BC Transit – Air Brake Course

Supply & Service Lines Crossed (no air in trailer reservoir)
With no air in the trailer reservoir, the trailer brakes are disabled. Now with the
lines crossed, the air from the trailer supply valve travels to the relay portion of the
emergency relay valve. Again, the emergency relay valve “tries” to comply with the
request for a brake application. However, the reservoir is empty, or contains very
little air pressure, so the trailer brakes now will not apply. A tug test would confirm
the lines were crossed since the trailer supply valve is open, the trailer is “charged,”
but the brakes don’t work.
Left click to start animation.
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