A rotary car dumper or wagon tippler (UK) is a mechanism used for unloading certain railroad cars such as hopper cars, gondolas or lorries (tipplers, UK). It holds the car to a section of track and rotates the track and car together to dump out the contents. Used with gondola cars, it is making open hopper cars obsolete. Because hopper cars require sloped chutes in order to direct the contents to the bottom dump doors (hatches) for unloading, gondola cars have a greater volume.

[edit] Overview

Originally, individual cars would be decoupled and placed in the dumper, but now it is possible to dump an entire unit train of coal without uncoupling any of the cars. The cars used for these trains are equipped with rotary shaft tightlock couplings (AAR Type F) on one end. The end with the rotary coupler is marked with a colored stripe, typically white, red or yellow. The dumper rotates the cars on the axis of the couplers.

Rotary dumping of cars provides a number of advantages. Firstly, rotary dumping eliminates the wasted volume under the sloping bottoms of a traditional hopper car. Secondly, a unit train of coal (100 cars) can be unloaded in approximately two and a half hours using a rotary dumper. Bottom dump cars require much longer to unload, partly because the area for the coal to flow out is less than one quarter of the footprint of the car and partly because the coal handling equipment is normally sized for the lower possible rate. Another advantage of rotary dumping is that loads that have gotten wet and/or frozen can still be unloaded quickly. A frozen load of coal in a "bottom dump" car has to be thawed out to be emptied. Since railroads charge demurrage for not unloading cars quickly, a frozen load represents an unwanted expense. However, most methods to thaw the car quickly in freezing weather present safety hazards including setting the coal on fire. The reduced labor, demurrage, and risks from thawing frozen loads offset the higher equipment cost of a rotary dumper at somewhere around a unit train per week.

Sometimes rotary dump cars are coupled in fixed pairs so that they are unloaded two cars at a time.

[edit] Alternatives

Alternatives to the rotary dump cars are bottom dump cars with bottom doors, and back end hoes which unload gondola cars. The former has the disadvantage that any imperfection in the seals of the doors allows material to spill onto the track.

[edit] See also

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