If you are a museum, it moves the needle toward "that which is correct for the car". However if it's a daily runner, you have to face the decision of whether you want to wear the remaining life out of the historic fabric (original parts).

If the coaches are not part of your core museum collection, and are just random coaches for Thomas to pull, then I'd say ABDfoo, as maintenance is practicable. Ditto if you are subject to FRA. Service interval on passenger brakes is like 15 months give or take; freight valves are 25 years.

I know much hand-wringing is made of different types of brakes interacting in-train, but think at railway museum speeds, this can be easily compensated with correct train handling. The main thing is that if you attempt graduated (fractional) release, the freight brakes will full-release, and ABD+ valves will "help" release more than you wanted to. So - don't use graduated release!

I'd say that if "historical accuracy" isn't important, then I'd go with ABDW, especially if our Federal friends are involved. Given the wide usage, parts and changeout valves are readily available and economical. Maintenance intervals are 2,208 days (6 years) which is about as good as it gets (49 CFR 238.309 which is good industry practive or longer under Appendix B to 49 CFR 232 if you follow the trail).

As far as a test stand, I'm not sure I'd bother obtaining and setting one up, unless the historical collection acquisition budget is footing the bill. I have always figured having a receipt from an AAR approved air brake shop is a handy thing to have in your hip pocket should somebody ask...

G.F.Payne
Baltimore, MD