334,456. Associated Electrical Industries, Ltd., (Assignees of Ross, M. D.). Dec. 7, 1928, [Convention date]. Dynamos and motors, cooling.-In a dynamo - electric machine, and especially a large turbo-alternator, which is ventilated by means of a double entry fan on the shaft somewhat removed from the rotor body, provision is made for admitting air to both sides of the fan and conducting the effluent air into an annular chamber adjoining the end of the rotor and communicating with the air gap and ventilation ducts of the machine, a stationary diffuser being arranged to surround the fan, this diffuser having hollow blades through which admission air to the fan is supplied from the side of the fan remote from the rotor body to the side of the fan adjoining the rotor body. Fig. 1 shows the application to a machine in which air enters through a base opening 15 within an end bell 16. The double fan 8 has an air entry on each side and is surrounded by a stationary diffuser 10, -shown separately in Fig. 2, which is attached to the stator frame by an annular plate 12 and to the outer periphery of a depending inner wall 13. Part of the air from the inlet 15 enters the fan axially from the outer side, as shown by the arrow 17, and part passes to the inner side of the fan through the hollow blades 11 of the diffuser and the chamber 18 which is bounded by the inner wall 13. The air on leaving the fan is thrown into the diffuser spaces 21 between the blades where it expands prior to emergence with a reduced velocity. A portion of the air may be bye-passed directly into the rotor through openings 19 in the rotor end without going through the fan, this action being produced by centrifugal action in the rotor ducts.