由图1-52可以看出,当用关小调节阀使流量由Q1减小到Q2或Q3时,泵的效率往往会有所下降,因为一般情况下总是按阀全开时所确定的工作点M来选泵的。至于功率,一般低、中比转速的离心泵,其功率性能曲线都是随流量减小而下有所下降的。但是从泵提供的能头利用程度来看,调节阀开度减小却增力加了附加阻力损失。设调节阀全开时,流量为Q1,管路特性系数为k1，则管路中流动损失为h=k1Q2;节流后，流大量变为Q2,总的流动损失为h=k2Q2,其中用于使液体在管路中进行输送时需要克服的流动损失仅为h=k,Qz 2,其余能头(k2 – k1)Qz 2则为节流调节损失。
由Hr。-42C2。m和Q:=nD:b-E2C20可知，离心泵的场程和流量都和转速有关。当n增大时,由比例定律可知,流量和扬程相应地与转速近似地按次二次方的正比关系变化,即系的H-Q性能曲线向右上方移动:当n减小时,H - Q性能曲线向左下方移动，如图1- 54所示、当管路特性h-Q不变时,就可得到不同的工作点,使流量改变。另外式(1-71)给出了调速的泵特性方程。
Adjustment of operation condition of slurry pump
If the flow rate of the working point is greater than or less than the required conveying capacity, try to change the position of the working point. Changing the working point of the running pump is called condition regulation. Since the working point of the pump is the intersection of the pipeline characteristic curve and the pump characteristic curve, there are two ways to adjust the working condition, i.e. changing the pipeline characteristic and changing the pump characteristic, which are discussed respectively below.
1。 Change pipeline characteristics
1) Pipeline throttling regulation
This is the simplest and most commonly used method to change the characteristics of the pipeline, that is, install a regulating valve on the discharge pipeline, open or close the opening of the regulating valve, so as to change the local resistance in the pipeline, change the coefficient K of the pipeline characteristics, and change the slope of the pipeline characteristics。 When the performance curve of the pump is constant, the working point changes to adjust the flow。
As shown in Figure 1-52, when the regulating valve on the discharge pipeline of the pump is fully open, the pipeline characteristic curve is set as 1. The intersection point with the H-Q performance curve of the pump is m, and the corresponding flow is Q1. As the regulating valve is gradually closed, the pipeline characteristic coefficient K is gradually increased, the pipeline characteristics 2 and 3 are correspondingly steeper, the working points are m2 and M3, the flow is gradually reduced to Q2 and Q3, and the pump lift is gradually increased from H1 to H2 and H3.
It can be seen from figure 1-52 that when the flow is reduced from Q1 to Q2 or Q3 by turning down the regulating valve, the efficiency of the pump will often be reduced, because in general, the pump is always selected according to the working point m determined when the valve is fully open. As for the power, the power performance curve of low and medium specific speed centrifugal pump decreases with the decrease of flow rate. However, from the utilization degree of the energy head provided by the pump, the reduction of the opening of the regulating valve increases the force and the additional resistance loss. When the regulating valve is set to be fully open, the flow rate is Q1, and the characteristic coefficient of the pipeline is K1, then the flow loss in the pipeline is h = K1q2; after throttling, the flow becomes Q2, and the total flow loss is h = k2q2, among which the flow loss to be overcome when the liquid is transported in the pipeline is only h = k, QZ2, and the other energy head (K2 – K1) QZ2 is throttling regulation loss.
It can be seen that when the pipeline characteristics are changed to regulate the flow by turning down the discharge regulating valve, the local resistance loss in the pipeline increases, and the pump is required to provide more energy head to overcome the additional resistance loss, so that the efficiency of the whole device is not high, and it is uneconomical to adjust in this way for a long time。 Especially for the centrifugal pump with steep drop head performance curve, it is more uneconomical to adjust by this method。 But because of
This method is simple and convenient to adjust, so it is still widely used in the condition adjustment of centrifugal pump.
2) Bypass Book Adjustment
As shown in Figure 1-53, a bypass is set at the pump outlet to connect with the liquid suction tank. A regulating valve is installed on the pipeline. The centrifugal pump works on the bypass regulating device as in the branch pipeline. H-q1 is the pipeline characteristic of the main pipeline, and h-q2 is the bypass
When the bypass control valve is completely closed, the intersection point of the pump performance curve H-Q and the main pipeline characteristic h-q1 is B1; when the bypass valve is opened, the intersection point of the H-Q curve and H-Q is a. According to the method of calculating the flow in each pipe in the branch pipeline, the flow through the main pipe is Q and the flow through the main pipe is qao when crossing point a as the horizontal line and point A1 and point A2 as the h-q2. It can be seen from the figure that the flow of the pump increases, but the flow in the main pipe is smaller than that in the main pipe when the bypass valve is closed, so the flow is regulated.
This method of regulation is also uneconomical because the fluid in the bypass wastes power. If the axial power of the pump decreases with the increase of the flow rate, this method is suitable for regulating.
In addition, when the liquid level in the drain tank changes, the pipeline characteristics will move up and down, and the working point and flow will change.
安徽快3开奖结果2. Change pump characteristics
安徽快3开奖结果In addition to the above-mentioned use of pumps in series and parallel operation to change the performance curve to achieve the condition regulation, the common methods to change the pump performance curve include changing the working speed, cutting the outer diameter of impeller and changing the impeller regulation。
1) Change the working speed
It can be seen from HR. - 42c2. M and Q: = Nd: b-e2c20 that the field path and flow rate of centrifugal pump are related to the rotating speed. When n increases, it can be seen from the proportional law that the flow rate and head change in proportion to the rotational speed approximately according to the quadratic power, i.e. the H-Q performance curve of the system moves up and to the right: when n decreases, the H-Q performance curve moves down and to the left, as shown in figure 1-54, when the pipeline characteristic H-Q remains unchanged, different working points can be obtained to change the flow rate. In addition, equation (1-71) gives the pump characteristic equation of speed regulation.
It is more economical to adjust the flow with variable speed because it has no additional energy loss caused by throttling. However, the adjustment of slurry pump requires the use of prime mover which can change the speed to drive, such as DC motor frequency conversion motor and steam turbine. At present, frequency converter and variable speed AC motor are widely used, or with hydraulic coupling drive.