This should be an easy one but here goes... I am trying to easily measure flow rate in a pipe which has an in line centrifugal pump (Grundfos UPS 25-60) creating the head in the system. I have been told that installing a pressure guage before and directly after the pump will give me system flow rate from a look-up table. Is this the case? My recolection is that you need some kind of orifice plate in the flow and between the two gauges to get a useful reading.