Figuring Out Pump Impeller Size for Pump Design Based on Given Motor?

Flow rate is more closely related to axial dimensions (and rpm) of the impeller. Diameter (and rpm) relates more closely to pressure.

9cm may, or may not be too big, depending on many factors. Sounds optimistic, but who knows.

If you are 3D printing, start there and trim if needed.

Even the pros don't get optimum performance without some tuning.

Send some pictures, please.

Why bother to print an impeller which may not withstand abrasion and cavitation? Just find a pump head or impeller with the curve you need. Let others do the R&D. Not easy to print the mounting thread, or machine it either. Blind inside threads ain't no fun.

I saw no mention of what you are pumping or the application. If there was a gear pump in place I would assume that the fluid is an oil or some other viscous material since one generally does not use a gear pump for non-lubricating fluids unless there is an external method of timing the gears to prevent tooth to tooth wear. Viscosity will have a major detrimental affect on a centrifugal impeller output when it gets above a certain range. Since a gear pump is a "positive displacement pump" it also means that your capacity vs. discharge pressure are pretty constant and have a linear relationship to speed as opposed to the the TDH and flow of a centrifugal which follow the curve and will vary based on the system losses. Hopefully you will not be operating anything of a critical nature will this "design" like your home furnace heating oil pump.

Sorry for the late reply. Have been incredibly busy.

Pumping water, nothing else.

There will be no major application for this other than simple fun and learning so no worry about safety issues.

Thanks for the replies. I've made a general housing and in the process of printing off a few different sized impellers to test.

Pictures as requested:

Wow! You've given us a tough one here. The basic premise of your investigations is correct as far as it goes. Again, as I have said in other discussions, centrifugal pumps are bound by the Laws of Affinity. In respect to the speed of the pump, here are some facts. There is only one way to increase or decrease the head (pressure) that a centrifugal pump will produce. That is to vary the "tip speed" of the impeller. If, for instance you have an impeller with a 5" diameter (I am from the US so you'll have to bear with me on this), and it is spinning at 1750 RPM, the tip speed would be 20.825 fps (English measurement again - sorry). There are two ways to increase the tip speed you can 1) - Speed up the driver (say from 1750 RPM to 2000 RPM) 2) - increase the diameter of the impeller thus increasing the travel of the tip of the impeller in each revolution. Now the Laws of Affinity say that the Head changes in proportion to the square of the speed. That is how you can predict the head you can get from the impeller. These laws also say that the flow changes in direct proportion to the tip speed. As you can see, these predictions are based on the CHANGES in the tip speed. The flow, for instance, is relative to the height and type of the impeller. A wider, thicker if you will, impeller delivers more flow than a lower, more narrow impeller. So you see where i am going with this. The element that is missing is satisfied by - testing. You test the impeller and adjsut as necessary with predictable calculations. You have selected a very tough task. Good luck.