Crank Case Doors

I didn't know there was one.. Why would they need one? Does that happen all that often?

Crankcase explosions are not that common anymore as nearly all of these engines are fitted with crankcase oil mist detectors often set up to reduce engine speed automatically if oil mist is detected.

Crankcase relief valves or explosion doors (usually one per cylinder) open when the pressure in the crankcase increases and relieve the pressure via a flame arrestor into the engine-room. They close again immediately the pressure drops (either by dead weight or more commonly a coil spring) in order to prevent ingress of air.

Does not answer the OP's question as I can not remember the pressure at which they open and anyway it would be specific to different makers engines. It is very low, because the crankcase doors are large in area and will not withstand much pressure.

You don't bother to register, you don't bother to tell us what brand, size, model or service of use of the engine, AND, you expect a useful, informed answer?

Pardon me but I sense a hint of a certain problem here.

TT3

EMD crankcase pressure detectors can be checked for proper operation by removing the vent cap and attaching a hose to the vent fitting. Human lungs can create enough vacumn to set it off.

Donnie