Wish i knew the correct name for those old style air brakes, someone looking might know though. L26 or R23 something like that. Newer style automatic air brake go threw these settings starting at released, initial, service zone, full service, supression, handle off, and emergency. Running with the old style that was on the SW units i ran went starting from release, lap, service zone..... i dont even think they had supression, maybe they did though, handle off, then emergency. So on newer style brakes when you move from the release position to initial or all the way to full service nothing else is required to hold and maintain the air you have set (unless the pressure maintain feature is bad, then you move it into the PASS postion). On the older style you would come out of intial past the lap position into the service zone till you've drawn off the amount you want, then shove the hand back, into lap, or it would continue to suck the air out of the cars, crappy crappy set up. Even in lap it would blead off and set more air. We use to come off some scare hills with Hazmat cars at the plant. Keeping her at 10 was nearly impossible, you had two choices, tip toe off the top, let her rock and roll till you got close to the bottom and then use the air, or scream off the top with a couple pounds set hold her in the 8th run and you might make the bottom without having to kicker off. I had my share of rides in the cab and riding the last car. I had to do the moves up on the caustic hill that first time i got to play hoghead all by myself. So steam if you heard a hog complain about the air on those older SW locomotives you know what there talking about.