BENDIX BW2764 Dépliant

1.  Chock the vehicle wheels.  Start the engine and charge the air brake system to 

governor cut-out, around 130 psi.

2.  The primary or secondary air gauge should start to rise.  As the pressure in one 

gauge reaches 110 psi, it may stop and the other gauge will start to rise.   As the 
second gauge reaches 110 psi, both gauges will begin to climb to 130 – 140 psi 
(due to the inaccuracy of the gauges) and stop.  The air dryer will then purge.  
Note that at the end of the purge cycle if the air dryer exhibits fl uttering, perform 
the unloader leakage test on the compressor, per the manufacturers guidelines, 
before continuing. 

3.  Shut off the engine and push in the yellow button to release the parking brakes.  

Note that the gauges will drop a small amount.  Check the air gauges.  If either 
gauge indicates a continued loss of pressure, check the system for leaks.

4.  Apply and hold the service brakes by fully depressing the brake pedal,  the gauges 

will drop a small amount and again check for a loss of pressure by watching both 
gauges.   If either gauge indicates a continued loss of air pressure, check the 
system for leaks.

5.  Release the service brakes.  Continue to apply and release the service brakes 

until the pressure drops below governor cut-in (approximately 100 psi).

6.  Start the engine and charge the air brake system again.  Turn the engine off.

Note:  The pressure protection valves in the Bendix

®

 AD-IS

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 air dryer help 

protect the  air brake system in the event that one circuit leaks.  If the pressure 
protection valves are functioning properly and one circuit leaks, the other circuit  
will not drain below 70 psi.  To verify that the pressure protection valves are 
working properly, perform steps 7 through 9 in the Pressure Protection Valve 
Test to the right.   The pressure protection valves are not serviceable and 
if found to be not functioning properly, the AD-IS air dryer must be 
replaced.

7.  Locate and manually drain a reservoir.  While this reservoir is being drained the 

other reservoir will start to lose pressure, but must stop showing a pressure drop 
when the pressure is above 70 psi.  If this reservoir continues to show a drop in 
pressure below 70 psi, the pressure protection valve located in the AD-IS air dryer 
is determined to be not functioning properly therefore, the AD-IS air dryer must 
be replaced.  

Note:  Although it is not required, a check valve may be located in the supply line 
of the secondary reservoir.  If a check valve is in the supply line to the reservoir, 
this reservoir will remain at full system (approximately 130 psi) pressure when the 
other reservoir is manually drained.  To properly test the pressure protection valve 
the reservoir check valve must be removed.  Note:  If check valves are installed  
in both the primary and secondary reservoirs, there must be at least one (600 in.

3

minimum volume) reservoir without a check valve connected to one of the four 
pressure protection valves in the AD-IS air dryer.

8.   Start the engine and charge the air brake system again.  Turn the engine off. 

9.  Repeat steps 7 and 8 manually draining the other (not previously drained manually) 

reservoir.  If a pressure protection valve is found to be not functioning 
properly when testing either reservoir, the AD-IS air dryer must be 
replaced.

Bendix

®

 AD-IS

®

 Air Dryer System

BW2764 © 2010 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse Group • All Rights Reserved • 8/10 • 

Printed on recycled paper

Bendix

Primary Reservoir

Secondary Reservoir

Compressor

To Accessories

AD-IS

® 

Air Dryer

Possible Single 

Check Valve 

(not required)

WARNING:  Be sure to follow all the General Safety Guidelines 

outlined in the Bendix

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  AD-IS

®

 Service Data Sheet, SD-08-2418, 

before performing any service on the air brake system.