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STEAM LOCOMOTIVE ENGINEMAN’S. Manual - part 19

Chapter 11: - General Engine Questions and Answers

CHAPTER 11

GENERAL ENGINE QUESTIONS

AND ANSWERS

Chapter 11: - General Engine Questions and Answers

CHAPTER 11

GENERAL ENGINE QUESTIONS AND ANSWERS

What are the fusible plugs, and what is their purpose?

There are two fusible plugs, generally known as lead plugs,
fitted into the crown sheet of each firebox in a central
position approximately one foot from each end of the crown
sheet, with the ends of the plugs projecting into the water
space. These plugs are made of brass and have holes
bored through them. The holes are filled with lead, which
melts at a comparatively low temperate.

Refer to FIGURE 8 in Annex A.

If the plugs are not covered with water the lead melts and
runs out, leaving a clear hole through which water and steam
will rush on to the fire, thus warning the enginemen of a
shortage of water in the boiler. Should this occur, the fire
must be smothered and withdrawn immediately.
Arrangements should be made to lock the fire door,
assistance should be obtained and the engine prepared for
towing.

Note: - Under no circumstances should the Injectors be
used if this should occur.

What is the purpose of the steam dome?

The purpose of the steam dome is to provide a space as
high as possible above the water in the boiler so that the
steam being fed from the boiler to the steam chests,
Westinghouse Pump and other appliances using steam will
be as dry as possible. Consequently the regulator valve,
through which boiler steam passes to the steam chests, is
situated in the dome.

The dome is also a convenient place for the safety valves to
be located.

What is the purpose of dampers?

Dampers are provided for the purpose of controlling the
admission of air to the under side of the firebed. They are
also used for the inspection and cleaning out of ashpans.

Chapter 11: - General Engine Questions and Answers

What is the purpose of the brick arch?

The brick arch acts as a baffle by protecting the tubes from
the cold draught of air that is drawn in through the fire door
when firing. It assists to prevent fine particles of fuel from
being drawn through the tubes and thus it also acts, to some
extent, as a spark arrester.

It aids combustion, by lengthening the path of the gases
from the firebed to the tubes and retaining the gases for a
longer period in the firebox, thus allowing more time for the
gases to mix with the air and ignite.

The brick arch also retains intense heat, which tends to
maintain a more even temperature in the firebox and
prevents sudden chilling of the firebox when the fire is
withdrawn.

Why are tubes provided in boilers?

The function of the tubes is to carry the smoke and gases of
combustion from the firebox to the smoke box and, in doing
so, to impart the intense heat to the water which surrounds
the tubes, thus giving a greater heating surface and causing
the steam to be generated quickly. On reaching the smoke
box, the gases pass to the atmosphere.

The tubes also act as stays for the tube plates.

What is the purpose of the safety valves?

The safety valves are for the purpose of releasing steam
pressure in the boiler when it rises above a predetermined
point, and they do this automatically under all conditions.
They are an adjustable spring loaded valve, their loading
being set by mechanical staff.

There are usually two or three safety valves situated on the
top of the dome.

Describe a locomotive boiler?

A locomotive boiler is a tubular boiler fitted with an internal
firebox. It has a cylindrical barrel with a smoke box at one
end and the firebox at the other. The firebox is constructed
with inner and outer walls, held together by stay bolts in a
manner, which permits water to circulate between the walls.

Chapter 11: - General Engine Questions and Answers

The walls are held together at the bottom by rive ts passing
through the foundation ring, i.e. the ring extending around
the bottom of the firebox. The crown sheet forms the top of
the inner wall of the firebox and is supported by stays
passing through threaded holes in crown sheet and outer
shell.

It is in this portion of a firebox that the most rapid
evaporation takes place. The lead plugs are placed in the
crown sheet, as this portion of the boiler is the first to be
affected by the fire when the boiler is too low in water.

The front inner wall of the firebox forms the tube plate, the
upper portion of which is drilled for carrying the tubes. The
tubes pass through the cylindrical barrel of the boiler, being
secured at the front end of corresponding holes in the front
tube plate. The tubes lead into the smokebox, which is
riveted to the front end of the barrel.

The front outer wall of the firebox, termed the throat plate, is
flanged and riveted to the barrel plate. This side outer walls
of the firebox form the casing or outer shell of the boiler.
The rear outer wall, termed the back plate, forms the end of
the boiler. In the back plate is the fire hole, which is the
opening through which coal is normally fed to the firebox.
The fire grate or the fire bars form the bottom of the firebox.

The heat and gases given off by the fuel in the firebox heat
the water circulating around the firebox and pass through the
tubes, heating the water surrounding the latter. The gases
are then carried into the smokebox and, after passing
through the spark arrester, escape up the chimney.

Removable plugs are fitted at suitable places on the boiler,
particularly around the firebox, to permit of the boiler being
kept clean and the water spaces kept free by washing out.

Refer to FIGURE 8 in Annex A.

What is the blower, and what is its use?

The blower consist of a copper tube connected to a steam
cock and extending along the outside of the boiler, then
entering the smokebox and terminating in a circle
surrounding the top of the blast pipe, where it is held in
position directly under the chimney. The circular portion of
the tube is banked off at the end and perforated with
numerous holes directly under the chimney.

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