US3717418A

US3717418A - Compressor barrel assembly

Info

Publication number: US3717418A
Application number: US00044446A
Authority: US
Inventors: K Pilarczyk
Original assignee: Carrier Corp
Current assignee: Carrier Corp; Elliott Turbomachinery Co Inc
Priority date: 1970-06-08
Filing date: 1970-06-08
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20
Also published as: DE2128233B2; CH523432A; NL7107688A; DE2128233A1; FR2096063A5; CA955570A; GB1357183A

Abstract

THE THREE STAGE CENTRIFUGAL COMPRESSOR OF THE PRESENT INVENTION EMPLOYS A ONE-PIECE CAST CASING HAVING A CYLINDRICAL BORE CONTAINING THEREIN A REMOVABLE BARREL ASSEMBLY, WHICH ASSEMBLY COMPRISES THREE DIRECTLY ENGAGING DIAPHRAGMS, THREE DIFFUSORS, THREE SHROUDS AND A ROTOR HAVING THREE IMPELLERS, ALL IN AXIALLY STACKED RELATIONSHIP. ONLY THE THREE DIAPHRAGMS ARE AXIALLY CLAMPED DIRECTLY TO EACH OTHER BY MEANS OF TENSION BOLTS. THE DIFFUSERS AND SHROUDS ARE HELD BY THE DIAPHRAGMS FOR AXIAL FREE PLAY AND BIASED IN ONE AXIAL DIRECTION BY AXIALLY COMPRESSED SEALING O-RINGS AND EFFECTIVE PISTON SURFACES UNDER THE INFLUENCE OF THE FLUID BEING PUMPED. THE END CLOSURE CONTAINING THE BEARINGS AND DRIVE FOR THE OVERHUNG ROTOR HAS A CYLINDRICAL SURFACE FLUSH WITH THE CYLINDRICAL BORE OF THE CASING, WHICH SURFACE IS OVERLAPPED BY THE OUTER CYLINDRICAL SURFACE OF ONE OF THE DIAPHRAGMS TO PROVIDE FOR AXIAL ALIGNMENT. FOUR ENGAGING CYLINDRICAL SURFACES ON THE DIAPHRAGMS FURTHER ASSURE AXIAL ALIGNMENT. FLUID PASSAGES ARE PROVIDED INTEGRALLY CAST IN THE DIAPHRAGMS AND CASING FOR CONDUCTING THE FLUID THROUGHJ INTERCOOLERS, BETWEEN STAGES.

Description

Feb. 20, 1973 K. PlLARczYK COMPRES SOR BARREL AS S EMBLY 5 Sheets-Sheet l Filed June 8, 1.970

WQ ,Umwdm @kyo V H fm m K. PILARCZYK Feb. 20, 1973 3,717,418 COMPRESSOR BARREL ASSEMBLY 5 Sheets-Sheet 2 Filed June 8, 1970 6% rneg r w f Vo/ .n /0 fw KW# ffmc W n L `E37: v E @S l r u E M,

K. PILARCZYK Feb. 20, 1973 COMPRES SOR BARREL AS S EMBLY 5 Sheets-Sheet 3 Filed June 8, 1970 Feb. 20, 1973 K. PILARCZYK 3,717,418

COMPRESSOR BARREL ASSEMBLY Filed June 8, 1970 5 Sheets-Sheet 4 K. PILARCZYK Feb. 20, 1973 COMPRES SOR BARREL AS SEMBLY 5 Sheets-Sheet 5 Filed June 8, i970 bw e @www ,U n, 0

y @Hmm @d United States Patent O U.S. Cl. 415-104 23 Claims ABSTRACT F THE DISCLOSURE The three stage centrifugal compressor of the present invention employs a one-piece cast casing having a cylindrical bore containing therein a removable barrel assembly, which assembly comprises three directly engaging diaphragms, three ditfusors, three shrouds and a rotor having three impellers, all in axially stacked relationship. Only the three diaphragms are axially clamped directly to each other by means of tension bolts. The diffusers and shrouds are held by the diaphragms for axial free play and biased in one axial direction by axially compressed sealing O-rings and effective piston surfaces under the inuence of the Huid being pumped. The end closure containing the bearings and drive for the overhung rotor has a cylindrical surface ush with the cylindrical bore of the casing, which surface is overlapped by the outer cylindrical surface of one of the diaphragms to provide for axial alignment. Four engaging cylindrical surfaces on the diaphragms further assure axial alignment. Fluid passages are provided integrally cast in the diaphragms and casing for conducting the fluid through intercoolers, between stages.

