Because It's Friday

Ex-C&O 1309

1309 is a Mallet, a compound locomotive; the steam from the rear cylinders exhausts to the front cylinders in normal operation. Mallets were heavy freight locomotivesand, as such, were usually rather slow in speed.

Observe where the connecting rods are coupled to the wheels. They are near the rim, in order to exert the most torque on the wheels and axles. Locomotives that were built for speed have their connecting rods fitted very close to the axle.

You can also see that the front set of cylinders are much larger, because they are working with lower-pressure steam. Simple articulated locomotives, like the Big Boy, had steam from the boiler going to all cylinders.

There was a lot of experimentation with compound-cylinder lcomotives from around 1880 through 1930. There were locomotives that had both a high-pressure and a low-pressure cylinder driving a sngle crosshead (the driving rod connected the crosshead to the main driving wheel and the connecting rods). They suppposedly achieved quite a fuel savings, but at the cost of higher maintenance and parts wear (the forces could never seem to be balanced on the crossheads).

Superheated steam proved to be a better solution. Compund locomotives disappeared from all but the mountain coal-hauling railroads, like the Norfolk & Western and the Chesapeake & Ohio, where the ability to pull heavy loads uphill at lower speeds was prized. On those two roads, the Mallets served to the end of the steam era.