.
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`United States Patent
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`Raible
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`
`[19]
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`US005368438A
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`[11] Patent Number:
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`[45] Date of Patent:
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`9
`9
`5 368 438
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`Nov. 29, 1994
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`[75]
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`[56]
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`-
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`[54] BLOOD PUNIP
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`Inventor: Donald A. Raible, Santa Ana, Calif.
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`Assignee; Baxter International Inc” Deerfield,
`111'
`~
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`[21] Appl. No.: 83,405
`.
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`[22]
`Ffled=
`Jun-28, 1993
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`[51]
`Int. 01.5 .............................................. .. F04D 1/08
`[52] us. Cl. .................................... .. 415/74; 415/143-
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`'415/2303415/9003416/177
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`..................... ..
`of
`72, 73, 74,
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`415/143, 230, 900; 416/176, 177
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`
`References Cited
`Us. pATENT DOCUMENTS
`
`
`3/1976 Rafferty et al.
`Rel 28,742
`I
`
`
`
`
`307,275 10/1984 Edmundson .
`
`
`
`
`
`
`415/74
`£1225 '
`
`
`
`
`
`3:087:435 4/1963 Bouche;I:1:ZZZZZZZZKZ 415/72
`
`
`
`
`
`5/1968 Rastoin .
`3,331,801
`
`
`
`
`
`
`
`.
`3,647,324 3/1972 Rafferty et 31.
`3,864,055
`2/1975 Kletschka et a1.
`.
`
`
`
`
`3,918,831 11/1975 Grennan .............................. 415/143
`
`
`
`
`
`
`
`
`3,957,339
`5/1976 mew et 31'
`-
`3,970,408 7/1976 Rafferty et al.
`.
`
`
`
`
`4,037,984 7/1976 Rafferty et a1.
`.
`
`
`
`
`5/1984 Kurahayashi .
`4,449,895
`
`
`
`4 456 437 6/1984 Kmahayashi
`
`
`
`
`
`
`4,625,712 12/1986 Wampler .
`4,846,152 7/1989 Wampler et al.
`
`
`
`5,040,944 8/1991 Cook .
`
`
`
`
`
`
`.
`
`
`
`
`5,139,391
`
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`
`
`8/1992 Carrouset ............................ .. 415/74
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`
`
`
`
`
`317687
`5/1989 European Pat. Off.
`............ 415/143
`
`
`
`
`
`364293 4/1990 European Pat. Off.
`.
`
`
`
`
`
`7/1990 European Pat. Off.
`.
`378251
`6/1956 France ................................ 415/230
`1118405
`
`
`
`
`2/1972 United Kingdom.
`1375287
`
`
`
`
`5/1972 United Kingdom.
`1368095
`
`
`
`
`
`
`
`
`3/1973 United Kingdom-
`1390741
`
`
`
`
`7/1991 United King‘bm -
`2239575
`W082/03176 9/1982 WIPO .
`
`
`
`W085/01432 4/1985 WIPO.
`
`
`
`_
`
`
`
`“logo/01347 2/1990 WIPO .
`
`
`
`
`
`
`Primary Examiner—Edward K. Look
`
`
`
`Assistant Examiner—James A. Larson
`R
`,
`F' —
`t,
`'
`
`
`
`
`
`Attorney Agen or
`trm Poms Smith Lande & ose
`
`
`[57]
`ABSTRACT
`
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`A dynamic blood pump includes a rotating core mem-
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`bet and rotating ring Ponion effective ‘0 Pfe‘SPin b1°°d
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`before the blood enteres helical pumping channels of
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`the pump. The blood is pumped and further rotated as it
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`moves axially along the helical channels toward a cen-
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`trifugal section of the pump_ At the centrifugal pumping
`
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`section circumferential velocity differentials are also
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`controlled to diminish damage to the blood. Outwardly
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`of the centrifugal pumping section, a forced-vortex
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`pumping section communicates the pumped blood to an
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`ex“ P0“-
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`32 Claims, 3 Drawing Sheets
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`fig71'1
`'2
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`a!!!
