Philip Marshall wrote: Apart from WW&F 9, the only other surviving narrow gauge locomotive with Eames vacuum brakes I'm aware of is Waynesburg & Washington 4 in Waynesburg, PA."
I have a couple of slides of #4's vacuum brake in action when Tim Sposato operated it after #4 was restored a number of years ago. Tim (who currently works with Mr. Jerry Jacobson at the Age of Steam Roundhouse in Ohio) may well be able to answer your questions about the vacuum brake system, since I believe he was the one who restored it.