Fuel injection pump oil and pressure oil, by plunger in the plunger sleeve in the reciprocating movement to complete. When the plunger is located in the lower position, the plunger sleeve on the two oil holes are opened, plunger sleeve cavity and pump body of the oil channel, fuel quickly filled with oil chamber. When the cam top to the wheel body of the wheel, the plunger will rise. Move upward from the plunger to the end of the plunger until the oil hole is blocked. During this period of time, because of the movement of the plunger, the fuel is squeezed out of the oil chamber and flows to the oil path. So this lift is called a pre stroke. When the plunger blocks the oil hole, it starts the oil-pressing process. Plunger line, oil indoor pressure increased sharply. When the pressure exceeds the spring elasticity of the delivery valve and the upper oil pressure, the top of the valve is opened, and the fuel is pressed into the tubing to be sent to the injector.