Patent ID: 8197214

Claim:
A variable pitch fan, comprising: a peripheral hub having a front side and a back side; a mounting plate on the back side of the peripheral hub; fan blades extending radially outward from the peripheral hub; a front plate on the front side of the peripheral hub; one or more of the peripheral hub, mounting plate and front plate defining a cylinder having an annular cylinder portion; the annular cylinder portion having an outer cylindrical wall and an inner cylindrical wall; a pitch change piston mounted within the cylinder, the pitch change piston having an annular piston portion with an outer piston wall and an inner piston wall, the pitch change piston having a driven side and a return side; the pitch change piston interconnecting with the fan blades to control pitch of the fan blades; the outer cylindrical wall forming a guide surface for the pitch change piston; an annular seal between the inner cylindrical wall and the inner piston wall; a rotary union housed within the inner cylindrical wall, the rotary union providing a hydraulic supply to the driven side of the pitch change piston; and a piston return drive on the return side of the pitch change piston.