Numbers follow the federal CDL air-brake checks: the compressor builds 85 to 100 psi in 45 s, the governor cuts out near 125 psi, the low-air warning must come on before 60 psi, spring brakes apply between 20 and 45 psi (drawn at 35), and a combination vehicle may leak at most 3 psi/min parked and 4 psi/min with the brake applied. Test speeds are sped up where the badge shows ×. Your state's CDL manual is the authority: check it before relying on any figure here.