Page 198 - Personnel Policy and Procedures Manual
P. 198
Page 2 of 2 Air Brakes
TEST LOW PRESSURE WARNING SIGNAL - Shut TEST AIR LEAKAGE RATE -
the engine off when you have enough air With a fully charged air system
pressure that the low pressure warning (typically 125 psi), turn off the
signal is not on. Turn the electrical power engine, release the service brake,
on and step on and off the brake pedal to and time the air pressure drop.
reduce air tank pressure. The low air The loss rate should be less than 2
pressure warning signal must come on psi in one minute for single vehicles,
before the pressure drops to less than 60 psi less than 3 psi in one minute for
in the air tank (or tank with the lowest air combination vehicles. Then apply
pressure, in dual air systems). 90 psi or more with the brake
pedal. After the initial pressure
If the warning signal doesn't work, you drop, if the air pressure falls more
could lose air pressure and you would not than 3 psi in one minute for single
know it. This could cause sudden vehicles (more than 4 psi for
emergency braking in a single circuit air combination vehicles) the air loss
system. In dual systems the stopping rate is too much. Check for air
distance will be increased. Only limited leaks and fix before driving the
braking can be done before the spring vehicle. Otherwise, you could lose
brakes come on. your brakes while driving.
CHECK AIR COMPRESSOR GOVERNOR
CHECK THAT THE SPRING BRAKES COME ON CUT - IN AND CUT - OUT PRESSURES -
AUTOMATICALLY -
Chock the wheels, release the parking Pumping by the air compressor
brakes when you have enough air pressure should start at about 100 psi and
to do it, and shut the engine off. Step on stop at about 125 psi. (Check
and off the brake pedal to reduce the air manufacturer's specifications.)
tank pressure. The "parking brake" knob Run the engine at a fast idle. The
should pop out when the air pressure falls to air governor should cut -out the air
the manufacturer's specification (usually in compressor at about the
a range between 20 -40 psi). This causes manufacturer's specified pressure.
the spring brakes to come on. The air compressor at about the
manufacturer's specified pressure.
CHECK RATE OF AIR PRESSURE BUILDUP - The air pressure shown by your
With the engine at operating RPM, the gauge(s) will stop rising. With the
pressure should build from 85 to 100 psi engine idling, step on and off the
within 45 seconds in dual air systems. (If the brake to reduce the air tank
vehicle has larger than minimum air tanks, pressure. The compressor should
the buildup time can be longer and still be cut-in at about the manufacturer's
safe. Check the manufacturer's specified cut-in pressure. The
specifications.) In single air systems (pre pressure should begin to rise.
1975), typical requirements are pressure
buildup from 50 to 90 psi within 3 minutes
with the engine at an idle speed of 600 -
900 RPM.
If air pressure does not build up fast enough,
your pressure may drop too low during
driving, requiring an emergency stop. Don't
drive until you get the problem fixed.
All Rights Reserved – As approved by the Commission on 05-07-2019 198 | P a g e
