Unstable operation of slurry pump

The H-Q performance curve of some centrifugal pumps with low specific speed is often a hump shape. This performance curve and pipeline characteristic curve may have two intersections m and M1, which are working points in theory. If the pump works at point m, and the working condition deviates to the direction of large flow due to some reasons (such as voltage fluctuation, frequency change, speed change, liquid level fluctuation and equipment vibration in the circuit), the pump head is greater than the energy head required by the pipeline system. The energy head has surplus, so that the liquid flow rate in the pipeline increases and the flow increases. The working point continues to move to the direction of large flow along the pump performance curve until the energy head given at point M1 is equal to the energy head required by the pipeline device again, and the flow stops increasing. The pump works stably at point M1, so point M1 is the stable working point. On the contrary, if the flow decreases due to some reason when the pump works at point m, the head of the pump is less than the energy head required by the pipeline system, so that the wave velocity in the pipeline decreases and the flow decreases until the flow is equal to zero. If no check valve is installed on the pipeline, the liquid will pour back into the pump. It can be seen that working point m is temporarily balanced. Once the actual working condition deviates slightly from HM and QM corresponding to point m, the working point will no longer return to point M. therefore, point m is called the unstable working point of centrifugal pump. The judgment of stability and instability of the working point is: when the slope of the pipeline characteristic curve at the intersection is greater than that of the pump performance curve, it is the stable working point; Conversely, if the slope of the pipeline characteristic curve at the intersection is less than the slope of the pump performance curve, it is an unstable working point. In this way, if the H-Q performance curve is humped, the points on the left section of the highest point t of the curve may become the unstable working points of the centrifugal pump.

There are two conditions that may lead to unstable working conditions during the operation of slurry pump: one is that the H-Q performance curve of the pump is humped, and the other is that there should be a liquid level that can rise and fall freely or other parts that can store and release energy in the pipeline device Therefore, when encountering a management device with this feature, in order to prevent unstable working conditions, do not choose a centrifugal pump with hump H-Q performance curve.