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`"ll/11 ilIAVAY’IIIIilllI
`'
`
`ill—i.
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`PAGE 1 OF 12
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`PETITIONERS' EXHIBIT 1103
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`PETITIONERS' EXHIBIT 1103
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`PAGE 1 OF 12
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`US. Patent
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`Nov. 29, 1994
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`Sheet 1 of 3
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`5,368,438
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`F/G.
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`F‘3
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`72“
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`\«A
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`20
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`42
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`44
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`mm: 56
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`62
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`54
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`66
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`PAGE 2 OF 12
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`E
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`38
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`30
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`PAGE 2 OF 12
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`US. Patent
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`Nov. 29, 1994
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`Sheet 2 of 3
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`5,368,438
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`[/0 I08
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`‘76 8
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`1%;
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`I‘IIIIIS
`\'
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`sun-Tum“!
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`6“
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`[III]
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`I ’”” F
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`KER“
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`ZIIIIIII
`‘IJI g5
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`PAGE 3 OF 12
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`4
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`PAGE 3 OF 12
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`US. Patent
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`Nov. 29, 1994
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`Sheet 3 of 3
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`5,368,438
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`PAGE 4 OF 12
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`PAGE 4 OF 12
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`2
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`roller pump and other conventional pumps. One of
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`these conventional blood pumps is known in accord
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`with US. Pat. No. Re. 28,742, reissued 23 March 1976,
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`to E. H. Rafferty, et al. The Rafferty reissue patent is
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`believed to teach a dynamic blood pump based on the
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`forced vortex principle. That is, the pump is based on
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`the principle that a spinning chamber forms therein a
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`spinning volume of liquid which is pressurized at its
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`outer periphery and flows radially outwardly. The
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`Rafferty pump defines one or a successive plurality of
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`such spinning chambers, the walls of which may be
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`smooth with the exception of strut members or other
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`such structural features arranged to connect the walls
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`together for rotation in unison, or which may include
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`radially extending and perhaps forwardly or back-
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`wardly inclined or swept vanes. In this context, the
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`terms forwardly or backwardly inclined or swept vanes
`refer to the circumferential direction in which the vanes
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`extend with respect to the normal direction of rotation
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`of such a pump rotor. When so equipped with vanes
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`extending into the pumping chambers from the rotating
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`wall surfaces, the pump configurations of Rafferty are
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`more akin to centrifugal pumps than to strict forced
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`vortex pumps, the latter which rely on viscous coupling
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`between the rotating walls of the pump and the liquid to
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`effect spinning and pressurization of the latter.
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`As may easily be appreciated, the struts and other
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`structural features of the pumps of Rafferty, and partic-
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`ularly the vanes of these pumps which are of centrifugal
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`configuration may impose severe damage on formed
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`blood cells. That is, the struts are spaced outwardly
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`from the axis of rotation and sweep through the blood
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`with a high relative circumferential velocity. Similarly,
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`the vanes of the centrifugal versions of Rafferty’s
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`pumps have edges which may result in abrupt changes
`in cross sectional area of the blood flow channels, in
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`turbulence and in shock to the formed constituents of
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`the blood.
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`Another series of dynamic pumps which are based on
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`the forced vortex principle and viscous coupling of the
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`blood with the pumping rotors are seen in US. Pat.
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`Nos. 3,864,055; 3,647,324; 3,970,408; 3,957,389; and
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`4,037,984. Considering particularly the first-listed one
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`of these patents, it is seen that the pumping elements are
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`based on forced vortex principles with the pumping
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`chambers being of disk-like, semi-spherical, conical, or
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`trumpet-shaped configurations. The pumping chambers
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`include a pair of axially spaced apart rotating end wall
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`members, and may include intermediate wall members
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`which are matched in shape to the end wall members.
