; and in most cases above 60 per cent. Stationary boilers in first-class order and regulation settings, with every convenience to obtain good results from the use of fuel at comparatively low combustion rates do not often run over 70 per cent. Q. What is most to be desired in designing a front end?

A. A design that will give the best possible result in the way of draft.

Q. What is meant by "the best possible result?"

A. The greatest possible amount of steam that can be produced from a given amount of coal consumed, to perform a given work in a given time.

Q. What is a cause of warping and cracking long front ends?

A. Leaky doors on the front, causing the hot cinders to burn.

Q. Describe a self-cleaning front end?

A. Referring to Figs. 83, 84, there is a perforated steel table plate A with manhole M; back of the exhaust pipes N and petticoat pipe P there is an ordinary adjustable daphragm, set as high as possible. An adjustable front diaphragm or baffle-plate carries the draft far enough ahead to make the front end self-cleaning.

Q. Can front ends without petticoat pipes be made self-cleaning?

A. Yes, as shown in Figs. 85 and 86.

Q. Why will not lead gaskets keep a blower joint in the smoke-box tight?

A. Because lead melts at 627 deg. F. (364 deg. C.) and the flue temperature is often as high as 1,000 deg. F. (say 575 deg. C.).

Q. Is the smoke-box temperature any gage of the capacity of the engine runner?

A. Yes, a good engineman can keep the temperature 100 deg. F. (55.6 deg. C.) lower than a poor one.

Q. What may the temperature of the gases in the smoke-box be?

A. Anywhere from 400 deg. to 900 deg. F.

Q. When it is hot enough to melt lead gaskets in the blower-pipe joints is it too hot?

A. As lead melts at about 625 deg. F. the melting of the blower-joints in the smoke-box should show that heat was going up the stack, which should be utilized in steam-making.

Q. How should the studs which fasten the steampipes to the saddle be put in?

A. First greased, then rolled in graphite (plumbago; black lead) so that they can more readily be got out.

Figs. 85 and 86.

Front End without Petticoat. Q. What causes burning or warping of the "long front end"?

A. Burning of cinders therein, caused by a leak in the smoke-box; or by the door being partly open, or being warped so as not to close air-tight.

Q. When should the long front end be cleaned out? A. When standing still, to avoid the sharp cinders cutting the machinery when blown back.

Q. What is the Sturm spark-arrester?

A. It is arranged so that the front and back screen sheets are closed automatically by a steam piston when the throttle is open; otherwise they are open, so as to give good draft.

112

Q. How may the draft be lessened, although the engine is running with a sharp exhaust, without opening the fire-door?

A. By a chimney-damper, as shown in Fig. 80. It admits air at the stack base, thus doing away with the necessity of opening the fire-door and admitting cold air into the box.

CHAPTER XVII

THE PETTICOAT-PIPE AND EXHAUST NOZZLES

Q. What is the use of the petticoat-pipe?

A. To insure uniformity of draft; that is, that the draft shall come from all the flues equally, notwithstanding the tendency of the upper ones to get the most; and that it is delivered centrally and at the right height in the stack.

Q. What is the effect of a petticoat-pipe set too high? A. Too much draft through the lower flues, and choking of the upper ones with soot and fine ashes.

Q. What is the sign of the petticoat-pipe being set at the right height?

A. Uniformly clean appearance of the flues, as judged from the front end.

Q. What is the effect, on the fire, of a badly-arranged petticoat-pipe?

A. Usually to tear it in spots.

Q. How may this be remedied?

A. Partially by firing very heavily.

Q. How may the working of the petticoat-pipe and nozzle be judged while on the run?

A. By opening the fire-box door on a hard pull and seeing if the combustion is more vivid in certain places than in others. If this is the case, on several inspections, it may be concluded that these places are getting more draft than their neighbors.

Q. What becomes of the exhaust steam?

A. In a single-expansion (non-compound) engine the exhaust passes from the exhaust-passage through the exhaust-pipe, thence through the nozzle and up through the smoke-box into the stack, drawing with and around