The fuel pump is situated on top of the fuel injection and the exhaustion drive mechanism.
It takes directly of straight, back and forth movement of fuel side roller guide.
When it gets compressed the piston of engine reaches to top.
And once it is completely compressed, with the fuel injection nozzle, it exhausts fuel to the inside of combustion chamber that it make it to burst.
Block of the large low-speed engine for the ship. At the bottom camshaft is placed.

When engine starts up according to suction/compress/exhaustion, from the center of the clench; through the chain wheel cam; the camshaft wheels around. And when this happens, the fuel cam and exhaustion cam also starts up. And this rotation gets changed its moving into back and forth movement.
This pursuits Fuel Roller Guide to start up and the fuel pump to deliver the fuel to its nozzle.
The exhaustion Roller Guide opens up exhaustion valve and sends out gas.