What is the pump surge phenomenon? Surge phenomenon preventive measures

What is the cause of fluid surge? Prevent the pump What are the measures of surge phenomenon? What is the pump surge phenomenon? Surge Prevention Measures When stainless steel corrosion-resistant centrifugal pumps and fans with a "hump" performance curve operate at the left-hand side of the curve at point K, that is, when working in an unstable region, surge phenomena often occur Flying phenomenon. Surge phenomenon, that is, the pump and fan flow and head can occur in an instant instability cyclical changes repeatedly phenomenon. When a hump-shaped fan performance curve is running on a large-capacity pipe, if the flow rate required by the outside is qVA, the pipe characteristic curve and the fan performance curve intersect at point A, and at this point The energy consumed by the pipeline is balanced with the energy generated by the fan, so the work is stable. When the outside world needs traffic increased to 9vb, the work point to the right of A to move to point B, then the work is still stable. When the traffic volume required by the outside world decreases, the working point moves to the left of A to point E, and as the flow rate required by the outside world further decreases to qVK, the corresponding working point is the ruler point and the ruler point is the critical point, The left of point X is the unstable work area. If the outside world needs to continue to reduce the flow to qWK, then the maximum energy generated by the fan will be less than the resistance of the pipeline, because the pipeline capacity is larger, in this moment the resistance is still in the pipeline Therefore, Resistance in the pipeline is greater than the energy generated by the fan head, the fluid began to reverse the reverse flow from the fan back in the pipeline (there is a negative flow), that is, the work point from K point to C point. Due to the backflow of pressure in the pipeline rapidly decreased, the work point quickly jump from C to Z) point, when the flow is zero. As the fan continues to operate, the pump or fan resumes output flow when the pressure in the line drops to the corresponding point pressure. From the hump performance curve we can see, in order to balance the resistance in the pipeline, the corresponding operating point and jump to E point. As long as the required flow outside the world to keep less than the above process is repeated, that occurs surge. If the frequency of this cycle and the system's oscillation frequency in time, it is necessary to cause resonance, often resulting in pump or fan damage. In theory, the occurrence of surge should have the following three conditions: ① pump and fan has a hump-shaped performance curve, and unstable operating conditions. ② The pipeline has enough volume and air in the water pipe. ③ the surge frequency of the entire system and the unit's rotation frequency overlap, resonance occurs. Essentially, spin-stalled and surge are two different concepts. Rotational stall is a hydrodynamic condition caused by the structural characteristics of the blade, while surge is a manifestation of the pump or fan performance coupled with the device oscillation. Surge and cavitation are also different, cavitation generally occurs at a larger flow at the same time, on the contrary, surge occurs at a small flow. Moreover, the vibration period of surge is longer, the frequency range is 10 ~ 0.1Hz, and the frequency range of cavitation is 600-25000Hz. The measures to prevent surge of pump and fan are as follows: ① try to avoid adopting in large-capacity pipeline system Pumps and fans with hump shape q tilted straight down with 9v - // performance curve. ② The flow rate under any conditions not less than qVKo If the device is required Shu Shu flow less than 9vk, can be installed recirculation pipe or automatic drain valve, the pump or fan outlet flow is always greater than 9VK. ③ change the speed or suction inlet valve installed. When increasing the speed or without a large suction valve, the performance curve 9v - // on the critical point A: moving to the upper right, on the contrary, when reducing the speed or closing the suction valve, the critical point K on the performance curve W- Bottom left to move, which can narrow the performance curve of the unstable section. ④ using adjustable blade. When the flow of external demand decreases, the line moves downward, the critical point moves to the lower left and the output flow decreases correspondingly. ⑤ in the pipeline layout, should try to avoid the accumulation of air out of the pipeline, for example, to avoid the ups and downs of the pipeline, but to have a certain degree of upward slope. In addition, try to adjust the valve and throttling device near the pump outlet installation. ⑥ in operation, when more than one pump or fan in parallel, if the load decreases, you should try to reduce the number of units put into operation to ensure that operating equipment at close to the normal flow of operation. Vertical pipeline centrifugal pumps and fans because of its start-up mode and axial flow is different, usually the valve is closed when the start, and then gradually open the valve to increase the flow, so when using a hump-shaped performance curve of the pump and the fan must pass Unstable working area. Surge in this area may occur, but time is very short, so there is no report of blade rupture due to surge. Analysis, the centrifugal pump and fan blades have front and rear plates fixed at both ends, the blade flow channel narrow, its rigidity than the axial flow cantilever beam and the blade width is much stronger, and thus in the stalling vibration excitation role It is much less likely to resonate under it. (Editor: Xiaoxia QQ:) Recommended reading: 2017 exhibition information

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