US2329696A - Centrifugal apparatus - Google Patents

Description

T CHESTER CENTRIFUGAL APPARATUS Filed Feb. 11, 1942 Sept. 21, 1943.

Patented Sept. 21, 1943 UNITED STATES PATENT OFFICE CENTRIFUGAL APPARATUS Thomas Chester, New York, N. Y.

Application February 11, 1942, Serial No. 430,467

Claims.

This invention relates to that type of centrifugal apparatus known variously as fans, pumps, blowers or exhausters, hereinafter termed b1owers, the uses of which are to pump, compress or expand, or otherwise generally tomove, fluids which may be gaseous or liquid.

The present application is a continuation in part of application Serial No. 314,738, filed January. 20, 1940, showing more clearly the types of blades in a rotatable impeller for centrifugal apparatus therein disclosed.

Such centrifugal apparatus comprises two principal parts, a rotatably mounted impeller, and a stationary casing therefor which is usually of gradually expanding or volute form. The impeller is of substantially radial outward flow type, provided with a plurality of blades concentrically arranged as in squirrel cage or other formation about it axis, so as toimpart motion to the fluid within the ports between the blades. This imparted motion causes the fluid to flow from the periphery of the impeller into the surrounding casing and thence through the discharge outlet of the casing. Since the impeller is of substantially radial outward flow type, the casing is provided with a circular inlet opening at one or both sides, throughwhich the fluid may enter the hollow of the impeller about which the impeller blades are arranged.

Considering one inlet opening only, flow of the fluid therethrough if not otherwise directed by extraneous conduits will be substantially parallel with the axis of the impeller, thence moving into the ports or spaces between the impeller.

blades, the characteristic path of flow thus including a change in direction of movement of around 90 degrees.

The impeller imparts no energy to the fluid until the latter actually enter the ports between the impeller blades, but the outward discharge of fluid from th periphery of the impeller produces a partial rarefaction or reduction in pressure of the fluid within the hollow of the impeller. This causes fluid which is under the pressure of the external atmosphere to enter the inlet opening to gain access to the lower pressure regions within the hollow of the impeller andin the ports between the impeller blades.

The compression head of the fluid, as denoted in some cases by the barometric pressure, is

therefore reduced in order to cause flow and to overcome resistance caused by impediments to flow and by any losse incident to-flow. This loss of compression head must of necessity be replaced by the rotating impeller in order to permil: the flow of the fluid dealt with, through the outlet of the casing to a region under the prevailing atmospheric pressure, or under a higher as vortical whirls or eddies are more easily pro-' I duced than prevented and once formed they continue in action for considerable distances of fluid travel. In generalsuch vortices are caused by dissimilar velocities of adjacent parts of a volume of fluid in motion, and it is therefore desirable to maintain substantiall uniform velocities in all parts of a stream of fluid, with reference to any particular cross section of said stream by a plane at right angles to the direction of flow.

It is also desirable that all parts of a stream of fluid in its passage through a blower should be caused to flow through channels which have cross sectional areas properly adapted to maintenance of uniform velocity, or alternatively to avoidance of abrupt acceleration or deceleration by sudden reductions or expansions of cross sectional area.

Consequently a large parabolic deflector, or a conical deflector with rounded apex closely approximating a parabolic deflector, should be provided within the hollow of an impeller about which the impeller blades are arranged. In this manner the reduction in cross sectional area available for the flow of the fluil which enters the casing inlet can be effected uniformly, so as to deflect the fluid through an angle of approximately degrees from its initial direction of movement and cause it to enter the ports between the impeller blades with little or no turbulence.

