System Parts第 7 / 60 题

Spring brakes on a truck are held in the released position by what?

a.Air pressure
b.Hydraulic fluid
c.Engine vacuum
d.Electrical current

解析

Spring brakes use powerful springs to apply the brakes, and air pressure holds those springs back so the brakes stay released while driving. If air pressure is lost, the springs push the brakes on automatically. This provides an automatic safety braking feature when air is lost.

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