Yanmar 4TNV98 Service Manual page 176

Regulating Valve
Figure 7-8
The regulating valve regulates the fuel feeding
pressure of the feed pump so that the fuel pressure
in the pump chamber is maintained within the
specified pressure range.
When the injection pump revolutions increase to
increase the fuel feeding pressure of the feed pump,
the fuel compresses the regulating valve spring to
lift the piston. The fuel is then returned to the
suction side as shown by the arrow in the figure.
It is therefore possible to regulate the pump
chamber pressure by changing the set force of the
regulating valve spring.
Figure 7-9
4TNV98 & 4TNE98 Diesel Engine
Figure 7-9 shows typical relationships between
pump revolutions and pump chamber pressure. The
hydraulic timer directly uses the pump chamber
pressure for controlling the injection timing.
174
Section 4. Fuel System