The needle valve body and needle valve are also a pair of precision parts that have been researched and matched. There are four nozzle holes with a diameter of 0.35mm on the nozzle head, evenly distributed, and the spray angle is 150°. There is a flange on the upper part of the nozzle, which is pressed onto the lower end of the injector body with a nut. The connecting plane between the nozzle and the injector body has been carefully ground to maintain oil tightness. There is a positioning pin on the plane at the upper end of the nozzle and the injector body to ensure that the two oil passages match, and the oil passage leads directly to the pressure accumulation chamber of the nozzle. The lower end of the long needle valve has a tapered surface, which is located on the needle valve seat in the fuel injection nozzle. Just on this valve seat are the four nozzle holes mentioned above. The small cylinder at the upper end of the needle valve is inserted into the hole at the lower end of the ejector rod. The spring tension at the upper end of the ejector rod presses the needle valve against its seat, closing the nozzle hole.

When the fuel injection pump presses high-pressure fuel into the pressure accumulation chamber below the nozzle through the pipe joint and the slotted oil filter element, the oil pressure increases. Due to the pressure of the fuel on the cone surface at the lower end of the needle valve, an axial force is formed, which strives to lift the needle valve. When the fuel pressure increases to overcome the elastic force of the pressure regulating spring, the needle valve leaves the valve seat and fuel is injected into the cylinder from the four injection holes at high speed. When the fuel injection pump stops supplying fuel, the oil pressure in the fuel injector drops, the needle valve falls back to the valve seat under the action of the pressure regulating spring, and fuel injection stops immediately.