Centrifugal fan or pump.

Application filed October 24,1904. Serial Ko. 228,875.

Patented May IB, 1906.

To all whom it may concern:

Be it known that I, Samuel Cleland Davidson, a subject of the King of Great Britain and Ireland, residing in Belfast, Ireland, 5 have invented certain new and useful Improvements in Centrifugal I* ans or Pumps, or which the following is a specification.

This invention aims to improve the efficiency of rotary fans or pumps m which the io fluid operated on enters the center of same axially and is discharged circumferentially against a material degree of back pressure or suction resistance. .

Specifically, mv invention relates more es_t, pecially to the multibladed drum form of centrifugal fan set forth in my Patent No,. 662,395, granted November 27, 1900. 1ms fan has a high volumetric efficiency when thfe fluid operated on is under little or no back 2o pressure or suction resistance; but its efficiency diminishes as the back pressure or resistance increases until a point is reached at which the type of fan shown m said patent possesses little advantage over other types of ₂ ς centrifugal fans which are designed for operating under, or against a considerable pres* sure.

In this specification the word “fan” is understood as including a pump. The word w i axially” means in a direction comciaent with' or parallel with the axis of rotation. The word “blades” is used to indicate the vanes or wings wljiich impart motion to the fluid. The expression “intake-chamber is employed to indicate a chamber or space in³⁵ closed within the series of blades. The word “eye” islused to designate the mlet-opening in the casing or stationary member of the fan, through which opening the fluid enters 40 the intake-chamber. By the intake _ end of the blades or ports is understood that end which is nearest the eye. The depth the blades is their width measured radially from the inner to the outer edge, the , length ₄ς of the blades is their axial measurement, and the “ports” are the intervening spaces between the blades. _v

The fan-wheel is the rotary member or runner as distinguished from the stationary ³ I have ascertained by experiments 'with a centrifugal fan-wheel of drum form such as that set forth in my aforesaid patent—as shown, for example, in Figures 1 and 2 or Fig. e e 13 thereof, where the fan-wheel is inclosed m the usual form of spiral or snail-shaped casing—that the action is materially altered when either the inlet or the discharge is ob; structed to cause a back pressure or Auction resistance as compared with that when the 6o fan is running with a free inlet and free discharge. Such a fan if unincased discharges the fluid radially from its blades and uniformly around its entire circumference in any given plane perpendicular to the axis of rota- 65 tion. If inclosed in a snail-casing with a free inlet and free discharge, this action is only slightly modified, due -to the tangentially-discharged currents being collected by the casing and delivered in one stream 70 through the discharge outlet. If, however, the discharge is obstructed, an inequality of action around the circumference of the tailwheel is caused, which inequality reaches its maximum when the discharge is wholly 75 closed. Under these circumstances instead of the air flowing outwardly through the ports or spaces between the blades around the entire circumfe· mce of the fan-wheel such outward flow mainly occurs from the 8c one half of the circumference of the fanwheel which approaches the discharge-outlet, while on the opposite half of the circumference, whichrecedes from the discharge-outlet there is a regurgitated or return stream of 85 fluid flowing first inwardly through the ports and then around inside the blades toward the other half of the circumference, where it finally passes outwardly again. This action will be better understood from Fig. 1 of the 90 accompanying drawings, which is a diagram illustrating the operation of a fan constructed in accordance with my invention. In this diagram, A designates the rotary fan-wheel with its blades a a, and B designates the snail- 95 casing. The eye or inlet-opening to the fanwheei is indicated by the letter 0. Assuming the outlet b of the casing to be closed and the fan-wheel rotated, the air-currents will be somewhat as indicated by the small arrows. 100 As the precise direction and velocity of these currents varies with different back pressures or suction resistances, different speeds of the fan-wheel and other conditions, only an approximate illustration can be given. lak- 105 mg however, the example indicated, it will be seen that from a point indicated approximately at x around (in the direction of rotar tion) to another point approximately indicated at y the air is discharged outwardly 110 and tangentially from the blades, while beyond y to a point adjacent to the nearest

