The present invention relates to a rotary positive displacement pump with impeller, where the impeller defines, within a pumping chamber, chambers with variable volume through which a fluid is mechanically conveyed from an inlet to an outlet of the pump.
Such pumps are known from a long time and are used in several technical fields.
The prior art pumps with impeller, which use eccentric rotating members, are often unsatisfactory in respect of one or more of the following aspects:
It is an object of the invention to provide a positive displacement pump with impeller, and a method of manufacturing the same, which do not suffer from the drawbacks of the prior art.
According to the invention, this object is achieved in that said chambers with variable volume are defined, at axially opposite ends, by a pair of rotational surfaces that axially close said pumping chamber and are arranged to rotate about mutually inclined axes.
Preferably, said surfaces are conical surfaces or surfaces shaped as spherical caps, and are the facing surfaces of a pair of discs or spherical caps, the axes of which coincide with the axes of said surfaces and which are made to rotate by the impeller.
Preferably, the impeller has a plurality of radial blades engaging with a certain clearance radial slots of the surfaces.
The invention also relates to a method of manufacturing the pump described above, including the steps of:
The invention will now be described in greater detail with reference to the accompanying drawings, which show a preferred embodiment given by way of non limiting example and in which:
Referring to
If necessary, rotary seals may be provided between discs 4, 5 and the walls of chamber 20, in order to avoid leakages.
In order to house the inclined discs, stator 2 and chamber 20 are elbow shaped.
Facing surfaces 40, 50 of upper disc 4 and lower disc 5 are rotational surfaces the axial sections of which have a height progressively increasing from the edge towards the axis of the disc. In the exemplary embodiment described herein, surfaces 40, 50 are conical surfaces, with axes coinciding with the axes of the discs, and the discs are preferably mounted in chamber 20 so that a generatrix of conical surface 40 of upper disc 4 is substantially parallel with a generatrix of conical surface 50 of lower disc 5, as shown in
The spacing between discs 4, 5 may be adjustable, and to this end at least upper disc 4 is mounted in chamber 20 so that its axial position can be varied. Preferably, both discs are substantially adjacent to each other in correspondence of the respective parallel generatrices. The variation of the disc spacing is obtained for instance by means of pneumatic actuators, not shown. In case of reverse rotation of the pump, the disc displacement may also occur starting from a given pressure.
Impeller 3 is a butterfly impeller, with substantially trapezoidal blades 30 joined by their small bases to a central hub 31, integral with a shaft (not shown) in turn connected to a suitable driving device. Impeller 3 rotates about its axis, is pivoted at the centre of both discs 4, 5, as shown in
Blades 30 of impeller 3 engage radial slots 41 and 51 with an axial clearance, as shown in
The swept volume of pump 1 depends on the angle between conical surfaces 40, 50 at their centres (hence on their aperture and the inclination of their axes of rotation), on the axial and radial sizes of discs 4, 5, as well as on the number and the thickness of blades 30. The relative inclination of the axes of conical surfaces 40, 50 also affects the rotation speed of pump 1. Actually, the smaller such an inclination, the smaller the stresses on the pump and hence the higher the rotation speed may be. Theoretically, the inclination of the axes may range from a value immediately higher than 0° to a value immediately lower than 90°. In practice, a suitable inclination for the preferred applications of the invention (e.g. vacuum pumps) will be lower than 10°, for instance of the order of 5°-6°. Clearly, if the conical surfaces are arranged so that respective generatrices are parallel, the angle defined by said surfaces in a position offset by 180° relative to the parallel generatrices will be twice the angle of inclination of the axes.
In the illustrated embodiment, impeller 3 is made to rotate by an external electric motor 6. In other embodiments, the drive may be a magnetic drive. The latter solution is particularly suitable for applications in which it is desired to keep the pumping module (chamber 20 and rotor 3, 4, 5) isolated from the outside. As a further alternative, an electric motor integrated into one of the discs could be employed.
Turning back to the intake and exhaust ports (inlet and outlet) 7 and 8, inlet 7 is connected to an intake duct 70 and is possibly associated with a nonreturn valve. Outlet 8 too may be associated with a valve. The provision of valves at the intake and the exhaust assist in improving the performance of pump 1. Yet, the greater the subdivision of the swept volume of the pump determined by the number of blades 30, the smaller the need to provide valves in order to ensure the proper operation.
The location of intake and exhaust ports 7 and 8 is not binding for the installation of pump 1. Advantageously however the exhaust is directed towards the rear side of one or both discs 4, 5. In this manner, the fluid exhausted assists in pushing the discs in central direction, thereby reducing the clearances during rotation. In case of application to a vacuum pump using external electric motor 6 to drive impeller 3, by directing the exhaust rearwards of the disc located on the drive side (lower disc 5 in the drawings), the exhausted fluid can be used to cool the electric motor, thereby increasing its efficiency. An exhaust directed inside the pump also assists in reducing noise. However, the exhaust could be even directed outside the pump.
Advantageously, the components of pump 1 can be manufactured by moulding plastic materials, for instance with the addition of elastomers in order to impart a certain flexibility to the materials. This allows mounting the components with a slight interference, without the components being damaged or without the components damaging other stationary or moving parts. Moreover, stator 2 may be made of transparent plastics. The specific material will depend on the nature of the fluid being pumped.
Use of such materials allows optimising the pump geometry and achieving a reduced weight, what makes attainment of high rotation speeds easier. In particular, blades 30 must be capable of bending in radial direction (referring to
It is to be appreciated that, in case the pump is used as a compressor or a vacuum pump, lubrication between the components moving relative to each other is not required. For instance, roller or ball bearings could be provided or materials with high slip coefficient, well known in the art, could be used.
As stated above, the rotational surfaces with mutually inclined axes result in a plurality of successive chambers 21 with variable volume being defined in chamber 20, whereby the operation includes expansion and compression steps of a fluid volume conveyed, with consequent intake and exhaust of the same. The maximum delivery pressure will be determined based on the geometry of disc surfaces 40, 50 and their axial sealing system. Such a delivery pressure may be adjusted by acting on the disc spacing.
The following operations are envisaged in order to manufacture the pump described above:
It is evident that the invention attains the desired objects. The number of components is lower than in prior art solutions and the components themselves are made of relatively cheap materials and allow wide tolerances, so that expensive precision workings are not required. Use of plastic materials makes optimisation of the geometry easier and, jointly with the reduced weight of the components and the absence of eccentrically rotating parts, allows using the pump at high speed, while further enabling the attainment of high performance. Moreover, some components, in particular discs 4, 5, are identical and also this feature assists in reducing the manufacturing costs. The shape of the rotor components further allows a wide flexibility in the design, in order to adapt pump 1 to different applications with different requirements. The peculiar geometry allows easily assembling the components. Lastly, the arrangement of the components results in a reduced axial size.
In the variant embodiment shown in
Both hemispherical bodies 2′a, 2′b further have holes 24a, 24b coaxial with the axes of rotation of caps 4′, 5′. One of such holes serves for the passage of members linking impeller 3′ to a rotation generator (e.g. an electric motor like motor 6 shown in
The operation of such a variant embodiment is the same as that of the embodiment shown in
With respect to the embodiment shown in
It is clear that the above description has been given only by way of non-limiting example and that further changes and modifications are possible without departing from the scope of the invention as defined by the following claims.
Number | Date | Country | Kind |
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TO2008A000976 | Dec 2008 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2009/055902 | 12/22/2009 | WO | 00 | 6/22/2011 |