40 free practice questions for this exam, each with the reason for the answer and where to look it up.
10 questions, graded as you go, with the reason for every answer. No sign-up.
| Exam | CDL air brakes |
|---|---|
| Who runs it | State DMVs |
| Where | United States |
Question count, time limit and pass mark differ by where you take it. Check the official candidate bulletin from the organisation that runs your exam.
At about what tank pressure does the governor stop the compressor from pumping air (cut-out)?
C. 125 psi
The governor cuts the compressor out at around 125 psi. About 100 psi is the cut-in level where pumping starts again, and 150 psi is where the safety valve opens.
Reference: CDL Manual Section 5.1, The Parts of an Air Brake System
At about what tank pressure does the governor let the compressor start pumping again (cut-in)?
C. 100 psi
When tank pressure falls to about 100 psi the governor cuts the compressor back in. The 125 psi level is the cut-out point where it stops pumping.
Reference: CDL Manual Section 5.1, The Parts of an Air Brake System
Why must air tanks be drained?
D. Water and compressor oil collect in them
Compressed air carries some water and compressor oil, which settle in the bottom of the tanks. In cold weather the water can freeze and cause brake failure, so the tanks have to be drained.
Reference: CDL Manual Section 5.1, The Parts of an Air Brake System
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