Comparison of methods for measuring pump flow ripple and impedance

Positive displacement pumps produce flow and pressure ripple due to their pumping mechanism. Two ISO standard methods for measuring pump ripple were compared in terms of accuracy, sensitivity, reliability and practical difficulty. These were the “secondary source” (SS) method (ISO 10767-1: 1996) and the “2 pressures / 2 systems” (2P2S) method (ISO 10767-1: 2015). The 2P2S method has recently replaced the secondary source as the ISO standard for precision testing although the UK has retained the SS method for its BS ISO standard.
The methods produced similar source impedance and flow ripple results. The SS method enabled a wider range of operating conditions to be tested due to the more flexible circuit arrangement but the impedance results were affected by interference between the test pump and secondary source at the pumping harmonic frequencies. It was found that the simpler 2P2S circuit allowed measurements to be taken faster, but measurements were only valid at the pumping harmonic frequencies. Both methods were found to produce repeatable results provided there was no trapped air in the circuit.
Overall, the SS method was considered the stronger technique in terms of repeatability, accuracy, sensitivity and practicality, but it had a more complex data processing and experimental set up. It had more flexibility, which enabled the pump to be tested over the widest range of operating conditions, and the fluid borne noise characteristics of the test pump could be evaluated completely. The authors consider that the 2P2S method could be improved by the inclusion of a third transducer, and that it would be beneficial to retain the SS method as an alternative Standard.