CA1258791A

CA1258791A - Pump improvement

Info

Publication number: CA1258791A
Application number: CA000501777A
Authority: CA
Inventors: Victorien Pilon
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-04-29
Filing date: 1986-02-13
Publication date: 1989-08-29

Abstract

ABSTRACT OF THE DISCLOSURE

A centrifugal pump for pumping fluids such as corrosive liquids and slurrys has novel sealing means for preventing the fluid being pumped from reaching the bearings of the impeller shaft. A small helical impeller having shallow vanes is mounted on the impeller shaft coaxial therewith in proximity to the rear surface of the pump impeller for rotation with the impeller. Fluid at the pump bearing is displaced back into the pump chamber as soon as the pump impeller is rotated and throughout operation of the pump.

Description

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BACKGROUND OF THE INVENTlON
This invention relates to centrifugal pumps for pumping fluids such as corrosive liquids and abrasive liquid slurrys and, more particularly, relates to an improvement to said centrifugal pumps for protecting the pump bearings, packings and seals.
U.S. Patent 4 269 566 issued May 26, 1981 discloses a centrifugal pump for abrasive liquids which utilizes a separate centrifugal chamber within which a liquid seal is formed when the pump is operating to prevent abrasive liquid slurry from contacting the pump packings. U.S. Patent 4 152 092 issued May 1, 1979 discloses a bypass passageway system for collecting particles which may have leaked past annular seals for protecting shaft bearings and packings to avoid erosion of pump components from said particles.
U.S. Patent 4 3B6 780 issued June 7, 1983 discloses another version of apparatus for cleaning liquids in centrifugal pumps. A disc separator positioned in a first of a pair of chambers relieves liquid entering the first chamber of impurities. U.S. Patent 3 635 581 issued January 18, 1972 discloses the incorporation of vanes on the backside of an impeller to reduce leakage across the back of the impeller inwardly towards the impeller drive shaft and bearings, the impeller shaft having a separate gear housing for lubrication.

SUMMARY OF THE INVENTION
In accordance with the present invention, a small impeller, preferably in the form of a helical impeller, is mounted on the impeller shaft of a centrifugal pump coaxial therewith in proximity to the rearside of the pump impeller.

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The helical impeller can be mounted on the impeller shaft as a retrofit between the said pump impeller and shaft stuffing box.
More particularly, the improvement to a centifugal pump comprises a pump casing enclosing a pumping chamber having an inlet and an outlet, an impeller in the pumping chamber mounted on an impeller shaft for drawing a fluid in through the inlet and for discharging said fluid through the outlet, said impeller shaft passing through an opening in the pump casing, and a small impeller having vanes with the same direction as the direction of rotation of the pump impeller mounted on the impeller shaft outside the pumping chamber in proximity to the pump impeller whereby any liquid escaping the pumping chamber is returned to the pump chamber to protect the pump bearings and seal from fluid from within the pump. The small impeller comprises a sleeve secured to the impeller shaft coaxial therewith for rotation with the impeller shaft and a plurality of upstanding equi-spaced shallow vanes formed on or secured to the sleeve having an angle in the range of 20 to 30 to the longitudinal axis forming a portion of a helix with the same direction as the direction of rotation of the impeller.
It is a principal object of the present invention to provide an improved apparatus for protecting the impeller shaft seal and bearings of a centrifugal pump.
Another object of the present invention is the provision of a seal protector which can be provided as a retrofit to conventional centrifugaI pumps.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects of the invention and the - .

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manner in which they can be attained will become apparent from the following detailed description of the drawings, in which Figure 1 is a perspective view, partially cut away, of a centrifugal pump which can incorporate the helical impeller of the present invention;
Figure 2 is a perspective view of the pump shown in Figure 1 from the opposite side thereof;
Figure 3 is an exploded perspective view corresponding to Figure 2 with the pump rear casing cover and impeller axially separated;
Figure 4 is a perspective view of the end of an impeller shaft of a pump showing the helical impeller of the present invention mounted thereon adjacent a stuffing box;
Figure 5 is a longitudinal vertical section of a centrifugal pump showing the installation of the helical impeller of the invention; and Figure 6 is an enlarged vertical sectional view corresponding to Figure 5 showing the helix device of the invention in more detail relative to the pump impeller and the impeller shaft.

