Over-Boost Protection
The 300 series is equipped with an over-boost protection circuit, consisting of a pressure switch, switch-over valve and wiring. When boost pressure exceeds 16 psi (1.12 kg/cm2 ), the pressure switch closes, grounding the switch-over valve.
The valve vents manifold pressure which would otherwise affect the aneroid compensator on the injection pump. This reduces the quantity of fuel injected and the engine speed.