Patent Application
20070177995
This invention relates to the field of centrifugal pumps.
In the field of liquid transfer, it is common to provide power to the impeller of a centrifugal pump by means of a shaft coupled to an external motor. This necessitates that a form of dynamic seal be provided around the shaft, to minimize egress of liquid, which seals have associated maintenance issues. Dynamic shaft seals also add a frictional resistance load to the pump, which is not desired. Other pumps have been constructed wherein the impeller is rotated by an externally-created magnetic field. This type of pump avoids the maintenance and frictional resistance issues associated with dynamic shaft seals. However, in order to ensure that the impeller is properly indexed for rotation in the pump, submerged bearings are generally employed, which bearings have their own associated maintenance and frictional-resistance issues. It has also been known to attempt to create pumps lacking both submerged bearings and dynamic shaft seals, by providing magnets which serve both to rotate the impeller and support same in spaced relation from the housing. However, known prior art pumps of this type are not completely successful in avoiding rubbing contact between the impeller and housing; among other things, wear continues to be an issue.
A centrifugal pump for use with a liquid forms one aspect of the invention. This pump comprises a housing and a rotor. The housing has an interior surface defining an interior cavity, an axis intersecting the cavity, an intake port for receiving liquid and communicating same to said cavity, and a discharge port in communication with said cavity. The rotor has an impeller, is positioned in said cavity and is rotatable in said cavity about said axis in spaced relation to the interior surface. The impeller is adapted to force said liquid to flow through said discharge port upon said rotation in use. The pump further comprises means for balancing the pressure in said cavity, adapted so as to avoid the creation of pressure differentials in said cavity that would otherwise in use tend to cause translation of said rotor in said cavity. The pump further comprises a rotating magnetic field generation device adapted to drive rotation of said rotor about said axis in use.
According to another aspect of the invention, the means for balancing the pressure in said cavity may be a liquid conduit.
According to another aspect of the invention, in use, the discharge port may be disposed above the impeller and the liquid conduit may extend between a first terminus in the cavity above the impeller and a second terminus in the cavity below the impeller.
According to another aspect of the invention, the liquid conduit may be defined at least in part by an arc-shaped barrier.
According to another aspect of the invention, the rotor may include a drive member to which is coupled the impeller, for rotation therewith, the rotating magnetic field generation device being adapted to drive rotation of said rotor about said axis in use by driving rotation of said drive member.
According to another aspect of the invention, the impeller may be a closed impeller having axially-spaced sides and the drive member may comprise a metal tube extending axially from one of the sides of the impeller and arranged coaxial with the axis.
According to another aspect of the invention, the rotor and housing may be adapted such that, in use, said liquid supports said rotor for rotation substantially about said axis in spaced relation to said interior surface.
According to another aspect of the invention, said adaptation of the rotor and housing, such that, in use, said liquid supports said rotor for rotation substantially about said axis in spaced relation to said interior surface, may comprise: a balance tube extending from the other of the sides of the impeller in a direction coaxial with and opposite to the drive member; and a circular groove forming part of said cavity in which a rim of the balance tube revolves in use.
According to another aspect of the invention, said adaptation of the rotor and housing, such that, in use, said liquid supports said rotor for rotation substantially about said axis in spaced relation to said interior surface, may comprise, for each side of the impeller, a plurality of protrusions defined by the interior surface such that the space between the rotor and the housing, in use, measured axially, undulates in magnitude around the impeller for stabilizing the rotor against axial movement.
According to another aspect of the invention, measured axially, in the direction of rotation of the rotor, in each undulation the space between the rotor and the housing may gradually decrease and then quickly increase.
According to another aspect of the invention, each plurality of protrusions may have associated therewith a series of radial grooves forming part of the cavity, the grooves separating the protrusions from one another.
According to another aspect of the invention, each protrusion may comprise a wedge-shaped slope inclined in the direction of rotation of the rotor.
According to another aspect of the invention, the impeller may have defined therethrough, coaxial with the axis, an intake hole, and the housing may comprise an inflow regulation boss projecting into the cavity that extends, coaxially with the axis, into the intake hole.
According to another aspect of the invention, the inflow regulation boss may be shaped to direct flow impinging thereupon into the impeller.
According to another aspect of the invention, the inflow regulation boss may have a conical tip to direct flow impinging thereupon into the impeller.
According to another aspect of the invention, the pump may further comprise a tubular intake portion attached to the rim of the intake port and extending, coaxially with the axis, into the intake hole and towards the inflow regulation boss, to direct flow thereupon.
According to another aspect of the invention, the impeller may have defined therethrough, coaxial with the axis, an intake hole, and the pump may further comprise a tubular intake portion attached to the rim of the intake port and that extends, coaxially with the axis, into the intake hole.
