Went to the local dealership yesterday to return the injector/filter. While there one of the techs called me over to watch part of his online tech course. It was on the Duramax fuel system. I had been bugging him to find more information on the double fuel pump. He clicked on the fuel pump and I got to see an animated video of the pumps working. The LP is a small gear pump. The HP is an three cylinder axial piston pump. It is completely different that the HP hydraulic pumps I have worked on. It has three cylinders 120 degrees apart. The piston is solid steel and looks like a short fat bolt with no threads or flats. The large diameter is toward the centerline of the pump. There is a three lobe cam that that pushes the piston in the cylinder. Each piston is returned by springs similar to valve springs. There was an excellent photo of the whole assembly labeling the pumps and pressure regulator. We could not figure out how to print the photo. I wish I could download the video also. Later! Frank Edited by: Frank Blum

Hey Frank,


Good info. I wondered if the topic was ever going to resurface. Such a good thread we had going and then kappoot, just like that?


Anywho, previously I had mentioned the HP pump being like a Mazda rotory engine, your description summed it up perfectly. With the 3 cylinders phased 120 degrees. I really wish we could gain a more complete understanding of the lp interaction with the hp and also the regulator. This would tell us alot about the possible benfits of a lift pump and what size it should be. A more thourough understanding would also help justify or negate the need for an air separator.


BTW, the reason I understand what the pump resembles and really have no explanation of how it works is because I have only seen a diagram showing it being a 3 clyinder operation but no literature to explain the thinking behind it. I am in the dark. Frank I would be interested in any more info. you can skim from the dealer/trainer.

I'm sure someone has dissected one already. Maybe we'll really find out!