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Fireman's duties
The fireman's main job is to ensure a steady supply of steam at the appropriate pressure to provide power to the engine. This is much more difficult than it sounds. The engine's steam requirements vary considerably according to the load it is pulling, and the gradient. The fireman has to predict the steam requirements for some distance ahead, and adjust the fire accordingly. Some of the more important controls on the fireman's side of the footplate are shown in the image below.
Controls on the fireman's side of the footplate. Not visible in
the photo, because they are down by the floor, are the injectors and
damper control (see text for details). The small platform above
the firebox door is the warming tray, used for keeping lubricating
oil liquified, and for keeping the crew's tea warm
In order to provide steam, there must be sufficient water in the
boiler. When the engine is cold, the boiler can be filled with
water at ordinary pressure. However, when the engine is running
the boiler will be under considerable pressure. To fill the boiler
requires the use of injectors. Injectors utilize the
energy generated by the sudden contraction of cooling steam to
drive water into the boiler against its pressure. To power the
injectors a supply of steam is required. Larger engines had two types
of injectors: live steam, and exhaust steam, injectors. A live steam
injector was powered by steam from the boiler itself, while an
exhaust steam inector is power by steam exhausted from the pistons.
Exhaust steam injectors are more economical to run, but do not
work when the locomotive is standing still (because there is
no exhaust steam).
The water level in the boiler must always be kept within
well-defined limits. If there is too much water, there will not
be space for the steam to develop. If too little, there is
a risk that the firebox crown (i.e., the top) would recieve
insufficient cooling, and melt. To determine the water level, the
fireman uses a sight glass mounted on the back of the
boiler and connected directly to it. His aim is to keep the
water level visible in the sight glass. Water will be consumed more
rapidly when the loco is working hard.
The fireman must also ensure that the steam pressure in the boiler
is maintained within working limits. This is done by adjusting
the height of the fire. To raise the fire, the fireman can
add more coal (up to a point), and/or increase the flow of
air through the firebed. Air can be drawn in through the firebox
door, which is also used for loading the firebox with coal.
When the firebox door is open, a greater volume of air can
be drawn through the fire, increasing combustion. Most locos
also have an adjustable damper which regulates air
intake through the front of the firebox. Using the coal
depth, firebox door, and damper, the fireman adjusts
the rate of combustion in accordance with the required
steam pressure. When the loco is moving, airflow through the
fire can be much greater than when it is stationary. In addition,
airflow will vary according to whether the loco is running
forwards (`chimney first') or backwards (`cab first').
If a greater airflow is required when the loco is stationary
(when building up steam at a station, for example), the blower
can be opened (see below).
Part of the fireman's skill is to be able to anticipate changes to
steam requirements, and adjust the fire height in advance.
It takes some time for pressure to raise, even with the fire
roaring, so steam cannot be generated on demand. It can be
embarrassing to run out of steam half-way up a hill.
Driver's duties
The driver is responsible for controlling the speed and direction of the locomotive. This control is achieved using the regulator, reversing gear, and brake.
Controls on the driver's side of the footplate. Not visible in
the photo, because they are down by the floor, are the rail sanding
gear and cylinder drain cocks
(see text for details)
The regulator is the `throttle' of the locomotive; it controls
the delivery of steam from the boiler into the cylinders. With the
regulator fully open, a high volume of steam is admitted, and maximum
power may be generated. However, the cylinder power is influenced by
the reversing gear. This control adjusts the proportion of
the piston stroke for which the steam valves are open into the
piston. It also controls whether steam is admitted in front or behind
the piston, thus controlling the direction of travel.
For maximum power, the regulator needs to be fully open and
the reversing gear fully forward or fully reversed. In practice,
both the reversing gear and the regulator contribute to the power
generated by the piston, and thus to the speed of the locomotive.
If the regulator is closed, the loco will gradually come to a halt.
However, all locos will have additional braking capacity, provided
either by mechanical or vacuum brakes, or both. Passenger locos
mostly used vacuum brakes, with the coaches and the engine on the
same vacuum circuit. A vacuum brake was released (that is, not
braking) by holding the braking system at a vacuum. If the vacuum
was destroyed (by admitting air to the system), the brakes are
applied. This system offers significant safety advantages over
mechanical or pressure operated brakes. In particular, if a leak
develops in the system, it will tend to stop the train. In addition,
if part of the train becomes decoupled, the rush of air into
the brake hoses will immediately apply the brakes on both parts
of the train.
As well as controlling the speed and direction, the driver has
numerous other controls to be concerned with. The drain cocks
allow condensation to be drained from the cylinders. Typically
the drain cocks are opened whenever the loco comes to a stop, and
remain open for the first few yards of motion. Water is not
particularly compressible, and if it condenses in the cylinders,
the motion of the piston will probably cause considerable damage.
The driver also has controls to deposit sand on the rails. This
improves traction between the wheels and the rails, particularly
on hills. The blower allows steam from the boiler to blast
directly up the chimney. Although this is wasteful of steam, it
has the effect of drawing a strong stream of air through the fire,
increasing its combustion rate. The blower is particularly important
in tunnels, to counter the back-pressure caused by the sudden
obstruction of free flow from the chminey. In some cases this
back-pressure could be large enough to `lift' the fire, that is,
raise it from the firebed. If the firebox door was open, there
could be a flashback onto the footplate, with catastrophic results.
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