All valves control by dissipating energy (Pressure).
With a pressure control valve, the pressure to be controlled, usually downstream, is monitored and fed back to the valve either as a pressure or as a signal through a control system. If the downstream pressure is too great, the valve is closed some, dissipating more pressure at the valve and restoring the downstream pressure to the setpoint.
With a flow control valve, instead of the system sensing pressure, the system senses flow. If the flow is too high, the valve closes down, causing more of the available process energy to be dissipated at the valve and leaving less to drive flow through the system. Since mass is conserved, the flow is the same at all points in the system so the flowmeter can go upstream of the valve or downstream of the valve. Some flowmeters work better upstream and other types work better downstream.
There are specialized, self contained pressure control valves (regulators) and there are flow regulators. However if you are using a control system, industrial control valves might be used interchangeably for controlling pressure or flow ( or temperature, level, pH, Conductivity, or any other of a jillion different variables)
Remember: The VALVE does not control the variable. The CONTROL LOOP controls the variable. Valves just go to wherever the controller tells them to be.
