Thank you both for the replies.
Waine,
I didn't realise that on your photo of the KD brake systems there were no AB valves. It is just after your explanation and reading the link you posted that I realised my mistake.
Ed,
The sketches you posted support Wayne's explanation very well and I am now well informed about brake systems used in the era I am modeling.
For the last fifteen years of modeling, I have not been much concerned about brake systems on the cars I assembled or bought RTR. It is just after building a few Tichy Train Group kits that I realised that there was some points there.
I just acquired a Sylvan Scale CNR caboose kit and I am preoccupied to build it as true to prototype as possible, such my interest in brake systems. Those cabeese were equipped with AB brakes.
Once again I realise that those MR forums are an invaluable source of information.
MR,
Thank you for letting us use those resources.
Guy
Modeling CNR in the 50's
I came across a few sketches that support Wayne's explanation and serve as a good visual reference:
The above diagram shows KC combined thype K triple valve and type C brake cylinder.
The KD features the detached type D Brake cylinder. Shortcomings of the type K valve brought about the type AB valve which, in it's day, must have seemed like a huge improvement. The improved "quick service" feature was instrumental in allowing the longer and heavier trains to be controlled.
There have only been relatively minor improvements since the introduction of the AB control valve in the early 1930s.
Here's a handy NMRA data sheet explaining some air brake developments BUT check some of the facts. I see in the chronology table they attribute the development of the AB valve to 1871, that seems a bit early!
http://www.nmra.org/sites/default/files/d9o.pdf
Regards, Ed
Guy, the AB brake was an improved version, and separated the components into three basic parts: the AB control valve, at top in the photo below, the air reservoir, below the frame, and the brake actuating cylinder, at right.
As on most of my rolling stock, most of the piping has been eliminated, as it's not all that visible with the car right-side-up and on the layout.On the real system, there were five pipes connected to the control valve, with two of them connected to the reservoir, one, as shown, to the cylinder, one to the train air line, and one to the retarder, usually located near the brake wheel on the car's end.The AB valve offered quicker brake application than previous designs and more control over the braking process.
There's a diagram HERE which should explain things more fully.
Wayne
In a thread published a few days ago,
http://cs.trains.com/mrr/f/13/t/260275.aspx
doctorwaine explained the difference between KC and KD types brake systems. After looking at some model cars, I wonder what is the difference between KD-type and AB brakes?