A pressure control valve (PCV) for controlling rail pressure can be located at one rail extremity (pump-external PCV), Figure 1, or at the pump outlet (pump-integrated PCV), Figure 2. The pump-external PCV leads to lower pump manufacturing costs but the proximity of the regulator to the injectors can introduce additional disturbances in injector dynamics. In the pump-integrated PCV solution, the fuel throttled by the control valve joins the leakage flow from the pumping chambers as well as the fuel flowing in the pump’s cooling and lubrication circuits. This combined flow is discharged from the pump to return to the fuel tank.
Figure 1. Common rail diesel fuel injection system with pressure control valve located on the rail
Figure 2. Bosch CP1 pump with integrated pressure control valve
Rail pressure control with a PCV is inherently fast because of the proximity of the system input (PCV) and system output (rail pressure sensor). In other words, the system does not include the delay resulting from fuel passing through the high pressure pump as would be the case for some of the pump metering approaches.