Reverse oil pump characteristics reflect the pump in the oil pump working condition, hydraulic turbine (hydraulic turbine) working condition and braking (energy consumption) working condition of all the full characteristic curve, because of the test is more complex, when necessary to use the model in the laboratory. Centrifugal pumps in the range of specific speed are commonly used in general devices. The comparison between the characteristic curves of reversed hydraulic permeability and those of pump conditions is shown in Figure 1-41.
As can be seen from the figure:
(1) The trend of hydraulic turbine is opposite to that of pump heads-flow characteristic curve. After zero output power, the pressure head rises rapidly with the increase of flow.
(Z) When used as a hydraulic turbine, its optimal efficiency value is almost the same as that used as a pump, but at large flow points; Moreover, the efficiency decreases slowly on the right side of the point, so it is suitable for operation under the optimal efficiency point or large flow rate.
(3) The output power and efficiency of hydraulic turbine decrease rapidly with the decrease of flow rate. When the flow rate decreases to 40% of the optimal efficiency point, the output power and efficiency are zero. When the flow rate is lower than this value, the turbine is in the state of power consumption. It is because of this hydraulic transmission that the pump is usually driven in series with the motor. When the flow becomes small, rely on motor drive.
In addition, the pressure drop generated when the liquid leaves the blade surface under the condition of hydraulic turbine is smaller than that generated when the liquid flows to the blade surface under the condition of pump, so it is less sensitive to cavitation than the oil pump.
The pressure head and flow rate of the best efficiency point for hydraulic turbine and pump have a certain corresponding relationship, depending on the specific speed N of the pump, its conversion coefficient is different.
