48.  Q. When and for what purpose is the use of a rake on the fire bed allowable?

A. The rake should be used on the fire very seldom, because raking the fire bed tends to form clinkers, especially when the rake is plunged down through the fire to the grate.  It may be used when necessary to rake the fire lightly when on the road for the purpose of breaking the crust, which may be found as a consequence of too heavy firing.

49.  Q. Within what limits may steam pressure be allowed to vary, and why?

A. Pressure should not be allowed to vary more than five pounds from the maximum for the reason that too much expansion and contraction will take place, which many times is the cause of flues leaking, cracked or broken side sheets and stay bolts.

50.  Q. Has improper firing any tendency to cause the tubes to leak?  How?

A. Yes; if the pressure is not regularly maintained, the fluctuations of temperature cause constant contraction and expansion to take place.  If the fire is not carried level, but is carried heavy in some parts of the fire-box and light in others, holes will be worked in, cold air drawn through, lowering the temperature, chilling the tubes and causing leaks.  Carrying the fire too heavy in some places, causes clinkers to form.  If the door is open too long, too much cold air is drawn over the fire, causing the tubes to leak.

51.  Q. What do you consider abuse of a boiler?

A. Careless or improperly supplying water to the boiler, improper firing or allowing steam to vary from high to low pressure, causing unnecessary expansion and contraction.

52.  Q. Does the stopping up of flues affect the steaming capacity of the engine?

A. Yes; obstructed flues reduce the heating surface, reduce the steaming capacity of the engine, and, as a rule, result in causing the flues to leak.  They also cause an increase of speed of the gases through the remaining flues and a poor steaming engine.

53.  Q. What causes honeycomb over the flues?

A. Honeycomb on flues is usually caused by the draft through the fire picking up the sulphur and molten clay which is in a molten and sticky condition in the fire; as it passes on its way to the stack, some of it strikes the flue-sheet and sticks or passes through the flues, clogging up the netting in the front end.

54.  Q. How would you take care of a boiler with leaky tubes or fire-box, and why?

A. Keep a bright, clean fire, especially up next to the flue-sheet, and as even a pressure of steam as possible and not use the blower any stronger than is absolutely necessary.

55.  Q. Why is it very important that coal should be broken so that it will not be larger than an ordinary sized apple before being put into the fire-box?

A. In order to get rapid and complete combustion, coal should be broken into small pieces; this aids combustion by exposing a larger surface to the flame and can be fired more economically and better results are obtained.