US3918852A - Pump - Google Patents

Abstract

Overloading and failures of the lower bearings in submersible electric motor driven centrifugal pumps having inducer impellers ahead of the main centrifugal pumping impeller are avoided by transferring the inducer thrust from the lower bearing to an upper bearing which has ample reserve capacity to accept the added thrust load without redesign of existing pump and bearing assemblies. The transfer of the inducer thrust from the lower to the upper bearing is accomplished by slidably keying the inducer impeller on a hollow motor driven main pump shaft and supporting the inducer impeller on a second shaft extending through the hollow pump shaft and suspended from a top main shaft bearing.

Description

United States Patent [191 Carter Nov. 11, 1975 1 PUMP [76] Inventor: James Coolidge Carter, 1735 San [52] US. Cl. 417/424; 415/62; 415/66; 415/68; 417/365 [51] Int. Cl.F04B 17/00 [58] Field 01 Search 415/60, 143, 62, 66, 68, 415/107; 417/424, 360, 366, 365

[56] References Cited UNITED STATES PATENTS 2.284.948 6/1942 Combs 415/143 2.469.458 5/1949 Dunnells et a1. 415/143 2.865.296 12/1958 Bungartz 415/143 3.143.675 8/1964 Haue nstein 417/424 3.369.715 2/1968 Carter i 415/143 3.494.291 2/1970 Carter, .lr 415/143 3.495.537 2/1970 Archibald 415/143 3.635.599 l/l972 Bryant 417/424 Zagar 417/424 Carter 417/424 Primary Examiner-C. .1. l-lusar Attorney, Agent, or FirnzHill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT Overloading and failures of the lower bearings in submersible electric motor driven centrifugal pumps having inducer impellers ahead of the main centrifugal pumping impeller are avoided by transferring the inducer thrust from the lower bearing to an upper bearing which has ample reserve capacity to accept the added thrust load without redesign of existing pump and bearing assemblies. The transfer of the inducer thrust from the lower to the upper bearing is accomplished by slidably keying the inducer impeller on a hollow motor driven main pump shaft and supporting the inducer impeller on a second shaft' extending through the hollow pump shaft and suspended from a top main shaft bearing.

10 Claims, 3 Drawing Figures US. Patent Nov. 11,1975 Sheet 1 of2 3,918,852

US. Patent Nov.11, 1975 Sheet20f2 3,918,852

PUMP

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the art of submersible electric motor driven inducer equipped centrifugal pump units especially suitable as cargo pumps for tanker ships and storage tanks and capable of pumping cargo such as cryogenic fluids or fluids at their boiling points. Particularly, the invention deals with the relieving of inducer thrust loads from the lower main pump shaft bearing.

2. Prior Art Submersible electric motor driven cargo pumps for the pumping of cryogenic fluids or fluids at their boiling points have heretofore had the inducer impeller mounted on and driven by the main pump shaft in the pump inlet ahead of the main pump impeller as, for example, in my prior US. Pat. Nos. 3,304,877 issued Feb. 21, 1967; 3,369,715 issued Feb. 20, 1968; and 3,764,236 issued Oct. 9, 1973. In these units the pump shaft was supported in bearings at the top and bottom of the motor with the bottom bearing carrying the thrust loads of both the main pump impeller and the inducer impeller while the top bearing functioned as a radial bearing for the pump shaft. Failures of the lower bearing after short periods of operation because of excessive thrusts, have been experienced in a number of cargo pump installations. Reduction of the thrust on the lower bearing by removing some of the blades of the inducer impeller and by a lift drum feature as in my U.S. Pat. No. 3,652,186 issued Mar. 28, 1972 have been attempted but reduction of inducer blades has lessened inducer capacity and decreased the efficiency of the pump while the lift drum feature of my prior patent is costly, requires recirculation of pumpage.

SUMMARY OF THIS INVENTION According to this invention the inducer thrust is removed from the main pump shaft bearing and transferred to an existing separate bearing in submersible electric motor driven centrifugal pump units which has adequate reserve capacity to accept the thrust loads without redesign or overloading. This is accomplished by slidably keying the inducer impeller on a hollow motor driven main pump shaft supported on a main pump bearing at the bottom of the motor and a top bearing at the top of the motor, and then supporting the inducer impeller on a second shaft extending through the hollow shaft and suspended from the top bearing. The inventive feature is easily applied to existing submersible electric motor driven centrifugal cargo pump units because the top bearings of such units have ample reserve capacity to carry the inducer thrust loads.

The top bearing not only provides radial bearing support for the main pump shaft, but all of the thrust load of the inducer impeller supporting shaft.