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point z of tlio cas’ng liicre is an inflow of air through the ports and thence a current or stream c c within the fan-wheel, which stream passes outwardly again between the blades 5 as it approaches the point x. By measuring or indicating the flow of this current or stream c at Afferent points within the fanwheel (which may be done with a thread on the end of a wire) a line may be plotted indiιό eating what I may call the “inner” margin of this stream or return-current. This line is the dotted line d d. As its position varies under different conditions, it is to be understood that'the location of this dotted line is is only approximate. This line d d may then be taken as the inner limit of the inwardlyregurgitated or return current from the latter portion of the discharge-outlet which the blades pass. If,this stream of air were with20 in the circumference of the eyeC, an outflow of air would occur through the same on the side coincident with the stream c c, so that if the eye were subdivided with a flat plate, in a flane coincident with the axis extended ap25 proximately in a line between x and y an outflow would be found to occur on the left side of this plate and an inflow on the right side thereof. Throughout the intake chamber or space inclosed within the blades to the 30 right of the line x y the air is found to be under a condition of partial vacuum, lyhich is most marked near the inner edges of the blades on the sides most remote from said line x y.

It is a remarkable fact that, the air-current c c if unobstructed in its course travels at a higher velocity than the blades. Repeated tests have shown its velocity to be nearly or quite double that of the inner edges of the 40 blades when the back pressure or suction resistance is high relatively to the speed of rotation of the fan-wheel.

My present invention is based upon a recognition of the phenomena above stated. I 45 have found by experiment that anything which obstructs the current c c within the fan-wheel at once lowers the efficiency of the fan and defeats its objects. Those fans in which occasional blades have been extended 50 inwardly farther than their fellows (whether this extension be for a part only or for the whole width of the blades) have had this result and are found by test to be notably inefficient under back pressures or stiction re55 sistances. Accordingly I avoid placing anything within the fan-wheel which will materially resist the current c c or retard it, and I fiermit it freely to flow with its wonted veocity—that is to say, considerably faster 60 than the movement of the blades/ I also provide means for preventing the axial escape of this current through the eye. In my application for United States Patent filed May 23, 1904, Serial No. 209,351, I have set 65 forth certain improvements based also upon

I the phenomena already stated. According to the invention claimed in my said application. 1 have altered the relative size and proportions of the revolving fan and the inclosing casing, so that the eye or inlet-opening, 70 which, as in Patent No. 662,395, is concentric with the axis of rotation and is of about the same area relatively to the size of the casing, is by reason of the relative enlargement of the revolving fan-wheel of materially 75 smaller size than the interior of the circle described by the inner edges of the fan-blades.

According to my present invention instead of making the eye or inlet-opening concentric, or substantially so, to the axis of ro- 80 tation I so form the inlet area that the boundary thereof extends more to one side of the circle of the fan-blades than the other, or I make the eye eccentric to the axis of rotation, whereby its position is more nearly concen- 85 trie to the outline of the casing than formerly. All these forms are intended to be included in the term “eccentric eye,” which is hereinafter used for the sake of .simplicity and clearness. By preference I make the 90 eye of non-circular shape, as illustrated in Fig. 1, conforming it on its side adjacent to the internal current or stream c c to the form taken by such stream, and on the opposite or suction side of the fan-wheel carry the eye 95 outward, preferably, to an outline corresponding more or less closely wfith the path of the fan-blades. Thus the eye assumes a shape roughly approximating to an ellipse somewhat flattened on its side nearest the return too or internal current and a shape which I will hereinafter refer to as approximately of D form.

I will proceed to describe the principle of my invention and its preferred embodiment 105 with reference to the accompanying drawing^ wherein—

Fig. 1 is a diagram illustrating the currents which are set up in fans constructed in accordance with my invention when.operat- 110 ing against back pressure or suction resistances, as already described. Fig. 2 is a diagram corresponding to a section on the line 2 2 in Fig. 1. Fig. 3 is a diagrammatic or outline elevation of the casing of the fan, illus- 115 trating one form of my invention. Fig. 4 is a front elevation of a fan, illustrating a further modified form of construction. Fig. 5 is a sectional elevation of a fan, illustrating the preferred contruction embodying my inven- 120 tion. Fig. 6 is a horizontal section thereof in a plane intersecting the axis. Figs. 7 and 8 are respectively side elevation and vertical section illustrating a modified construction. Figs. 9 and 10 are similar views in the same 125 planes as Figs. 5 and 6, showing a modified construction.

