Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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.