Usually the fluid which enters an inlet of a blower has no spin or angular rotation, In entering the space or port between two adjacent blades of a revolving impeller, the fluid moves.

in a substantially outward direction radially. The port entrance however has high angular velocity and in consequence the fluid enters the port angularly, with an angularity which is the resultant of the radially outward velocity of the fluid and the angular or circumferential velocity of the port entrance. As variations in resistance to flow extraneous to the blower occur, the radially outward flow of the fluid changes and consequently the angularity of fluid flow into the port entrance increases as extraneous resistance is decreased, and decreases as the said resistance is increased. As blowers are applied with con-- siderable amplitude or range in what is known as ratio of opening or relationship in volumetric capacity and consequently variation in radially outward flow of fluid through the ports of an impeller with respect to extraneous resistance, a corresponding amplitude in range of the resultant angularity of fluid flow into the port entrances is necessarily required. This makes it necessary to provide latitude in the conformation of impeller blade ports and therefore precise angles of the blade sides which form the ports cannot be stated.

In entering the port between .two adjacent.

blades ofa revolving-impeller, the fluid acts ,as though it were a high velocity stream directed angularly into the port of a stationary impeller. This results in the fluid striking the advancing side of any impeller blade and receding from the back or following side of the next adjacent preceding blade in the direction of impeller rotation. Consequently the port or space between each two adjacent blades should conform in shape to the natural path of the fluid stream, the said path varying in angularity in-accordance with the particular. application as regards ratio of opening as previously stated. Improvements in blade shapes are desirable in blowers generally, and particularly in blowers having impeller blades which have greater axiallength than radial-depth and which have concave frontal surfaces facing in the direction of impellerrotation.

According to my invention,. 1- provide novel means for reducing energy losses within the ports between any two adjacent blades of an impeller. I'also-employ means in the form of a parabolic deflector within the hollow of an impeller, or a conical deflector with a'rounded apex closely approximating a. parabolic deflector, for co-acting with novel blade means for preventing or minimizing the production and continuance of energy dissipating vortical whirls and eddies within a blower.

-The exact nature of my invention together with-further objects and advantages thereof will be apparent from the following description taken in connection with the accompanying drawing in which Fig. 1 isa sectional elevation as in the plane of the line |I of Fig. 2;

Fig. 2 is a side elevation of the same with a part in cross section to show one embodiment of the relative positions and types of the substantially crescent shaped blades having their forwardly inclined concave frontal surfaces facing in the direction of impeller rotation I employ to provide a space or port between each two next adjacent blades conforming in shape to the natural path of the fluid stream.

Fig. 3 is a vertical cross section through the impeller similar to the part in cross section in Fig. 2, but to a larger scale in order to show more clearly the contours of the front and back surfaces of the substantially crescent shaped blades which form the side walls of the ports which conform in shape to the natural path of the fluid which flows through them,

Like numerals refer to like parts throughout the several views.

With reference to the embodiment of the invention shown in Figs. 1 to 3 of the drawing, I is the impeller of the blower which is secured to a shaft 2 mounted in suitable bearings, not shown, so as to be rotatably driven.

The casing 3, arranged about the impeller, has an inlet opening 4 leading into a hollow 5 within the impeller and surrounded by blades 6 of the latter. These blades may have a variety of different forms as regards contours of their frontal and rear sides providing they are substantially crescent shaped in cross section. In general the blades employed in the present invention have greater axial length than radial depth, usually having a length which is at least four times their radial depth and the radial depth of the blades is usually small with respect to the radial distance of the blades to the axis of the impeller. For example, as shown in Figure 1, the radial depth of the blades may be approximately oneseventh of the radius of the impeller, this being approximately the greatest radial depth of the blades used in impellers of the multiblade type.

