1. The problem statement, all variables and given/known data It is proposed to pump 1500 m3 of a liquid (density 1100 kg m–3) each day through a total head of 10 m (including all losses) by using either a centrifugal pump or a reciprocating pump. The centrifugal pump discharges 2.0 m3 min–1 when driven by an electric motor supplying a power of 5 kW. The reciprocating pump has a discharge rate of 1.75 m3 min–1 when driven by an electric motor supplying 3.5 kW. 1) Calculate the efficiency of the pumps. 2. Relevant equations Po = QvρGHP ηp = Po/PI ηm = PI/Pe ηo = Po/Pe 3. The attempt at a solution Data Collection ρ = 1100 kg m–3 G = 9.81 m/s-1 Hp = 10m Convert flowrate from m3/min-1 to m3/sec-1: 2/60 = 0.033m3/sec-1 for the centrifugal pump. 1.75/60 = 2/60 = 0.029m3/sec-1 for the reciprocating pump. Calculate output power of the centrifugal pump: Po = QvρGHP Po = 0.033 * 1100 * 9.81 * 10 Po = 3561.03 Watts Calculate centrifugal pump efficiency: ηp = Po/PI * 100 ηp = 3561.03/5000 * 100 ηp = 0.712 * 100 ηp = 71.2% efficiency I'm a little bit stumped from this point on as I cannot calculate the overall efficiency of each pump without knowing the electrical input power, Pe or even the motor efficiency. Should I assume that the motor is running at 100% efficiency and that the electrical input power Pe is the same as the input power to pump PI? If not, is there a way that I can calculate Pe without knowing the overall/motor efficiency? Cheers!