According to another aspect of the invention, the impeller may have axially-spaced sides and the pump may further comprise extension plates attached around the perimeter of the impeller to increase the area of the impeller sides.
According to another aspect of the invention, the pump may further comprise a liquid detection sensor, capable of detecting the existence of liquid within the cavity and producing a liquid detection signal, and a controller that uses the liquid detection signal from said liquid detection sensor to control the pump during startup.
A centrifugal pump for use with a liquid forms another aspect of the invention. This pump comprises a housing, a rotor, a liquid conduit and a rotating magnetic field generating device. The housing has an interior surface defining an interior cavity, an axis intersecting the cavity, an intake port for receiving liquid and communicating same to said cavity, and a discharge port in communication with said cavity. The rotor has an impeller, is positioned in said cavity and is rotatable in said cavity about said axis in spaced relation to the interior surface. The impeller is adapted to force said liquid to flow through said discharge port upon said rotation in use. The liquid conduit is for balancing the pressure in said cavity so as to avoid the creation of pressure differentials in said cavity that would otherwise in use tend to cause translation of said rotor in said cavity towards said discharge port. The magnetic field generation device is adapted to drive rotation of said rotor about said axis in use.
A pump constructed according to a preferred embodiment of the invention is described hereinafter with reference to
The specifications for the pump device in
Both the outer magnets 33 and inner magnets 34, that form part of the rotating magnetic field generation device, come in 4 pairs. These magnets are made of neodymium. The driving motor 37 is a 3-phase, 200V type, with an output of 0.4 kW. Inclined wedge-shaped surfaces B1-B8 alternate with grooves 25-3, that are used to introduce water onto the wedges, for a total of 8 faces. Each inclined wedge-shaped surface has an angle of inclination θ of 2°. Also, the pump has a discharge rate of 50 l/min, an 8 m discharge head, and a pump efficiency of 24%.
As seen in
The impeller 20 is installed within the impeller casing 21. Affixed to one side of this impeller (the drive side), along the same rotary axis A-A as the impeller and casing 21, is the aluminum drive member 30. Accordingly, by loosening and removing the tightening bolts, it is easy to remove or re-install the impeller 20 and drive member 30. As earlier indicated, the drive member 30 is a non-magnetic electrical conducting hollow aluminum cylinder, the exposed surface of which is coated in a Teflon™ resin.
The impeller 20 and drive member 30 (hereafter referred to individually as rotating parts or collectively as rotor) are installed such that they rotate freely in the casing 21 and the can 38 (inner can 31, outer can 32). The casing 21 and the can 38 together define a housing 21,38 having an interior surface 100 defining an interior cavity 102 in which the rotor 20,30 is positioned and rotatable about axis A-A in spaced relation to the interior surface 100.
The can 38 (inner can 31, outer can 32) is a dual layer cylindrical structure made from a non-magnetic high electrical resistance material. The lower part of the inner can 31 (the part near the impeller 20) is closed, and the part at the other end (the part near the drive motor 37) has the inner can 31 joined up with outer can 32, creating a closed form. Arranged on the inside of the inner can 31 and the outside of outer can 32 is a gap. Installed into each gap are a grouping of several magnets, the inner magnets 34 and outer magnets 33, respectively. The outer magnets and inner magnets, respectively, are attached to outer magnet yoke 33-1 and inner magnet yoke 34-1, said yokes 33-1,34-1 being formed by a dual layer cylindrical magnet holder 35. This magnet holder 35 is connected to the output shaft (not shown) of the drive motor 37 at its axis A-A by a holder connective shaft 36.
As shown in
By rotating the inner magnets 34 and outer magnets 33 together with the magnet holder 35 in this way, a rotating magnetic field is established in the space between the inner magnets 34 and outer magnets 33; the magnetic flux between the inner magnets 34 and the outer magnets 33 intersect the drive member 30, generating an induced current and generating a rotational force and repulsive force in the drive member 30. These rotational and repulsive forces serve as the rotational driving force for the impeller 20.
Since the drive member 30 is attached to the impeller 20 only on one surface (the drive side surface), the center of gravity of the rotating part or rotor composed by joining the impeller 20 and the drive member 30 is positioned in the part of impeller 20 close to the drive member 30, such that there is a possibility that the impeller could swing to the left and right. To minimize the likelihood of this outcome, attached to the intake surface of impeller side plate 20-1, which constitutes the side of the impeller positioned opposite the drive side surface (the surface to which the drive member 30 is attached) of impeller 20, is a cylindrical balance tube 20-3 that projects out to the side opposite the drive member 30. The balance tube 20-3 is positioned about the same rotational axis A-A as the impeller 20. The rim of the balance tube 20-3 fits into a circular groove 21a in the corresponding inner surface of the intake casing side plate 21-1. By placing a balance tube 20-3 and a groove 21a like this, a radial wedge effect, that occurs from the existence of liquid in the gap between the balance tube in 20-3 and 21a, causes the balance tube 20-3 to be forced away from the inner wall of groove 21a and to rotate in a suspended state inside groove 21a. Consequently, by coupling the wedge effect that occurs in the gap between the drive member 30 and can 38, and the wedge effect that occurs between the balance tube 20-3 and groove 21a, stability of the drive member 30 and the impeller 20 is provided in operation.
