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First, what kind of impeller and pump is this? I mostly see centrifugal impellers in the net.

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I googled about this but didn't find direct reference to it. Most are about centrifugal pumps. Although I managed to find a video that discussed something similar to it. But in the following, the vane is flexible and the upper wall seals it and the presenter says it creates negative pressure right at the part pointed by the screwdriver. However, in the impeller above, the vanes are solid and not flexible, so where is the negative pressure created that suck the water and how is the cavitation performance of the above?

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It is called a Regenerative Turbine Pump. It is lower efficiency than a staged centrifugal, but would fill the higher pressure single stage niche. Even though its max efficiency may be lower than a staged centrifiugal, it may be a good fit for your application. When considering efficiency, you should focus on the whole system not just the pump. Select a pump that matches your flow and pressure requirements.

For air it is called a "Regenerative Blower" or sometimes a "Reblower". They are not especially efficient, but have low capital cost, no rubbing surfaces, and fill a niche of having a higher single stage pressure than a centrifugal fan.

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    $\begingroup$ Thanks. Can finally google them wit d right words. Say, about pushing. I read pump can push or pull. Pushing means like a submersible pump where liquid is being pushed up. Here there is abundance of water so cavitation is harder to occur. And in a shower, pushing means the water has to push up the showerhead located at higher position hence the pump needs to push water up and hence there is more abundance of water at inlet and there not limited by cavitation or atmospheric pressure? And therefore pushing can lift the entire meters of water but is in lifting in the discharge side or inlet side? $\endgroup$
    – Jtl
    Commented Sep 30, 2020 at 1:13
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    $\begingroup$ Same rules apply. Just don't go below atmospheric pressure on your inlet and you will be fine. $\endgroup$
    – ericnutsch
    Commented Sep 30, 2020 at 1:26
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    $\begingroup$ Flow and pressure are different things. Pressure is a potential like voltage. Flow is movement like current. A D battery and a AAA battery have the same voltage but can deliver much different currents. Similarly pumps can be different sizes but have the same pressure. A river has thousands of gallons an hour of flow but only inches of water pressure moving it. $\endgroup$
    – ericnutsch
    Commented Oct 1, 2020 at 23:13
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    $\begingroup$ For a certain user however (like your shower nozzle), the pressure determines the flow rate. Just like if I have a light bulb it will draw a certain amount of current at a certain voltage. It doesn't matter if I use a AAA battery or a D battery the current or the flow will be the same because the voltage or the pressure is the same. $\endgroup$
    – ericnutsch
    Commented Oct 1, 2020 at 23:16
  • $\begingroup$ I would recommend posting a new question, drawing a diagram with all known pressures and flows at each location. Then ask specifically for what info you need out of the diagram. I think that will be the best way to proceed. $\endgroup$
    – ericnutsch
    Commented Oct 2, 2020 at 6:51

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