In Fig. 3 of the drawing I have shown seven blades. The blades 1, 8 and 9 shown in the middle portion of said drawing are of the usual uniform thickness, forwardly inclined type. The blades l0 and H shown to the left of said figure embody therein blades similar, as regards their concave frontal surfaces, to the blades 1, 8 and 9, but have on the back thereof, in relation to the direction of rotation of the impeller, rearward portions 14 and I5, respectively, positioned as shown and so formed asto substantially reduce the port width between next adjacent blade formations in relation to their circumferential pitch or spacing, so that this port will conform in shape to the natural path of the fluid stream passing through said port, the port width at approximately half the radial .depth of said blades however being made as great as can be efficiently filled at a substantially uniform velocity with all the fluid which can pass through the port entrance having regard to the angularity of the fluid stream with respect to said port entrance resulting from the radially outward flow of the fluid and the rotation of the impeller. In this manner, space unneeded for outward flow of fluid is eliminated, and the consequent formation of energy absorbing eddies is prevented. When a liquid is passed between blades having uniform thickness of the types shown at I, 8. and 9 in Fig. 3, cavitation commences under conditions conducive to cavitation immediately behind the radially inner blade tips and extends upwardly behind the blades having regard to the direction of impeller rotation. The formation of cavitation voids indicates that uniform thickness blades are incorrect and that substantially crescent shaped blades should be provided.

The blades l2 and I3 shown at the right of Fig. 3, are also substantially crescent shaped and their frontal concave surfaces face in the direction of impeller rotation. These blades are provided with rearward portions l6 and I1, respectively, The width of the port between these two blades decreases in the direction of fluid flow from the entrance between the radially inner blade tips to the outlet between the radially outer blade tips at the periphery of the impeller. The radially inner and outer tips of the blades of the present invention are also preferably rounded as indicated in Fig. 3. As also shown in the drawing, the blades l0, ll, I2 and I3 are preferably made hollow, for example by welding together at their edges two pieces of properly curved sheet metal.

In Fig. l, a distributing deflector is shown at l8, which preferably is secured to the impeller l as shown and rotates therewith. The method of mounting the distributing deflector within the impeller is immaterial as far as the operation of the apparatus is concerned.

The shape of the distributing deflector l8,

shown in Fig. 1, is preferably determined as follows: Divide the axial length of the blades 6 into any suitable. number of equal parts, illustrated as four parts for simplicity. These four equal parts are bounded and defined by lines I9, 20, 2|, 22 and 23 which represent planes at right angles to the axis of the impeller l. The apex or nose of the deflector I8 is shown positioned in the plane which touches the front ends of the blades 6 as indicated-byline [9; The opposite end of the deflector is shown positioned inthe plane indicated by line 23, at which end the deflector 18 preferably approaches closely to the inner tips of the blades 6 as shown, so as to substantially close the hollow within the impeller I.

As shown by Fig. 1, there willbe different annext adjacent blades increased, due to lessening of the resistance to flow extraneous of a blower,

nular areasbetween the radiallyinner tips of the blades 6 and the deflector 18 at the indicated by the lines 20, 2| and 22-. I

The annulus at the plane indicated by the line 2| should preferably have an area equal tohalf the area of the full circle contalnedwithin the inner tips of; the blades 6. The annulus at the plane indicated byline 20 should have an area planes equalto three quarters of the area of the, full.

circle contained within the inner tips of the blades 8 and the annulus at the plane denoted by line 22 should have an area equal toone quarter of the area of the full circle contained within the inner tips of the blades 6. On this basis the distributing deflector will be parabolic in contour but for inexpensive construction a deflector of conicaliorm having a rounded apex can be used pro viding that. it has a contour substantially similar to a parabolic deflector the sh peof which has been determined as indicated and described.

With either of the contours mentioned there is a progressively and uniformly reduced annular area available for fluid flow between the radially innerblade tips and the exterior surface of the distributing deflector l8 at the different planes I9, 20, 2|, 22 and 23, so that substantially uniformoutward'fiow is caused by the progressively increased displacement of the deflector, within the hollow 5.

The deflector maybe made of portional axial' length when required, in some cases to avoid the expense of fitting it around radial spokes or other structural members which extend from the impeller hub to the circumferentlally spaced blades, as in blowers for heavy duties. The nose or apex end of the deflector is of chief importance, so that when portlonalaxial length is desirable for the above stated reason, or for other reasons, the apex end of the deflector should be provided and positioned as shown in Fig. 1, and shortening should be done by eliminating the large diameter end of the deflector to any required extent.

