The big difference is that we can measure a surrogate for pressure, but we cannot measure a surrogate for flow rate (we have to calculate it).
With pressure control, we can set a local device to integrally maintain downstream pressure, but you have to make sure that the valve at less than maximum opening can pass the required flow at the required downstream pressure.
For a flow control valve you need an independent measurement device that feeds some sort of PLC that positions a control valve in the flow to maintain flow rate regardless of downstream pressure. Your sizing has to take into account the probable range of downstream pressures.
All a control valve can do is apply a variable resistance to flow. This results in an increased pressure drop relative to flowrate.
What control function you want the valve to do is irrelevant, the valve doesn't know this or care.
So it is the data and cases you put into the data sheet which impact on the choice and sizing of the valve.
If you're controlling flow, then the boundary cases are normally max flow with lowest differential pressure allowed, lowest flow with highest differentia pressure possible and then maybe a "normal flow case with "normal" flow and pressure drop
For pressure control which can be pressure upstream, downstream or differential then the boundaries are similar if reversed,
So controlling on a fixed downstream pressure the boundary cases are:
lowest upstream pressure at max flow
highest upstream pressure at max flow
highest upstream pressure at min flow
So in short, forget about the "designation" - it's a control valve.
Remember - More details = better answers
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