Parking brake pressure loss!!!

[BZRoamin24]

Can anyone tell me what the blue and red needle on the air pressure gauge for my 2004 international FE 300 bus signify. I need to pass a MD state inspection but failed for the parking brake pressure not holding. Replaced the parking valve, couple air fittings on the firewall, and both T fittings on the parking valve. Now the blue needle is holding at 115 psi but the red needle bled down to 30 psi over 24 hrs?

[TheHubbardBus]

Whether or not you still have a mechanical problem requiring immediate repair I couldn't tell you. Our bus bleeds down over 24 hours but it's still tight enough to easily pass pre-trip inspection. A near-future job, before we start travelling, is to find & eliminate even the tiniest sources of leaks. But for now it's roadworthy, at least according to the state.

What you do have for certain, however, is an educational problem. You need to educate yourself as to how the air brake system functions, how to perform a pre-trip inspection of the air brake system, what it means if you fail a portion of it, and most certainly what those needles mean. You can't just hop in a bus and drive it like a car. You need to understand how the system functions in order to use it properly & safely.

Just one link, but there are countless more resources out there. Please consider it a starting point.

https://cdlstudy.com/manuals/Air_Brakes.pdf

[Jolly Roger bus 223]

it should be if your blue needle is ahead of the red needle then your brakes release if good around 90 psi if you step on the brake and it goes to 60 or less then the capacity is not there yet in the brake tanks.
if you push your air brake valve in and it pushes back out then you do not have adequate air pressure for your brakes.
not just buses but everything i deal with is 60 low and 90 where that second needle starts passing it and if you hit the brake pedal and you get your alarm or the button pops then your brakes are locked until you build enough air brake pressure .