What's a steam engine?
And how do you operate a steam locomotive? An explanation using models from the Deutsches Technikmuseum
By German Museum of Technology
Deutsches Technikmuseum 2019
Dampflokomotive Gattung S 3 mit Schnellzug (1908) by Werner HubertGerman Museum of Technology
Steam locomotives played an important role for railways and in the modern world. Their impressive appearance and movement and their noise and smell were fascinating. Young boys wanted to be locomotive drivers. Steam locomotive were ubiquitous.
Dampflokomotive Gattung S 3 "Erfurt 208" (around 1905)German Museum of Technology
There were over 1000 examples of class S 3 locomotives like this one from the Prussian State Railways. In use from 1893 to 1927, this is the most widely produced series of German express railway locomotives ever.
Konstruktionszeichnung zur Dampflok Gattung S 3 (1903) by Königlich Preußische StaatseisenbahnenGerman Museum of Technology
The locomotives were the result of knowledge developed over decades: every screw of this complex technology was well thought out and was constantly refined by operational experience.
Underframe of an express steam locomotive, Class S 3, 1:5 scale model Express steam locomotive, Class S 3, Side view 1 (on the right) by Clemens KirchnerGerman Museum of Technology
Knowledge about steam locomotive technology was a widely taught subject right from the start. Many of the model railways from around 1900 were built specifically for this purpose. They continue to impart that knowledge today.
Tank locomotive, class T 4.2, "Breslau 1458", 1:5 scale model Tank locomotive, class T 4.2, Side view from the front right at an angle. by Clemens KirchnerGerman Museum of Technology
How exactly does a steam locomotive work?
A steam locomotive actually works like a water kettle on the kitchen stove. The kettle is heated by a fire. The water boils and becomes steam.
Tank locomotive, class T 4.2, "Breslau 1458", 1:5 scale model Tank locomotive, class T 4.2, Detail view of locomotive cab 3 (on the left) by Clemens KirchnerGerman Museum of Technology
In contrast to a stove, the fire is not beneath the water kettle (boiler) but instead on one of its ends in the so-called firebox. It juts into the driver's cab.
The fireman in the cab tends the fire by adding fuel through the firebox door. The fuel was usually coal.
Tank locomotive, class T 4.2, "Breslau 1458", 1:5 scale model Tank locomotive, class T 4.2, Front view by Clemens KirchnerGerman Museum of Technology
The fire's heat is conducted through the water-filled boiler in boiler tubes (flues). The tubes taken together have a much larger surface than a simple plate, as in a stove. This allows the water to be heated up to 180-200°C an evaporate.
The flues end at the front of the boiler in the smokebox. The exhaust smoke and the remaining heat of the fire are diverted from here out through the chimney.
Underframe of an express steam locomotive, Class S 3, 1:5 scale model Express steam locomotive, Class S 3 by Clemens KirchnerGerman Museum of Technology
The hot steam now contains the energy of the fire. It is under high pressure - in the S 3 up to 12 bar. The steam is conducted into the locomotive's actual power unit, the steam engine with cylinders.
Underframe of a passenger train steam locomotive, Class 3.1, 1:5 scale model Passenger train steam locomotive, Class 3.1, Side view 1 (on the right) by Clemens KirchnerGerman Museum of Technology
Cylinders are tubes that are closed on both ends. There is a piston in every cylinder. It is a disc that fits exactly in the cylinder and can move back and forth.
Underframe of a passenger train steam locomotive, Class 3.1, 1:5 scale model Passenger train steam locomotive, Class 3.1 by Clemens KirchnerGerman Museum of Technology
In some models, the cylinders and pistons are schematically cross-sectioned, so that the functional sequences are clearer:
The hot steam is let into the right side of the cylinder. ...
... the inflowing steam pushes the moveable piston in the direction away from the steam since the cylinder is closed on all other sides. ...
... The movement of the piston is transmitted to the piston rod. ...
Underframe of a passenger train steam locomotive, Class 3.1, 1:5 scale model Passenger train steam locomotive, Class 3.1, Side view 1 (on the right) by Clemens KirchnerGerman Museum of Technology
... From the piston rod, the movement is transmitted via a bearing called a crosshead to the connecting rod. …
The connecting rod finally transmits the movement via a bearing to the wheel, which is then set in motion (rotates). This is how the longitudinal movement of the piston is converted into the rotational movement of the wheel.
This principle is simple. It gets a little more complicated when the piston has reached the end of its movement in the cylinder. One stroke of the piston only moves the locomotive a small distance.
