Pressure Valve

Fig. 7 Pressure Valve:

The pressure valve, Fig. 7, closes the injection line off from the pump and has the job of relieving the injection line by removing a defined volume of fuel after the delivery phase. It also determines the precise point at which the injection nozzle closes at the end of injection. At the same time, stable pressure conditions between the injection pulses are created, regardless of the quantity of fuel being injected at the particular instant.
The pressure valve is a fluid-controlled plunger type, opened by fuel pressure and closed by its return spring. Between plunger delivery strokes it is closed; pressure line and distributor head outlet bore are thereby separated. During delivery, the valve is lifted from its seat by the high fuel pressure; fuel then flows via longitudinal slits into a ring groove and through the pressure-valve body, the pressure line and nozzle holder to the injection nozzle.
As delivery concludes (plunger cutoff bore opens), pressure on the high-pressure side falls to that of the pump cavity and the pressure valve is closed by its spring.