What is the purpose of a double rotary coal porter?

[ouengr]

Recently I have seen several ads for the models of a double rotary coal porter. My understadning is that the prototype for this car has roatry couplers on both ends of the car. Does anyone know excatly what this car is used for? How many are used in a train? Any assistance will be appreciated.

[Jordan6]

This might help ya

http://www.deluxeinnovations.com/rolling/rollingtub01.html

[CShaveRR]

That's one possibility.

If you're going to keep the train intact while dumping, you have to have a rotary coupler next to the locomotive. So now, with distributed power, what if you have a locomotive at each end? Somewhere in the train, two non-rotary couplers would have to be tied together. Unless you had a car with rotary couplers at each end!

(A dumper capable of unloading two cars at a time would render unnecessary the double-rotary cars, and the need to keep all cars oriented in the same direction. You'd still need to have rotary couplers next to the locomotives, though.)

[sd90macphII]

It is still a FRA rule violation to couple rotary couplers together on cars equiped with a rotary on one end and a standard nonrotary on the other.

[CShaveRR]

It may be a violation, but I see it fairly often around here--some trains have quite a few; others are "clean". That would suggest to me that the company that unloads the cars is somehow involved in this.