Abstract: Apparatus and process for automatically measuring and controlling the instantaneous flow rate of a liquid in a piping system by varying the speed of a centrifugal pump in response to a flow rate signal determined indirectly by sampling two flow-related parameters associated with the pump and pump motor and then converting in an on-line computer the two measurements to the corresponding unique flow rate value by the use of previously determined mathematical relationships stored in the computer. The mathematical relationships are derived from data correlating flow rate with the two flow-related variables, which data is taken with a flow meter and control valve temporarily installed in the piping system during the "shake-down" testing of the piping system. A third flow-related variable is sampled, a pair of flow rate values determined, and an alarm activated in response to the difference between the values to provide the additional feature of pump mechanical performance monitoring.