This seems to be a grey area, the so called mini filter is on the return of the pump, ie the line that goes back to the tank, it's purpose is to stop any debris blocking the very small restrictor orifice in the control valve that is AFTER the mini fiter, the control valve is a spring and shuttle that gives varying degree's of restriction depending on pressure and fuel flow, the idea is to stabilise the internal pump pressure, a blocked filter will raise the internal pressure too high giving problems, Rick