Q. Where is it usual for such a check-valve to be placed?

A. Outside the boiler, in the feed-pipe.

Q. What is the objection to an outside check-valve? A. It is liable to be knocked off in a collision or other accident; and in this case there would be an escape of hot water, followed by steam, which is liable to injure the engineer and fireman or other persons, and also tends to cripple the boiler.

Q. Where, then, should the check-valve be placed? A. Just inside the shell, where the feed-pipe discharges into it.

Q. Why are boiler checks set so far ahead?

A. So that the cooler water of the lower temperature will enter as far as possible from the firebox and work from the point of least evaporation to where the greatest evaporation is taking place; this helps out the circulation and reduces the strains from expansion and contraction when the feed is increased or diminished.

Q. What is a common trouble of inside-hinged boiler checks?

A. Tendency to stick open.

Q. How can an inside check be made that will not have this disadvantage?

A. As in Fig. 106, where there is an angle poppet valve with a finger which limits its lift; this being the P. RR. standard.

CHAPTER XXVIII

FEEDING THE BOILER*

Q. Where is the feed water usually introduced, and why?

A. Pretty well forward, so that the cold entering feedwater will not strike the hot part of the boiler.

Q. What would be the result of introducing it right on the fire-box sheets?

A. To crack them by sudden cooling and contraction. Q. What is usually the best hight to carry water? A. At such a hight that the top try-cock will show both water and steam.

Q. Why not carry water so that it will show solid at the top try-cock?

A. Because there would be no knowing whether there was 1/4 inch or three inches of water above the cock.

Q. How should water be carried in approaching a down grade?

A. There should be enough to keep the crown-sheet covered on the grade.

Q. If you should strike a down grade and show both steam and water in the lower gage, what should be done? A. The feed put on and the fire kept bright.

Q. What would be the result of putting on the feed with low water and not keeping the fire bright?

A. The flues would be apt to be made to leak.

Q. Does it make much difference what kind of water locomotive boilers get?

A. A great deal. If acid it tends to corrode the boiler on the inside; if it has much mineral matter in solution this is dropped when evaporation takes place, and becomes baked on the shell and tubes as a stony scale; if

* See also under "Pumps" and "Injectors."

there is undissolved vegetable or mineral matter, this is deposited on the bottom as slush and sometimes baked on. Q. How can acid get in the water?

A. The water from streams in the Pennsylvania coalmining regions is impregnated with sulphuric acid; the same or similar causes produce similar results elsewhere. Q. Would alkaline water be an advantage?

A. Not usually, because the dissolved alkali would be deposited on the shell when the water was evaporated. There are, however, cases where by using an acid water from one station and an alkaline from another, one will counteract the other; but it is not well to trust to any such luck.

Q. When should the injector be on, and when off?

A. On between stations, but not in pulling out, when more steam is used. It also lessens the smoke nuisance.

BLOW-OFFS

Q. How may loose mud and other loose dirt be removed from a locomotive boiler?

A. Through large blow-off cocks near the bottom of the fire-box, and which may be opened when steam is on, thereby letting much of such loose material be blown out. Q. How is the remainder removed?

A. By hand-holes or mud plugs in the fire-box corners near the bottom; sometimes also by a hand-hole at the bottom of the front tube-sheet. By this the mud may be loosened and much of it removed, and a hose used to clean out the loose material.

Q. When the check-valve is near the front of the boiler, as usually the case, what may be said about the blowoff cocks?

A. There should be one right under the check-valve, by which to blow off the material that has dropped under it.

Q. What is the blow-off cock usually like? And where is it placed?

A. A plug valve having a large opening and usually screwed into the front water leg, but sometimes into the back head above the crown-sheet.

Q. Is it safe to depend entirely on one blow-out cock? A. No; it is better to have more than one.

Q. Is the front of the boiler always the only place, or even the best place, to put one?

A. No; sometimes the rear is also desirable; occasionally also the side or sides; depending upon the general design of this boiler, the position of the machine parts, the character of the water and even the gradients of the road, as it may in case of accident be necessary to blow out the boiler on a steep up grade or in a derailment accident in which the front end was well uptilted.

Q. Will the blow out cocks discharge mud and scale that are not entirely loose?

A. No; the mud plugs and hand holes are needed.