Oil Inlet Process:
After the cam's protrusion rotates past, the plunger moves downward under the spring force, creating a vacuum in the upper space of the plunger (called the pump chamber). When the upper end face of the plunger opens the oil inlet hole on the plunger sleeve, diesel fuel filling the oil passages of the upper pump body enters the pump chamber through the oil hole. The plunger reaches its bottom dead center, ending the oil inlet process.
Oil Return Process:
The plunger supplies oil upward. When it reaches the point where the inclined groove (stop supply side) on the plunger connects with the oil return hole on the sleeve, the low-pressure oil passage in the pump chamber connects with the central hole, radial hole, and inclined groove on the plunger head. The oil pressure drops sharply, and the delivery valve closes rapidly under the spring force, stopping the oil supply. The plunger then moves upward again. After the cam's protrusion rotates past, the plunger moves downward under the spring force, thus beginning the next cycle. A plunger pump operates on the principle of a single plunger. It has two check valves operating in opposite directions. When the plunger moves in one direction, a negative pressure is created inside the cylinder, opening one check valve and drawing fluid into the cylinder. When the plunger moves in the other direction, it compresses the fluid, opening the other check valve and expelling the fluid. This continuous operation creates a continuous fuel supply.
