A pump was installed in a field to supply water to the crops. The duty for this crop is 432 hectares/cumec on the field and the efficiency of pump is 50%. The sown area of the field is 5 hectares. Determine the maximum output required (H.P) of the pump, if the highest water level is 4 meters below the highest portion of the field. Assume negligible field channel losses.

Correct Answer: 0.31H.P
Area of field to be irrigated = 5 hectares Duty of water for crop = 432 hectares/cumec Discharge required for the crop is = (5 / 432) = 1/86.4 cumec Volume of water lifted per second = 1 / 86.4 cumec Therefore, weight of water lifted per second = (1 / 86.4) x 9.81 = 0.1135 KN/sec (unit wt. of water = 9.81 KN/m3) Maximum static lift of pump = 4 metres Work done by the pump in lifting water = 0.1135 x 4 = 0.454 KWatt The input of the pump = (0.454 / 0.735) = 0.62 (1 metric H.P = 0.735 KWatt) Output H.P of the pump = (input/η) = (0.62 / 0.5) = 0.31 H.P.