jelle

It sits in the train station and every once in a while goes wooOOP followed by a low pitched "growl" sound.Thanks-

jelenaj

whooooooooo

JeffTheGodOfBiscuits5930

Seems likely to be the main air compressor kicking in, I would think.

jehen

Yep. Air compressor. 10 pts for the gent above.

jeffs2861

Yep, bleeding off excess air from air lines for brakes and other auxiliary. Some thing on other vehicles with AB. You can still see the claw marks on the street when My air bus air brakes released air when a cat ran in front of bus stopped at light. Poor thing probably never crossed a street again.

jehen

I got here too late. But yes, it's the air compressor. The brakes operate on compressed air, and the engine also has a compressed air holding tank. When the air pressure drops to a certain level, the compressor refills the tank so that air is available. The compressor is driven by the motor, or engine, and is engaged by a pneumatic (what you heard) clutch.