A further object of my invention is to provide a blower having forwardly inclined blades with their concavities facing in the direction of impeller rotation, which will have limit load characteristics. The use of substantially crescent shaped blades will enable this requirement to be fulfilled. This is due to the fact that the ports between such blades will present approximately the same aspect area for fluid flow through a wide range of variation of resultant angularity of the stream entering the inner ends of the ports between such blades. With the old type blades having uniform thickness as shown by blades 1, 8 and 9 in Fig. 3, as the upward inclination of the entering stream with reference to a base line drawn between the radially inner tips of two the area presented for flow into the port increased. This resulted in increased flow to an extent in some cases detrimental, because of the corresponding increase in power consumption. With substantiallycrescent shaped blades the port area presented. for fluid flow remains about the same notwithstanding an increase in upward angularity of the streams entering the ports, and

in consequence. the increase inpower consumption is minimized, thereby producing self limiting load characteristics.

Blades suitable for employment in the apparatus of the present invention aregenerally of hollow construction as shown'by the blades In, ll, 12 and i3 ofFig. 3; but in impellers a: very small diametersfisblid blades can be used. When required, as in heavy duty apparatus involving 'high peripheral velocities, hollow blades can be provided with. internal cross braces (not shown) attached to the. concave and convex sides within each blade to increase its resistance to centriiuga stresses. 7

As previously stated the port between any two next adjacent blades should'be'of the maximum width which can efilciently be filled by thefluid which can enter said port, having regard-to the entrance angularity determined jointly by the radially outward fluid, velocity and the-circumferential velocity of the radially inner-blade tips. Provision of the maximum port width on this basis makes-it possible to obtain the maximum volumetric capacity from a given size of blower and hencefor algivenfirstcost. In most cases the width of .the port between any two next adjacent substantially crescent shaped blades measured along the circle at half the radial depth should be approximatelyhalf the distance measured on the same circle from the hollow of the concavity of the frontalsideof one of such blades to the hollow of theconcavity of the frontal side of the next adjacent preceding blade'ln the direction of impeller rotation. If the port width measured as above between any two'next adiacent blades is less than thirty percent of the distance from the hollow of the concavity of the frontal side of one of such blades to the hollow of the concavity of the frontal side of the next adjacent preceding blade in the direction of impeller rotation, the volumetric capacity ofthe impeller provided with such blades will be needlessly impaired. On the other hand if this port width is which whirls and eddies will be formed thus needlessly increasing the power consumption of the apparatus. For best result the width of the ports measured along the circle at half the radial depth of the blades will fall between,3 5. and 60% and will generally fall between 40 a d 60% of the distance between corresponding points on adjacent blades. Thus, this port width will vary with the circular pitch or spacing of the blades and such pitch or spacing may vary within wide limits, for example, the pitch or spacing may be much greater than that shown for illustrative purposes in the drawing.

Suitable port shapes are shown between blades l0 and I l, and between blades l2 and 13 in Fig. 3. In both cases fluid can flow into the port en- -..a chord drawn from the radially inner tip, is, the most rearward tip contacts the inner trance and along the exterior surface of the convex or rear face of one of such blades at an upward angle in excess of degrees to a line drawn from the radially inner tip of said blade to the radially inner tip of the next adjacent following blade with respect to the direction of impeller rotation. -The angularity of the upward slope of the convex or rear face of one of such blades adjacent to its radially inner tip is critical and as this angularity is reduced the fluid is correspondinglyv andincreasingly prevented fromgaining easy access to the port between the convex surface of said blade and the concave or workingface of the next adjacent following blade with respect to the direction of impeller rotation. This invention relates particularly to the formation and contour of the convex or rear faces of substantially crescent shaped blades, as the formation and contour of the concave or working faces of such blades which face in the direction of impeller rotation do not need to be changed from the standard and proven design shown in Fig. 3, which is old in the art. The angularity of the upward slope of the convex or rear face of a substantially crescent shaped blade adjacent to its radially inner tip; with respect to a line drawn from the radially inner tip of said blade to the radially inner tip of the next adjacent following blade should not be in excess of approximately 50 degrees.

