Rough and Tumble Engineering Part 8

Q. Steel?

A. 2532 degrees.

Q. What cla.s.s of boilers are generally used in a threshing engine?

A. The flue boiler and the tubular boiler.

Q. About what amount of heating and grate surface is required per horse power in a flue boiler.

A. About 15 square feet of heating surface and 3/4 square feet of grate surface.

Q. What would you consider a fair evaporation in a flue boiler?

A. Six pounds of water to I pound of coal.

Q. How do these dimensions compare in a tubular boiler.

A. A tubular boiler will require I/4 less grate surface, and will evaporate about 8 pounds of water to I pound of coal.

Q. Which do you consider the most available?

A. The tubular boiler.

Q. Why?

A. It is more economical and is less liable to "collapse?"

Q. What do you mean by "collapse?"

A. It is a crushing in of a flue by external pressure.

Q. Is a tube of a large diameter more liable to collapse than one of small diameter?

A. Yes.

Q. Why?

A. Because its power of resistance is much less than a tube of small diameter.

Q. Is the pressure on the sh.e.l.l of a boiler the same as on the tubes?

A. No.

Q. What is the difference?

A. The sh.e.l.l of boiler has a tearing or internal pressure while the tubes have a crushing or external pressure.

Q. What causes an explosion?

A. An explosion occurs generally from low water, allowing the iron to become overheated and thereby weakened and unable to withstand the pressure.

Q. What is a "burst?"

A. It is that which occurs when through any defect the water and steam are allowed to escape freely without further injury to boiler.

Q. What is the best way to prevent an explosion or burst?

A. (I) Never go beyond a safe working pressure. (2) Keep the boiler clean and in good repair. (3) Keep the safety valves in good shape and the water at its proper height.

Q. What is the first thing to do on going to your engine in the morning?

A. See that the water is at its proper level.

Q. What is the proper level?

A. Up to the second gauge.

Q. When should you test or try the pop valve?

A. As soon as there is a sufficient pressure.

Q. How would you start your engine after it had been standing over night?

A. Slowly.

Q. Why?

A. In order to allow the cylinder to become hot, and that the water or condensed steam may escape without injury to the cylinder.

Q. What is the last thing to do at night?

A. See that there is plenty of water in boiler, and if the weather is cold drain all pipes.

Q. What care should be taken of the fusable plug?

A. Keep it sc.r.a.ped clean, and not allow it to become corroded on top.

Q. What is a fusible plug?

A. It is a hollow cast plug screwed into the crown sheet or top of fire box, and having the hollow or center filled with lead or babbit.

Q. Is such a plug a protection to a boiler?

A. It is if kept in proper condition.

Q. Can you explain the principle of the fusible or soft plug as it is sometimes called?

A. It is placed directly over the fire, and should the water fall below the crown sheet the lead fuses or melts and allows the steam to flow down on top of the fire, destroys the heat and prevents the burning of crown sheet.

Q. Why don't the lead fuse with water over it?

A. Because the water absorbs the heat and prevents it reaching the fusing point.

Q. What is the fusing point of lead?

A. 618 degrees.

Q. Is there any objection to the soft plug?

A. There is, in the hands of some engineers.

Q. Why?

A. It relieves him of the fear of a dry crown sheet, and gives him an apparent excuse for low water.

Q. Is this a real or legitimate objection?

A. It is not.

Q. What are the two distinct cla.s.ses of boilers?

A. The externally and internally fired boilers.

Q. Which is the most economical?

A. The internally fired boiler.

Q. Why?

A. Because the fuel is all consumed in close contact with the sides of furnace and the loss from radiation is less than in the externally fired.