Delivery valve Above each pump element is a delivery valve consisting of a valve housing 5 and valve piston 4. The valve piston is held against its seat 3 by a spring 2. The delivery valve opens and releases fuel into the delivery pipe when opening pressure is attained in the pump element. When fuel pressure drops after injection, the valve piston is forced back against its seat by the spring. When the delivery valve piston has closed, the available volume for the fuel in the delivery pipe increases. This lowers the pressure in the delivery pipe and injectors, reducing the risk of fuel dripping from the injectors. The change in capacity is adapted to the length of the delivery pipe and this length must never be changed. The delivery valve is held in the pump housing by the delivery valve holder 1, which is bolted to the housing from above.
1. Delivery valve holder 2. Valve spring 3. Valve seat
4. Valve piston 5. Valve housing
A) Closed B) Injection Delivery valve holder with delivery valve
Single-speed engines have delivery valves of 0-hole type, i.e. without idling hole.
Certain types of engine have delivery valve holders with a relief brake to counteract delivery pipe cavitation. When injection starts, the spring-loaded valve plate 3 is lifted and the fuel flows freely to the injector. At the end of injection, when the injector closes, a pressure wave is generated in the opposite direction. The valve plate is then pressed against its seat by the return spring 2 and the fuel flowing back is forced through the valve plate’s restrictor hole.
A) Delivery valve with idling hole B) Delivery valve without idling hole
1. 2. 3. 4.
A
B
Delivery valve holder Compression spring Valve plate Valve housing
Delivery valve holder with return restrictor hole