Correct gov cut-in psi.

I think it's 100.

 

Have you respectfully asked the instructor for clarification, and shown him/her the guide?

 

Go by what the book says ,that's the number the DMV will use.

 

It should be in the Commercial Handbook DMV prints out, makes a pdf of, etc.

 

This is for 'motorcoaches' I couldn't find anything for trucks.

Air compressors typically have a "cut-out" pressure between 110 psi and 130 psi and a "cut-in" pressure about 20 psi lower. Air pressure build-up from 85 psi to 100 psi should take 45 seconds or less

 

Cut-in: 85psi minimum
Cut-out: 130psi max
Blow-off: 150psi
Low air warning: 55-75psi
Auto application: 20-45psi

Leak down static(1min);
Single: 2psi
Combo: 3psi
Doubles/triples: 5psi

Leak down applied;
3
4
6

Build-up:
85 to 100 in less than 45 seconds.

TA

 

The correct cut in PSI is 100. It is stated clearly several times in the CDL manual. Cut out is 125 PSI.

The only time 85 PSI is mentioned is when you check the compressors refresh rate, which should be from 85 to 100 PSI within 45 seconds for a dual air system. This has nothing to do with governor cut in and cut out pressure.

150 PSI - Safety Valve
125 PSI - Governor cut out
100 PSI - Governor cut in
60 PSI or above- Low pressure warning
20-45 - Emergency (spring) brake activation.

The examiner is an idiot....they usually are.

 

I expect low air warning when both or either P and S reach 60 and fall through.

I expect the compressor to wake up and get to work feeding tanks at 85 or higher. 100 is outstanding. I love to keep as much as I can get into those tanks. Never know when you can use them. I have had several real world problems of air loss and failure of braking systems in my time out there. Everyone of those events demanded me to write my own book on how to get out of the situation safely before the spring brakes clamp everything down.

Tests are difficult. Learn the book for your location and parrot it. When you get assigned a truck and be on your own you will discover that all trucks have a certain amount of... personality in regards to air and everything else.