My present invention in its preferred embodiment follows the general principles of construction of a drum-shaped rnultibladed 130

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rent has first passed outwardly through the ports between the blades. I imd by Actual tests that the strongest suction tending to draw fluid into the fan-wheel occurs on the . siile onposite the return-current c c and ap- 70 tfld casing, and K proximately on the side Hi of. the eye, and led to the fan- by extending the radiiis or outer m argin of the eye on this side so as. to coincide with the path of the inner edges of the blades not only is the maximum area afforded for the admis- 75 sion of air to the fan, but the admissi on is rendered as free as possible, since the admission is directly into that portion of the intakechamber where the suction is strongest.

The shape of the eye is subject to variation under varying conditions. For example, the precise shape of the casing may affect the shape best given to the eye. The eyb need not necessarily be a close approxiirtafion to the form shown in Fig. 3, since my invention permits of any suitable variation of this shape. It is an important advantage of my invention that with the eccentrically-located eye, which best adapts the fan to working against a maximum back pressure or suction .resistance for any given 'speed, the fan is equally suited for working against any lower back pressure or even with a free discharge. Hence it.is no longer necessary to construct a variety of different fans to suit different con- 95 ditions of pressure.

An example of a modification of which my invention is susceptible is shown diagramatically in Fig. 4, where the eye c is of .circular contour and arranged eccentrically to the 100 axis of rotation and approximately concentric to the contour of the casing.

Figs, b and 6 show one construction of a fan according to my invention. I.i these, figures, A is the rotary fan-wheel or drum, and B the casing. The blades a a are curved, being concave on the advancing sides, and pitched slightly forward at their outer edges, as disclosed in my said Patent No. 662,395, to which reference is made for an illustration of the details of attachment ami uonstruction. The circular series of blades is shown in Fig. 6 as connected to the central revolving shaft D by means of a disk E, forming the closed inner eml of the fan-wheel, the opAn an...____ _____ ________,-- - ends of the blades are attached, ajrl the outer plate G of the casing is extended inward beyond this plate so that its inner margin forms the boundary of the eye. Preferably the annular plate F' has its inner edge slightly incurved to increase its stiffness, and the eccentrically-located eye is formed in a separate annular plate G', fastened to the. side .plate G of the casing and having its inner edge turned or curved inwardly and to nearly meet the plate F'’of the fan-wheel on the side Hi of closest proximity of the eye to the fan-wheel.

fan-wheel as set forth in my said Patent No. 662,395, of November 27,1900,. although, as hereinafter explained, it is. applicable to other types of Tans. In the construction set forth In my said pending application the fanwheel is enlarged relatively to tfid casing, and the casing is more closely ad apted to the f^_ ~ wheel. The c^sjng. preferably follows as closely-as practicablethq outline of the fan10 Wheel from a point indicated approxifnately at/.in Fig.'l anttfor a suitable distance to a point inaicatedat/' /Preferably, also', the caSing pFovideS ft .tapering space y to facilitatetne'mflow of the current c c to the inte-.

