US2709035A - Air streaming fan - Google Patents

Description

May 24, 19355 w, sc 2,709,035

AIR STREAMING FAN Filed NOV. 15, 1950 3 Sheets-Sheet l INVENTOR ATTORNEY y 19755 F. w. SCHMIDT 2,709,035

AIR STREAMING FAN Filed Nov. 13, 1950 s Sheets-Sheet 2 ATTORNEY y 1955 F. SCHMIDT 2,709,035

AIR STREAMING FAN Filed Nov. 13, 1950 5 Sheets-Sheet 3 awn gigl5 w 5 9 50 INVENTOR elbdwsw ATTORNEY 6o nited States atent Shine i i-J rateriteo P iay A time:

Fig. 7 is a View like Fig. 4 showing a preferred relationship of the impeller surrounding funnel shell to the 1 1, 1 1: 2,789,033 path swept by tne impencr ol accs. H

Mg. 8 IS a View of the impeller hub iooning in the di AFR STREAMING FAN 5 rection of arrow 3 in Fig. 7 showing the twisted and w e o" Frederick W. Schmidt, Branford, Comm, assignor to The dish-ed natal I EDI-ads J A, C. Gil Cmmany New Haven can a cargo Figs. 9 to l3,'rnciusive, show truncateo portions of tne a as q e I. n ration of Maryland blade or Fig. 8 when cut oil along circumtere tial lines designated by corresponding reference numerals in Fig. 7. to Figs. 14 to 20, inclusive, are sections delineating the 1 cg g (CL 230 117) profile contort: or" the blade on planes designated by corresponding reierence numerals in Fig. 7.

The standard of this improved fan comprises a hollow ease incorporating a downward concavely dished top span 14- against the under surface of which is fixedly clamped by clips 15 the bottom ends of a discontinuous straight beam of air in contrast to the usual breeze lliC rigid circular frame ring i8. This ring for lightness may air flow sent out by ordinary fans to be dissipated in be hollow and formed from metal tubing. inside the ent directions. base there is mounted an electrical reactance unit (not There is much waste in the type of movement imparted shown) whose circuits are controlled by a conventional to air by the conventional household fan because the air four position snap switch (not shown). The operating reclrculalfis at random in y cllfl'fillls bah/66H a handle of the snap switch is a turnable knob 24 accessible around tips of the air impelling blades. This inefficient at the front of the base for switching different strengths action is due partially to vacuum eifects set up close to of current to the fan motor to produce off, high, methe intake face of the revolving impeller blades. 25 diurn and low speeds. Current is derived through a fiexi- One object of the present invention is to direct prac- 1 attachment cord 26. tically the whole volume of air displaced by the impeller The fan motor, impeller and funnel shell of the imblades into a narrow concentrated straight beam of air roved onstruction comprise assembled air stream that is fm'cefuny i' l away {will the fan impeller enerating unit shown in Fig. 3. This may be termed the along H1165 p with ihfi aXiS 0f imp ller t -d0 air streaming unit. it is pivotally mounted and yieldably W that The displacfid air Streams 0m {0 an unusually far stayed on the stationary frame ring 18 at 32 for swinging adjustment about a horizontal diametral axis. it comdistance from the tan at a wind velocity as high as 25 prises a rigid assembly of an electric motor 5 carrying miles per hour.

A Cumribuml'? 6056951.?) to Obtain the ilfmesflid results impeller 55, and funnel shell structure 28. This shell y novfil Principles 0f coopel'filive Shape and la i n hip 35 is composite, forming a hollow annular structure consist- Of the impeller hill) and me impeller blades, in P ing for lightness and manufacturing feasibility of two drawn sheet-metal parts. The circumferentially inner tion with a stationary air directing funnel shcll arranged according l0 newly dlswvered pfmcipls 9f aerodynamic part or air conduit shell 46 in conjunctionwith the shape of impeller hub 82 forms an axially short annular Venturi effect.

A fllfihfir i i5 efieciivcly l0 shield the whirling 4.0 passageway for the air traveling through the fan in the direction of arrows L2 in Figs. 2 and 3 which tapers to a impeller blades of the fan so that they cannot accidentally minimum girth of passageway at about the tip of the fan Application November 13, 1950, Serial No. 195,210

This invention relates to air streaming electric fans 15 capable of generating and forcefully projecting a narrow come in contact with or damage the person or anyone 116211 the fan W611 when lhfi fan is being handled f0]? blades 90. The circumferentially outer part of the funnel relocating it Or for aiming it in flifiefeni directions While shell structure is a casing shell 44. This casing shell and running.

