Tuning of primary loop valves in primary/secondary loop setup?

Al Roethlisberger

So, adding a primary/secondary loop adds a little complexity to the design I am considering, which is OK.

In some of the diagrams I've seen for the primary loop, two valves are located in the loop. These seem similar to the two valves on a "passive" bypass loop, which I've read that one manually adjusts to maintain optimal primary loop temps.

What I am unsure of is if these valves perform a similar function on a primary/secondary loop setup with a circulator.

One valve is located on the bypassed loop back from the boiler supply to the return to mix in the hot water, and the second valve goes from the boiler output to second Tee to the supply of system. I assume one manually tunes these two valves "once"(I hope) to achieve an optimum boiler water temp then leaves them alone?? If so, how does one "tune" them?

Or are these valves just for service and left "wide open" for the primary loop when in operation? These two valves are one area that doesn't seem to be covered in depth in Dan's books.

Thanks Al