This is written like Richard Ehrenberg writes and just like him, it only tells part of the story.
True, the 4 wheel drum cars do NOT have a proportioning valve but they DO have a distribution block where all the lines converge. To some, they might think these are the same thing.
Telling the story in better detail, one should elaborate by also saying that the distribution block may appear similar, internally it is different and has no proportioning function to it at all.
