User:Colin Douglas Howell/Galleries/Planet and other similar 2-2-0s of the 1830s
From Wikipedia, the free encyclopedia
During the early to mid 1830s, the 2-2-0 became the most popular configuration for British and European passenger locomotives.
The cylinder layout of Robert Stephenson's 0-2-2s had serious drawbacks. With the cylinders at the rear next to the firebox, and the driving wheels at the front, the driving wheels only supported a minority of the locomotive's weight, which limited the tractive force available. This was further aggravated by the fact that when the locomotive pulled a train, its front end could be lifted by the force on the drawbar, reducing traction even more. The solution was to move the driving wheels to the rear and the cylinders to the front. This layout was adopted by most later steam locomotives.
The other problem with the cylinder arrangement on the Stephenson 0-2-2s was that they had cylinders outside the frames together with a short wheelbase. This combination allowed the alternating piston thrusts to easily torque the locomotive left and right, producing a "boxing" serpentine motion. To counter this, Stephenson and many other British builders adopted cylinders placed inside the frames driving a crank axle. With inside cylinders, the lateral lever arm of the piston thrusts was shortened, reducing the left-right torques and the locomotive's tendency to "snake".
Another major reason for the adoption of inside cylinders was that it insulated the cylinders within the hot smokebox, reducing heat losses from radiation. This significantly improved the engine's efficiency.
This altered arrangement of rear driving wheels with inside cylinders was the defining feature of Stephenson's next major locomotive class, the Planet, and gave rise to the popular 2-2-0 type.