is conduit shell 46 slightly overlap at circular meeting mar- A Sim fllTlhfiI' 051.59? is insreflse the air displacing gins in a manner to bind the funnel shell parts permanentefiiciency of a light three-bladed impeller of small size l d fixedly together, y JTIOVBI p g and manner of assfimbly 0f Various The front opening of funnel shell is spanned by a Sheet metal P of which it is COITIPOSedgrid 41% which may be mold produced as an integral These and relalvd OblECfiVES will PP in greater unit of stiff plastic material. The border rim of grid 48 particular from the following description of a Successful is removably secured by screws is in an annular rabbet @mbfidimfilli of invemlim having reference the formed in the front face of casin shell 4-4. Screws 5t) accompanying drawings wherein: have threaded engagement with casing 44. The shape 1 is a from elevation Of a fan embodying lh'presto which grid 48 is molded produces intersecting thin out improvements drawn on a smaller scale than its preregg vane 52 of sufiicient depth to guide air in the rred actual size, a porti n of he a e b ing broken single direction desired as the air passes through the grid, away to expose the mounting of the frame ring upon th possessing a thinness that tapers according to principles base. of airfoil contour as shown in enlarged detail in Fig. 2. 2 is an enlarged view taken in s ct o On either Grid 58 thus divides the discharge opening for the im- Of the planes 22 in Fig. 1 l ing in the dir fiti ns 0f 0 pcller driven air into cubicles of honeycomb nature. One the arrows. function of these cubicles is to counteract vortex or whirlg- 3 is a side i f the f l mo r, fan impeller and in motion of the outstreazning beam of air. Tests have funnel; shell assembly shown partly in section on'the prover. that mere parallel spaced vanes in the form of plane 3-3 in Fig. 1 looking in the direction of the ardisconnected slats cannot function as an equivalent for rows. the cubicles herein described for the purposes of the Fig. 4 is an enlarged fragmentary front view of the air present invention. it will be noticed that the passageways impeller.

- Fig. 5 shows a true or non-foreshortened outline View constraining conduits for the streaming air in the central of the blade before its assembly to the impellerhub. region of the grid than in the border regions of the grid Fig. 6 is a view taken in section across the root end of because the vanes are deeper in the central region, the an impeller blade looking toward the axis of the impeller outermost edges of the vanes comprising the front face from the curved line 66 in Fig. 4. of the grid imparting to the overall grid face a shape for the air through the cubicles afford somewhat longer.

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that merges pleasingly of the bordering front of somewhat spherical contour with and forms a continuation face contours of the casing 44.

The torpedo s sped body of the fan motor is desig nated 54. it derives its support coaxial with conduit is solely from the funnel shell structure through th "sodium of four stiff spider fins 55 each of triangular shape and which place a substantial portion of the length of the motor body in outboard or rearwardly offset relation to funnel shell Fins 56 are equally spaced about the motor body and tired to the case of the la ter by lugs 55% welded thereto, and with the strengthening assistance of three hoops 7d, 72-, 7d of round wire, increasing in diameter in the order named. These hoops are nested in not hes in the edges or" the spider fins. Fins 56 are fixed to conduit shell 46 by holding screw 66 engaging nuts 63 and surrounded by vib1....on deadening washers 6d of distortable resilient material.

Fig. 3 shows the impeller to include central hollow stud shaft 76 removably fixed on the motor shaft 73 by set screw till. Fixedly supported at the front end of stud shaft 76 is the nose end of the bullet-shaped hollow hub of the r whose sheet metal wall is lanced in three cir spaced locations to form the ventilating openings 8 a W The tongues which are struck inward at these openings revolve in unison with the peller and act as fan blades to set up a region of partial vacuum inside the hub 33 which sucks ambient air into the motor case through apertures 85 in the rear end thereof, thence past the body of the motor inside of the case for cooling the motor, which air is finally scooped outward from the hub 82 through openings $4 by tongues 3 3 and joins the main stream of air generated by he impeller blades i A hole 83 in the hub wall gives access for a screw driver to the set screw The mutually facing convexities of conduit 46 and impeller hub in all diametral planes containing the axis of rotation of the impeller produce an annular passageway therebetween of Venturi nature whose narrowest portion is spanned by each of three impeller blades N). But it will be noticed that such narrowest portion of the annular passageway is not concentrated at the axial end of the passa eway having the smallest overall girth but is distributed well over the total length of the passageway which calls for the blades 90 to extend forward or toward the left in Fig. 3 as they proceed outwardly from the hub and sweep sucn full axial length.

