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渣浆泵的不稳定工作
添加时间:2020.03.07

渣浆泵的不稳定工作
    有些低比转速的离心泵,H-Q性能曲线常常是一种驼峰形的,如图1-56所示。这种性能曲线和管路特性曲线可能有两个交点MM1,理论上讲都是工作点。设泵在M点工作,由于某种原因(如电路中电压波动、频率变化导致转速改变、液面位置波动以及设备振动等)使工况向大流量方向偏离,则泵的扬程大于管路系统所需的能头。能头有富余,使管路中液体流速加大,流量增加,工作点沿泵性能曲线维续向大流量方向移动,直至M1点时来给出的能头重新与管路装置所需的能头相等,量停止加。泵在M1点稳定工作,所以M1点是稳定工作点。相反,如果泵在M点工作时,由于种原因使流量减小了,则泵的扬程小于管路系统所需的能头,使管路中波体流速减小,流量减小,直到流量等于零为止。若路上不装止回阀,液体将倒灌进泵内。由此可见,工作点M是暂时平衡,且实际工况与M点对应的HmQm略有偏离时,工作点便不再回到M点,所以称M点为离心泵的不稳定工作点。工作点的稳定与不稳定的判别是:当交点处管路特性曲线的斜率大于泵性能曲线的斜率时是稳定工作点;反之,如交点处管路特性曲线的斜率小于泵性能曲线的斜率,则是不稳定工作点。这样,凡是H-Q性能曲线呈驼峰形的,曲线最高点T的左侧线段上的各点都有可能成为离心泵的不稳定工作点。
    渣浆泵工作中可能产生不稳定工况的两个条件:一是泵的H-Q性能曲线驼峰形,二是管路装置中要有能自由升降的液面或其他能储存和放出能量的部分(1-57)。因此,当遇到具有这种特点的管理装置时,为防止发生不稳定工况,则不要选用具有驼峰形H-Q性能曲线的离心泵。

Unstable operation of slurry pump

For some low specific speed centrifugal pumps, the H-Q performance curve is often a hump shape, as shown in figure 1-56. This kind of performance curve and pipeline characteristic curve may have two intersections, m and M1, which are working points in theory. If the pump is set to work at point m, and the working condition deviates from the direction of large flow due to some reasons (such as voltage fluctuation in the circuit, frequency change resulting in speed change, liquid level position fluctuation, equipment vibration, etc.), the pump lift is greater than the energy head required by the pipeline system. The surplus of the energy head increases the flow rate and flow rate of the liquid in the pipeline, and the working point moves along the pump performance curve to the direction of large flow until M1 point, when the energy head given is equal to the energy head required by the pipeline device again, the flow rate stops increasing. The pump works stably at M1, so M1 is the stable working point. On the contrary, if the flow is reduced due to some reason when the pump is working at point m, the head of the pump is less than the energy head required by the pipeline system, which reduces the wave body flow rate in the pipeline and the flow until the flow is equal to zero. If no check valve is installed on the pipeline, the liquid will be poured back into the pump. It can be seen that the working point m is temporarily balanced. Once the actual working condition deviates slightly from the HM and QM corresponding to the m point, the working point will not return to the m point, so the m point is called the unstable working point of the centrifugal pump. The judgment of the stability and instability of the working point is: when the slope of the pipeline characteristic curve at the intersection is greater than the slope of the pump performance curve, it is the stable working point; otherwise, if the slope of the pipeline characteristic curve at the intersection is less than the slope of the pump performance curve, it is the unstable working point. In this way, any H-Q performance curve is humped, and each point on the left line segment of the highest point t of the curve may become the unstable working point of the centrifugal pump.

There are two conditions that may produce unstable working conditions in the operation of slurry pump: first, the H-Q performance curve of the pump is in the shape of a hump; second, the pipeline device should have a liquid level that can rise and fall freely or other parts that can store and release energy (Figure 1-57)。 Therefore, when encountering a management device with this feature, in order to prevent unstable working conditions, the H-Q performance curve with the hump shape should not be selected Centrifugal pump。





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