Pressure reducing valve at house connection defective?

I have the problem that my water pressure drops when I am already withdrawing water at one tap. I have 2 photos with and without water being drawn at a tap. I had a pressure reducing valve with a manometer installed on purpose.

How can this be, is the pressure reducing valve defective? Is the pressure from the valve too low?

Good morning

It is correct that static and flow pressure differ.
At the top of the pressure reducer, you can adjust the pressure on the outlet side.
If the pressure cannot be adjusted, the pressure reducer must be replaced.

Olli