BACKGROUND OF THE INVENTION It is known to provide axially removable barrel assemblies for pumping devices, but these have uusally included a large number of axially stacked elements, so that there will be a relatively large tolerance accumulation in the axial direction and provide for increased axial length, as well as complexity. These problems would be even further increased with respect to an open type of centrifugal impeller. Further, considerable alignment problems are encountered when an overhung rotor is employed, so that overhung rotors are normally employed only with a single stage of compression. With the considerable axial length of removable barrel assemblies for multi-stage impellers, the problems of whipping that would be encountered if an overhung rotor were employed in such devices would be considerable so that their speed of operation would be quite limited. Further, various piping connections are normally employed between stages with a tendency to further increase the axial extent of any multi-stage device, which would further make the use of an overhung rotor more difficult.

The temperature gradients throughout a barrel assembly and casing for a multi-stage compressor are considerable, which will have a great eifect with respect to expansion upon the various elements, particularly shrouds and diffusers with respect to open type impellers. Since the shrouds and diffuers are closest to the impellers and most difficult to cool, their temperatures are usually quite high so that their thermal stresses and axial thermal expansion are correspondingly quite high, which will further produce disadvantages with respect to tolerances in the 3,7l7,4l8 Patented Feb. 20, 1973 axial direction when they are interposed in the clamping of the barrel assembly.

CROSS-REFERENCING TO= RELATED APPLICATIONS The features of the invention of this application may be used in combination with the features of the inventions in applicants following related applications of the same filing date and assignee as the present application, the disclosures of which are incorporated herein in their entirety by reference: Variable Capacity Compressor, Ser. No. 44,263, Compressor Power Recovery, Ser. No. 44,463; Interchangeable Compressor Drive, Ser. No. 44,403; Compressor Base and Intercoolers, Ser. No. 44,034.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome many of the disadvantages as mentioned above and provide a compressor with a relatively small axial extent and diameter, and which may use intercoolers without a considerable amount of piping about its casing. The axial limitations with respect to length are of considerable advantage in providing a minimum length to the cantilevered portion of an overhung rotor so that high speed operation may be possible, The piping connections between stages are cast into removable diaphragme and one piece casing.

The removable barrel assembly includes a diaphragm, a shroud, a diffuser, and an impeller for each stage, with only the diaphragms being directly clamped to each other and the casing so that tolerance accumulation in the axial direction will be held to a minimum. The shrouds and diffusers are stationarily mounted between the diaphragms, with axial free play so that their tolerances in the axial direction will not pass from one stage to another andl their considerable thermal expansion will not be an accumulating problem. Means are provided to bias the shrouds and diffusers in one axial direction, and include sealing O-rings compressed in the axial direction and piston surfaces on the shrouds and ditfusers that will produce a net axial force in response to the pressure of the fluid being pumped. In this manner, the barrel assembly has the advantages of a rigid construction, separate pieces for each barrel element and only three elements axially clamped together that would produce a tolerance accumulation for the entire length of the assembly.

