I re-read my post and I did a poor job in answering a question, I come across as a complete A** Hole!! Sorry that I did not fully answer your question --- if I could cut/paste on this forum I'd supply the exact info. Let me see if I can do a better job (I don't consider myself as a complete AH <grin>
So here goes (and others, please feel free to jump in --- this is how I do it on both my bus and truck).
Chock the vehicle to prevent it from rolling!
Fully charge the air system -- (125#)
Turn off engine, release parking brake and time air pressure drop. Should not be more than 2# in 1 minute. (note: my truck failed this when one air brake canister was leaking)
Apply service brake (brake petal) (90# on brake application gauge if your vehile has this feature). After initial pressure drop - time for 1 minute -- no more than 3# should be lost. (note that these figures are for truck only -- not truck with trailer with air brakes)
Turn key "ON". engine "OFF". Rapidly depress the brake petal up/down while observing the air gauge. Warning light/flasher/buzzer (whatever your vehicle might have) should come on when pressure reaches 60#.
Continue the rapid on/off of the brake petal while observing the air gauge. The emergency parking knob should pop out when air pressure is between 20 - 40 #.
Start engine and observe how fast the air pressure builds up. Should reach 85 - 100 in about 45 seconds. This depends on vehicle, number and size of air tanks, etc.
There are also checks for the governer cutin/cutout pressure.
It takes less time to do the test than it does to read it. But I'd recommend getting the straight info that is available in various Drivers License Manuals.
Hope this helps.
Also it is good to note your vehicle has three brake systems:
Service (foot petal)
Parking (pull out knob)
Emegrency (knob comes out when air pressure is between 20 - 40#