In the early 1960's, my father bought a 20x60 stave silo with a P&D unloader, couple P&D elevators and a P&D auger bunk feeder.  

The auger feeder had a paddle on the end of the tube that would trip a switch when silage got to the end.  

The tube would then rotate one revolution, dumping the forage.  It would repeat this when the silage got to the switch again. 

The bunk was used to feed corn silage to the dairy herd.  The cows would get dry hay and grain while in their stanchions.

By the early 70's, the silo unloader was replaced with a Badger brand unloader.

Bill