thank you "Gary?" for your reply. I'm going to take some more time to review the drawings but wanted to thank you for your interest and help right away.
Unfortunately my German is weak and the drawings do not illustrate the particular Vetus pumps I have. I do have the drawings and model numbers etc but can not share them now as I am only barely computer literate.
I can say that the non return valves are integral and that there are no adjustment points or check valves external to the pump.
I saw the pump in its disassembled state and the only operator service point is the top of the reservoir.