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What is a trolley valve?


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The trolley valve, or trailer hand valve or Johnson bar, operates the trailer brakes on a combination vehicle. 

The trolley valve should only be used when testing the tailor brakes, and should never be used while driving. 

If you use the trailer hand brake while driving, you can cause the tailor to skid. 

While driving, your foot brake will send air to the trailer brakes, which reduces the chances of a skid versus if you were to operate the trolley valve on its own. 

You should also avoid using the hand valve for parking as it may cause the air to leak. 

Use wheel chocks to stop the trailer from moving if it is not equipped with spring brakes for parking. 

You can find more information about this topic in the Combination Vehicles (6) section of your official driver’s handbook. 

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