Centrifugal pump adjustment methods commonly used

Centrifugal pumps are widely used in water conservancy, chemical industry, etc, on the point of the selection and analysis of energy consumption is increasingly attention. Point, refers to the actual water yield and head of the water pump device in a transient, shaft power, efficiency, and on the vacuum suction height, etc. , it said the pump work ability. Usually, the centrifugal pump flow rate and pressure head may be inconsistent with the piping system, or because the production task change, technological requirements, need to adjust the flow of the pump, its essence is to change the working condition of centrifugal pump. In addition to the engineering design stage centrifugal pump selection is correct or not, working condition of centrifugal pump in the actual use of choice will directly affect the user's energy consumption and cost. Therefore, how to change the working condition of centrifugal pump reasonably point is particularly important. Oil drum pump centrifugal pump working principle is to put the motor high speed rotating mechanical energy into kinetic energy and potential energy of liquid was promoted, is a process of energy transfer and conversion. According to this characteristic, the working condition of centrifugal pump is based on the pump and piping system on the balance between energy supply and demand, as long as the two changes, one of the point will shift. Point change caused by two aspects: one. Piping system characteristic curve changes, such as throttle valve; two The characteristic curve of pump itself changes, such as frequency control of motor speed, cutting impeller, pump series or parallel. Here is that several ways are analyzed and compared: a change, valve throttling flow centrifugal pump is the most simple way is to adjust the pump discharge valve opening, and the water pump speed remains the same, Are generally rated speed) , its essence is to change the position of the pipeline characteristic curve to change the point of the pump. Q - as shown in figure 1, the water pump characteristic curve Q - H and pipeline characteristic curve ∑ H intersection of limit condition of A pump when the valve is fully open. Turn down the valve, pipe local resistance increases, the pump point to the left to the point B, corresponding flow decreases. Valve fitted, equivalent resistance is infinite, flow is zero, the pipeline characteristic curve and the vertical overlap. You can see from figure 1, in order to close the valve to control flow, capacity of the pump itself remains unchanged, lift characteristics unchanged, pipe resistance characteristic will change along with the change of valve opening. This method is simple, continuous flow, can be in one of the maximum flow between zero and adjust at will, and no additional investment, applicable occasions is very wide. But the throttling is extra energy consumption of the centrifugal water pump ( The shaded part of the figure) To maintain a certain supply, the efficiency of the centrifugal water pump will be down, the economy is not reasonable. Second, frequency control of motor speed point deviates from the high efficiency area is the pump need to control the basic conditions. When the water pump speed change, valve opening unchanged ( Usually for the biggest opening) Characteristics, pipeline system unchanged, while water supply capacity and lift characteristics change. As shown in figure 2, A balance point for pumps ( Also known as the working point) , the corresponding efficiency & eta; a。 Speed can be reduced to reduce the flow, and the point B, corresponding efficiency & eta; B, the pump is still in high efficiency zone. If adopt the method of valve throttle to adjust, the point of C, corresponding efficiency & eta; C, the efficiency of the pump. Thus, in the case of the required flow rate is less than the rated flow, frequency control of motor speed when the head is smaller than the throttle valve, so the frequency control of motor speed is smaller than the throttle valve, water power required by the shadow portion of figure 2 said is power frequency control of motor speed to save the water supply. Obviously, compared with the throttle valve, the energy saving effect of variable frequency speed regulation is very outstanding, the work efficiency of centrifugal pump is higher. In addition, using variable frequency speed regulation, is not only beneficial to reduce the risk of deeloping cavitation in centrifugal pump, and can be controlled by the acc/dec time to extend the preset starting/stopping process, thus greatly reducing the dynamic torque, thus eliminated very greatly and destructive water hammer effect, greatly extend the life span of the pump and piping system
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