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How to solve the problem of super high lift of the pump?
- Dec 03, 2018 -


(1) The existing impeller of the pump must be replaced with an axial flow impeller with a lower number of revolutions (in the case of constant power, the head is increased and the flow is reduced). Since the lift of the impeller is increased, the speed of the impeller outlet or the amount of the momentum moment loop is increased, so that the expansion and derotation functions of the outlet vane are required to be stronger. At present, large vertical axial flow pumps with a domestic impeller diameter of 2.8 m and above have guide vanes fixed in the reinforced concrete of the outlet flow passage, so it is quite difficult to replace the guide vanes when the impeller is changed. According to the working principle of the horizontal centrifugal pump, after the impeller lift is lifted, the absolute liquid flow angle (guide vane inlet mounting angle) cc3 of the inlet flow of the vane is reduced, and the curvature of the vane is increased. If the vane is not replaced, at the same flow rate, the water flow will form a vortex zone on the back of the vane inlet, causing the pump to be less efficient and the outlet pressure to pulsate, so it is best to replace the vane when replacing the modified impeller. For difficulties in replacing the guide vanes, it is best to work with the relevant research unit to try to find improvement measures under the existing equipment conditions. The final modification plan should be determined by model tests.


(2) Increasing the pump speed is known by the similar law. Increasing the pump speed can increase the pump flow and head, but the shaft power of the water pump increases, and the power machine needs to increase capacity. For pumping stations with ultra-high heads, the key to this approach is the choice of speed-increasing mode and variable speed equipment. Due to the small size of the unit, the small-scale drainage and pumping station is easy to realize (such as adjusting the fuel intake of the internal combustion engine and changing the diameter of the pulley). For AC motor-powered, the synchronous speed can be adjusted (infinitely variable frequency speed regulation and stepless frequency control), or the slip can be adjusted (for asynchronous motors, the stator voltage of the motor can be adjusted separately, and the series winding can be changed) Two kinds of adjustment methods, such as additional resistance of the wire motor rotor circuit. The former is energy-saving and the latter is energy-consuming. Large and medium-sized agricultural pumping stations are limited in their use due to their large capacity and high speed control equipment.

However, in recent years, combined with the single-stage centrifugal pump speed increase and motor transformation needs, the relevant experts of the pump and pump station teaching and research section of Wuhan University of Hydraulic and Electric Power advocated the two functions of capacity increase and speed adjustment while replacing the aging motor coil. That is, when the aging motor is modified, the thickness of the insulating layer is thinned, the cross section of the winding wire is increased, and the motor power is increased under the condition that the original motor structure is unchanged; at the same time, the motor speed is increased by using the method of “drag pole” to adapt to the high The operation of the pumping station at the head is required.


(3) New problems brought about by the increase of pump speed may include problems such as cavitation, unit structural strength, bearing life and critical speed verification. The pump speed increase may also change the flow pattern of the inlet flow, which makes the flow velocity and pressure distribution at the inlet of the pump uneven, which exacerbates the vibration of the unit. With this transformation plan, it is recommended to work with the relevant research units and the manufacturers of pumps and motors to agree on specific transformation plans based on the specific conditions of the station.

 


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