Crankcase Explosion Relief Doors Operation
The crankcase explosion relief door should be made of as light a material as possible but still maintain its strength, and must be self-closing to prevent a backflow of air into the crankcase. This will certainly lead to further explosions, being much more severe than the initial one.
The relief door mounting frame is bolted onto the main door, the frame containing the components.
These consist of several layers of fine, medium, and course wire gauze stretched across the framework on the crankcase side, acting as a flame trap as opposed to the older type of relief door which had the flame trap on the engine room side. This has reduced the incidence of flames escaping into the engine room and being constantly sprayed with lube-oil has made it a superior flame trap.
A spring arrangement holds a light aluminum circular relief valve shut against a seat inside the frame. The valve face has an oil and heat resistant seal which prevents any ingress of oil to engine room during operation. The spring is set to lift at a few pounds. A rise in crankcase pressure above this will lift the valve, relieving the pressure, and immediately reseating to prevent any air being drawn into the crankcase. There is a deflector plate on the outer cover so that if the valve lifts any flames are directed downwards towards the engine room plates.
We shall now look at the operation of an oil mist detector…