Air tank pressures unbalanced and Parking break question

If he got you for the yellow button he erred. Red button different ball game.

 

Bert it is very respectable that you are trying to do everything to be safe. A company I worked for in the 80's had button poop out pressure test on all their service inspection sheets. May have meet the same inspector SNOWWY did.
Now why are-were parking brake valves supposed to pop out? Air brake vehicles did not always have spring parking brakes. If one was parked on a grade in neutral it would roll away when it ran out of air. If all the air was lost it had totally no slowing down other than the engine and tranmission or ditching it. Some terrible accidents happened and the first recourse was to have the park brake valves poop up at low air pressure. That stopped the vehicle while there was still enough air to do so. The parking brakes were also air applied. The second was probably the tractor protection valve. If the trailer became disconnected an air line would be dumping air. That valve automatically shuts that air off.
All modern trucks and trailers have spring parking brakes, even Old Blue to the left. If your truck runs out of air you are going to stop. Just maybe not when and where you want to.
So who decides when these old rules are out dated, should not be enforced or rewritten?
Some of the newest trucks around here have the most uneven air pressure, from low air, build up I have ever seen.
Thanks dibstr. I am a little behind on those rules. Are you able to do one of those fancy click here to the rules or just post where to find them? Thanks for the information even if you cannot.

 

You can start here. 49 CFR 571.121 - Standard No. 121; Air brake systems.

 

I got shut down for the same thing.....VA scale on 81 long time ago.... Mechanic came out and changed my tractor protection valve.... on the back of the truck where the air lines plug in and begin to run under the truck..

 

Ok...so here in WA state the low air warning should come on at or above 60psi. The valves should pop around 40 psi. They both don't need to pop at the same pressure and your 20 psi would be acceptable as close enough to 40psi.