Steam locomotive throttle question

[North Dakota Train Guy]

Thanks for your answer. When I look at the picture with magnification, as well as some other reading I have done, I can understand what you told me and how it works. Thanks for your help and reply.

[Wizlish]

What, no comments?

It's the kind of throttle that is pivoted vertically on the engineer's side, hanging down "like a grape vine", as compared with the horizontal throttle found on most locomotives with dome throttles.

The arrangement optimizes connection to the side-of-boiler linkage that goes to a typical front-end throttle.

[North Dakota Train Guy]

I just finished Trains "611 In Steam" publication about the Norfolk & Western Class J No 611. There were several references in the magazine about a "Grapevine Throttle", what is it and how does is work?