Pressure Control Valve as Flow Control Valve

It isn't possible without changing the loop measuring device.

the other consideration would be in relation to the value or setpoint in which the flow will be controlled falls on the =% curve of the control valve. then one would need to evaluate the response required from the control valve to meet the set point demands required by the control valve. With Fisher valves it is possible to change the charaterisitics of a valve to a certain degree, you would need to get with that supplier to see what options you have available. A good instrument/control engineer should also be able to help evaluate the needed changes you would require...

Agree. If the valve is electrically controlled, so the problem goes to the point that you must change your sensors and control loop to read flow instead of pressure. If the valve is mechanical, you still have to change all the stuff and insert some sort of flow measuring device capable of feeding the valve the required delta-P signal to move it.

OR

If you are very very lucky, you could make a flow control arrangement by inserting a calibrated orifice or a needle valve (that you could calibrate in the line) after the pressure regulating valve. In this arrangement, you would cause the press reg valve to feed the restrain element with constant pressure, resulting in constant flow. This obviously only works if the element output is at constant pressure, i.e., opened to ambient or a vented tank, for example.