When lifting water to a high height like a water tower, I see where water pumps have an efficiency curve, that drops off fast. Could building a reservoir at the height of the curve, and then installing a second pump to finish the lift save electricity? Could bubbles improve the efficiency curve or save electricity by inserting a vortex jet into the pipe?
closed as off-topic by ZeroTheHero, Kyle Kanos, Jon Custer, user191954, Qmechanic♦ Sep 22 '18 at 14:35
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You can absolutely get more efficiency from doing this properly.
There are many ways to run pumps in series to get a better efficiency than if you used a single pump with one curve. I found a pretty good article on this page.
You can match the curves to use less horsepower to get the same head pressure and flow rate.
The main downside is the increased equipment costs of buying and maintaining multiple pumps. You would also have to make sure that the final pump can operate with the maximum head pressure in your system.
As far as inserting a vortex into the pump; I don't think this is often a good solution. Generally you want to avoid having any air in the system. For this reason, pump designs have to be wary about suction pressures to avoid forming air bubbles on the propellers (called cavitation).