It is then an object of this invention to increase the wear life of the bearings of inducer impeller equipped centrifugal pumps by relieving inducer impeller thrust loads from the main pump bearing.

Another object of the invention is to provide electric motor driven centrifugal impeller equipped cargo pumps with top bearings supporting the thrust loads of the inducer impeller.

A specific object of the invention is to provide a submersible electric motor driven centrifugal cargo pump any of my aforesaid US. Pat.

with an inducer impeller in the pump inlet driven by the main pump shaft but suspended from a bearing at the top of the motor.

Another specific object of the invention is to provide a submersible electric motor driven inducer impeller equipped cargo pump suitable for pumping cryogenic fluids and-fluids at their boiling points wherein the main pump shaft is hollow, drives both the main centrifugal impeller and the inducer impeller, receives an inducer impeller supporting'shaft therethrough and has a top bearing suspending the inducer impeller shaft to relieve inducer impeller thrust loads from the main shaft.

Another object of the invention is to relieve inducer impeller thrust loads from the main bearing of a centrifugal pump by slidably keying the inducer impeller on the main bearing supported pump shaft and suspending the inducer impeller from a second bearing to carry the thrust loads.

Other and further objects of this invention will become apparent to those skilled in this art from the following detailed description of the annexed sheets of drawings which, by way of a preferred example, illustrate one embodiment of the invention.

IN THE DRAWINGS 7 FIG. 1 is a vertical cross sectional view of a submersible electric motor driven inducer impeller equipped centrifugal cargo pump according to this invention;

FIG. 2 is a plan view of the pump inlet along the line II-II of FIG. 1; and

FIG. 3 is a broken partial vertical cross sectional view of the bearing and shaft assembly for the inducer impeller and main centrifugal impeller of the cargo pump of FIG. 1.

AS SHOWN ON THE DRAWINGS In FIG. 1 thereference numeral 10 designates generally a submersible electricmotor driven inducer impellerequipped centrifugal cargo pump according to this invention suspended from avertical discharge pipe 11 in the bottom of atank 12 containingcargo 13 such as cryogenic fluids or fluids at their boiling point including for example, ammonia, liquefied natural gas, propane, and the like. Such fluids are frequently stored in land based storage tanks or in the holds of tanker ships and thetank 12 is representative of such storage means. Thepipe 11 suspends theunit 10 in thetank 12 so that its bottom inlet will be close to the bottom of the tank and it will be understood that thepipe 11 delivers the fluids from the top of theunit 10 to the top of the storage means. Theunit 10 can be mounted as disclosed in Nos. 3,304,877; 3,369,715; 3,652,186; and 3,764,236.

Theunit 10 has a generally cylindricalouter casing 14 and a concentricinner casing 15 spaced therefrom to provide anannular passage 16 therebetween. The bottom of thecasing 14 has a reduced diameter dependingneck portion 17 with an outwardly flaredbottom flange 18 carrying a downwardly dishedplate 19 with an upturnedperipheral rim 20 spaced above the bottom of thetank 12. Thisplate 19 directs fluids to the bottom opening inlet mouth 21 into achamber 22 provided by theneck 17 in the bottom of the unit.

Theinner casing 15 has abottom end wall 23 with acentral hub portion 24 carrying a bottom or mainball bearing assembly 25 for themain pump shaft 26. Aflat plate cover 27 overlies the casings l4 and 15 and is clamped between a conical head ordome 28 and aperipheral flange 29 around thecasing 14 by bolts such as 30.Slots 31 through thiscover 27 and through anoutturned flange 32 at the top end of the inner casing resting on a shoulder 29a of theouter casing 14 connect theannular passage 16 with anoutlet passage 33 to thepipe 11. The bottom end of thecasing 15 slidably fits in a ring ofvanes 34 extending inwardly from theouter casing 14 to direct fluid from the main impeller of the pump axially into thepassageway 16.

Thecover 27 has acentral hub 35 with an inturnedshoulder 36 receiving and supporting a top bearingassembly 37 for theshaft 26. The outer race ring of thebearing 37 is bottomed on theshoulder 36 and clamped thereagainst by a cover plate 38 underlying acap 39 which is bolted to thecover plate 27 by bolts such as 40. Thebearing 37 is thus locked against axial shifting in thehub 35. However, the top end of theshaft 26 has a reduced diametercylindrical portion 26a which is slidable through the inner race ring of thebearing 37. Thus, this bearing 37 is not subjected to axial thrust loads of theshaft 26 and only provides radial bearing support for the shaft.