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`Experience has shown that with blood pumps made
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`according to the teachings listed immediately above,
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`the pumped blood experiences a higher than preferred
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`level of damage. Also, some of these pump configura-
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`tions are rather complex and expensive to manufacture.
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`In the present medical environment with concerns
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`about Hepatitis and AIDS mitigating toward a minimi-
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`zation of contact with a patient’s blood, and the disposal
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`of blood wetted equipment,
`the discarding of such
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`pumping devices after a single use constitutes a signifi-
`cant expense.
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`Still additional conventional dynamic blood pumps
`are seen in US. Pat. No. 4,625,712, issued 2 December
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`1986; and US. Pat. No. 4,846,152, issued 11 July 1989,
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`each having R. K. Wampler as a sole or coinventor. The
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`blood pumps of the Wampler patents are small, high-
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`speed, axial-flow designs of single or multiple stages,
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`5,368,438
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`1
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`BLOOD PUMP
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`15
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`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
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`The present invention is in the field of liquid pumps.
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`More particularly, the present invention is in the field of
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`combined axial and centrifugal pumps for pumping
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`liquids. Still more particularly, the present invention
`10
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`relates to a combined axial and centrifugal pump having
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`a centrifugal-flow section and an axial-flow helical in-
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`ducer section conveying liquid flow to the centrifugal
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`section. The present inventive pump has particular util-
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`ity for pumping blood with minimal damage to the
`formed cells and other constituents of the blood.
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`2. Related Technology
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`Blood is a complex and delicate fluid. Blood is essen-
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`tially made up of plasma, which is a pale yellow liquid
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`containing microscopic materials including the formed
`20
`constituents of the blood. These formed constituents
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`include the red corpuscles (erythrocytes), the white
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`corpuscles (leukocytes), and the platelets (thrombo-
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`cytes). These and other constituents of the blood, as
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`well as the suspension of the formed constituents of the
`25
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`blood in the plasma, are affected by the manner in
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`which blood is physically handled or treated. More-
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`over, blood is susceptible to damage from a variety of
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`physical effects. These include depressurization, shock,
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`shear, impact, other forms of physical stress, as well as
`30
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`turbulence, and sudden changes in cross sectional area
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`of a flow path which causes eddy currents, and which
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`may cause small clots to form in the blood.
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`Further to the above, it is well recognized that the
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`conventional type of positive-displacement roller pump
`35
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`which has many uses in the medical field, and which
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`employs a length of flexible tubing squeezed in progres-
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`sive sections between a housing and moving rollers is
`hard on the formed constituents of the blood. These
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`formed blood constituents become caught in the mov-
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`ing nips formed as the rollers move along and squeeze
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`the flexible tubing. When so caught and squeezed, the
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`formed constituent cells are ruptured and destroyed.
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`During many major surgical procedures, such as
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`open heart surgery, or cardiovascular-respiratory sup-
`45
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`port, the need to pump blood arises. This blood pump-
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`ing necessity arises in connection with the requirement
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`to move blood for the patient through heart-lung sys-
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`tems which filters the blood, removes impurities, oxy-
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`genates the blood, and controls its temperature to a
`50
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`level which reduces the patient’s metabolism during the
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`surgery. However, as pointed out above, pumping of
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`blood is a particularly difficult problem. Such is the case
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`because blood is not a simple liquid which can be
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`pumped as though it were water or oil, for example. As
`55
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`explained above, blood contains many cells, such as red
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`and white corpuscles, and other constituents which are
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`living tissues of the body. These living blood tissues are
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`particularly susceptible to damage and destruction by
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`pumping actions which squeeze the blood, as do roller
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`type pumps. Also, pumps which subject the blood to
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`sudden changes in direction or velocity, which exces-
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`sively stir the blood, which subject the blood to high
`relative velocities, or which submit the blood to exces-
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`sive levels of shear, all impose damage on the blood, and
`65
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`impose a trauma on a living tissue of the patient under-
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`going the surgery or medical procedure.