It is apparent that the inner tip of the blades need not necessarily terminate in as small a rounded end as shown in the preferred embodiment of the drawing. Thus the inner tip may have a sharp point or alternatively may have a rounded end of larger radius than that shown.

For example, if a rounded or other contoured tip is employed a small portion of the surface of the rear face of the blades immediately adjacent such tip or forming part of such tip will make an angle with the line joining such tip with the inner tip of the next succeeding blade which is less than the 20 angle given above. In such case the angle referred to may be measured between that point at which said inner circle touching the blades. through a point on the rearward surface of the blades spaced 20% of the periphery of said rearward face from said radially inner tip and a line joining said inner tip with the inner tip of the next succeeding blade. As stated above, this angle should be between 20 and 50. Thus there may be considerable variation of the shape of the blade immediately adjacent the radially inner tip, but the arc of the surface between the points on the chord above referred to should not depart substantially from 'said chord. In general the contour of the rearward faces of the blade should preferably be a smooth curve without sharp changes of direction. The radial distance from the circle through the inner tips of the blades to a point on the rearward surface of said blades which is one quarter of the perimeter of the contour of such surface measured from the radial inner tip, will usually fall within 20 and 30% of the radial depth Of the blades and for best results this distance will be approximately Also the line joining the radially inner and outer tips of one of the blades thereby forming the chord of the arc of concavity thereof falls short of the nearest point on the convex surface of the next adjacent preceding blade, that is to say, this chord does not touch or cut the body of the next preceding blade.

It is not my intention to limit the invention to the precise details of construction shown in the accompanying drawing, since it is apparent that such may be varied without departing from the spirit and scope of the invention.

I believe it to be broadly new to provide in an apparatus of the character described, a plurality of substantially crescent shaped blades which have greater axial length than radial depth, which have their concave or working faces facing in the direction of impeller rotation, and which are of formations and contours adapted to provide ports between each two next adjacent blades suited to the natural path of fluid flow and thereby permitting the maximum volumetric capacity consonant with high mechanical efficiencyto be obtained from said apparatus. I also believe it to be broadly new to provide in an apparatus of the character described, an impeller of substantially radial outward flow type with a plurality rection of impeller rotation, and their convex or of substantially crescent shaped formations with their concave or working faces facing in the direar faces of such contours as to give said impeller limit load characteristics. I further believe it to be broadly new to provide in an apparatus of the character described a parabolic deflector, or conical deflector with a rounded nose or apex approximating a parabolic deflector, which will co-act with substantially crescent shaped blades having their concave or working faces facing in the direction of impeller rotation, so as to conserve the kinetic energy of the stream of fluid which enters said apparatus by preventing or minimizing the formation of whirls and eddies throughout all portions of said apparatus.

Having described the invention, what I claim as new and desire to have protected by Letters Patent is:

l. Centrifugal apparatus of the class d scribed for imparting motion to a fluid, embodying therein a rotatable impeller which is stream lined from its initial inlet for the entry of fluid to its periphery by its combination with a substantially parabolic distributing deflector which is mounted coaxially within said impeller to provide for substantially uniform outward flow of fluid to said impeller, said impellercomprising a plurality of substantially crescent shaped blades which have greater axial length than radial depth arranged in spaced relation around the periphery of said impeller with their concavities or working faces facing in the direction of impeller rotation, said blades bounding ports for fluid flow between said blades, each of said ports between the exterior surfaces of the convex and concave sides of any two next adjacent blades having a; width measured at half the radial depth of said two next adjacent substantially crescent shaped blades between approximately 35% and 60% of the distance between corresponding points on said two next adjacent blades at half their radial depth, the contour and formation of the convex side of one or more of said blades being such that at a point on the surface of said convex side of said blade located at twenty percent of the perimeter of said convex side of said blade measured from its radially inner tip, a line drawn from said point to the said radially inner tip of said blade will have an angularity between twenty and fifty degrees to a line drawn from the radially inner tip of said blade to th radially inner tip of the next adjacent following blade with respect to the direction of impeller rotation.

