Abstract: A reverse running centrifugal pump is one of the most convenient choices with lower cost in micro-hydropower development and industrial pressure energy recovery.One of the main limitations in utilizing pump as turbine(PAT) technique is that the PAT usually runs at part load for several months in a year due to insufficient water availability for the power production.Variable speed operation offers an effective solution to this problem.Pump manufactures normally do not provide performance curves of pump running in turbine mode, especially when working at variable speed condition.In addition, performance test may often be required to be carried out in order to accurately obtain the operation parameters before high power PAT working in industrial pressure energy recovery.Due to the limitation of the laboratory power capacity, the performance of rated rotational speed condition is often estimated through decreasing rotational speed in the test.It is difficult to accurately obtain the performance parameters of the rated condition.Therefore, experimental research at different rotational speed is useful to understand the correlations between PAT’s performance parameters and rotational speed.In the present research, an open PAT test rig was set up.An electric eddy current dynamometer (EECD) was installed in the rig to measure and consume energy generated by PAT.And an automatic control system was used in the test to regulate rotational speed of PAT.The rotational speed of PAT was varied by adjusting the rotational speed of EECD.To study the effects of rotational speed on the performance, the operation of PAT was simulated by using computational fluid dynamics (CFD) technique at different speed ranging from 900 to 2100 r/min with a step of 300 r/min.Through the comparison of performance curves obtained by experiment, we could find that the trend at different rotational speed was similar.The head and shaft power curves both increased with the increase of flow rate.And the PAT efficiency first increased to the maximum and then decreased with the increase of flow rate.Rotational speed had an obvious effect on the performance of PAT.The results showed that PAT’s BEP(best efficiency point) shifted towards higher discharge and its high efficiency range became wider with the increase of rotational speed.The comparison of the results obtained by CFD and by using proportional law theory calculation showed that the performance parameters of BEPs at different rotational speed were almost consistent.However, CFD could not objectively reflect the effects of variable speed on efficiency completely.The comparison of the results obtained by experiment and by theory calculation showed that the performance parameters of BEPs at different rotational speed had a certain degree of deviation.And the flow rate deviation was the minimum, followed by the head deviation and the shaft power deviation.Comparing the theory calculation values, the deviations of flow rate, head and shaft power obtained by experiments were about 10%, 12.17% and 15.4%, respectively, when the rotational speed declined from 1 500 to 900 r/min.At the same time, the rotating speed had also obvious influence on the PAT’s efficiency.The maximum efficiencies were reported as 65.4%, 67.86%, 69.83% and 70.25% at 900, 1 200, 1 500 and 1 800 r/min, respectively.Through theoretical analysis, decreasing speed had a negative influence on the volumetric efficiency and mechanical efficiency, while increasing speed had a nonlinear positive influence.At part load operating conditions, the more the speed was below the rated speed, the more the efficiency declined.And variable speed operation was more meaningful.While the hydraulic resource and strength both met the requirements of operating conditions, the rotational speed should be equal to or slightly higher than the rated speed, which could effectively use the energy.