System PartsQuestion 18 of 60
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
Explanation
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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Related questions on this topic
- What is the purpose of the slack adjuster?
- What controls the parking brakes on a vehicle with air brakes?
- Why should you NOT use the parking brakes if the brakes are very hot, such as after coming down a steep hill?
- Why should the trailer hand valve NOT be used for parking?
- What is a one-way check valve used for in an air brake system?
- On many air brake vehicles, what is the purpose of the safety relief valve on the first air tank?
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