PREVOST H3-45 2023 Operator's Manual page 84

4-28 Controls and Instruments
Rear Brake Air Pressure Gage (Primary System)
Indicates the rear brake air system pressure in psi. The normal
operating pressure is from 122 to 140 psi.
The low air pressure indicator LED on the gage and the STOP telltale
light illuminate when the rear brake air system pressure drops below
85 psi. An audible alarm will sound.
WARNING
The driver is responsible for monitoring the pressure as part of a
regular sweep of the instruments.
In the event of a pressure loss in the primary brake system, the drive
and tag axle service brakes will not function normally. It is critical to
bring the coach to a safe stop as quickly as possible.
If there is sufficient pressure in the secondary brake system,
modulated spring brake pressure (using the park brake chambers)
will be used to apply the drive axle brakes, proportional to the
braking pressure on the front axle. It must be noted this is an
emergency and a significant amount of secondary air pressure is lost
with each apply/release cycle. The spring brake modulation will only
function two or three times, depending on the amount of secondary
air pressure that was on hand when the primary brake pressure was
lost.
Once the secondary air pressure drops below 60 psig, the park
spring brakes are fully applied and cannot be released until pressure
is restored.
Do not drive the coach when the brake air pressure is low.
PA-1652 Operator's Manual H3-45 Coach
STOP telltale light