Delivery Valve Assembly

Fig. 8 Delivery Valve Assembly:

The delivery valve assembly, Fig. 8, relieves the fuel injection tubing and maintains a residual pressure in the fuel injection tubing.
The task of the delivery valve assembly is to separate the fuel injection tubing from the high pressure circuit and to relieve the fuel injection tubing. During delivery, the delivery valve is lifted off its seat by the pressure generated in the high pressure chamber. The fuel is delivered via the delivery valve holder and the fuel injection tubing to the injection nozzle. As soon as the helix of the pump plunger opens the spill port, the pressure in the high pressure chamber drops. As a result, the valve spring forces the delivery valve back onto its seat. The injection circuit and the high pressure circuit are thus separated until the next delivery stroke.
A part of the valve stem has the form of a piston and is ground into the valve guide. At the end of pump delivery this retraction piston first enters the valve guide and closes the fuel injection tubing from the pressure chamber above the pump plunger. Thereby the volume available to the fuel in the fuel injection tubing is increased by the swept volume of the retraction piston. The retraction volume is matched to the length of the fuel injection tubing and, therefore, the length of the fuel injection tubing must not be changed. In order to obtain a desired fuel delivery characteristic, torque control valves are used in special cases. They have an additional machined section on the retraction piston.
Relief throttles are used to reduce the HC share in the exhaust gas. An annular groove is located on the delivery valve holder for identification. The relief throttle is a reed valve with a 0.6mm orifice that opens in the direction of the injector.