Bendix Commercial Vehicle Systems BA-921 COMP - Manual (Page 4)

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Bendix
®
BA-921
®
Compressor Installation and Application Review
Section III Vehicle/Engine Requirements and Expectations
Life expectation (in hours or miles): _________________________________
Duty Cycle expectation (percent time compressor operates loaded):
5% to 25%
greater than 25%
Duty cycle is considered the percentage of time that the compressor is operated in the
loaded (pumping) condition. To calculate duty cycle, the total loaded time is divided by
the total operating time of the compressor.
Maximum charge time should not exceed 90 seconds.
Charge duration is the amount of time the compressor runs continuously. Discharge
temperature rises while the compressor is loaded so the longer the compressor runs the
higher the discharge temperatures. Keeping the charge times low helps to minimize
discharge temperatures, hence, reducing carbon formation. In addition, the air dryer can
only process a limited amount of air before requiring a purge cycle. Minimizing the
charge time reduces the burden on the air dryer.
Recommended Test Procedure:
Note: The test conditions should be indicative of worse case conditions for the vehicle’s
vocation (i.e highway use versus city use).
Install a pressure switch (60 - 90 psi) in the governor signal line. Record the switch
voltage or continuity during vehicle operation. The duty cycle is the quotient of the
compressor loaded time (low pressure in the signal line) and the total time. Alternate
methods to measure the duty of the vehicle can be utilized; for example, a pressure
transducer installed at the unloader port of the air dryer with a data logger to collect the
data.
The duration of the test should reflect the typical operating cycle of the vehicle. The
duration of the vehicle test should be 1 to 3 days minimum. For vocation that exhibit
large amounts of braking (i.e. city use); one day is adequate. Under conditions with less
braking (i.e. highway use), the duration should last at least 3 days.
Was duty cycle measured? NO
YES Measured value: ______________%
Average charge time during test _______________________________
Maximum charge time during test _________________________________
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