A typical air compressor can produce air pressures of up to 500 psi (over 3,000 kPa), far higher than required for safe operation of the brake system. Therefore, an air compressor governor is employed to keep tank pressures within a relatively narrow range. When tank pressure rises to the “cut-out” level the governor prevents the compressor from pumping more air into the tanks. When the tank pressure falls to the “cut-in” level, the governor allows the compressor to pump air into the tanks again.