BRIEF DESCRIPTION OF THE DRAWING Further objects, features and advantages of the present invention will become more clear from the following detailed description of a preferred embodiment of the present invention as shown in the attached drawing, in which:

FIG. l is a perspective view of a complete compressor employing the features of the present invention;

FIG. 2 is a schematic flow sheet showing the path of the fluid as it moves between stages and through the intercoolers;

FIG. 3 is a partial cross-sectional view taken on a vertical plane passing substantially through the axis of rotation of the compressor of FIG. l;

FIG. 4 is a partial perspective exploded view, with portions cut-away, of the one piece compressor casing and its relationship with the top wall of the intercooler chambers;

FIG. 5 is an enlarged cross-sectional view of the barrel assembly and its relationship to the compressor casing and drive, taken substantially in the same plane as FIG. 3;

FIG. 6 is a cross-sectional View taken along line 6-6 in FIG. 4;

FIG. 7 is a cross-sectional View of the casing taken along line 7-7 of FIG. 4;

FIG. 8 is a cross-sectional view of the casing taken along line 3-8 in FIG. 4;

FIG. 9 is a cross-sectional view of the casing taken along line 9-9 in FIG. 4 and FIG. 5;

FIG. 10 is a cross-sectional View of the casing taken along line 10-10 of FIGS. 4 and 5;

FIG. ll is a cross-sectional view of the casing taken along line 11--11 of FIGS. 4 and 5; and

FIG. 12 is a cross-sectional View of the casing taken along line 12-12 of FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE DRAWING With reference to FIGS. l-3, the compressor base 1 securely mounts an electric drive motor 2, which has an output shaft 3 for driving the rotor 4 through gear train 5. The gear train 5 is mounted within a separate casing 6 that forms the end closure for the compressor casing 7. The

casings

6 and 7 are each cast in one piece from iron, and the base 1 is Welded sheet steel fabrication. Inlet uid is provided for the compressor through an inlet housing S having mounted therein an inlet valve 9 controlled by a suitable mechanism 10.

Within the base 1, there are two separated intercooler chambers 11 and 12 for cooling the fluid between the first and second stages and between the second and third stages, respectively. For the purposes of the present invention, these intercooler chambers may be of any construction and include any type of conventional intercooling equipment, such as a parallel tube waterdluid heat exchanger. A shown in FIG. 2, inlet fluid passes through the first stage impeller 13, the intercooler chamber 11, the second stage impeller 14, the intercooler chamber 12, and the third stage impeller 15.

As somewhat schematically shown in FIG. 3, and more accurately in FIG. 4, the cast iron casing 7 is provided with an axial cylindrical bore 16 and a planar surface 17, with a plurality of integrally cast passages therebetween for conducting the tiuid between stages and the intercoolers. Particularly, passage 18 conducts fluid from the first stage output to the intercooler chamber 11, passage 19 conducts fluid from the intercooler chamber 11 to the second stage, passage 20 conducts fluid from the second stage to the intercooler chamber 12, and passage 21 conducts Huid from the intercooler chamber 12 to the third stage. The passages in the top of the intercooler chambers have been given numbers corresponding to those used with respect to the casing 7, but with the addition of primes. The passages 18', 20' extend directly through the top plate of the base for discharge directly into the chambers 11 and 12, while the return fiuid from the chamber 11, 12 is conducted respectively, in passages 19', 21 which extend for substantially the full height of the base 1 between the intercooler chambers 11 and 12.

In FIG. 5, a three stage removable barrel assembly is shown Within the cylindrical bore of the casing 7. The first stage includes a diaphragm 22, a shroud 23, a diffuser 24 and the impeller 13; the second stage includes diaphragm 25, shroud 26, diffuser 27, and impeller 14; and the third stage includes diaphragm 28, shroud 29, diffuser 30, and impeller 1S. Each of the diaphragms is a one piece iron casting, and each of the diffusers and shrouds is a one piece aluminum casting. Each of the

diaphragms

22, 25, 28 has an outer cylindrical surface in direct engagement with the inner cylindrical bore 16 of the casing 7. The end closure formed by the gear casing 6 has an adjacent inner cylindrical surface 31 that is flush with the cylindrical surface 16 of the compressor casing 7, with the outer cylindrical surface of the diaphragm overlapping these ush inner cylindrical surfaces to accurately align the gear casing 6 with the barrel assembly for proper positioning of the rotor 4. The gear casing 6 determines the positioning of the rotor 4, by means of the radial bearing 32 and the combination radial-thrust bearing 33 that rotatably mount the rotor 4 in an overhung position. These bearings provide the sole rotational support for the cantilever-ed rotor. The rotor may be of any rigid type construction, but preferably the

impellers

13, 14, 1S are integrally secured to the rotor shaft, with the interposition of suitable labyrinth seals as shown.

