I think there is one more reason why gallery pressure may affect injection performance, and that is cavitation. Even if the supply pump provides sufficient volume to satisfy the injection pumps maximum delivery, if it cannot maintain sufficient pressure in the gallery the plungers may cavitate. The pressure in the gallery must be sufficient to fill the plungers quickly through the very small inlet ports while maintaining sufficient pressure within the plunger to prevent cavitation during filling.

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1987 W201 190D