On cavitation in positive displacement pumps
Thread Content
A sliding vane pump (a type of positive displacement pump) was installed recently. Its flow rate is 60 m3/H, the height of the receiving tank is 20 meters, and both the inlet and outlet of the pump are DN80 in size. When the motor’s frequency is increased beyond 70%, a cavitation sound is heard inside the pump chamber; as the frequency increases further, the cavitation noise in the pipes and within the pump intensifies. The hot water drawn is from an underground tank; its temperature is around 85°C, the depth of the tank is about 2 meters, and the liquid level remains at a level roughly 1 meter below the axis of the pump inlet. How can experts solve the problem of cavitation? All I can think of is 1. Pressurizing the pump inlet (it’s not a closed tank, so it’s difficult to increase pressure) ； 2. Lower the temperature of the liquid in the underground tank. Could someone expert help calculate the water temperature at which vaporization can be eliminated? Initially, it is planned to install a mixing pipe for cold and hot water at the end of the suction pipe, in order to add an appropriate amount of cold water to lower the inlet temperature. I’m not sure if this approach will work ? Thank you all! !
Check whether the inlet pipe is too small
Temperature is 85, the liquid level is still below that of the pump; there’s a problem only if cavitation occurs.
I wonder how the liquid is drawn in; the positive displacement pump is higher than the tank, which is open-top, and the water temperature is 85°C
Positive displacement pumps have a strong self-priming ability
Personally, I think it’s better to add some buffering by widening the entrance.
The pump needs to be primed in advance; as a precaution, a buffer tank is installed at the pump inlet.