Spring brakes will automatically engage when air pressure drops to between:
a.60 and 80 PSI
b.20 and 45 PSI
c.100 and 125 PSI
d.5 and 10 PSI
Explanation
Spring brakes are held in the released position by air pressure. When air pressure drops to between 20 and 45 PSI, the springs are strong enough to overcome the remaining air pressure and apply the brakes automatically.