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Air Brakes · Air Brake System Components

What does the air compressor governor do in an air brake system?

1.It controls the compressor's on/off cycle, stopping it at a cut-out level and restarting it at a lower cut-in levelCorrect answer
2.It reduces air pressure delivered specifically to the front brakes whenever road conditions turn slippery or icy outside
3.It automatically releases air the instant tank pressure climbs above a fixed, pre-set safe limit value
4.It transfers air back and forth between the primary and secondary systems in every dual air brake setup

Explanation

The governor is what decides when the air compressor is pumping and when it idles: once tank pressure climbs to a cut-out level, around 125 psi, the governor stops the compressor, and once pressure falls back to a lower cut-in level, around 100 psi, it lets the compressor start again. 49 CFR 383.111(b)(1) requires CDL applicants to know general air brake system nomenclature, the required-knowledge area the governor falls under; the specific psi figures are the manual's typical settings, not a number stated in federal regulation. Reducing pressure to the front brakes describes a front brake limiting valve, a different and largely obsolete component, not the governor. Releasing air automatically above a safe limit describes the safety relief valve, not the governor. Transferring air between the primary and secondary systems does not happen at all: a dual air brake system deliberately keeps those two systems separate so a failure in one does not take down the other.

Source: 49 CFR 383.111(b)(1)

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