A pump is filling water in to a rectangular overhead tank of 5 m x 4 m with a height of 8 m. The inlet pipe to the tank is located at height of 20 m above ground. The following additional data is collected :
Pump suction : 3 m below pump level
Overhead tank overflow line : 7.5 m from the bottom of the tank
Power drawn by motor : 5.5 kW
Motor efficiency η : 92%
Time taken by the pump to fill the
overhead tank upto overflow level : 180 minutes Assess the pump efficiency.
CALCULATION
Volume of the tank = 5 x 4 x 7.5 = 150 m3 Flow
= 150/3 = 50 m3/hr
Hydraulic power = Q (m3/s) x total head (m) x 1000 x 9.81 /1000
= (50/3600) x (20 –(-3)) x 1000 x 9.81/1000
Hydraulic power = 3.13 kW
Power input to pump = 5.5 x 0.92 = 5.06 kW
Pump efficiency = 3.13/5.06 = 61.9%
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