1. The prelube pump turns on.
2. Oil is pulled from the engine's sump to the Prelube pump.
3. Pressurized oil fills the oil filter and begins to fill the passages within the engine.
4. Oil is forced into all the tight bearing clearances so they will be protected before the engine begins to move.
5. Oil pressure reaches the far side of the engine.
6. Pressure can be detected by ether a pressure gage or a pressure switch.
7. Pressure signals it's safe to start the engine ether manually or automatically.
8. The engine starts to turn and is instantly protected by oil.
9. Engine's own survice oil pump takes over oil pumping duty and prelube is shut down.