DESCRIPTION OF THE PREFERRED EMBODIMl~NT
Referring to Figures 1, 2 and 5, cen~rifugal pump 10 comprises a casing 12 having a central flanged inlet 14 and tangential flanged discharge 16~ Impeller shaft 18, which extends from a motor drive 20 illustrated in Figure 5, is centrally disposed with the pump rear casing cover 22 by means of motor bearings 24, 26 and stuffing box 28, stuffing box 28 being rigidly secured to stationary rear casing cover 22 by threaded bolts 30 shown most clearly in Figures 5 and 6.

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Figure 3 illustrates casing cover 22 retracted axially from pump casing 12 with threaded stub shaft 36 of impeller 38 axially spaced from threaded central opening 40 formed axially at the end 42 of impeller shaft 18.
With particular reference now to Figure 6, rear casing cover 22 has a central opening 46 with an annular shoulder 48 permitting the end 42 of shaft 18 to extend freely therethrough to receive impeller 38 by screwing of threaded stub shaft 36 into threaded socket 40. A small impeller 52 formed of a sleeve 54 adapted to frictionally fit onto or to be keyed onto shaft 18 has a plurality of equi-spaced upstanding vanes 56 formed or secured by welding generally longitudinally thereon with an annular ring 58 at the end remote from shoulder 48 to provide strength and rigidigy to the vanes 56. Vanes 56 define a portion of a pitch of revolution, i.e. about 10 - 30 of the angle of revolution about the shaft axis 57, from one end defined by ring 58 to the opposite end 64 which is open-ended for reasons which will become apparent as the description proceeds. Each of vanes 56 is wrapped about a portion of the right circular cylinder surface 55 of sleeve 54 and defines with the longitudinal axis 51 of shaft 18 an-angle alpha to form a portion of a helix with the same direction of rotation as impeller 38. Angle alpha may be in the range of 20-30.
The open end 64 of impeller 52 is adjacent the shoulder 48 of casing cover 22 and the opposite end defined by ring 58 is adjacent a packing ring 70.
In operation, rotation of shaft 18 and impeller 38 therewith causes helical impeller 52 to rotate within annulus 46 in the same direction. Helical vanes 56 effectively return ~2S87g~L

any fluid such as a corrosive liquid discharging from the pump back into the pump chamber thereby maintaining annulus 46 free of corrosive liquids and/or abrasive slurrys of particulate material in the liquid.
The present invention provides a number of important advantages. The provision of a small helix either as a retrofit impeller or supplied with new pumps on the impeller shaft as illustrated discharges any fluid from the packing and/or bearings in proximity to the pump shaft back into the pump chamberO The helical impeller can be easily incorporated in a pump design with surprising improvement in bearing, packing and seal life. Installations of the impeller improvement in pumps for pumping highly corrosive liquids such as sulphuric acid and the like have extended the life of the pump components from two weeks to as much as one year.
It will be understood, of course, that modifications can be made in the embodlment of the invention illustrated and described herein without departing form the scope and purvue of the invention as defined by the appended claims.

Claims

1. A centrifugal pump comprising, in combination, a pump casing enclosing a pumping chamber having an inlet and an outlet, an impeller in the pumping chamber mounted on an impeller shaft for drawing a fluid in through the inlet and for discharging said fluid through the outlet, said impeller shaft passing through an opening in the pump casing and journalled for rotation in pump bearings, and a small impeller mounted on the impeller shaft outside the pumping chamber in proximity to the pump impeller and adjacent a packing ring, said small impeller comprising a sleeve in the form of a right circular cylinder adapted to be fitted onto the impeller shaft, shallow equispaced helical vanes affixed to said sleeve with the same direction as the direction of rotation of the impeller, said vanes having an angle in the range of about 20 to 30° to the longitudinal axis and defining a portion of a pitch of revolution of about 10 to 30°, whereby any liquid escaping the pumping chamber is returned to the pump chamber to protect the pump bearings and packing ring from fluid from within the pump and, an annular ring coplanar with the periphery of the vanes secured thereto at an end remote from the pump impeller adjacent the packing ring.