In assembling the barrel assembly, the various components are assembled outside the casing and slid from left to right, as viewed in FIG. 5, into the

casings

6 and 7. Thereafter, the

diaphragms

22, 25, 2S are rigidly secured to the gear casing 6 by means of a plurality of tension bolts 34. In this manner, the gear casing 6 forms the main axial reference element, with the thrust bearing 33 forming the axial fixed reference point for the rotor 4 and the end face 35 forming the axial reference point for the diaphragms; since the gear casing 6 is of a one piece cast construction, the axial distance between points 33 and 35 is fixed and may be accurately determined. Thus, tolerance accumulation in the axial direction will occur only from point 35 to the left, as viewed in FIG. 5, and then only with respect to the three

diaphragms

22, 25, 28 that are directly clamped to each other.

The shrouds 23, 26, 29 and

diffusers

24, 27, 30 radially engage the diaphragms to fix their radial position and axially engage, in only one direction, the diaphragms to fix their axial position while allowing free axial play or clearance movement in the opposite axial direction with respect to the diaphragms. r)This axial free play is taken up by biasing means including the axially compressed sealing O-rings 36, 37 and the piston action of the surface exposed to the pumped fluid on the diffusers and shrouds. More particularly, the O-ring 36 will exert an axial force to the right, as viewed in FIG. 5, directly upon the shroud 23 and therethrough indirectly upon the diffuser 24 to tightly clamp the shroud 23 and diffuser 24 against the diaphragm 28, and the O-ring 37 exerts an axial force to the right, as viewed in FIG. 5, directly upon the shroud 29 and indirectly upon the axial stacked diffuser 30, diffuser 27, and shroud 26. In this manner, any tolerance accumulation as between the shrouds and diffusers is not transferred to the diaphragms. Thus, the advantages of providing separate shrouds and separate dilfusers with respect to manufacturing procedures, replacement and the like, are provided without also providing the heretofore correlated disadvantages of tolerance accumulation. Further, the thermal expansion of the shrouds and ditfusers will not be transferred to the diaphragms, which is of considerable importance considering the extremely high temperatures encountered immediately adjacent the impeller and in view of the relatively high thermal expansion of the aluminum, from which the shrouds and diffusers are constructed. With respect to the piston biasing action, with reference to FIG. 5, it is seen that the shroud 23 has a considerable surface area facing to the left that is exposed to the high pressure diffuser outlet of the first stage, which will produce an axial force to the right greater than the axial force to the left produced by the rightwardly facing area exposed to the high speed low pressure gas moving through the impeller 13 and blades of the diffuser 24; the diffuser 24 has substantially only a left-hand surface exposed to the pressurized gases to produce a net force in the righthand direction; analysis of the shroud 29 would be similar to that of the shroud 23, but with considerable affects obtained by the left-hand exposure of the shroud 29 t0 the gases within the first stage, to produce a net rightwardly oriented axial force; together, the diffusers Z, 30 have opposed surfaces exposed respectively to the outlet gases of the second and third stages, with the higher pressure gases of the third stage predominating to produce a net axial force in the right-hand direction; due to the c011- struction of the diaphragm 25, the shroud 26 has only a relatively small piston area exposed to the inlet gases for the second stage and has its full radial area exposed to the gases passing through the impeller 14 and blades of the diffuser 27 so that a net axial force is again produced in the right-hand direction. Wherever needed for purposes of sealing, additional O-rings are provided between adjacent surfaces, with many of these O-rings not being shown since they are conventional, but it being understood that these additional sealing O-rings do not contribute to the above-mentioned axial biasing of the shrouds and diffusers. The axial biasing of the piston effects and the axially compressed O-rings 36, 37 are in the same righthand direction to complement each other. Thus, while the compressor is idle and during start-up, the shrouds and diifusers will be biased into their proper position by the forces of the O-rings 36, 37, while at high speeds, the piston effect will predominate.

