Home » CDL Questions & Answers » What is a trolley valve?

What is a trolley valve?

ATTENTION!

The CDL test is hard. Set yourself up for success!

Order a CDL Cheat Sheet to help you pass.

  • Over 97% pass rate!
  • 100% money back guarantee if you don't pass.
  • Study on your computer, phone, or tablet anywhere, anytime.

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. 

More CDL Questions & Answers:

Air Brakes Questions & Answers

CDL Braking Questions & Answers

How should you drive a commercial vehicle in reverse?

What are CDL retarders?

What is a pre trip inspection?

What is a standee line?

What is another name for front end header boards?

What is the “crack the whip” effect?

What is the average driver’s reaction time?

What is the bridge formula?

What is the only way to sober up after drinking?

What must be included on your Individual Vehicle Distance Record (IVDR) or Driver Trip Report?

What should you do if you are being tailgated?

What should you do when driving on slippery roads?