Pump housing pressure acts on an internal timing piston (t), Figure 1, to partially advance the injection timing at
idle, and fully advance the timing when the engine RPM reaches approximately 60% of rated speed. As pump
pressure increases, timing advances.
The pump housing pressure is controlled by the pressure regulator valve (2) (a spring loaded slider valve). The
valve is shown in the open and closed position.
When housing pressure is low, the spring (3) forces the slider (4) into the closed position. This permits the housing
pressure to increase by preventing fuel drainage through the return passage (5).
As housing pressure increases, it forces the slider (4) to compress the spring (3). This action opens the return
passage (5) and relieves the housing pressure.
A relief port (6) located on the spring side of the slider valve, allows fuel that seeps past the slider (4) to drain. Relief
port drainage is necessary to avoid a hydraulic lock of the slider valve, which would render the pressure regulator
valve (2) inoperable. In fact, it is this characteristic that is used in conjunction with the KSB to advance the timing
during cold engine operation.