The bottom bearing 25 has its outer race ring mounted in an invertedcap 41 in thehub 24 with a hollow neck 41a freely receiving theshaft 26 therethrough and anoutturned flange 41b underlying the hub and clamped against the bottom of the hub by abottom plate 42 which is bolted to the hub by bolts 42a. Theclosure plate 42 has arim portion 42b clamping the outer race ring of thebearing 25 against aninternal shoulder 41c of thecap 41. Thus, the bearing 25 is held against axial shifting in thehub 24.

Theshaft 26 has a reduceddiameter portion 26b fitting through the inner race of thebearing 25 and providing ashoulder 26e which is bottomed on top of this inner race. The lower end of the reduceddiameter portion 26b has splines or keyways 26c.

The maincentrifugal pump impeller 43 of theunit 10 has acentral hub 43a splined or keyed on the portion 26c of theshaft 26 and extending through asleeve 44 carried by theplate 42 to bottom against the inner race ring of thebearing 25. Anut 45 threaded on theshaft portion 26b below the splines 26c thrusts against the bottom of thehub 43a to clamp the hub against the inner race ring of the bearing.

Theimpeller 43 has ashroud 43b with acollar 43c riding in abearing sleeve 46 carried in theneck portion 17 of the bottom casing and a plurality ofcentrifugal pumping vanes 43d are provided between theshroud 43b and a flat base plate 43e of the impeller. These vanes centrifugally discharge the fluid from theinlet chamber 22 to theannular chamber 16 for flow therethrough to theoutlet pipe 11.

Since the outer race ring of thebearing 25 is clamped relative to thehub 24 and since the inner race ring of this bearing 25 is clamped between the impeller and theshoulder 26e of thepump shaft 26, thebearing 25 not only cooperates with thebearing 37 to provide radial support for theshaft 26 but also carries all of the axial thrust load imposed by theimpeller 43 on the shaft.

In accordance with this invention, theshaft 26 is hollow with abore 46 therethrough freely receiving asolid shaft 47. The bottom end of theshaft 26 is key slotted as at 26d to slidably receive aninducer impeller 48 with a central hub 480 having internalkey slots 48b mating with theslots 26d of the shaft and receivingkeys 49 to slidably key the shaft and impeller while allowing axial shifting of the impeller on the shaft. Four blades 48c extend from thehub 48a into close running clearance relation with the internal wall of theneck 17.

Anut 50 is threaded on the bottom end of thesolid shaft 47 and locked thereon by acap nut 51 to support thehub 48a of theimpeller 48.

The top end of theshaft 47 has acap member 52 threaded thereon with a recess 52a slidably receiving thetop end portion 26a of thehollow shaft 26 and surrounded by arim 52b bottomed on the inner race ring of thebearing 37. Anut 53 is also threaded on theshaft 47 and tightened against thecap 52 to lock the assembly on the shaft.

Thus, theinducer impeller 48 is rotated by theshaft 26 but is suspended through theshaft 47 from thetop bearing 37 and thrust loads of this impeller are relieved from the bottommain bearing 25 which carries the thrust loads of themain impeller 43.

Anelectric motor 53 is mounted in theinner casing 15 and includes astator 54 mounted in a sealedannular container 55 in thecasing 15 and a rotor orarmature 56 secured around the intermediate portion of theshaft 26.

OPERATION From the above descriptions it will be understood that thepump unit 10 of this invention has its maincentrifugal impeller 43 driven by theelectric motor 53 from amain shaft 26 which is supported radially by two axially spacedbearings 25 and 37 but is only supported axially by thebearing 25. Thismain shaft 26 is hollow and also drives aninducer impeller 48 in the pump inlet ahead of the maincentrifugal impeller 43. The inducer impeller has blades 48c which exert downward thrust loads when propelling fluid and developing a head pressure in the pump inlet. However, thrust loads of thisinducer impeller 48 are supported by thetop bearing 37 through ashaft 47 which extends through the hollowmain shaft 26. In this manner, excessive loads on the main pump bearing 25 are relieved and heretofore encountered bearing failures are avoided.

Fluids to be pumped enter the bottom of apump unit 10 through the bottom opening 21 and are immediately acted upon by the blades 480 of theinducer 48 to feed the fluid through achamber 22 to the inlet of the maincentrifugal impeller 43. Thisimpeller 43 centrifugally discharges the fluids into theannular chamber 16 between thecasings 14 and 15.Vanes 34 in this chamber diffuse the rotating fluid from the discharge of theimpeller 43 into an axial flow. The fluid flows through theannular passage 16, throughslots 31 at the top of theannular passage 16 into anoutlet 33 from which the fluids are discharged to theoutlet pipe 11. The vanes 48c of theimpeller 48 can be as numerous as desired to provide desired inlet head pressures for the main pump impeller since heavy thrust loads on the inducer will not have any effect on the main pump .bearing 25.