The impeller blades 9%? are alike, having a root portion E2. or maximum transverse blade width relatively near the impeller axis and having in general the outline shape of a partial. crescent delineated by a convex air entering or leading edge 93 and a concave trailing edge 1%, both of which edges extend from the root portion 92 of the blade and. converge throughout the arcuate length of the blade form a trailing end portion ml of the blade terrninatingin a blunt trailing tip M32 relatively distant from the impeller axis. The trailing edge Hill is the only part of the blade which lies in a plane represented g 'caily by the broken line P common to Figs. 14 to 20, inclusive. The trailing end portion 161 of the blade aligns in general with its own orbit of circular travel and its tip 1&2 points backward with respect to the direction R of blade travel. Between the leading edge '93 of the blade and the trailing edge 13% of the blade the front or air-attack surface of the blade extends \Viih concave curvature from one to the other of said edges in all planes that are normal to the blade edges or crosswise the blade as shown in Figs. 14 to 20, inclusive, as well as all paths that are shown in Figs. 9 to 12, inclusive.

In addition to delineating the contour of the blade surfaces, Figs 8 to 12, inclusive, serve to show twisted nature of the blade wherein its angle A relatively steep pitch in the root portion 92. of the blade merges into an iii angle B of relatively mild pitch in the trailing portion ltll of the blade.

The back or trailing surface 196 of the blade is convex d of contour corresponding to that of the front or air attacking concave front surface 104 of the blade if the blade be formed from thin sheet metal of uniform thickness. This results in its being fashioned on airfoil or streamlined principles of contour. A very thin blade so formed from sheet metal will on the cats ear principle possess the advantageous stiffness of a tapering trough tied U. S. Patent Reissue No. 21,443, granted y 7, 1948 to Alfred C. Gilbert et al. Such trough line lvll*-/l of the blade in Fig. 5. Figs. 14 to 20, elusive, show this trough to be deepest in the root tion the blade and to become progressively less the trailing tip N2. if it is desired to make the blade ot' molded or cast solid material, the trailing sur- "ace i596 need not be changed but the front or air attacksur"ace can be such as would be generated by raight line radial to the axis of propeller rotation svi about said axis while simultaneously advancing .lon said axis. An air attaching blade surface so generated will be that of a helical ramp.

The root end of each blade has at least three fastening tongues such as 94 which project edgewise from the blade and penetrate closely fitting slots 96 in the impeller hub to be bent over in opposite directions close to the inner surface of the hub wall as shown in broken lines in Fig. 6, where if preferred they may be copper brazed in place.

The aerodynamic action of blades having the improved shape and disposition with respect to their path of travel provided by this invention as shown in Figs. 8 to 20, inclusive, is as follows: The air as it enters funnel shell 46 through the swirl bafiling fin planes S6 is immediately cleaved near the right end of the annular Venturi passageway by the convex leading edge 95's of each impeller blade traveling in the direction of arrow R in Figs. 4, and 7 to 14, inclusive. The root portion of this leading edge at and near the hub 82 first attacks the air after which the remaining portion of the edge slices into the air at a slant or with a diminishing angle of attack along the trailing end portion of the blade thereby to compensate for the higher linear speed of those portions of the blade located at a greater radial distance from. the impeller axis. It will be apparent from the arrows R appearing in all of Figs. 9 to 13, inclusive, that with respect to the direction of travel of the blade no portion of the concave front surface ltl i of the blade forms a hollow or pocket following the entrance of the leading edge of the blade into the air. Such is undesirable because it could set up the disturbing suction or back-dragging effect of a partial vacuum pocket existing in front of the blade. The blade advances into the air with relatively less linear speed at its root end portion which has the greater air displacing {2 area and With relatively greater linear speed at its trailing end portion which has less air displacing area so that air is displaced with uniform volumetric effect at all radial distances from the axis of rotation as it is scooped up by the curved trough of the blade and the duty of displacing the air is uniformly distributed all over the working blade surface. Backward escape of the air around the trailing edge of the blade is minimized and maximum pick. up and displacement of air occurs with a relatively small. impeller. As the blade advances ahead of space from which it has displaced air it leaves a minimum of vacuum in its path. This is because the trailing end portion lill of the blade tapers all the way to its trailing tip 102, and also because the trailing end portion aligns longitudinally with its own circular path of travel while pointing backward with respect to its direction of travel wherefore the blade withdraws gradually rather than abruptly out of the space from which it has displaced air.

