U.S. Patent Specifications

In a variable‐pitch propeller in combination, a hub, a plurality o£ blades arranged on said hub for adjustment about their longitudinal axis, means displaceable by the action of a hydraulic pressure medium and operatively connected to said blades, an operation of said means effecting an adjustment of the blades and thus a variation of the propeller pitch, a source of hdyraulic pressure supplying liquid under pressure to said blade‐adjusting means, an additional source of hydraulic pressure also adapted to supply liquid under pressure to said blade‐adjusting means, a member determining the magnitude of the hydraulic pressure acting upon the blade adjusting means, a governing member operated by the action of centrifugal forces and a change‐over member, both these members controlling the distribution of the hydraulic pressure medium to said blade‐adjusting means, a further member adapted to interrupt the supply of hydraulic pressure medium to said blade‐adjusting means when a limit of a normal predetermined pitch range is reached, auxiliary valve means for the hydraulic‐pressure medium, which permit a further actuation of said blade‐adjusting means for the purpose of moving the blades beyond that predetermined pitch range only after increased hydraulic adjusting pressure has been able to open said auxiliary valve means, and means connecting said governing member and said change‐over member in such a way that they can be adjusted by a deliberate manual operation for the purpose of connecting said additional source of hydraulic pressure to said other source of hy‐draulic pressure, said member determining the magnitude of the hydraulic pressure acting on the blade‐adjusting means being thereby acted upon in such a way as to increase the hydraulic pressure, so that a greater quantity of pressure medium and an increased hydraulic pressure are available for adjusting the blades beyond the said normal pre‐determined pitch range.