From FIG. 5, it is seen that the previously described

passages

18, 19, 20, 21 are in communication with

annular chambers

38, 39, 40, 41, respectively, formed by opposed outwardly opening annular channels on the outer surfaces of the

diaphragms

22, 25, 28, and inwardly opening annular channels axially spaced along the bore 16 of the compressor casing 7. These annular chambers 38-41, are sealed with respect to each other by any appropriate means, for example, O-rings (not shown). The

diaphragms

22, 25, 28 are provided with integrally cast passages or externally congurated surfaces cooperating with surfaces of adjacent diaphragms to form passages for conducting air between the annular chambers 38-41 and respective ones of the shrouds inputs and diffuser outputs.

In addition, the output from the last stage diffuser 30 is connected by the diaphragms into the annular chamber 42 formed by opposed annular channels in the diaphragm 25 and casing 7. From the annular chamber 42, the high pressure compressor output may pass upwardly, as shown in FIG. 11, through an outlet 43 to the point of use, storage tank, conventional blow-off device, or the like. Also, the compressor output may be conducted from the annular chamber 42 downwardly through outlet 44 into the compressor base 1 to be connected to piping to the point of use and/ or be connected to various pressure responsive control and monitoring devices, which for example may have meters, warning lights or the like on the control panel 45 as shown in FIG. 1. Also, in FIG. 1, the outlet 43 is shown with a sealing plug or cap that is used when an excess pressure blow-off device is not employed and the compressor output is directed downwardly into the compressor base for connection with piping to the point of use. Further, the compressor output from annular chamber 42 is conducted by means of a generally axially extending passage 46 (FIG. 1l) that is cast into the casing 7, but not in communication with any of the previously described passages of the casing 7 except for those shown in FIG. 1l. The passage 46 conducts a portion of the compressor output to annular chamber 47, which is shown in FIG. 5 as being formed by opposed annular channels respectively in the casing 7 and diffuser 22. From the annular chamber 47, the high pressure compressor output is directed into an annular chamber 48 formed between the shroud 23 and diaphragm 22. If desired, a nozzle may be inserted through the shroud 23 to direct the gases from chamber 48 against the blade tips of impeller 13 to produce a power recovery turbine action to take care of excess pressure on partial load. The structure and function of this power recovery will not be described in detail, because it forms the subject matter of one of the previously mentioned co-pending applications. For the purpose of this application, it is important that this capacity is built into the structure so that the chamber exists and if desired, appropriate pressure responsive valving may be incorporated into the passage 46 for dumping excess pressure into the annular chamber 48, and the shroud 23 may be drilled for reception of one or more nozzles to complete the turbine. This capacity is built in whether used or not.

From the above, it is seen that the compressor barrel assembly of the present invention may be removed from the one-piece cast casing for inspection, repair and replacement of the various individual uid guide elements, particularly, the diaphragms, shrouds and diffusers. The construction of these elements as individual pieces greatly facilitates the casting of the internal piping, a reduction in manufacturing cost, ease of replacement, and ease of modifying for power recovery. These advantages are gained without the heretofore correlated disadvantages of tolerance accumulation, thermal expansion problems and extreme difficulty with respect to sealing and alignment.

Since the diaphragms are the only axially clamped elements, tolerances involved in the manufacture of the diffusers and shrouds will not contribute in any accumulated tolerance error; further, thermal expansion of the shrouds and diffusers will not be transferred through the diaphragms. Thermal expansion would otherwise be a particular problem in view of the close proximity of the shrouds and diffusers to the impellers, the difficulty of cooling the same, and the desirable construction of light weight material such as aluminum that has a high thermal expansion. These advantages are gained by mounting the diffusers and shrouds between the diaphragms with axial free play. The free play is taken up, particularly for starting purposes, by means of axially compressed O-rings, which further serve the function of sealing. Once pressure has been built up in the compressor, the piston effects heretofore mentioned will predominate to hold the diffusers and shrouds tightly and sealingly in their proper positions. The piston effects will increase proportionately with increased compressor pressures, to produce a desired corresponding increase in sealing effect.

