RCO Training – Mechanical Practice Test

When crankcase pressure becomes positive, protection is provided by the Crankcase Overpressure Protective Device (EMD). This device is wired into the engine protection system and is specifically designed to sense a rise in crankcase pressure above ambient. If the pressure goes positive, it triggers a shutdown to prevent damage to seals, gaskets, and bearings, and to avoid oil leaks or other failures that could occur from overpressure. Other systems are about different conditions: the engine governor controls speed, not shutdown due to crankcase pressure; the low oil device reacts to insufficient oil pressure; dynamic brakes handle braking, not engine protection. So the protective device for crankcase overpressure is the one that trips the engine when crankcase pressure becomes positive.