US2984189A - Inducer for a rotating pump - Google Patents

Description

y 1961 w. JEKAT 2,984,189

INDUCER FOR A ROTATING PUMP Filed Aug. 7, 1958 WA LTER K. J'E KAT INVENTOR.

United States Patent Walter K. Jeltat, West Orange, N.J., assignor to Worthington Corporation, Harrison, N.J., a corporation of Delaware Filed Aug. 7, 1958, Ser. No. 753,749

1 Claim. (Cl. 103-88) This invention relates to a rotating pump having improved suction characteristics, and more particularly relates to an improved unit used to obtain these character istics for the pump and commonly known as an inducer.

The primary function of an inducer is to increase the pressure of the incoming fluid to the pump impeller by inducing a swirl and thus a vortex pressure pattern in the fluid. This allows higher suction specific speeds to be attained by the pump before incipient cavitation occurs in the impeller suction eye and pump inlet passage. Higher pump speeds in turn result in lower costs since high speed prime movers can then be used as driving units.

An inducer, as presently constructed, consists of one or more helical vanes formed along an axial projection extending centrally of the impeller suction eye into the central portion of the pump inlet passage. The axial projection is often the end of the shaft on which the impeller is rotatably mounted or the impeller nut used to mount the impeller on the shaft, In either case, however, the helical vanes extend from the axial projection in the central portion of the pump inlet passage outwardly in the direction of, and to within close proximity of the inner wall of the pump inlet passage.

Experiments have shown however that at high suction pump speeds, some cavitation will occur, and this usually is at the vane tips. Since cavitation is conducive to high wear, in presently constructed inducers, the close proximity of the vane tips to the inner wall of the pump inlet passage subjects the latter to Wear and is objec tionable.

Accordingly, it is one subject of the present invention to provide an inducer in which cavitation occurring at the tips of the vanes is rendered harmless. To accomplish this object, the improved inducer of the present invention consists of a cylindrical member connected at one end about the suction eye of the impeller of a centrifugal pump and provided with a central bore for the passage of fluid to the impeller, and in which helical vanes are formed along the wall of the bore to extend in towards the center of the bore. Thus, as fluid being pumped flows through the bore to the impeller, cavitation occurring at the centrally situated vane tips harmlessly collapses cushioned by the flowing fluid.

A further object in constructing the inducer to have peripherally mounted and inwardly extending vanes as described above, is to induce the centrifuging of bubbles of cavitation occurring other than at the vane tips to the central portion of the bore, and thus to localize all cavitation to this comparatively safe area.

A still further object of the improved construction for an inducer as described above, is to minimize the adverse effect of dynamic loading on the vanes. Since the vanes extend perpendicularly into the stream of fluid flowing to the impeller, they obstruct flow and cause an increase in velocity and thus a reduction in pressure in the fluid. This reduced pressure condition is commonly known as dynamic depression and encourages incipient 2,984,189 Patented May 16, 1961 cavitation. While dynamic depression cannot be eliminated, its ability to cause cavitation is greatly minimized by the peripheral mounting of the helical vanes inasmuch as this arrangement most readily permits making the first encountered vane coil smallest in height and each succeeding upstream vane coil progressively greater in height. As a result, the fluid easily slips over the first and smaller vane coils, and is not materially obstructed in its flow until reaching the last and larger vane coils. At this point however, a vortex pressure pattern is already induced in the fiuid, and there is less likelihood that dynamic depression will result in cavitation.

Still another object of the improved inducer of the present invention is to minimize the adverse effect of front wearing ring leakage. More particularly, it has been found that fluid at discharge pressure leaking past the front wearing rings of an impeller can itself cavitate or produce cavitation on entering the pump inlet passage. In the present invention, this occurrence is minimized by the connection of the inducer about the impeller suction eye, since this adds a scalable surface on the inducer to that of the front wearing rings along which seals may be utilized to prevent excessive leakage into the inlet passage.

The invention will be better understood when considered in connection with the accompanying specification and drawing forming a part thereof, in which a side view, in cross-section, of a centrifugal pump is shown, having the improved inducer of the present invention connected to its suction inlet.

Referring tothe drawing, the centrifugal pump 1 has a casing 2 in which an impeller chamber 3 is formed. Extending through an axial bore 4 in the right side of easing 2 and into impeller chamber 3 is a rotatable shaft 5 on an end of which an impeller 6 is securely mounted in a conventional manner by an impeller nut 7. Suitably connected to the left side of casing 2 is a conduit 8 having a central through bore 9 in axial alignment with the suction eye 10 of impeller 6, the said bore 9 serving as the inlet passage for the pump 1.

Rotating with the impeller 6, and connected thereto about its suction eye 10, as for example by welding, is a cylindrical member or the improved inducer 11 of the present invention. As shown, the inducer 11 extends into the inlet passage 9 thus serving essentially as an extension of the suction eye 10 of impeller 6 and is provided with a central bore 12 through Which fluid to be pumped passes to the impeller 6. More particularly, bore 12 of the inducer 11 has a taper 13 in the direction of impeller 6 and its larger end opening 14 is the one connected about the impeller suction eye 1'0. A pressure breakdown means shown as labyrinth seal 15 is provided in the outer wall 15 of the inducer 111 to minimize leakage through the running clearance which must necessarily be left between the said outer wall 15' and a sealing sleeve 16 disposed in the inlet passage 9 about the inducer 11.

