Rotary car dumpers are massive rotating drums that can turn a train car upside down to unload contents. Most commonly used for unloading coal, rotary dumpers can unload any commoditity carried in a hopper or gondola car; coal, coke, ore, woodchips, and stone. Dumpers are typically found at power plants, steel mills, export piers, and other places where massive quantities must be unloaded quickly and efficiently.
The first rotary dumper was installed at Newport News, Virginia in 1895. The technology didn't become widespread until the 1970s however. Today, solid unit trains of coal cars are among the most common sights on the rails. While many railroads and utility companies prefer gondolas for these trains to cut maintenace costs (no moveable doors,) hoppers can also be dumped in rotary dumpers and offer more flexibility for serving older or smaller plants or if the rotary should fail.
Cars enter the dumper and are locked into place with strong clamps. The drum then rotates until the contents are spilled out and the car is righted. Some dumpers are large enough to handle two cars at once. Cars equipped with rotary knuckle couplers don't even need to be seperated as they pass through the dumper. A modern dumper can empty up to 125 tons of coal in under two minutes. An entire train can be emptied in a few hours.
Modeling this action can add a lot of excitement to a model railroad. Several manufacturers have offered working rotary dumper kits in different scales in the past.