Underframe of a passenger train steam locomotive, Class 3.1, 1:5 scale model Passenger train steam locomotive, Class 3.1 by Clemens KirchnerGerman Museum of Technology
The piston must also go back again if a continuous rotation of the wheel is to be achieved. For this, the steam must now be fed into the other side of the piston. The piston then moves in the opposite direction.
This constant rerouting of the steam inlet and outlet, and thus the piston movement, is carried out in a steam locomotive by a mechanism called the valve gear. A schematic view of part of this mechanism is shown here.
Underframe of a passenger train steam locomotive, Class 3.1, 1:5 scale model Passenger train steam locomotive, Class 3.1 by Clemens KirchnerGerman Museum of Technology
The valve gear continually follows the movement of the piston and by doing so ensures that the steam alternately flows in and out in front of and behind the piston.
Underframe of an express steam locomotive, Class S 3, 1:5 scale model Express steam locomotive, Class S 3 by Clemens KirchnerGerman Museum of Technology
The valve gear can be set in such a way that the relationship of the steam inlet and the steam outlet is exactly the opposite. The locomotive then travels in reverse. In terms of its effect, a valve gear is similar to a gearshift in the car.
Underframe of an express steam locomotive, Class S 3, 1:5 scale model Express steam locomotive, Class S 3 by Clemens KirchnerGerman Museum of Technology
The valve gear is controlled by a reversing lever in the driver's cab. Here the device is set for moving in reverse. Forward position means forward travel. When set in the middle or zero position, no steam flows to the inlet and the locomotive stands still.
Vorführung auf dem Führerstand einer Dampflokomotive Gattung S 3German Museum of Technology
The man at the cab controls has his right hand on the reverse lever. The left is touching the regulator. The regulator is the actual steam valve and comparable to a gas pedal: If you open it too fast when starting, the wheels of the locomotive will spin freely.
Führerstand einer Damflokomotive Gattung S 3German Museum of Technology
Finally we will take a look at the cab of the steam locomotive.
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There are further operating controls besides the valve gear and the regulator that are important for safe operation of a steam locomotive.
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The most significant unit in the driver's cab is the inconspicuous water level gauge. It shows how much water is in the boiler. If there is too little water, the boiler cooling will fail, the firebox walls will melt because of the 1100°C heat of the fire, and it will explode.
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Accidents like that are usually fatal. For this reason there is a second safety feature on the opposite side: The water level can be checked with three different faucets, even when the gauge on the left is defective.
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The manometer shows the pressure in the boiler. While it should not be above 12 bars for the S 3, the T 4.2, a smaller locomotive for secondary lines, had an operating pressure of 10 bars.
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The brakes are another important element. They are activated by the locomotive driver by means of the brake valve. Brakes in railways are still operated with air pressure to this day and brake all the wheels of the train simultaneously.
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The fireman stands next to the driver in the cab. His place is on the left. He not only provides enough coal for the fire, but also controls the supply of new water in the boiler by means of pumps.
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Last but not least is the steam whistle. The distinctive warning signal and sign of life on every steam locomotive is triggered by a pull rod on the ceiling of the cab.
Employees of a railway workshop in Leipzig (1911)German Museum of Technology
Are you ready for a trip on a steam locomotive from the 1900s?
Curator: Frank Zwintzscher
Producer: Bettina Gries
With photographs by Clemens Kirchner
and 360° photographs by Manuel Dahmann
Historical footage: Deutsches Technikmuseum, Historical Archive
Videos: Smidak Filmproduktion
Technical support: Jannes Repke
Translation: Barry Fay
Special thanks to: Michael Bergmann, Helen Böhland, Maria Borgmann, Karsten Fuchs, Alexander Glowasz, Mario Günther, Carsten Hein, Jürgen Heinrich, Gianna Hidde, Joseph Hoppe, André Ilausky, Marcel Jahre, Steffi Jira, Lars König, Thomas Krüger, Sabine Pakusa-Lerch, Klaus Marzik, Patrick Mehnert, Christopher Meyer, Lars Quadejacob, Arnfried Rohde, Marcel Ruhl, Dietmar Ruppert, Stefan Schleyer, Jörg Schmalfuß, Patrick Schönenberg, Konrad Simon, Stefan Soos, Tanja Sprang, Sandra Stahl, Matthias Stier, Antje Stritzke, Tatjana Teller, Philipp Wolff, Michael Wölfle, Ivo Woutskowsky and Tiziana Zugaro.