2. In apparatus of the class described for imparting motion to a fluid a rotatable impeller with substantially crescent shaped blades the hollows of which face in the direction of impeller rotation, said blades having their outer tips arcuately in advance of their inner tips and a port width between two next adjacent blades measured along the circumference of a circle passing through points at'half the radial depth of said blades being between thirty-five and sixty percent of the distance measured along the circumference of said circle from the hollow of one of said blades to the hollow of the next adjacent preceding blade with respect to the direction of impeller rotation, the contour of the portion of the rear surface of the blades between the tip of a blade at the entrance of fluid into a port and a point'spaced approximately twenty percent of the periphery of the rear surface from said tip providing for flow of fluid along said portion at an angle between approximately twenty and fifty degrees with respect to a line joining said tip and the corresponding tip of the next succeeding blade.

3. Impellers for apparatus of the class described for imparting motion to,a fluid having vanes of substantially crescent shaped formation, in which the said vanes each have a concave frontal face facing in the direction of impeller rotation and a convex rear face, the said'convex rear vane surfaces being of such contours adjacent to their radially inner ends with respect to the axes of said impellers that fluid in contact with said convex rear vane surface can flow angularly upward at an angle between approximately and 50 degrees to a line drawn from the radially inner endof one convex rear vane surface to the radially inner end 'of the convex rear surface of the next adjacent following vane with respect to the direction of impeller rotation, and the pitch or spacing of the said vanes is such that at half their radial depths the port width between two next adjacent blades is between approximately 40 and 60% of the distance apart of the hollows of the frontal surfaces of said two next adjacent blades at half their radial depth.

4. Apparatus of the character described, embodying therein a plurality of substantially cres cent shaped vanes arranged in spaced relation about the periphery of an impeller, in such manner that port widths at half the radialidepth of the blades are between approximately 40 and 60% of vane pitch or spacing at half the radial depth of the blades, said vanes being of greater axial length than radial depth and inclined forward in the direction of impeller rotation, said vanes having their concave or working sides in advance of their convex backs, the contour and formation of said convex backs being such that at one quarter of their perimeters measured from their radially inner tips the distance measured in a radially outward direction from a circle passing through said inner tips will be between twentyand thirty per cent of the radial depth of said vanes.

5. Impellers for apparatus of the class described for imparting motion to a fluid, having circumferentially positioned substantially crescent shaped blades having a radial depth of approximately one-seventh or less of the radius of the impeller, in which each said blade has a concave frontal surface facing in the direction of impeller rotation and a convex rear surface, and in which the said frontal and rear surfaces are of approximately equal pitch or spacing measured on the circumference of a circle which passes through points on said blades at half their radial depth, whereby each port bounded by two next adjacent blades is approximately equal in width to the width of a said blade from its concave frontal surface to its convex rear surface, bothsaid widths being measured on the circumference of a circle which passes through said blades at half their said radial depth, the contour of the portion of the rear surface of the blades between the tip of a blade at the entrance of fluid into a port and a point spaced approximately twenty percent of the periphery of the rear surface from said tip providing for flow of fluid along said portion at an angle between approximately twenty and fifty degrees with respect to a line joining said tip and the corresponding tip of the next succeeding blade.

6. Apparatus for imparting motion to a fluid which comprises a rotatable impeller having a plurality of substantially crescent shaped blades providing ports between said blades for flow of fluid, said blades having a radial depth of approximately one-seventh or less of the radius of the impeller and having concave frontal surfaces facing in the direction of impeller rotation and convex rear surfaces, each said port being approximately equal in width to each said blade, said widths being measured on the circumference of a circle passing through said blades at half their radial depth, and a substantially parabolic distributing deflector which is mounted coaxially within said impeller, said deflector having its apex adjacent the fluid inlet side of said impeller and its base adjacent to a plane at right angle to the axis of said impeller at a position corresponding to a fractional width of said impeller, whereby the axial length of said deflector is such that said deflector will fall short of any radial spokes or other structural members which exten'd from the central hub of said impeller to the said substantially crescent shaped blades, the contour of the portion of the rear surface of the blades between the tip of a blade at the entrance of fluid into a port and a point spaced approximately twenty percent of the periphery of the rear surface from said tip providing for flow of fluid along said portion at an angle between approximately twenty and fifty degrees with respect to a line joining said tip and the corresponding tip of the next succeeding blade.

