A reduction in orifice size results in decreased flow as only so much liquid can pass through the orifice. In all of the above cases, the inlet pressure is constant and the outlet pressure is, effectively, zero (atmospheric) as there is nothing to restrict flow on the exit side of the orifice.

Does pressure reducing valve affect flow rate?

You may need a bigger meter or increase pipe size from 3/4 to 1"..... As Mike was saying, the PRV will limit pressure, but does not significantly limit flow rate (GPM).

Does increasing water pressure increase flow?

The amount of water passing through a pipe at any given time is described as water flow. ... Through any pipe size, higher water pressure will cause greater water flow. The pressure will decrease downstream, however, because of loss of friction and water velocity increase.