or decrease? and to be clear, since we are closing the control valve and therefore restricting flow, wouldnt the liquid pressure up before the control valve?
A pressure control valve is a pressure regulator. Its basic requirement is the input pressure must be higher than the output.
It automatically adjusts flow to maintain a steady output pressure.
It is not something you shut or open, but just adjust output pressure (if meant to be variable).
Most are set for a particular out pressure, and sealed off at that.