The delivery valve closes off the high pressure line from the pump. It has the job of relieving the pressure in the line by removing a defined volume of fuel upon completion of the delivery phase. This ensures precise closing of the injection nozzle at the end of the injection process. At the same time, stable pressure conditions between injection pulses are created in the high-pressure lines, regardless of the quantity of fuel being injected at a particular time.
The delivery valve is a plunger-type valve. It is opened by the injection pressure and closed by its return spring.
Between the plunger’s individual delivery strokes for a given cylinder, the delivery valve in question remains closed. This separates the high-pressure line and the distributor head’s outlet-port passage. During delivery, the pressure generated in the high pressure chamber above the plunger causes the delivery valve to open. Fuel then flows via longitudinal slots, into a ring-shaped groove and through the delivery-valve holder, the high-pressure line and the nozzle holder to the injection nozzle.
As soon as delivery ceases (transverse cutoff bore opened), the pressure in the high-pressure chamber above the plunger and in the high pressure lines drops to that of the pump interior, and the delivery-valve spring together with the static pressure in the line force the delivery-valve plunger back onto its seat again.
Distributor head with high-pressure chamber
1 Control collar, 2 Distributor head, 3 Distributor plunger, 4 Delivery-valve holder, 5 Delivery-valve.