Why can not use low-lift deep well water pump

Why can not use low-lift deep well water pump
  The basic concept of lift:
Head (water head) - pump weight per unit
(1kg) of liquid work done, that is, the unit weight of liquid through the pump after the value of its energy. To the letter H said, commonly used liquid column height m said.
Other units: Pa (kPa), atm (1 engineering atmospheric pressure)
1 atm = 98.0665 kPa ≈ 0.1 MPa
The head is calculated as H = E2-E1
When a deep well water pump is used at low head, the motor power will exceed the rated power. Because it is clear from the characteristic curve of the pump that the flow rate increases as the pressure drops, the power curve also rises and the efficiency of the pump decreases, so the pump flow and lift selection are important so that the pump operates at its highest efficiency curve nearby.
Deep well water pump head is used to overcome the height and resistance, high-lift deep-well pump in the work of high-lift point of his flow is the design point of the flow, if the work in low head, the pump is equivalent to reducing the export resistance, The pump flow will increase, the motor will be overloaded, super to a certain extent, will burn the motor. For example, a boiler feed pump has a head of 25 m and a flow rate of 25 m³ / h. When it feeds water at 25 m, its flow rate is 25 m³ / hr. When it feeds water at 10 m , Its height and resistance to reduce its flow rate may reach 20-50 cubic meters / hour or more, then supporting the motor power will exceed the rated power, the motor will heat or burn.