When the camshaft rotates and the protrusion of the cam lifts the roller body, the plunger spring is compressed, the plunger moves upward, and the fuel is compressed. Some of the fuel flows back to the upper body oil chamber of the fuel injection pump through the oil hole. When the top surface of the plunger covers the upper edge of the oil hole of the sleeve, due to the small cooperation space between the plunger and the sleeve (0.0015-0.0025mm), the pump oil chamber at the top of the plunger becomes a sealed oil chamber. The plunger continues to rise, and the oil pressure in the pump oil chamber increases. When the pump oil pressure is greater than the spring force of the oil outlet valve and the remaining pressure of the high-pressure oil pipe, the oil outlet valve is pushed open, and high-pressure diesel enters the high-pressure oil pipe through the oil outlet valve and is injected into the combustion chamber through the injector.

The plunger supplies oil upwards. When the inclined groove (stop supply edge) on the plunger is connected to the return hole on the sleeve, the low-pressure oil circuit in the pump chamber communicates with the middle hole, radial hole, and inclined groove of the plunger head. The oil pressure suddenly drops, and the outlet valve closes flexibly under the action of the spring force, continuously supplying oil. Afterwards, the plunger still needs to move upwards. When the protrusion of the cam rotates slightly, under the action of the spring, the plunger moves downwards again. At this moment, the next cycle begins