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`Many attempts have been made to provide dynamic
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`pumps which avoid the deficiencies of the conventional
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`PAGE 5 OF 12
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`PAGE 5 OF 12
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`

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`5,368,438
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`15
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`3
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`and the single stage design includes a slight increase in
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`inner diameter of the flow path so that some centrifugal
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`pumping effect is asserted.
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`The Wampler pumps have been found by experience
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`to impose severe damage on the formed constituents of 5
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`blood. It is believed that the high rotational speed
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`which are required for the Wampler pumps to achieve
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`significant volumes of pumped blood against ordinarily
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`head pressures encountered in the use environments of
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`such pumps is a significant factor in the great damage
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`these pumps impose on the pumped blood.
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`Finally, another conventional blood pump of novel
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`design is shown in US. Pat. No. 5,040,944, issued 20
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`August 1991, to E. P. Cook. The Cook teaching in-
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`cludes a pump with an elongate central ribbon-er
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`member which is helical and stationary. Around this
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`central member rotates an elongate helical rod-like
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`member which has a direction of helix opposite to the
`central member and which also rotates in this direction.
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`20
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`While the blood pump according to the Cook patent
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`is believed to offer advantages in pumping volume and
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`developed head pressure in comparison to other con-
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`ventional blood pumps, the rotational speed required of
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`this pump is still much higher than desired. Conse-
`25
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`quently, the Cook pump also imposes somewhat more
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`damage on the pumped blood than that which is consid—
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`ered minimal and acceptable.
`SUMMARY OF THE INVENTION
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`In view of the above, a primary object for the present
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`invention is to provide a blood pump which results in
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`significantly reduced damage to pumped blood.
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`Yet another object for the present invention is to
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`provide such a blood pump which is economical to
`manufacture.
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`Another object for the present invention is to provide
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`such a blood pump which avoids bluff or sharp-edged
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`moving through the blood at excessive relative veloci-
`ties.
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`Additional objects for the present invention are to
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`provide a blood pump which is dependable, reliable,
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`durable, and fully effective to accomplish its intended
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`purposes of pumping blood with significant head pres-
`sures and volume flow rates without the level of dam-
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`45
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`age to the blood which conventional blood pumps
`would cause.
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`Accordingly, the present invention provides a liquid
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`pump with a housing defining an inlet, an outlet, and a
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`flow path extending between the inlet and outlet for
`50
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`communicating a flow of liquid therebetween; a rotor
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`member joumaled in the flow path for impelling said
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`liquid flow in response to rotation of said rotor member;
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`the rotor member including a circumferentially continu-
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`ous ring portion defining an inlet end for said rotor
`55
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`member and defining an inlet recess receiving therein
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`said liquid flow from said inlet; a helical auger pumping
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`section including plural helical flutes extending from
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`said ring portion and cooperatively defining a like num-
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`ber of helical pumping channels open radially out-
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`wardly toward a circumferential wall portion of said
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`housing and extending axially and circumferentially
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`toward said outlet; said helical channels opening radi-
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`ally, axially, and circumferentially from said inlet re-
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`cess; and a centrifugal pumping section including plural
`65
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`vane portions like in number to said helical flutes and
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`each extending radially outwardly into a circumferen-
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`tial chamber of said flow path to cooperatively define
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`circumferentially extending chamber sectors therebe-
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`4
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`tween, each of said helical auger flutes merging with a
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`respective one of said vane portions, and each of said
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`helical pumping channels communicating with a respec-
`tive one of said chamber sectors.
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`An advantage of the present inventive pump is that it
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`avoids sudden changes in cross sectional area of the
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`developed fluid flow area through the pump. Conse-
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`quently, sudden changes in fluid flow velocity, turbu-
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`lence, and impacts to the fluid, are also avoided. Also,
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`the present inventive pump does not require the high
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`rotational speeds of some conventional blood pumps in
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`order to pump significant quantities of blood against the
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`head pressures commonly encountered in such uses of
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`the pump. As a result, the present inventive blood pump
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`does not whip the blood like some of the conventional
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`blood pumps.
