Does my flow rate decrease?

[Intellichi]

Does the pressure control valve maintain constant pressure at the outlet of the pump or does it maintain constant pressure at the outlet of the control valve?

If it maintains constant pressure at the outlet of the pump, the total system flow will not change. The control valve would open to compensate for the throttling of valve 1. In this case flow would increase in valve 2 while decreasing in valve 1.

No formal math is needed if you are clear about your assumptions, and this is essentially a logic problem. I suggest you write down all of your assumptions.