Cylinders, Pistons And Valve Gears Move Steam Locomotives
Walschaerts Valve Gear one of six solutions to controlling steam!
Ever wonder why the all that steam comes out of the locomotives cylinders when starting at the station?
This is a function of steam pressure and the amount of steam let into the cylinder slide valve. In a reciprocating steam engine, the slide valve moves back and forth over the piston by admitting steam to the front end of the cylinder and then to rear in a continuous motion. At the end of the piston stroke, the valves shifts and opens to allow the remaining steam (spent steam) to escape.
This is the “choo, choo” sound you hear when the train starts to move at the station. Maximum steam pressure being released after each stroke of the piston. The steam escapes out of the top of the smoke stack along with gases and smoke from the boiler. Excess steam is also allowed to escape from the cylinder overflow valves as well.
The Walschaerts valve gear was invented to control the amount of steam being let into the pistons of the steam locomotive. The Walschaerts valve allowed the engineer to apply maximum steam when starting the locomotive from a standstill at a station and then dial back the amount of steam needed when the train reached desired speed.
Other valves used to control steam on locomotives include:
- Stephenson valve
- Baker valve
- Southern valve
- Young valve – used with single compression locomotives such as Big Boy
The cylinders are designed to handle tremendous amounts of steam pressure generated by the boiler. Let us know if you have ever built your own miniature steam locomotive! We would love hear about your experience.