Accurate alignment is obtained by means of telescopically engaging annular surfaces between the casing, diaphragms, diffusers and shrouds. The cylindrical bore of the one piece casing forms the primary radial reference point, by providing engagement With the diaphragms and one piece impeller mounting housing. The impeller has a thermal expansion reference point at its furtherest end provided by a thrust bearing, to provide additional length for thermal expansion of the rotor assembly, which additional length will have a greater thermal expansion than the corresponding relatively cool and massive casing 6, to compensate for the rather high thermal expansion to be encountered with the aluminum diaphragms, shrouds, and diflusers.

With interstage piping being integrally cast into the casing and diaphragms, the size, complexity and cost of the compressor is greatly reduced. Correspondingly, setup time, sealing problems and maintenance are greatly reduced.

Although a preferred embodiment of the present invention has been illustrated to show a specific advantageous form, further modifications, variations and embodiments are contemplated according to the broader aspects of the present invention.

What is claimed is:

1. A pumping device, comprising: a casing; a rotor rotatably mounted in said casing and having a plurality of centrifugal impellers; a plurality of annular diaphragms axially stacked Within said casing corresponding in number and respectively surrounding said impellers; means clamping said diaphragms axially directly to each other; a plurality of separate stationary diffusers correspondingly associated with and corresponding in number to said impellers, means mounting said difusers to said diaphragms about their respective irnpellers with axial free play with respect to said diaphragms; and resilient means axially biasing each of said diffusers relative to said diaphragms whereby axial expansion of said diffuser relative to said diaphragms will be absorbed.

2. The device of claim 1, wherein said axially biasing means include a plurality of sealing G-rings.

3. The device of claim 1, wherein said axially biasing means including separate piston means for each diffuser having at least one axial face subjected to the iluid being pumped for producing a net axial force biasing its associated diffuser toward an adjacent diaphragm.

4. The device of claim 3, wherein said axially biasing means include a plurality of sealing O-rings.

5. The device of claim 1, constituting a multi-stage centrifugal compressor wherein said casing is a one piece casting having an inner cylindrical bore provided with a plurality of annular inwardly opening channels in fluid communication with respective impellers; and said dia-V phragms and casing having a plurality of integral passage means for conducting fluid out of the casing from each impeller and into said casing for at least some of said impellers.

6. The device of claim 1, including an end closure for one axial end of said casing; bearing means providing the sole rotational support of said rotor and being located solely on the side of said rotor with said end closure; and means providing removal of said rotor, said diaphragms and said diifusers axially from said casing in the direction opposite from said end closure.

7. The device of claim 6, wherein said end closure has an inwardly facing cylindrical surface and said casing has an inwardly facing cylindrical surface flush with and abutting said end closure cylindrical surface; and one of said diaphragms having an outwardly facing cylindrical surface overlapping and engaging each of said end closure and casing cylindrical surfaces.

8. The device of claim 6, constituting a multi-stage centrifugal compressor wherein there are three impellers on said rotor, with the first stage impeller having an inlet facing axially away from said end closure, the second stage impeller having an inlet facing said end closure, and the third stage impeller being located axially intermediate said first and second stage impellers and having an inlet facing away from said end closure.

9. The device of claim 1, including means for holding said diaphragms concentric with respect to each other in said casing, including cylindrical outer surfaces on said diaphragms in engagement with said casing, and telescopically interengaging cylindrical surfaces.

10. The device of claim 1, wherein said means clamping include an end closure rigidly secured to said casing and a plurality of tension bolts axially extending through said diaphragms and into said end closure.