In order to induce a vortex pressure pattern in the incoming fluid to impeller 6 and thus increase the suction specific speed at which the centrifugal pump 1 can safely operate without cavitation, the improved inducer 11 of the present invention is provided with two similarly constructed and formed continuous helical vanes 17 and 18, preferably degrees out of phase with each other. That the effect of these vanes is to induce a vortex pressure pattern in the incoming fluid is well known to those familiar with the art, and thus need not be discussed herein. Further, it is not the use of helical vanes in the inducer which is being claimed as the invention, but rather the novel manner in which these said vanes are mounted and provided therein.

As clearly shown in the drawing, each of the helical vanes 17 and 18 follows a continuous spiral path along central bore 12, with the base of each formed integral with the tapering wall 19 of the said central bore 12. Accordingly, the tips 20 of the vanes 17 and 18 are centrally located in the central bore 12, and should bubbles of cavitation occur at these tips during pump operation, these bubbles will harmlessly collapse cushioned by the fluid flowing through the central bore 12 to the impeller 6. The peripheral mounting of the helical vanes 17 and 18 as just described also centrifuges bubbles of cavitation occurring other than at the vane tips 21) to the central portion of central bore 12, and thus serves to localize the collapsing of all bubbles of cavitation to this comparatively safe area.

When viewed in cross-section, the shape of the vanes 17 and 18 is substantially triangular, and the height of each succeeding coil thereof progressively increased in the direction of the taper 13 of the central bore 12. In other words, and using helical vane 17 by way of illustration, the first coil 21 encountered by fluid flowing to the impeller 6 is of a comparatively smaller height 22 relative to succeeding upstream coils, and particularly so relative to the height 23 of the last encountered coil 24. Thus at the off-design condition, the incoming fluid easily slips over coil 21 and flow is not materially obstructed until coil 24. During normal operation, the effect of this gradual increase in vane height from zero height to maximum height substantially minimizes the occurrence of cavitation due to dynamic depression or reduced pressure conditions in the fluid. To obtain this advantageous feature without any sacrifice in efliciency of the inducer 11, the increased surface area of the upstream or larger vane coils must compensate for the decreased surface area of the downstream vane coils, and yet the upstream vane coils cannot be made so large in height as to restrict the flow of fluid to the impeller 6. This dilemma is readily resolved in the improved inducer 11 of the present invention by the provision of the taper 13 in the wall 19 of the central bore 12. More particularly, taper 13 enlarges end opening 14 of the bore 12 of the inducer 11, and thus allows adequate flow space centrally of the upstream vane coils despite their increased height.

A further advantageous feature of the improved inducer 11 of the present invention is its ability to minimize cavitation resulting when fluid at discharge pressure in the pump discharge chamber 25 leaks past the impeller front wearing rings 26 into the inlet passage 9. Heretofore it has been difiicult to prevent excessive leakage of this nature by the use of sealing means along the comparatively small axial length of the said wearing rings 26. However, due to the connection of the inducer 11 about the impeller suction eye 10, the length along which pressure breakdown means may be utilized to prevent this leakage into the inlet conduit 9 is increased. More particularly, it has been found that the conventional labyrinth seal 17 provided along the outer surface of the inducer 11 is adequate to substantially decrease leakage into the inlet conduit 9 to almost entirely eliminate cavitation due to wearing ring leakage.

While it is preferred that two helical vanes 17 and 18 be utilized in the improved inducer 11, it will be understood that only one, or more than two may also be utilized without departing from the essence of the invention. Other modifications of this nature also being possible, it will be further understood that the invention is not to be limited to the specific construction or arrangement of parts shown, but that substantial changes may be made within the invention defined by the claim.

What is claimed is:

In a rotating pump having, in combination, a casing in which an impeller chamber is formed, said casing integrally including a peripheral volute portion a back wall portion and a back cylindrical drum portion adjacent said back wall portion, said back wall portion defining an axial bore opening into said impeller chamber, a rotatable shaft axially penetrating through said bore and having a shaft end which extends into said impeller chamber, an impeller mounted on said extended shaft end, said impeller including a back shroud on the side of said impeller in proximity with said back wall, a front shroud formed by said impeller and defining a central suction eye, a plurality of vanes connected between said front shroud and said back shroud, said shrouds and said vanes defining flow passages to communicate said central suction eye with said peripheral volute, said casing defining a front opening suitable to receive said impeller, a cylindrical inlet conduit axially disposed relative said shaft and connected to said casing at said peripheral volute portion to effect closure of said impeller chamber, said inlet conduit communicating with a supply of fluid, a stationary sleeve mounted about the inside of said inlet conduit, a cylindrical inducer element with an outside wall and an inside wall, said inside wall defining a central bore, said inducer element connected to said impeller for rotation therewith, said inside wall defining a progressive flare to form a boundary for the introduction of fluid to said suction eye, an inwardly extending continuous helical vane formed along said inside wall, said helical vane progressively increasing in height in the direction of said suction eye and adapted to swirl incoming fluid before it reaches said suction eye so that volatile liquids can be pumped without their gas phases clogging the pumps, labyrinths formed on said outside wall of said inducer element to minimize leakage from said peripheral volute between said outside wall of said inducer element and said stationary sleeve, said back shroud defining a cylindrical periphery engaged in a running fit with said back cylindrical drum portion of said casing.

References Cited in the file of this patent UNITED STATES PATENTS

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