As a result, contact and rubbing between the impeller 20 and impeller casing 21, and the drive member 30 and can 38, is minimized, and it is possible to limit the chance of breakdown flowing from rubbing contact of these parts. In the case of the illustrated preferred embodiment, the inner diameter and outer diameter of the balance tube 20-3 are identical to the inner diameter and outer diameter of the drive member 30, providing exceptional stability to the drive member 30 and the impeller 20.
Also, as shown in
By attaching the auxiliary intake tube 21-1-1, it is possible to mitigate movement in the impeller 20's thrust direction due to liquid intake into the impeller 20 when the pump starts rotating, or during operation. As a result, it is possible to prevent rubbing and contact of the impeller 20 and impeller casing 21 during operation, or when the pump starts rotating.
Also, an inflow regulation ‘boss’ 31-1 that protrudes out into the intake hole 20a, is attached onto inner surface in the center (the lower part of the inner can 31) of the impeller casing side plate 21 that faces the impeller 20 drive surface. By attaching this inflow regulation boss 31-1 as above, it is possible to mitigate movement in the impeller 20's thrust direction due to liquid intake into the impeller 20 when the pump starts rotating, or during operation. As a result, it is possible to prevent rubbing and contact of the impeller 20 and impeller casing 21 during operation, or when the pump starts rotating.
Furthermore, a tip of one end of the inflow regulation boss 31-1, the top of which is positioned into the center of the impeller 20's rotary axis, has attached to or formed thereon a conical protrusion 31-1a. By having this protrusion 31-1a, it becomes possible to evenly guide the dispersion of fluid flowing along the impeller 20 rotary shaft and into the inflow hole 20a, by radiating it along the perimeter of the protrusion 31-1a. This eases the movement of the impeller 20 thrust direction, and further increases the stability of the impeller 20 during startup and during operation.
The construction shown in
By these means, the barrier 23-1 and the outer wall 23-2 form a dual-walled arc shape. Positioned opposite this dual wall is a closed arc-shaped wall 23-5. Also, established between each end of the barrier 23-1, at one end 23-1a and the other 23-1b, and the closed wall 23-5, connecting each through to the impeller 20's outer perimeter, are discharge holes 23-3, and 23-4, whose widths are roughly identical. The liquid flow that passes thorough the lower facing discharge hole 23-4 flows along the liquid discharge pathway, between the outer wall 23-2 and the barrier 23-1, and merges with the liquid flow that passes through the upward facing discharge hole 23-3 that faces the discharge 27. To restate, the barrier in combination with the casing 21 defines a liquid flow conduit 108 that extends between a first terminus 106 in the cavity above the impeller and a second terminus 104 in the cavity below the impeller. By attaching arc shaped barrier 23-1 onto the impeller casing 21, in the outer perimeter area inside the impeller casing 21, and outside the impeller 20, with one end 23-1a facing the inner opening of the discharge 27 and the other end of the barrier 23-1b positioned opposite the discharge 27, the pressure at the discharge hole 23-3, P1 is made to roughly equal P2, the pressure at discharge hole 23-4. As a result, the impeller 20 is no longer urged towards the discharge, away from the axis of rotation, and can rotate in a stable position. Also, the rotating parts will not tilt, thus eliminating the phenomenon, due to tilting of the impeller, of rubbing and contact between the rotor 30 and the inner can 31 and outer can 32, and of the impeller 20 rubbing and contacting the casing 21, as shown in
With this barrier in place, there exists a thrust force against the impeller 20 (the force along the axis of rotation=the force along the holder connective shaft 36), whose magnitude depends on the pump discharge head, and discharge quantity. All things being equal, this thrust force would tend to force the impeller 20 to tilt to the left and right, which would result in wear.
Arresting this, as seen in
By placing these kinds of wedge faces 25-1, 25-2, when the impeller 20 approaches the casing side plate 21-1 or 21-2 due to the aforementioned thrust force, the wedge effect due to the flow of liquid through the gap between the impeller 20 and the wedge face 25-1, 25-2 will force the impeller sides and housing away from one another.
Without intending to be bound by theory, here follows a detailed explanation of the wedge effect referenced in
F A∝(b2×L×n)/g12
(b: wedge shaped slope width, L: wedge shaped slope length, n: number of wedge shaped slope)
Here, g2 is the gap at the liquid entry side towards the wedge-shaped slopes B1-B8, g1 is the gap at the discharge side, and g2/g1 normally has a value from 2-4. Therefore, L and θ can be determined.