`As will be further elaborated hereinafter, actual com-
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`parative tests of several conventional blood pumps, and
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`of blood pumps made according to the teaching of the
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`present invention, have shown significant advantage for
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`the present pump. That is, the rotational speeds required
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`for the present pump are significantly lower. The dam-
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`age imposed on the pumped blood per unit of time at a
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`given pumping volume and head pressure, or per unit of
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`blood pumped,
`is significantly lower for the present
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`inventive blood pump than for the best of the conven-
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`tional blood pumps discussed above. When it is remem-
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`bered that the formed constituents of blood are living
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`tissues of the patient, and that damage and destruction
`of these tissues results in necrotic factors which must be
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`eliminated from the patient’s system by the liver and
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`kidneys for the most part, the burden on the patient’s
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`system from this cell damage must be minimized. In
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`addition to slowing the patient’s recovery, the damaged
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`blood cells must eventually be replaced by the patient’s
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`system, which is another factor in patient recovery.
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`These recovery-slowing burdens and trauma to the
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`patient can be minimized by the use of the present in-
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`ventive blood pump.
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`These and additional objects and advantages Of the
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`present inventive pump will be apparent from a reading
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`of the following description of a particularly preferred
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`exemplary embodiment of the present invention, taken
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`in conjunction with the following drawing Figures, in
`which:
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`DESCRIPTION OF THE DRAWING FIGURES
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`FIG. 1 provides a fragmentary elevation view, par-
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`tially in cross section, and somewhat schematically
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`presented, of a pump embodying the present invention;
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`FIG. 2 is a fragmentary cross sectional view taken
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`along line 2—2 of FIG. 1, and with parts of the struc-
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`ture omitted to better depict salient features of the in-
`vention;
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`FIG. 3 is a fragmentary cross sectional view taken at
`line 3—3 of FIG. 1;
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`FIG. 4 is a cross sectional view taken at line 4—4 of
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`FIG. 1;
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`FIG. 5 is a cross sectional view taken at line 5—5 of
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`FIG. 1;
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`FIG. 6 presents an isolated perspective view of a
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`component part of the inventive pump depicted in FIG.
`1;
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`FIG. 7 is an enlarged fragmentary cross sectional
`view taken at line 7—7 of FIG. 1; and
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`FIG. 8 is a fragmentary elevation view partially in
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`cross section like FIG. 1, but showing an alternative
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`embodiment of the present inventive pump.
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`30
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`35
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`PAGE 6 OF 12
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`PAGE 6 OF 12
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`

`

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`DESCRIPTION OF THE PREFERRED
`EXEMPLARY EMBODIMENTS
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`Viewing FIGS. 1—6 in conjunction, it is seen that a
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`pump 10 includes a housing 12. The housing 12 includes
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`an inlet port, generally referenced with the numeral 14,
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`plural outlet ports, each referenced with the numeral
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`16, and a flow path 18 communicating the inlet port 14
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`with the outlet ports 16. More particularly, the housing
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`12 includes a wall portion 20 which is circumferentially
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`and axially extending to define a cylindrical bore 22.
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`The cylindrical bore 22 at its upper end defines inlet
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`port 14, and communicated downwardly to a larger
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`diameter bore portion 24. Cooperatively, the bore por—
`15
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`tions 22 and 24 define a somewhat tapered shallow
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`conical shoulder 26 on the housing 12. A circumferen-
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`tial wall portion 28 of the housing 12 cooperates with
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`the shoulder 26 and with a planar back wall portion 30
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`to define a circumferential chamber 32 in the flow path
`20
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`18. The wall portion 28 defines plural outlet ports 16
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`opening circumferentially outwardly from the chamber
`32.