I claim as my invention:

1. In a pump and motor unit having a main pump impeller and an inducer impeller ahead of the main pump impeller driven by the same motor from a hollow main drive shaft supported in axially spaced bearings in the unit, one of which is adjacent the main pump impeller and the other of which is remote from the main pump impeller, the improvement which comprises a second shaft extending through the hollow main shaft suspended from the remote bearing and supporting the inducer impeller to relieve the other bearing from thrust loads developed by the inducer impeller.

2. The improvement of claim 1 wherein the inducer impeller is slidably keyed on the hollow main shaft and is free to slide axially on the main shaft.

3. The improvement of claim 1 wherein the bearings are respectively at the bottom and top of the motor.

4. The improvement of claim 1 wherein the bearings are ball bearings.

5. A submersible electric motor driven centrifugal pump adapted for pumping cryogenic'fluids and fluids at their boiling points which comprises a casing adapted to be mounted in the bottom of a tank and having a bottom inlet and a top outlet, an electric motor in the casing, a hollow shaft driven by said motor, a centrifugal impeller mounted on said shaft for corotation therewith receiving fluid from said inlet and discharging fluid through the casing to the top outlet, a second shaft extending through said hollow shaft, an inducer impeller slidably keyed on said hollow shaft in said pump inlet, means suspending said second shaft from the top of said casing, and means axially supporting said inducer impeller on said second shaft.

6. The pump of claim 4 wherein the casing has a main antifriction bearing supporting the hollow shaft radially and axially and a top antifriction bearing radially supporting said shaft and axially suspending said second shaft.

7. The pump of claim 4 including a first antifriction bearing radially and axially supporting the hollow shaft and a second antifriction bearing spaced from the first bearing also radially supporting the hollow shaft and radially and axially supporting the second shaft.

8. The pump of claim 4 wherein the second shaft is suspended from a top antifriction bearing in the top of the casing.

9. The pump of claim 4 wherein a ball bearing in the casing at bottom end of the motor carries thrust and radial loads of the hollow shaft and a second ball bearing in the casing at the top end of the motor suspends the second shaft.

10. The pump of claim 4 wherein the inducer impeller has a hub slidably keyed on the bottom end of the hollow shaft and four blades extend from the hub across the pump inlet to develop inlet head pressure for the centrifugal impeller.

Claims (10)

1. In a pump and motor unit having a main pump impeller and an inducer impeller ahead of the main pump impeller driven by the same motor from a hollow main drive shaft supported in axially spaced bearings in the unit, one of which is adjacent the main pump impeller and the other of which is remote from the main pump impeller, the improvement which comprises a second shaft extending through the hollow main shaft suspended from the remote bearing and supporting the inducer impeller to relieve the other bearing from thrust loads developed by the inducer impeller.

2. The improvement of claim 1 wherein the inducer impeller is slidably keyed on the hollow main shaft and is free to slide axially on the main shaft.

3. The improvement of claim 1 wherein the bearings are respectively at the bottom and top of the motor.

4. The improvement of claim 1 wherein the bearings are ball bearings.

5. A submersible electric motor driven centrifugal pump adapted for pumping cryogenic fluids and fluids at their boiling points which comprises a casing adapted to be mounted in the bottom of a tank and having a bottom inlet and a top outlet, an electric motor in the casing, a hollow shaft driven by said motor, a centrifugal impeller mounted on said shaft for co-rotation therewith receivIng fluid from said inlet and discharging fluid through the casing to the top outlet, a second shaft extending through said hollow shaft, an inducer impeller slidably keyed on said hollow shaft in said pump inlet, means suspending said second shaft from the top of said casing, and means axially supporting said inducer impeller on said second shaft.

6. The pump of claim 4 wherein the casing has a main antifriction bearing supporting the hollow shaft radially and axially and a top antifriction bearing radially supporting said shaft and axially suspending said second shaft.

7. The pump of claim 4 including a first antifriction bearing radially and axially supporting the hollow shaft and a second antifriction bearing spaced from the first bearing also radially supporting the hollow shaft and radially and axially supporting the second shaft.

8. The pump of claim 4 wherein the second shaft is suspended from a top antifriction bearing in the top of the casing.

9. The pump of claim 4 wherein a ball bearing in the casing at bottom end of the motor carries thrust and radial loads of the hollow shaft and a second ball bearing in the casing at the top end of the motor suspends the second shaft.

10. The pump of claim 4 wherein the inducer impeller has a hub slidably keyed on the bottom end of the hollow shaft and four blades extend from the hub across the pump inlet to develop inlet head pressure for the centrifugal impeller.

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