From above, when the diameter of the impeller 20 is small, the corresponding area of the wedge face 25-1 (25-2) (b×L) becomes narrow and the wedge effect is decreased, and especially as the width b decreases, the wedge effect tends to decrease dramatically. To avoid suppression of the wedge effect when the outer diameter of the impeller is small, it may be preferable to provide for the area of the impeller and wedge faces to be larger than the area of the impeller. This can be done by increasing the impeller 20 side plate, and also expanding the corresponding wedge faces 25-1, 25-2 of the casing side plate 21-1, 21-2. In other words, just as seen in
The only liquid-contacting component of the illustrated pump that must utilize metal is the drive member 30. To prevent corrosion (including galvanic corrosion) of the drive member 30, it is advantageous to apply a sufficient coating of a resin, etc., or apply a lining to surface in contact with liquid. However, when coatings and the like are applied to the drive member 30, and it is attached to the impeller 20, it becomes troublesome to directly attach them together by screws etc., and thus it may be preferable to indirectly attach them. In other words, just as shown in
In
The applied repulsive force Fm to the drive member 30 due to the rotating magnetic field is a repulsive force when S*Rm>1, and is an attractive force when S*Rm<1. Here, Rm, is a value determined by the magnetic gap between magnets 33, 34 and the thickness and material of drive member 30, etc. It is called the Magnetic Reynolds' number.
As can be understood from the graph shown in
On the other hand, as the rpm of the drive member 30 increases, in other words, the rpm of the impeller 20 increases, S=0, that repulsive force becomes 0. However, the repulsive force due to the wedge effect that occurs between the can 38 and the drive member 30 becomes proportionally larger as the rpm of the drive member 30 increases, so long as there is liquid. If S1 is the slip when the drive member 30, i.e. the impeller 20, reaches normal rotation, the applied repulsive force to the drive member 30 becomes FmS1+FAS1, and the drive member 30 has risen and stabilized. However, if there is no liquid, FA=0, the rpm of the drive member 30 further increases, Fm becomes extremely small, and the repulsive force almost disappears. This fact shows that when there is no liquid, the repulsive force becomes extremely small, and rubbing occurs between the drive member 30 and the can. Accordingly, in this pump, an empty operation preventative counter-measure is advantageous, to prevent operation of the drive motor 37 when the inside of casing 21 is empty or liquid.
Therefore, in the illustrated preferred embodiment, as shown in the aforementioned
In the preferred embodiment, wedge effects provided by the balance tube/groove, drive member/can, impeller/protrusion, intake regulation boss/intake hole and intake portion/intake hole combinations support the rotor for rotation substantially about the axis in spaced relation to the interior surface of the housing. In testing, absolutely no trace of rubbing between the rotating parts (drive member 30, impeller 20) and the surrounding walls (casing 21, can 38) were observable, during startup, operation, and shutdown, for every condition starting with a completely open discharge valve to completely closed. Inspection for the existence of rubbing was conducted by coating the rotating parts in an inspection coating, and after operating the pump, inspecting the inspection coating for the existence of peeling. Also, in tests with fine slurries, and liquid limestone, no obstacles were observed. Also, by attaching a reflux valve (not shown) to the inflow tube (not shown) to the inflow 26, it was possible to confirm the possibility of ordinary restart.
In the illustrated preferred embodiment, which has a no-seal construction, no submerged bearings, and rotating parts (drive member 30, impeller 20) that can rotate in an extremely stable floating state without contacting the surrounding walls (casing 21, can 38), in testing there was found to be no contamination due to rubbing, etc.
Also, since it is possible to manufacture the liquid-contacting parts but for the drive member entirely from plastic, resin coating, or ceramic materials, there is no necessity to use metal materials in the liquid-contacting surfaces. This fact shows that it is possible to eliminate or minimize the elution of metal ions into the transported liquid. Also, the fact that there are no rubbing parts in operation provides a relatively maintenance-free pump having a relatively long lifespan and a relatively low breakdown risk.
The pump in this invention has a wide variety of possible uses, in various fields, transporting, drawing, etc., all kinds of liquids, in addition to pure liquids and corrosive liquids, fine slurries, mixed liquids, etc.
The various parts of the pump described are listed below.
Parts List
Finally, it is to be understood that while but a single preferred embodiment of the pump, and a single alternative embodiment of the rotor, have been herein shown and described, it will be understood that various changes in size and shape of parts may be made. These modifications, and others which may be routine to persons of ordinary skill in the art, may be made without departing from the spirit or scope of the invention, which is accordingly limited only by the claims appended hereto, purposively construed.