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`Below the back wall 30, the housing 12 includes a
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`boss 34 which defines therein a stepped bore 36. In this
`25
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`stepped bore 36 at an upper larger diameter portion 38
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`thereof are received a sealing member 40 and a next
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`adjacent upper bearing member 42. The bearing mem-
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`ber 42 rests upon an upwardly disposed shoulder 44
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`formed on the bore 36 by cooperation of the portion 38
`30
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`thereof with a smaller diameter bore portion 46. This
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`smaller diameter bore portion 46 also cooperates with a
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`lower larger diameter portion 48 of the bore 36 to define
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`a downwardly disposed shoulder 50. In the bore portion
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`48, a second bearing member 52 is disposed in engage-
`35
`ment with the shoulder 50.
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`As is seen in FIGS. 1 and 6, a rotor member, gener—
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`ally referenced with the numeral 54 is rotatany jour-
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`naled in the flow path 18. The rotor member 54 includes
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`an elongate shaft portion 56 having an upper seal runner
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`58 disposed in the sealing member 40, and a smaller
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`diameter stem portion 60 rotationally supported by the
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`bearing members 42 and 52. The seal runner portion 58
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`bears on the upper bearing member 42. Below the hear-
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`ing 52, the stern portion 60 of shaft 56 includes a circum-
`45
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`ferential groove 62 in which is received a retaining ring
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`64. The retaining ring 64 bears on bearing 52 to capture
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`the sealing member 40, bearings 42 and 52, and shaft 56
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`in the boss 34. Consequently, the rotor member 54 is
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`rotatany journaled and axially constrained in the flow
`50
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`path 18. In order to rotationally drive the rotor member
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`54, a lower drive portion 66 is hexagonal in cross sec-
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`tion to drivineg engage with a driving motor 68, which
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`is schematically depicted. Rotation of the rotor member
`54, when viewed from the stem end 66 is clockwise, as
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`55
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`is indicated by arrow 680.
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`Viewing FIGS. 1—6 in conjunction with one another,
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`it is seen that the rotor member 54 includes an elongate
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`central core member 70, which includes a conical por-
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`tion 72 having a tip 72a confronting the inlet port 14,
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`and leading to an elongate cylindrical portion 74. Cir-
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`cumscribing the core member 70 at the conical portion
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`72 thereof is a circumferentially continuous ring portion
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`76. This ring portion 76 defines an axial entrance end 78
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`for the rotor member 54, and also defines an opening
`65
`into a conical and annular entrance recess 80. The coni-
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`cal entrance recess 80 includes conical surface portions
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`82, which are best seen viewing FIGS. 2, 3, and 6. It
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`will be noted that in FIG. 2, the wall portion 20 and
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`5
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`PAGE 7 OF 12
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`5,368,438
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`10
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`6
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`shoulder 26 are omitted to provide a better view of the
`rotor member 54 in the chamber 32. The inner diameter
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`84 of the conical entrance recess 80 is slightly larger in
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`diameter than the cylindrical portion 74 of core member
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`70, and is about coextensive with the upper end of this
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`conical core portion, to define a radial clearance 86. As
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`is seen in FIGS. 1, 3, and 6, the conical portion 72 of the
`core member 70 extends out of the recess 80 toward the
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`inlet port 14 so that upon liquid flow approaching the
`rotor member 54, the cross sectional flow area of flow
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`path is first gradually decreased by the conical portion
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`72 of the core member 70, and then is additionally grad-
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`ually reduced as the liquid flow enters into the conical
`entrance recess 80.
