Volkswagen 1.9-Liter TDI Owner's Manual page 23

The injection cam has a steep leading edge
and a gradual slope to the trailing edge.
As a result of the steep leading edge, the
pump piston is pushed down at high
velocity. A high injection pressure is
attained quickly.
The gradual slope of the cam trailing edge
allows the pump piston to move up
relatively slowly and evenly. Fuel flows into
the pump/injector high-pressure chamber
free of air bubbles.
Pump Injection System
Roller-Type
Rocker Arm
Injection Cam
Roller-Type
Rocker Arm
Injection Cam
Pump
Piston
SSP209/016
Pump
Piston
SSP209/017
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