In-line centrifugal fan

Claim 1

An in-line centrifugal fan comprising: a generally cylindrical tubular housing having a central longitudinal axis, a fluid inlet at a forward end of the housing and an axially opposite fluid outlet at the rearward end of the housing; an annular centrifugal impeller mounted for rotation about an axis of rotation concentric with the central axis of the housing, the impeller beiNg of the type which includes a plurality of radial-type impeller blades arranged in an annular configuration around a central eye and including radially inner leading edges adjacent the eye and radially outer trailing edges adjacent the outside diameter of the impeller, said outside diameter of the impeller at the trailing edges of the radial-type impeller blades being smaller than the inside diameter of the housing such that there is an annular space between said trailing edges and the housing, and a shroud along the forward ends of the radial-type impeller blades, whereby fluid will be drawn by the impeller blades from the eye adjacent the radially leading edges of the blades and will be discharged along a radial path extending from the radially outer trailing edges of the blades, into the annular space, and toward the housing; means for conducting fluid from the inlet of the housing to the eye of the impeller, said conducting means being located forward of said annular space and establishing a zone within said housing axially forward of said annular space; and a plurality of independent axial-type impeller blades mounted for rotation within the housing rearward of the radial-type impeller blades and extending radially between said outside diameter of the centrifugal impeller and said inside diameter of the housing such that the leading edges of the axial-type impeller blades are juxtaposed with said annular space, to the rear of said annular space, whereby the fluid discharged from the radial-type blades into the annular space will be drawn into the axial-type blades so that the fluid will pass in unobstructed free flow from said radial path into an axial path and thereby directed away from said zone to be discharged from the axial-type blades axially toward the outlet of the housing.