For high-temperature centrifugal pumps that experience cavitation during operation and fail to achieve the desired flow rate and head, can cavitation be reduced by cutting the impeller?
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The company has a process circulation pump that can operate at temperatures of 270 degrees Celsius. There is a positive pressure of about 60 KPa at the pump’s inlet, and the pump’s rated flow rate is 200 m3/h, with a head of 80 meters. The actual operating flow rate is around 140 m3/h (it cannot be increased any further, as the pressure gauge and ammeter show significant fluctuations), with a pressure of 0.4 MPa (and a density of around 0.9). The pressure at the pump inlet can no longer be increased; the inlet pipe has a diameter of 250 mm and is less than 3 meters long, yet cavitation still occurs in the pump (there is significant noise in the impeller chamber). I personally think it is because cavitation results in the flow rate and head not reaching the rated values. Is it possible to reduce cavitation by reducing the diameter of the impeller? If cavitation is reduced, will the flow rate and head still increase? Is that correct? I would appreciate it if experts could give me some advice. Thank you.
No, cutting the impeller will reduce both flow rate and head. It is better to replace the pump entirely or add another one. Also, remember that the inlet pipeline must also be modified to meet the requirements.
If conditions permit, reducing the speed is possible.
“Cutting the impeller will reduce both flow rate and head; this is generally the case, but is it the same when the pump is operating under cavitation conditions? I think it is appropriate to cut the impeller appropriately, so as to control its designed flow rate at 180 m3/h, with the pressure needing to be no less than 0.4 MPa. With the design flow rate and head of the impeller reduced, does cavitation in the pump decrease? As cavitation decreases, is it getting closer to the design flow rate and head (180 and 0.4)?
As for the cavitation issue with this pump, it is mainly caused by problems with the inlet pipeline. I have encountered similar problems before; since the inlet cannot be changed, we modified the impeller by replacing it with a three-dimensional flow impeller, and now the problem has been largely resolved
Is it possible to improve the cavitation condition of the pump in other ways, such as by increasing the inlet pressure?
The parameters specified on the pump’s nameplate are measured using water as the medium; it is normal for the medium being used in operation to differ from those specified on the nameplate. To address cavitation, it is necessary to increase the inlet pressure and reduce the temperature of the medium, so that the pump’s inlet pressure is higher than the saturated vapor pressure of the medium at that temperature
With a circulation pump, it’s not possible to change the temperature or the height; the only option is to use an inverter to reduce the speed and thus maintain normal circulation
Currently, both the flow rate and head do not reach the design values. If a frequency converter is installed to reduce the speed, cavitation will be eliminated, and the flow rate and head should increase instead of decrease (coming closer to the design values). I’m not sure if that’s correct? ?