Because the bowl assembly is submerged, so the impellers are permanently flooded. There is no suction lift to establish and no suction line to lose prime in. That is the format's central advantage and the reason it is chosen wherever the liquid level sits well below the driver.

The stack of impellers and diffuser bowls at the bottom of the column that does the pumping. Head is built by adding bowl stages, so the same design covers a wide duty range - stages determine pressure while column length accommodates the depth to the liquid.

By the pumped liquid itself, by injected clean water, or by oil, and the choice follows the liquid. Product lubrication suits clean water; injected clean water suits liquid carrying grit that would destroy the bearings; oil lubrication cannot be used where the liquid must remain potable.

Deep boreholes and water wells, wet pits and sumps, river and canal intakes, cooling tower basins and fire pumps drawing from underground tanks. The common condition is a liquid level too far below the driver for a surface pump to lift from reliably.

Pulling the complete column and bowl assembly out of the pit or bore, which requires lifting equipment and headroom directly above the pump. It is a substantial operation and should be planned for at installation, since without the clearance the pump cannot be serviced in place at all.

A bent or misaligned column, worn line shaft bearings, or a shaft that has lost straightness. Diagnosis is difficult because the problem is underwater and only its effects are visible at the surface, and left unaddressed the vibration will eventually break a shaft.

On a vertical turbine the motor is usually at the surface, dry and accessible, driving through a line shaft. On a submersible the motor is underwater directly below the bowls, which removes the line shaft and its bearings but puts the motor where it cannot be inspected and where a seal failure floods it.