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`Extending axially and circumferentially from the ring
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`portion 76, the rotor member 54 includes three helical
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`flute portions 88. As is best seen in FIGS. 1 and 6, the
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`ring portion 76 includes transition sections 90 connect-
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`ing the circumferentially extending body of the ring
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`member 76 with the axially angulated helical flutes 88,
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`and the flutes 88 are equally spaced apart circumferen-
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`tially. Each flute portion 88 includes a radially extend-
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`ing pressure surface 92 disposed toward the chamber
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`32, and an axially opposite radially extending suction
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`surface 94 which is disposed toward the inlet 14. Cir-
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`cumferentially successive ones of the flutes 88 cooper-
`ate with one another at their surfaces 92 and 94 to define
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`a like plurality of radially extending helical channels 96,
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`which open radially outwardly toward the housing wall
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`portion 20. An outer circumferential and helical surface
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`98 is spaced from the wall portion 20 to define a radial
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`gap 100. Preferably, the gap 100 is in the range from
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`about 0.025 to about 0.040 inches (about 0.6 to about 1.3
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`mm).
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`Viewing FIGS. 2 and 6, it is seen that each of the
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`channels 96 opens radially outwardly, axially, and cir-
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`cumferentially from the entrance recess 80. Conse-
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`quently, when viewed in axial view as is seen in FIG. 2,
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`the channels 96 each define what appears to be a tear
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`drop shaped entrance opening 102 opening outwardly
`from the entrance recess 80 into the helical charmels 96.
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`Still considering the axial view of FIG. 2, it is seen that
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`what appears as a floor of these entrance openings 102
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`is the suction surface 94 of the next preceding flute in
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`the direction of rotation. Also, a' circumferentially ex-
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`tending and helical leading edge 104 for the pressure
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`surface 92 of the respective flute 88 is spaced axially
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`toward the viewer of FIG. 2 with respect to the viewed
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`portion of surface 94.
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`FIGS. 1 and 6 illustrate that the flutes 88 each pro-
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`ceed through slightly more than one complete turn
`around the core 70 and then define a termination end
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`106 on an axially disposed surface 108 on a respective
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`one of plural centrifugal vanes 110. That is, the number
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`of vanes 110 is equal to the number of flutes 88. Viewing
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`FIGS. 2, 4, and 5, it is seen that the vanes 110 are gener—
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`ally radially extending, but are offset slightly in the
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`circumferential direction of rotation to define a larger
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`radially and axially extending pusher surface 112, and a
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`smaller follower surface 114. In other words, viewing
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`FIG. 5 more particularly, it is seen that the vanes 110
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`are of generally constant width, extend generally radi-
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`ally, and are circumferentially offset in the direction of
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`rotation with respect to the rotational axis of the rotor
`member 54 which is defined at the stem 60. As a result,
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`the pusher surfaces 112 would be tangent to a larger
`circle about the rotational axis at stem 60 than would
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`the follower surfaces 114. This result of the circumfer-
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`PAGE 7 OF 12
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`5,368,438
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`5
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`15
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`25
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`7
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`ential offset of the vanes 110 can easily be seen by refer-
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`ence to the dash circle 124 of FIG. 5 because the pusher
`surfaces 112 are outside of this circle, and would not
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`intersect with it if projected inwardly. In contrast, an
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`inward projection of the follower surfaces 114 would
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`intersect with the dash circle 124. Considering FIGS. 1
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`and 6 again, it is to be noted that each of the channels 96
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`opens smoothly into a respective circumferentially ex-
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`tending sector of the chamber 32 between the vanes
`10
`110, which chamber sectors are referenced with the
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`numeral 116.
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`Viewing FIGS. 1, 6, and 7, it is seen that the vanes
`110 have rounded surfaces, and define an outer end 118
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`which is spaced radially from the circumferential wall
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`28. Additionally, these vanes taper radially outwardly
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`as they extend into the circumferential chamber 32.
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`FIGS. 1 and 7 depict that the vanes 110 are also taper-
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`ing axially toward the inlet 14 on their back surfaces
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`120. That is, the vanes 110 cooperate with the generally
`20
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`planar back wall 30 of the chamber 32 to define an
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`axially extending and radially outwardly increasing gap
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`122. It will be noted that between the van