System Parts第 18 / 60 题
What is the trailer hand valve (trolley valve) used for?
a.To drain the trailer air tanks
b.To adjust the trailer brake slack
c.To release the trailer parking brakes
d.To apply only the trailer brakes
解析
The trailer hand valve, sometimes called the trolley or Johnson bar, applies only the trailer brakes. It should be used only for testing, not for parking, because trailer air could leak out and release the brakes. Using it for normal braking can also cause the trailer to skid.
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