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Interesting pump - what is the diameter of the main body?
indeed, Admiral is correct. the curve of the vanes should be in the other way.
From what has been said ST knew what they were doing when they designed this pump, one feature I have never seen is the holes through the impeller, it only has 0.002” clearance from the casing round the outer edge so no meaningful quantity of water would travel behind it,it also has a 0.031” gap behind it, so is there a reason for the holes?
That gearbox made a huge difference! What ratio is it?
It certainly does increase the flow of the display setup but bear in mind that if you actually want the pump to do real work eg lift water to a head or against a restriction then it will have an adverse effect as the engine has less mechanical advantage.