Pressure Control Valve
The pressure-control valve is connected through a passage to the upper (outlet) kidney-shaped recess, and is mounted in the immediate vicinity of the fuel-supply pump. It is a spring loaded spool-type valve with which the pump’s internal pressure can be varied as a function of the quantity of fuel being delivered. If fuel pressure increases beyond a given value, the valve spool opens the return passage so that the fuel can flow back to the supply pump’s suction side. If the fuel pressure is too low, the return passage is closed by the spring.
The spring’s initial tension can be adjusted to set the valve opening pressure.