When the stream of air efiiciently generated by this improved impeller becomes discharged at a resulting high velocity through the cubicles defined by grid vanes 52, practically all swirling motion of the stream that then exists is baffled by the considerable depth and crosswise intersecting relationship of the vanes 52. The spherical contour of the front face of the grid appearing at the extreme left in Fig. 3 produces a longer extent of the grid vanes 52 in the path of air flow near the center of the grid than at the circumferential margin of the grid and this contributes to the effectiveness of the gridin breaking up and rectifying the swirling of the air stream so that its distance of projected travel away from the fan will be increased. The combined result of the foregoing described features upon the generated stream of air is to project it in a narrow, non-flaring, stream flowing forcefully in a concentrated beam in whatever single direction the fan is aimed.

The particular construction by which the fan shell 28 is pivotally supported at 32 upon the fro. o ring 32 is the subject of claims in a copending application, Serial No. 183,524, filed October 5, 1950, now Patent No.

2,660,368 granted November 24, 1953. The particular construction of the fin plates 56 and their combination with the funnel shell 46 and motor 54 is the subject of claims in a copending application, Serial No. 188,523, filed October 5, 1950, now Patent No. 2,672,280, granted March 16, 1954.

The following claims are directed to and intended to cover not only the precise shapes and relationship of parts which are herein disclosed to explain the underlying principles of the invention but all fair equivalents thereof falling within a broad interpretation of the language of the claims.

I claim:

1. An air streaming fan embodying in combination, a rotary impeller huh outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impellet hub presenting inwardly a convex profile in said planes and of sufiiicently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, the bladespannned shortest distance between said impeller hub and said conduit shell lying across said passageway in a direction that is obliquely disposed in relation to said axis of rotation, whereby the wholebody of each of said imp-ailing blades sweeps through an axial extent of said passageway greater than the axial extent of any individual blade at any given distance from said axis thereby to work against air drawn through said passageway substantially throughout the axial extent of said passageway.

2. An air streaming fan embodying in combination, a rotary impeller hub tapering throughout a major portion of its axial length from a relatively large end to a relatively small end and outwardly presenting between said hub ends a convex profile in planes containing its axis of rotation, a funnel-shaped stationary air conduit shell coaxial with and encompassing said hub tapering throughout a major portion of its axial length from a relatively large end to a relatively small end and inwardly presenting between said shell ends a convex profile in said planes facing said outwardly convex profile of said hub, said lengths of hub and shell being concordant in axial position and forming therebetween an annular air passageway increasing in radail width in both axial direc-.

tions from an intermediate point in the length of said passageway having a minimum width substantially no greater than the maximum transversedimension of said hub, and air irnpelling blades having their root ends' mounted'on said hub extending therefrom in a direction to span and sweep around in said minimum Width of said passageway.

3. An air streaming fan as defined in claim 2, in which each of the said impeller blades is of dished contour making one face of the blade concave and the other face thereof convex, the blade being so shaped and so pitched with respect to the plane of impeller rotation that said concave face of the blade attacks the air Without being reentrant with respect to the air attached thereby.

4. An air streaming fan as defined in claim 2, in which the nearest together points of the said shell and hub convexities occur respectively at the said relatively small end of said shell and at a point on said hub substantially midway the axial length of the latter, wherefore the said annular passageway is relatively wider in a radial direction at both of its ends than intermediate its axial length.

An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impeller hub inwardly presenting a convex profile in said planes and of su'iliciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having an arcuate curvature extending backward with respect to the direction of rotation of said hub defined throughout by a convex leading edge of the blade and a concave trailing edge of the blade, said blades being of such twisted shape that the portion of each blade nearest said hub has relatively steep pitch and the portion of each blade nearest said conduit shell has relatively less pitch in relation to the plane of rotation of the impeller hub.

6. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impeller hub presenting inwardly a convex profile in said planes and of sufficiently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades being longitudinally of arcuate curvature and tapering like a partial crescent from a crosswise broadest root end portion of the blade at said hub to a crosswise narrowest trailing end portion of the blade at said conduit shell.

7. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impeller hub presenting inwardly a convex profile in said planes and of sufficiently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having ani arcuate curvature extending backward with respect to the direction of rotation of said hub defined throughout by a convex leading edge of the blade and a concave trailing edge of the blade.

8. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impeller hub presenting inwardly a convex profile in said planes and of sufliciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having the general outline shape of a partial crescent delineated by a convex air entering edge and a concave trailing edge both of which edges extend from an air attacking root portion of the blade having maximum breadth rela tively near said axis of rotation and converging toward and throughout an elongate trailing end portion of the blade relatively distant from said axis, said trailing end portion of the blade aligning with its orbit travel about said axis and pointing backward with respect to its direction of travel, the air attacking surface of said blade between said blade edges extending with concave curvature from one to the other of said edges of the blade in all planes normal to said edges.

9. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a tunnelshaped stationary air conduit shell encompassing said impeller hub presenting inwardly a convex profile in said planes and of sufiiciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having an outline shape that is arcuaely curved throughout the length or the blade and whose length tapers like a partial crescent merging from a relatively broad root end portion of the blade into a bluntly pointed relatively narrow tip portion of the blade, one surface of said blade being contoured to form a smooth trough progressively extending throughout said arcuate length or" the blade and diminishing in depth from said root end portion to said tip portion of the blade.

10. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnelshaped stationary air conduit shell encompassing said impeller hub inwardly presenting a convex profile in said planes and of sufiiciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having an areaate curvature extending backward with respect to the direction of rotation of said hub defined throughout by a convex leading edge of the blade and a concave trailing edge of the blade, said leading edge of the blade.

progressing from a relatively more radial disposition near the said impeller hub to a. relatively more circumferential disposition in the said trailing end portion of the blade,

ll. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnel-shaped stationary air conduit shell encompassing said impeller hub inwardly presenting a convex profile in said planes and of sufficiently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, each of said blades having an arcuate curvature extending backward with respect to the direction of rotation of said'hub defined throughout by a convex leading edge of the blade and a concave trailing edge of the blade, said concave trailing edge of the blade lying sub stantially completely in a single plane.

12. An air streaming fan. embodying in. combination,

,arotary impeller hub outwardly presenting a convex profile in planes containing its. axis of rotation, a funnelshaped stationary air conduit shell encompassingsaid impeller hub presenting inwardly a convex profile in said planes and of sufiiciently large compass to leave an-annular air passageway of progressively varying size along said planes between said shell and said hub, and air inipelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, together with a grid extending across said conduit shell at the air discharge side of said air intpelling blades comprising intersecting cross vanes of substantial depth dividing the pathway for the discharged air into cubicle passageways thereby to inhibit 33 g in the stream of air projected away from the fan.

13. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, a funnel-shaped stationary air conduit shell encompassing said impeller hub inwardly presenting a convex profile in said planes and of sufiiciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, together with a grid extending across said conduit shell at the air discharge side of said air impelling blades comprising intersecting cross vanes of substantial depth dividing the pathway for the discharged air into cubicle passageways thereby to inhibit swirling in the stream of air projected away from the fan, said vanes being of air foil shape tapering in thinness in the direction of air fiow therethrougr 14. An air streaming fan embodying in combination, a rotary impeller hub outwardly presenting a convex profile in planes containing its axis of rotation, 21 funnel-shaped stationary air conduit shell encompassing said impeller hub inwardly presenting, a convex profile in said planes and of sufficiently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impelling blades carried by said hub in positions to span and circularly sweep substantially the narrowest portion of said annular passageway, together with a grid extending across said conduit shell at the air discharge side of said air impelling blades comprising intersecting cross vanes of substantial epth dividing the pathway for the discharged air into cubicle passageways thereby to inhibit swirling in the stream of air projected away from the fan, the front face of said grid most remote from said impeller hub being comprised. of the edges of said vanes and convexly contoured in a manner to produce a greater length of said cubicle passageway near the center of the grid than near the margin of the grid.

15. An air streaming fan embodying in combination, a

rotary impeller hub outwardly presenting a convex-profile] in planes containing its axis of rotation, at funnel-shaped stationary air conduit shell having relatively small and large ends and encompassing said impeller hub presenting inwardly a convex profile in said planes f cing said convex profile of said hub and of suiliciently large compass to leave an annular air passageway of progressively varying size along said planes between said shell and said hub, and air impell'ng blades having their root ends mounted on said hub so that said blades are positioned to span and sweep around in the portion of said annular passageway that intervenes between the nearest together points of the mutually facing convcxities of said hub and of said shell,

together with an electric motor carrying the said impeller hub, said motor having a hollow casing containing ventilating openings in its end opposite said impeller hub, and said impeller hub being perforate and hollow and carrying air iznpelling tongues on the interior thereof arranged to induce a motor ventilating flow of air inward of said en's-- ing through said openings and outward through said perforate impeller hub.

{References on following. page) References Cited in the file of this patent UNITED STATES PATENTS Wells Nov. 6, 1923 Hoover Nov. 2, 1926 Leinweber Apr. 5, 1927 Lawaczeck Dec. 13, 1930 Gilbert Nov. 26, 1935 Bentley Feb. 15, 1938 10 Anderson Dec. 17, 1940 Thorp May 23, 1944 Prisbie Mar. 6, 1945 Hagen Dec. 11, 1945 De Flon Apr. 16, 1946 Sutton May 29, 1951 Sutton Nov. 11, 1952

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