Fuel pump -Constant pressure or constant volume?

[danalinscott]

A fundamental disagreement has ocurred which a search of this forum did not provide the definitive answer for. Maybe someone here can settle it.

On Mercedes diesel engines is the fuel pump (not the Injection pump) a constant voume or constant pressure design?Or were there two differnt plunger type fuel pump used?

One of our (VO conversions) fourm members seems to believe that the fuel pumps on MBs use a cam to push a constant volume of fuel to the IP..the other that the cam merely provides for make up fuel and the internal spring provides a constant pressure to the IP.

Here are the actual description of the individual with the "constant volume" opinion.

The Benz pumps I've seen are basically a siringe.... that is operated by a cam in the IP... it bolts to the side of the IP... the cam preforms the function of compressing the piston (pushing out the fuel) ... a spring returns it for another push... check valves make sure the suction pulls from the suction side ands discharge goes to the dscharge side...

And heres the link to the discussion itself.

If anyone can settle this definatively it would be of immense help.
Thanks.