Re: The Strange Story of Sumpter Valley Caboose #4 / U.S.A. Caboose #909

To add to the confusion, Wabco did later make an "ABC” brake valve. This was an attempt to convert existing AB valves which were ring and piston to the current diaphragm design which began with the ABD which eliminated most of the issues with leakage and sticky Pistons. As I recall, it only was on the service portion.

I only ever saw one of them which was incomplete when I was working at an air brake shop. I was able to obtain it for Dave Garcia. Evidently the ABC never gained favor with the railroads to convert too many, likely to the lack of sufficient economic benefit.

Upgrading valves to a newer design wasn't unheard of. Many quick action triples were converted to K type. Most 6 distributing valves were upgraded to 6E.