Pressure fluctuations in double-suction centrifugal pumps are greatly affected by the flow rate and rotational speed. An experimental investigation was carried out to determine effects of the flow rate and rotational speed for optimizing the hydraulic design and realizing stable operation. Pressure fluctuation signals were obtained at five measurement points along the suction chamber and four measurement points along the discharge chamber by means of pressure transmitters. The flow rates ranged from 0% to 150% of the design flow rate, and the rotational speed was reduced to 850 rpm from the rated speed of 1450 rpm. Results show that the third harmonic of rotational frequency is detected as the dominant frequency in the upper part of the suction chamber at low flow rates. At zero flow rate, the pressure fluctuations increase by 200% above that at the design flow rate. The pressure fluctuations decrease by 50% as the speed is reduced from the rated speed of 1450 rpm to 1250 rpm. At 850 rpm, the pressure fluctuations at partial flow rates are larger than those at higher rotational speeds, and the maximum efficiency is 5% less than that at the rated speed of 1450 rpm. (C) 2018 Elsevier Ltd. All rights reserved.