A fan that consists of several streamlined blades mounted in a revolving casing. The cross section and spacing of the blades are designed aerodynamically. This design ensures that the air flows without recirculation between the blades and leaves the rotor in a steady and regularly distributed stream. This appreciably reduces frictional, conversion, and recirculation losses. Fans of a convenient size can handle large volumes of air at the highest pressures likely to be required in mine ventilation.