rotational speed the use of these laws is well known the efficiency of the centrifugal pump is directly related to its specific speed and may achieve values of 90 percent or greater it would be higher if the pump handling large flows and low pressure rises and generally will be lower for small flows and high pressures the data for the four flows is plotted and four lines are constructed as shown in fig2 and 3 constant speed points can also be connected equations for both the four straight lines and the constant speed curves are formulated thus as seen in fig2 there is shown a graph of the total head tdh versus torque while fig3 shows a graph of torque versus capacity gallons per minute gpm at three different speeds to determine whether the pump motor has degraded as indicated above only one sensor needs to be installed on the pump this sensor measures the differential pressure across the pump or discharge pressure or flow could also be used any one of the three measurements is compared to its expected value based on the speed and torque the motor is producing if the actual parameter has deviated from the calculated value then the pump is deemed to be degraded to a point.