Check valves permit water flow in one direction only and generally are recommended for all submersible pump installations, explains Robert Pelikan.

It is hard to convince a NEMA guy IEC is better and vice cersa.

The type of charging system used depends on whether the water system uses a suction-type pump, like a shallow well jet pump, or a pressure pump, like a submerisble or deep well jet pump.

Logic states if you have the same amount of air available to push the water out, you will be able to deliver the same amount of water between the pump cycles regardless whether the tank has a diaphragm separating the air from the water.

In fact utilities often limit size of motor that can be stated "across the line" to protect their distribution system.

Operating a three-phase motor on unbalanced power can also cause serious overheating that will dramatically storten its life.

But who says you can't pre-charge a conventional tank?