Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Radially extending web or end plate
Reexamination Certificate
1999-04-02
2001-04-03
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Radially extending web or end plate
C416S18600A, C416S19800R, C416S22300B, C416S228000
Reexamination Certificate
active
06210116
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns pumps and more particularly impellers for non positive displacement pumps.
A particular type pump impeller which has long been known is comprised of a stack of spaced apart discs. This type of pump uses a boundary layer effect causing a boundary layer adhesion of the fluid to the disc faces to cause liquid to be pumped upon rotation of the impeller, creating pressure and flow at an outlet in an enclosing pump housing.
Another well known impeller configuration has a series of radially extending vanes, which accelerate the fluid by directly acting on the fluid with the faces of the vanes as the impeller rotates.
The spaced disc impellers have the advantage of largely eliminating the low pressure regions and cavitation characteristic of vane pumps. Disc impellers also are more efficient in pumping viscous fluids and can pump fluids having entrained abrasives with less impeller wear.
On the other hand, the induced flow rate per unit area of the discs is low, and reduced efficiency is encountered in this type of impeller at high flow rates.
Turbulence and cavitation can still occur as the fluid exits the outer perimeter of the disc and flows into the volute space in a confining housing. Further, there is a tendency for adhesion of the fluid to the outer perimeter of the discs to create turbulence and thereby reduce the efficiency of the pump.
It has been heretofore been proposed to combine a vaned and spaced disc impeller, see U.S. Pat. No. 4,255,081 issued on Mar. 10, 1981 for a “Centrifugal Pump”.
This combination is intended to provide most of the advantages of both types of impellers.
However, cavitation may still occur of the outer ends of the vanes and turbulence in the regions beyond the impeller perimeter.
It is the object of the present invention to provide an improved pump impeller of a hybrid vane-disc type in which the tendency for cavitation is greatly reduced and which operates more efficiently than prior designs.
SUMMARY OF THE INVENTION
The above recited object and others which will become apparent upon a reading of the following specification and claims are achieved by combining a multiple disc impeller with a series of radial vanes defining intervening flow spaces which are convergent in a direction towards the outer perimeter of the impeller. This convergency has been found to minimize the tendency to cavitate by eliminating regions of low pressure as the fluid flow exits those spaces.
The vanes terminate at a relatively steep angle to the outer circumference so that flow is directed substantially radially outward when emerging from the convergent intervening spaces to reduce the adhesion tendencies.
The convergency is created in one embodiment by an increasing vane thickness to a maximum at the outer ends, which shape causes a decreasing flow space cross sectional area to a minimum area at the impeller perimeter spaces. In another embodiment, a cover sidewall is tapered to create the convergency of the flow spaces.
The disc stack may extend into the vane area, or may be confined within an inner diameter of the impeller.
Another improvement is in the scalloping of the outer edge of the discs between the ends of the vanes, which scalloping also contributes to a smooth nonturbulent transitional flow from the impeller perimeter into the pump housing.
In one version, the impeller may also have only a single cover plate, to simplify and lower the cost of manufacturing the impeller.
REFERENCES:
patent: 4025225 (1977-05-01), Durant
patent: 4253798 (1981-03-01), Sugiura
patent: 4255081 (1981-03-01), Oklejas et al.
patent: 4280791 (1981-07-01), Gawne
patent: 5192183 (1993-03-01), Wilkinson
patent: 5427503 (1995-06-01), Haraga et al.
patent: 5741118 (1998-04-01), Shinbara et al.
Kuczaj John E.
Oh Dong Chul
Benefiel John R.
Look Edward K.
Nguyen Ninh
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