7. Q. What type of fire tube superheater is in most general use in locomotive service?

A. The top header fire tube type, known as the "Schmidt Superheater." A system of units located in large flues through which the steam pa.s.ses on its way from the dry pipe to the steam pipes, and a damper mechanism which controls the flow of gases through the large flues.

8. Q. Describe the construction and location of the header.

A. The header is a simple casting, divided by part.i.tion walls into saturated and superheated steam pa.s.sages. It is located between the dry pipe and the steam pipes, the same as the n.i.g.g.e.r head in a saturated locomotive. The dry pipe is in communication with the saturated steam pa.s.sages and the steam pipes with the superheated steam pa.s.sages and these are in communication with each other through the superheated units.

9. Q. Describe the construction of superheater units and their connection to the header.

A. The units are composed of four seamless steel pipes, connected by three return bends. Of the four pipes, two are straight and two are bent upward and connected to the header by means of a clamp and bolt; one end of the unit is in communication with the saturated steam pa.s.sage and the other with the superheated steam pa.s.sage in the header casting.

10. Q. Trace the flow of steam through the top header fire tube superheater.

A. When the engine throttle is open, saturated steam pa.s.ses through the dry pipe into the saturated steam pa.s.sage of the header casting. From this pa.s.sage it enters one end of the unit, pa.s.sing backward toward the fire-box, forward through one of the straight pipes and the front return bend, backward through the other straight pipe to the back return bend, and forward through the bent pipe and upward into the superheater steam pa.s.sage of the header, from which it enters the steam pipes and is carried to the steam chest.

11. Q. What should be the position of throttle valve when running a superheater locomotive?

A. The engine should always be run with as wide open throttle as the conditions will permit, regulating the steam admission to the cylinders according to work to be performed.

12. Q. What should be the position of throttle while drifting?

A. The throttle valve should be kept slightly open while drifting, so as to admit a small quant.i.ty of steam in valve chamber and cylinder above atmospheric pressure, to prevent the inrush of hot air and gases which destroy lubrication, also to prevent excessive wear to valve, cylinder and piston rod packing.

13. Q. How should the water be carried in boiler of superheater locomotives?

A. As low as the conditions will permit, because this practice reduces the tendency to work water over into the dry pipe and units, as the superheater locomotive will use one-third less water than the saturated locomotive.

14. Q. What care should be exercised in lubricating a superheater locomotive?

A. The supply of oil to steam chest should be watched very closely by the engineer, he to know that lubricator is feeding constantly and evenly over entire division, and according to work performed.

15. Q. Describe the general form of a locomotive boiler.

A. A locomotive boiler is cylindrical in form, it usually has a rectangular shaped fire-box at one end and a smoke-box at the other, and flues extend through the cylindrical part, and, like the fire-box, are surrounded by water.

16. Q. How does the wide fire-box type of boiler differ from the ordinary boiler, and what are its advantages?

A. The wide fire-box type of boiler is built so the fire-box is above the frame and extends out over the driving wheels. The advantages of this are to obtain a larger grate area in the same length of fire-box and to give a slower rate of combustion per square foot of grate surface. The deep fire-box is limited in width to the distance between the frames, while the shallow fire-box sets on top of the frames and between the driving wheels.

17. Q. Why have two fire-box doors been placed in the large type of locomotive boilers?

A. For convenience of the fireman on account of the greater width of the fire-box, so that coal can easily be distributed to all parts of the fire-box.

18. Q. Describe a locomotive fire-box.

A. The modern form is a rectangular shaped structure located at the back end of the boiler. It has a door and is composed of two side sheets, a crown sheet, a back sheet and a flue sheet from which the flues extend to the smoke-box at the other end of the boiler.

19. Q. To what strains is a fire-box subjected?

A. To crushing strains and to those of unequal contraction and expansion.

20. Q. How are the sheets of a fire-box supported?

A. They are supported by staybolts screwed through the inside and outside sheets with their ends riveted over.

21. Q. In what manner is a crown sheet supported?

A. By crown bars or radial staybolts.

22. Q. What are the bad features about crown bars?

A. They are hard to keep clean and frequently cause crown sheets to become mud burned.

23. Q. What are the advantages of radial stayed crown sheets?

A. They are easier to keep clean and cheaper to repair.

24. Q. How are the inside and outside sheets of a fire-box secured at the bottom?

A. They are riveted to a wrought iron ring called a mud-ring.

25. Q. Describe the ash-pan and its use.

A. It is a receptacle secured to the fire-box and usually provided with dampers to regulate the flow of air to the fire. It collects the ashes that drop from the fire-box and prevents them from setting fire to bridges or other property along the track. Engine-men must know that ash-pan slide and hopper bottoms are closed before leaving enginehouse.

26. Q. What is a "wagon-top" boiler?

A. It is a boiler that has the fire-box end made larger than the cylindrical part to provide more steam s.p.a.ce.

27. Q. Why are boilers provided with steam domes?

A. To furnish more steam s.p.a.ce and to obtain dryer steam and to provide a place for the safety valves, steam pipes, throttle valve and whistle.

28. Q. What must be the condition of a boiler to give the best results?

A. It must have good circulation and be clean and free from mud or scale.

29. Q. What is meant by "circulation" in a boiler?

A. Free movement of the water, so that it may come in contact with the heating surface and after being converted into steam be immediately replaced by a fresh supply of water.

30. Q. What would be the effect if a "leg" of the fire-box became filled with mud?

A. There would be no water in contact with the fire-box sheets and they would quickly become overheated and mud-burned.

31. Q. What would be the result if the fire-box sheets became overheated?

A. They would be weakened and forced off the staybolts and an explosion would occur.