Rotary car dumper

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 rail 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 allow cars to be shorter, thus lowering their center of gravity, while carrying the same gross rail load.

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 AAR Type F rotary couplers on one end, with this end generally indicated with contrasting paint color. The dumper rotates the cars on the axis of the couplers. The cars must all oriented the same way, failure to do will result in a broken coupler when the dumper rotates.

Rotary dumping of cars provides a number of advantages and disadvantages:

• Rotary dumping eliminates the need for maintaining the additional components of a traditional hopper car, such as hopper doors and door locks.
  • While Hopper cars may be used in rotary service, they are occasionally first converted into Bathtub Gons
• Rotary dump installations are generally associated with faster train unloading times, although this time varies widely depending primarily on the ability of the system to remove product once dumped.
  • A unit train of coal (perhaps 100 cars) can be unloaded in approximately two and a half hours using a rotary dumper.
  • Some older rotary dumpers require that cars be separated, significantly reducing efficiency.
  • Some newer rotary dumpers may be capable of dumping two cars at a time.
  • Hopper cars bottom-dumped individually may take 2-3 minutes per car for freely-flowing product, not including thaw time.
  • Hopper cars bottom-dumped over a trestle may see the entire train emptied as quickly as 4 minutes
• 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 holding cars beyond an arranged time period, a frozen load represents an unwanted expense.
  • Most methods to thaw the car quickly in freezing weather present safety hazards, including setting the coal on fire.
  • Thaw sheds may cause significant damage to the cars themselves, such as melting rubber air brake components and burning paint.
• Unfortunately, poorly designed or poorly maintained rotary dumpers can significantly reduce the serviceable life of a car.
  • Most rotary dumpers do not provide a full bearing surface on the side of the car, resulting in bent side stakes.
  • Rotary dumpers set too far from the side of the car results in a shock load when the car is rotated, particularly when the product is frozen together.

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.

See also