Commercial Driver Handbook ( PDF ) - California Department of ...

*Applied Leakage Test
With a basically fully-charged air system (within
the effective operating range for the compressor),
turn off the engine, release all brakes so the entire
system is charged. Allow the system to settle (air
gauge needle stops moving), apply firm, steady
pressure to the brake pedal (brake on), and hold.
After the system settles again, time for one minute.
The air pressure should not drop more than:
— 3 psi for single vehicles.
— 4 psi for a combination of two vehicles.
— 6 psi for a combination of three or more
vehicles.
An air loss greater than those shown indicate a
problem in the braking system and repairs are
needed before operating the vehicle.
Note: You must be able to demonstrate this test and
verbalize the allowable air loss for the examiner
on this test.
If the air loss is too much, check for air leaks and
fix. For testing purposes, identify if the air loss
rate is too much.
*Air Compressor Governor Cut-Out
Pressure Test
To perform this test, the air pressure for the vehicle
must be rising when the engine is running. Run the
engine at a fast idle. The air compressor governor
must cut-out prior to the needle reaching 130 psi.
Where the needle stops rising is the governor
cut-out pressure.
For testing purposes, identify where the air
governor cuts out the compressor and verbalize
the maximum pressure at which this can occur.
Note: The air dryer exhausting should not be
referenced as governor cut-out.
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*Air Compressor Governor Cut-In Pressure
Test
To perform this test, the air pressure for the vehicle
cannot be rising when the engine is running. With
the engine idling, slowly pump the brake pedal
to reduce the air tank pressure. Watch the air
pressure gauge between pumps to identify when
the compressor cuts in (needle starts to rise). This
should occur no lower than 85 psi.
For testing purposes, identify where the air
governor cuts in the compressor and verbalize the
minimum pressure at which this can occur.
*Low Air Pressure Warning Device Test
This test may be performed with engine on or off.
To perform the test with the engine off, turn the
electrical power on and have enough air pressure
to keep the low air pressure warning device from
coming on. Slowly pump the brake pedal to reduce
air tank pressure. The low air pressure warning
device must activate between 55 and 75 psi. For
testing purposes, identify when the warning signal
activates, and verbalize the legal range in which
the signal must activate.
If the warning signal does not work, you could
lose air pressure and not know it. This could cause
sudden emergency braking in a single circuit air
system. In dual systems the stopping distance will
be increased. Only limited braking can be done
before the spring brakes come on.
*Check that the spring brakes come on automatically.
Chock the wheels. Release all parking
brakes and shut the engine off. Pump the brake
pedal to reduce the air tank pressure. The trailer
air supply valve knob should pop out when the air
pressure falls to the manufacturer’s specifications
(usually in a range between 20 to 45 psi). This
causes the spring brakes to engage. Some trailers
use an air applied emergency brake system and
some trailers use spring brakes as the emergency
brake system.