The delivery valve is mounted on the distributive head of injection pump. The valve spring and delivery valve are mounted in the delivery valve holder. The surface of the delivery valve seat is made with high precision.
The delivery valve closes the fuel line quickly at the end of fuel injection in order to keep the residual pressure inside the injection pipe. At the same time, the fuel is drawn back in allowing the injection nozzle to snap shut, thus preventing fuel dribble (dripping).
(1) Start of fuel injection
<1> The highly pressurized fuel from the injection pump is sent to the delivery valve before injection.
<2> The highly pressurized fuel pushes the delivery valve to open the fuel line.
<3> The highly pressurized fuel is sent into the injection nozzle.
(2) End of fuel injection
<1> Pumping from the injection pump ends, and the fuel pressure lowers.
<2> The delivery valve is pushed back by the valve spring.
<3> The delivery valve returns until the valve face adheres the valve seat.
<4> The above process ensure a sudden drop in pressure inside the injection pipe. The nozzle needle then draws back the fuel, which would otherwise be fuel dribble. (3) Keeping airtightness (keeping residual pressure and preventing reverse flow) Airtightness (for keeping residual pressure and preventing reverse flow) is maintained by the valve seat and the surface of the delivery valve. If the pressure inside the injection pipe after the fuel injection is low, the fuel volume is decreased. Because the injection pressure does not reach quickly if the pressure inside the pipe is low. Therefore, it is necessary to keep the pressure constant inside the injection pipe all the times.