Banki Turbines

CWarner is right. There is plenty of valid information available on Banki and similar crossflow turbines, but what you are reading is partly false and the rest too vague to be useful.

Banki turbines (known by various other names in slightly variant forms) are impulse turbines - that is they operate mainly by changing the velocity vector of a stream of incoming fluid. Potential energy is converted to kinetic energy in the inlet nozzle, and this high-velocity stream is deflected by the blading in the process of doing work on the blading.

This distinguishes them from reaction turbines that operate mainly by generating pressure differentials within a stream of more or less constant velocity. One quick way of distinguishing reaction and impulse hydro turbines is to check whether the casing is filled with water during operation. If it has to be full of water for the turbine to work, it's a reaction type; if the water runs through the casing as a distinct jet, it's an impulse type.

Bankis are interesting because they are easy to build - their blading is constant-chord, untwisted and supported at both ends (intermediate support is also possible) - and because they have possibly the widest range of usable head and flow combinations of any hydropower equipment available on the market. Other equipment tends to be very specialized - Francis turbines for high flows, moderate heads; Kaplan turbines for low head, high flow; Pelton turbines for very high heads and low to moderate flow, and so forth. But Banki machines overlap the range of application of all of the above - mainly the Francis and Kaplans, but also the low-head end of the Pelton range. At least one European firm (Ossberger?) takes advantage of this to offer this kind of turbine for a wide range of sites.