7. Apparatus for imparting movement to a fluid, which comprises, a rotatable impeller having a plurality of substantially crescent shaped hollow blades with ports between said blades for flow of fluid, said blades having widened mid portions and being provided with concave front surfaces facing in the direction of rotation of said impeller and convex rear surfaces, said rear surface of each of said blades having a contour between the tip thereof at the entrance of fluid into the port bounded by said rear surface and a point spaced approximately 20% of the said rear surface from the tip which doesgiot depart substantially from a chord throughsaid point and said tip, said chord making anangle with the line joining the tip and the Qorresponding tip of the next succeeding blade between approximately 20 and 50 whereby said apparatus has limit load characteristics, said blades having a radial depth of one-seventh or less of the radius of the impeller.

8. Apparatus for imparting movement to a fluid, which comprises, a rotatable impefler having a plurality of axially extending substantially crescent shaped blades arranged around the periphery of said impeller and providing ports between said blades for flow of fluid, said blades having widened mid portions and being provided with concave front surfaces facing the direction of rotation of said impeller and convex rear surfaces, the rear surface of each of said blades having-.a-icontour between its radially inner tip and arpoint spaced approximately 20% of the periphery of said rearlsurface from said tip which does not depart substantially from a chord through said point and said tip, said chord making an angle with a line joining said tip and the corresponding tip of the next succeeding blade between approximately 20 and 50, said ports "having a width between adjacent blades which is between approximately 35% and 60% of the distance between corresponding points on said blades, said width and distance being measured on the circle at half the radial depth of the blades.

9. Apparatus for imparting movement to a fluid, which comprises, a rotatable impeller having a plurality of axially extending substantially crescent shaped blades which have a radial depth of approximately one-seventh or less of the radius of the impeller, arranged around the periphery of said impeller and providing ports between said blades for flow of fluid, said blades having widened mid portions and being provided with concave front surfaces facing the direction of rotation of said impeller and convex rear surfaces, the rear surface of each of said blades having a contour between its radially inner tip and a point spaced approximately 20% of the periphery of said rear surface from said tip which does not depart substantially from a chord through said point and said tip, said chord making an angle with a line joining said tip and the corresponding tip of the next succeeding blade between approximately 20 and said ports having a width between adjacent blades which is between approximately 40% and of the distance between corresponding points on said blades, said width and distance being measured on the circle at half the radial depth of the blades and means for introducing fluid substantially uniformly into said ports.

10. Apparatus for imparting movement to a fluid, which comprises, a rotatable impeller having a plurality of axially extending substantially crescent shaped blades which have a radial depth of approximately one-seventh or less of the radius of the impeller, arranged around the periphery of said impeller and providing ports between said blades forflow of fluid, said blades having widened mid portions and being provided with concave front surfaces facing the direction of rotation of said impeller and convex rear surfaces, the rear surface of each of said blades having a contour between its radially inner tip and a point spaced approximately 20% of the periphery of said rear surface from said tipwhich does not depart substantially from a chord through said point and said tip, said chord making an angle with a line joining said tip and the corresponding tip of the next succeeding blade between approximately 20 and.50, said ports having a width between adjacent blades which is between approximately 40% and 60% of the dis-' tance between corresponding points on said blades, said width and distance being measured on the circle at half the radial depth of the blades and means for introducing fluid substantially uniformly into said ports, said means comprising a substantially parabolic distributing deflector mounted coaxially within said impeller.

THOMAS CHESTER.

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