(1) MPROP (rail pressure control valve)
• The MPROP receives fuel from the feed pump and feeds fuel toward the plungers of the supply pump in such a quantity that the fuel pressure (target common rail pressure) corresponds to that required by the engine electronic control unit.
• When the MPROP is not operating, i.e., when current is not flowing, fuel flows at its maximum rate. When current flows, the piston in the MPROP is pressed down such that fuel is not fed toward the plungers.
• The engine electronic control unit controls the ratio of current-off time (duty ratio).
(2) Zero delivery throttle
• A small amount of fuel can flow through the MPROP (rail pressure control valve) to the plunger even when the MPROP reduces fuel flow to the fullest extent. To stop the fuel feed to the plunger, the zero delivery throttle is opened to return fuel to the feed pump, causing the fuel flow for the plunger to reach zero.
(3) Overflow valve
• The overflow valve opens when the pressure of the fuel sent from the feed pump exceeds the predetermined level to return the excess fuel to the inlet side of the feed pump. The fuel which has overflowed enters into the eccentric drive shaft chamber to lubricate the parts in the chamber.
(4) Flow control valve
• The flow control valve diverts the excess of fuel sent from the feed pump into the eccentric drive shaft chamber for the part lubrication.