Rotary kinetic fluid motors or pumps – With means for re-entry of working fluid to blade set – Turbine regenerative pump
Reexamination Certificate
2000-04-20
2001-10-02
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With means for re-entry of working fluid to blade set
Turbine regenerative pump
Reexamination Certificate
active
06296440
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a side-channel centrifugal pump having a housing which forms a side channel and whose surface which is adjacent to the side channel forms a front face which is contiguous to the impeller except for a narrow gap, the transition edge from the side channel to the front face being rounded in those regions where it deviates from the circumferential direction, and having an impeller whose vanes have a predetermined web width in the circumferential direction in the front plane of the impeller.
Side-channel pumps are used, inter alia, whenever a high pressure is to be obtained in conjunction with a small conveying flow. A disadvantage of these pumps is the cavitation tendency at those locations on the housing where it has sudden changes in its shape in the direct vicinity of the impeller. Cavitation damage may occur both on the housing and on the impeller. A relatively high level of noise is associated therewith. These disadvantages are particularly noticeable at high rotational speeds, which are understood as being speeds of over 2,800 rpm. Pumps of this type are therefore generally used at a lower rotational speed of around 1,500 rpm.
In the case of the similarly constructed peripheral pumps (DE-A 40 02 027) it is known to provide the transition edge from a wide housing part to the front face of the housing, specifically in the region of the outlet opening, with a rounded portion, in order thereby to reduce the generation of noise.
SUMMARY OF THE INVENTION
The invention is based on the object of reducing the cavitation tendency and generation of noise in a pump of the type mentioned at the beginning. The invention is further based on the recognition that cavitation and formation of noise should be taken into account not only at those locations where the flow rate of the conveyed medium is particularly great, but also at other transition edges. The invention is furthermore based on the recognition that a rounded portion only achieves an optimum effect if its radius of curvature is matched to the vane speed and the web width of the vanes. The vane speed is understood to be its circumferential speed at the location under consideration in each case. The web width is understood to be the width of the impeller in the circumferential direction in the front plane of the impeller. The greater the vane speed and the web width, the larger the rounded portion should be.
The effect of the rounded portion resides in the fact that the vane edge, on reaching the end of the front face and the beginning of the side channel, does not enter suddenly into the liquid which is virtually at rest there, but rather already prior to this in the region of the rounded portion a circulating flow is built up around the vane edges, leading to pressure equalization and reducing the impact. This preparatory circulating flow is more intense the higher the relative speed of the vane is with respect to the housing edge and the shorter the rounded portion is. It has furthermore been established that the said circulating flow proceeds more favourably the smaller the web width of the vane is. The teaching of the invention for the first time takes into consideration this inter-relationship between these effects and the use of a certain minimum value of the ratio of the edge radius and web width for a given vane speed.
This rounded portion is expediently also used on the corresponding edges of the air-displacing channel, if such a channel is present. It may also be expedient not only for the edges at which the vanes emerge from the region of the front face and pass into the region of the side channel or of the air-displacing channel, to be rounded in the specified manner, but also those edges where the vanes emerge from the region of the side channel or air-displacing channel and pass into the region of the front face.
Since the rounded portion reduces the effective circumferential length of the sealing region between the end and the beginning of the side channel (apex region), provision is made according to the invention for this circumferential length including the rounded section to amount at least to the spacing of 2.5 vanes. It has furthermore proven expedient for the depth of the side channel to increase shortly before its end.
REFERENCES:
patent: 5336045 (1994-08-01), Koyama et al.
patent: 5401147 (1995-03-01), Yu
patent: 5486087 (1996-01-01), Treiber et al.
patent: 6086325 (2000-07-01), Ellinghaus
patent: 6126387 (2000-10-01), Yoshida et al.
patent: 1196016 (1965-07-01), None
patent: 36 44 356 (1988-07-01), None
patent: 1281842 (1970-02-01), None
Alix Yale & Ristas, LLP
Look Edward K.
McAleenan James M.
Sterling Fluid Systems (Germany) GmbH
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