The controls in the cab of a
steam locomotive can be very simple but as sophistication increases, the cab
can become a nightmare of pipes, controls and gauges; all of them very hot!
I shall describe the controls
of a basic steam locomotive. There is little standardisation of controls, so
a 'generic' description is given.
Usually, one will find a
column in the cab with a red handle mounted on top. By screwing down the
handle, the brakes are applied. The brakes can also be applied by steam.
There will be a brake lever in the cab. Progressive braking is effected by
the degree of movement of the lever.
Locomotives are usually built
with two sight gauges to allow for redundancy. These show the level of water
in the boiler through a special glass tube. As the water is under high
pressure, this tube is protected by very heavy glass in the event of fracture
of the sight glass. Above and below the sight glass are cut off valves which
can be deployed in the event of failure of the sight glass.
The rear of the sight glass
is fitted with a black and white striped metal sheet. The water in the sight
glass reverses the direction of the stripes due to refraction, which makes it
much easier to see the level. Some sight glasses may have a red line marked
on it which shows the minimum permissible level of water over the boiler
crown. This will vary due to the use of steam, but also when the locomotive
climbs or descends.
All steam needed for
equipment and controls is obtained from the manifold. It is situated over the
top of the firebox. A large valve is provided to shut of all steam should
leakage occur in any of the plumbing. The valve is usually placed so any
leakage will burn you when you shut this off!
Another essential item is the
steam gauge which is always prominently displayed. In the UK and the
USA, they have been traditionally marked in lbs per square inch. Sadly, more
gauges have caught the 'continental disease' and show steam pressure in bars.
Sadly, a bar is some bizarre form of foreign pressure measurement rather than
a place where one can seek sustenance!
Usually a second gauge is
provided which shows the steam pressure in the valve chests. This is very
helpful in controlling the locomotive smoothly and efficiently.
One valve will open and shut
a flow of steam to the blast pipe. This will draw the fire and is usually
used when a locomotive is having its fire made up when stationary.
Two injectors are fitted to
locomotives, one either side. There is a a gate valve to open the flow of
water from the tank and a valve to inject steam into the injector. Once water
is dropping from the injector body, the steam is switched on, and hopefully
the water is picked up and pushed into the boiler. Sometimes one has to mess
about with the valves until the injector picks up. As soon as cold water
enters the boiler, the steam pressure begins to drop.
The drain cocks at the bottom
of the cylinders are either operated with a mechanical linkage or by steam
pressure. Either way, there is either a lever or control valve in the cab.
This is the large lever
mounted at the back of the boiler. It will operate either side to side or
push/pull. These are quite stiff as the regulator controls a large valve
under boiler pressure. Usually one has to tap or nudge them in order to
gently open and close them. Below is a photo of a regulator handle on a GWR
This is usually a large lever
moving in the direction of travel, held in a notched frame. The centre
position is 'stop'. When a loco is started, the lever is moved fully forwards
or backwards which gives the greatest amount of steam pressure to the
cylinders. As the loco speeds up, the lever can be moved back towards the
centre. This increases the cut-off and saves on steam. Larger locomotives may
have a large screw rather than a lever.
Access to the fire is via a
door which generally slides open with a linkage that hopefully is not to hot
Apart from the whistle chain
hanging from the underside of the cab roof, these are all the controls of a
basic steam locomotive.
Further controls and gauge
appear with vacuum or air brake systems, gravity or steam sanding, electrical
generation and steam heating. The list of possible 'extras' is rather long!