FCV and PCV Valve Differences

Where do you get the idea that flow and pressure are the same?

FVC FEV₁ PEF
I can out acronym him any time!
Del (RSVP)
MTBF BWFT

Presure control valve opens or closes in order to increase or decrease the pressure. The pressure can be measured upstream or downstream of the valve.

A flow control valve does the same in order to control flow.

Also you select the type of control valve based upon the parameter you want to control. If you want to control or maintain a flow rate such ft3/min (gas), then you need a flow control valve. You will measure the flowrate by some appropriate flow meter such as an orifice plate and transmitter - this will give you your control variable input. I assume you know the principles of the PID controller that adjusts the FCV in response to changes in the flow in order to maintain the control variable (flow rate) at the setpoint. If you want to maintain or control pressure in psi (pounds per square inch) you measure pressure by means of a pressure transmitter which will give you your control variable input. Similarly a PID controller will then adjust your PCV to maintain your pressure at the setpoint.

"I assume you know the principles of the PID controller ..."

When faced with an OP (Original Post/Poster) such as this, it is not safe to assume anything.

Valve construction is based on process data and not on controlling parameter, so PCV/FCV/TCV/LCV are all same in construction. Terminology is given as FCV/PCV etc just indicate the controlling transmitter. It may be possible that this terminology continuing from earlier times when single loop controllers are used and they may be different for flow/pressure/temp which other member in this forum can tell better.