282OPERATION
ParkingBrake/TrailerSupplyValves
Trucks/Tractorsmayhavetwoaircontrolvalvesontheinstrumentpanel:
•TrailerSupply(redoctagonalknob)
•SystemPark(yellowdiamondknob)
W5001116
TheSystemParkvalveknob(yellow)shouldbepushedinrst,aftersufcientair
pressureisbuiltup(applyfootbraketopreventvehiclefromrolling).TheTrailerAir
Supplyvalveknobmaythenbepushedin.
TheTrailerAirSupplyvalveknobandSystemParkvalveknobwillautomatically
popoutifthesystempressure(bothfrontandrearcircuits)dropsto170to240kPa
(25to35psi).Thetractorprotectionvalvewillthenclose,thetractorspringbrakes
willapplyandthetraileremergencysystemwillbeactivated.