iior of. thp drum; The return-cureent c c traverses apath which,.approximately stated, is nearly parallel with the .outline of the ca§iig, aemdieated by the Arrows and its marginal line d. In the construction of my said ao pending Application this marginal line intersects the outline of the codcentric eye, whereby a tendency exists to a portion of the return-current spilling out through the intersected arc -of said^: concentric eye Unless said' a 5 eye be sufficiently reduced in diameter to prevent same; but the area for inflow of fluid through state would be thereby so much diminished as to materially reduce the volu^ njetriQ capacity of the fan, and consequently such construction would involve practical disadvantages. According to my present invention I avoid this detrimental result by locating the eye eccentrically Co the axis of th* fan-wheel to such an extent as to be sub35 star!tially and preferably entirely to one side of the return current or streajn c e. The shape pf.the. eye shown in diagram‘in Fig. 3 is again indicated by the lineC and is of somewhat irregular form, its portion toward the left (marked fc A) following approximately the inner outline of the stream or return-current of fluid c c, as shown in Fig· 1, while its opposite side (marked i i i) follows, preferably, the path of. the inner edges of the fan45 blades. By this conformation of the eye a twofold advantage is gained. On its side A A..A4he retittn-current of fluid is so confined laterally that -no loss by the spilling oitt of this fluid* through the eye is incurred, to 50· which fluid in practical operation power has .— been exerted to put it into rotary motion, posite side being open to the eye C. Ai and any portion 01 this current which escapes nular metal plate F' is used, to which the must be replaced from the source of the fluid-^{! e} -»-1—1 --·' + supply, which being at rest requires the ap55 plication of power to impart to it the same velocity of motion as the escaped fluid possessed, which consequently represents an equivalent wastage or power. This loss or waste is entirely prevented by the confornia60 tion A A of the eye, while at the same time the conformation i i t of the eye affords the utmost facility for.-the admission of fresh fluid to the intake edges of the blades to replace the volume driven out of the casing through the discharge-outlet after the return-cur8ο

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820,397 ports between the blades.

’ ______________{_} „_ieuca somewhat deeper in proportion to the diameter of the fan-wheel than in the preceding diagrams, as I find that deepening them to this extent greatly enhances stiffness and rigidity 10 of construction and does not to any very material extent diminish their. efficiency in operative effect. My invention is not limited to any definite proportion between the depth of the blades and the'diameter of the 15 drum or between their depth and length. In the construction of pressure-fans according to my present invention I may advantageously make the blades shorter and deeper than the proportions stated as preferred in ao my former patent.

The present invention is not limited to what I have herein referred to as the “ drum form” of fan, nor to the general type of fans set forth m my aforesaid patent. It is also ² 5 applicable, although with less advantage, to centrifugal fans of the ordinary pressureblower type. As one illustration of such application of my invention I show in Figs. 7 and 8 a fan somewhat resembling the ordinary 30 pressure-blower, but modified so as to embody in part the principles of my invention. In these figures, A is the fan-wheel, and B' the casing. The fan-wheel has curved blades a' usually mounted between conical or dished 35 plates Η H, one or each of which has a central mlet-opening forming the eye. Such rotary member may be variously mounted—for example, by means of a central disk I, attached at its outer part to the blades and at 40 its center to a hub on the shaft D'. It is common in the hitherto ordinary construction of such fans to provide a series of short blades of approximately the shape of the blades a' and at intervals to extend these 45 blades inwardly, forming long blades, as shown in dotted lines at a². These inward extensions u² have been thought necessary to impart the requisite pressure To the air. They have .been commonly tapered at their 50 inner edges in the manner shown by dotted lines a³ in Fig. 8 and projected more or less within the circumference of the eye. In applying my invention to a fan of this character it is necessary to cut away the portions ⁵⁵ κι f ’ P^referably entirely, so that all the blades shall be of approximately equal depth radially, as shown by full lines in Fig. 8, whereby a free and unobstructed space is provided within the series of blades for the

Fig £ SS'thepS a?d ihe'Xw f W ^{80 thal s}“ ><* ^cumnt “‘°-^the^pr& ,o dotted lines a¹ indicate the hitherto ordinary and detrimental inward extension of the blades and the solid lines a³ the extent to which they should be cut away to give best results in accordance with my herein-de- 7« scribed invention. The outer contour of the inclosing casing of this fan is shown in Fig 9 in solid lines B' B as hitherto ordinarily made, and while my herein-described invention is applicable in conjunction with such 80 outer contour of the casing it is preferable to have the casing of the form shown by the dotted lines B² B², which is in accordance with the construction shown in my pending application. The same reference-letters are 85 used for the parts of the eccentric eye as in the previous description as the application will be clearly apparent from the drawings.

Although I have described my invention as a fan for acting upon air, yet. it is to be un derstood that it is applicable also witn othei nmds. It is highly advantageous for use as a centrifugal pump for water or other liquids. The operation with a liquid differs from the operation with air only to the extent that the 95 fluid operated upon is of different weight and specific gravity and is incompressible.

My invention may be otherwise modified m many respects without departing-from its essential features. _roc