[Difference?] Fuel Pump Pressure Regulator Vs Fuel Pump Actuator

The commonrail pressure relief valve is on the end of the rail. It's not called out on your diagram. It is located at the #16 relief valve drain line.

 

#12 is the outlets. If you are talking about #10 it controls the "medium" pressure" in the pump that feeds the HP pumping units. #11 controls amount of fuel entering the the high pressure pumping unit, this controls the effective stroke which controls amount and pressure of common rail.

 

I think the OP is asking if the Nexgen pump was dead headed before the commonrail, where would the fuel pressure relief? inside the pump? ....with no return.

I was going to dig further, busier than a 1 armed wall paper hanger at the moment.

 

Yes, the movement of the plunger. Here is description directly from Cummins of fuel flow which you may have already read.
A priming pump is used for priming the gear pump at start-up. The priming pump runs for approximately 60 seconds after key ON and any time the ECM detects engine speed of 400 rpm or less. Once the engine is started, the gear pump is able to maintain prime without any assistance from the lift pump.

Fuel flows through the priming pump to the gear pump. The fuel passes through a 4 micron, pressure-side filter. Filtered fuel is then fed to the high-pressure fuel pump through an 86-micron filter located in the pump body at the high-pressure pump inlet.

The high-pressure fuel pump head actuator housing contains an air-bleed fitting and fuel pump actuator. The air-bleed orifice fitting in the fuel pump head actuator housing aids in purging air from the fuel supply. Because of the air-bleed orifice fitting, some fuel supplied by the gear pump will return to drain at all times.

The fuel pump actuator is opened, or closed, by the ECM to maintain the appropriate fuel rail pressure. Fuel metered past the fuel pump actuator enters the high-pressure fuel pump inlet drilling, flows past the inlet check valve, and fills the pumping chambers. When the camshaft pushes the pumping plunger upward, fuel reaches rail pressure and causes the outlet check valve to lift. Fuel then enters the outlet drillings of the fuel pump and exits the high-pressure fuel lines to the fuel rail.

 

Still remember first time I dealt with common rail on an ISL. Truck died on road with low rail pressure faults. Had towed in. Started the troubleshooting and pulled head off the HP pump, and wow looked like a creek bed with the detonated ceramic plungers! I thought, ceramic really. This was prior to me replacing multiple Mack cams with ceramic lifters. Took Cummins awhile to wise up.