11. A pumping device, comprising: a casing; a rotor rotatably mounted in said casing and having a plurality of open centrifugal impellers; a plurality of annular diaphragms axially stacked Within said casing corresponding in number and respectively surrounding said impellers; means clamping said diaphragms axially directly to each other; a plurality of stationary shrouds corresponding in number and respectively associated with said impellers; at least one shroud and one diaphragm being provided with confronting surfaces arranged in spaced relation one to another to define an axial clearance space and resilient means in said clearance space biasing said shroud relative to said diaphragm whereby engagement of parts in an axial direction is assured.

12. The device of claim 11, wherein said axial biasing means include a plurality of O-rings compressed in the axial direction between at least some of said shrouds and some of said diaphragms.

13. The device of claim 12, wherein said shrouds are piston means for producing a net axial force, in the same direction as the force produced by said Oerings, from the pressurized -fluid during operation.

14. The device of claim 11, wherein said rotor includes only three centrifugal impellers with the first stage impeller having its inlet opening in one axial direction,

the second stage impeller having its inlet opening in they".

and the third stage shroud, the third stage diffuser, the

second stage diffuser and the second stage shroud being axially mounted, in order, between the third stage diaphragm and the second stage diaphragm.

15. The device of claim 14, wherein said rotor is overhung with bearing means at only one axial end.

16. A multi-stage pumping device for fluids, comprising: a cast one piece casing having an inner cylindrical bore; a plurality of diaphragms corresponding in number to the number of stages being received within and engaging said bore in axial stacked relationship, each of said diaphragms being of a one piece casting; each of said diaphragms having integrally cast non-communicating passage means extending radially completely therethrough and corresponding to at least a first stage Outlet passage, a second stage inlet passage, and a second stage outlet passage; and said casing having integrally cast non-com'- municating passage means extending radially therethrough respectively in -uid alignment with each of said diaphragm passage means.

17. The device of claim 16, wherein said diaphgragms have outwardly opening annular chan-nels in respective communication with and corresponding in number to said diaphragm passage means; and said casing having a plurality of inwardly opening channels radially opposite corresponding ones of said diaphragms outwardly opening channels to form therewith a plurality of annular uid chambers. 1

18. A centrifugal pumping device, comprising: an open centrifugal impeller mounted for rotation about an axis; a separate stationary shroud and a separate stationary diffuser operatively mounted about said impeller to form a single pumping stage; a first axial abutment; a second axial abutment; at least one of said axial abutments being provided with a surface confronting a surface on at least one of said stationary parts in spaced relation thereto to define an axial clearance space; and an Oring sealingly and axially compressed between said one axial abutment and said one stationary part to provide means for axially biasing said diffuser and shroud axially toward said other axial abutment.

19. The device of claim 18, including piston means responsive to the pumped iluid to' produce a net axial force on said diffuser and shroud complementary to the axial force produced by said O-ring.

20. The device of claim 18, including a second open centrifugal impeller drivingly secured to said first mentioned centrifugal impeller; a second shroud and a second diffuser operatively associated with said second impeller and mounted in axial stacked relationship between one of said axial abutrnents and said first mentioned shroud and diffuser; and said O-ring clamping all of said diffusers and shrouds in the axial direction.

21. The device of claim 20, wherein said impellers have inlets opening in axially opposite directions away from each other; and said diffusers being axially between said shrouds.

22. The device of claim 21, including casing means operatively mounting said diffusers, shrouds and impellers for axial removal in the direction opposite from the direction of the axial force applied by said O-ring.

23. The device of claim 22, including an overhung rotor rigidly carrying said impellers and having bearing means only at its axial end opposite from said O-ring.

(References on following page) References Cited UNITED STATES PATENTS Salzer 415-106 Anderson 415-106 Sherwood et al. 4715-105 Brose 415-104 MacMeeken 415-199 'Spillmann et a1 415-108 Howard 415-199 Holzhausen 415-196 Hall 415-199 10 FOREIGN PATENTS 19,470 9/1906 Great Britain 415-106 539,373 9/1941 Great Britain 415-199 R 964,020 5/1957 Germany 415-199 1,029,676 5/1958 Germany 415-199 956,732 4/1964 Great Britain 415-219 959,711 6/1964 Great Britain 415-219 U.S. C1. X.R.