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6. A motor is used to drive a pump having an efficiency of 85% and 70% respectively. What is the combined efficiency of pump and motor? 7. In a boiler feed pump, the enthalpy at the entrance is 765 kJ/kg. If pump has a head of 900 m, what is the exit enthalpy of the pump? 8. A submersible pump delivers 350gpm of water to a height of 5ft from the ground. The pump was installed 120ft below the ground level and draw down of 8ft during the operation. If water is 25ft above the pump, determine the pump power. 9. Determine the number of stages needed for a centrifugal pump if it is used to deliver 400gal/min of water and pump power of 15hp. Each impeller develops a head of 38ft. 10. A boiler feed pump receives 50 liters /second of water with specific volume of 0.00112 m3/kg at a head of 750 m. What is the power output of the driving motor if pump efficiency is 65%? 11. What power can a boiler feed pump can deliver a mass of 35 kg/s water at a head of 500 m ? 12. A pump running at 100rpm delivers water against a head of 30 m. If pump speed will increased to 120 rpm, what is the increase in head?