Double-suction pump

Abstract

 A full-circumferential-flow double-suction pump having impellers on respective opposite ends of the shaft of a motor, with an annular space or flow passage defined around the motor. The vertical double-suction pump has an outer cylinder and a motor housed in the outer cylinder. The motor has a stator and a rotor rotatably disposed in the stator. The outer cylinder defines a flow passage defined around the stator. A main shaft which supports the rotor extends substantially vertically. The pump also includes a pair of upper and lower impellers mounted respectively on upper and lower ends of the main shaft in communication with the flow passage.

Description

BACKGROUND OF THE INVENTION

Field of the Invention:

[0001] The present invention relates to a full-circumferential-flow pump, and more particularly to a full-circumferential-flow double-suction pump having impellers on respective opposite ends of the shaft of a motor, with an annular space or flow passage defined around the motor.

Description of the Prior Art:

[0002] One conventional full-circumferential-flow double-suction pump is known from Japanese laid-open patent publication No. 6-74197. Further, double-suction pumps are disclosed in German patent DE 1,653,692 and British patent GB 2,007,770. All the above prior pumps comprise a horizontal pump having a main pump extending horizontally.

[0003] Generally, however, horizontal pumps are unable to meet recent demands in the market for space-saver pumps. This is because, except for some horizontal pumps of very low output capability, the horizontal pumps have an extended overall length depending on the thickness of the laminated core of their motors, and hence require a relatively large installation space on the floor.

[0004] Furthermore, the horizontal pumps suffer additional disadvantages as follows:

1) Since thrusts are substantially balanced on the main shaft, the main shaft is not required to be supported by thrust bearings of large load capacity. However, the rotor of the horizontal pumps is susceptible to vibrations because the direction of thrusts is unstable.

2) The liquid handled by the horizontal pumps is subject to insufficient convection in the rotor chamber, possibly resulting in a pump cooling capability failure.

3) When they are primed, the horizontal pumps need to vent off any air which has been trapped in many air trapping regions that are contained in the pump units due to structural limitations. Therefore, the horizontal pumps should have a number of air vent valves. If trapped air were not vented off, then the pump performance would be lowered and the bearings would not be properly lubricated.

4) When the horizontal pumps are drained, water or the liquid that is handled tends to remain undischarged due to the horizontal structure thereof. The undrained water or liquid may possibly cause the pump casing to crack when frozen.

5) Radial bearings which support the rotor in the horizontal pumps are open to localized wear owing to the weight of the rotor, and will be damaged by such localized wear in a long period of usage.

SUMMARY OF THE INVENTION

[0005] It is therefore an object of the present invention to provide a double-suction pump which is a space saver, is subject to thrusts that are directionally stable, and allows a pumped liquid to be subject to good convection in a rotor chamber.

[0006] Another object of the present invention is to provide a double-suction pump which is free of air traps, contains a reduced amount of water or liquid remaining undischarged when drained, and has radial bearings that are not open to localized wear.

[0007] To achieve the above object, there is provided in accordance with the present invention a vertical double-suction pump comprising: an outer cylinder; a motor housed in the outer cylinder, the motor having a stator and a rotor rotatably disposed in the stator, the outer cylinder defining a flow passage between the outer cylinder and the motor; a main shaft supporting the rotor and extending substantially vertically; and a pair of upper and lower impellers mounted respectively on upper and lower ends of the main shaft.

[0008] According to the present invention, there is also provided a full-circumferential-flow pump comprising: an outer cylinder having a suction window and a discharge window; a motor housed in the outer cylinder, the motor having a stator and a rotor rotatably disposed in the stator, the outer cylinder defining an annular space between the outer cylinder and the motor; a main shaft supporting the rotor; a pump unit having an impeller mounted on an end of the main shaft; a suction case mounted on the outer cylinder and having a pump suction port for introducing a fluid through the suction window into the annular space; and a discharge case mounted on the outer cylinder and having a pump discharge port for discharging a fluid through the discharge window.

[0009] The flow passage is defined around the stator, and the impellers are mounted respectively on the lower and upper ends of the vertical main shaft. With this arrangement, the double-suction pump is constructed as a vertical pump which requires a smaller installation space than horizontal pumps.

[0010] The main shaft, the rotor, the impellers, and associated components jointly make up a rotating assembly. The rotating assembly is subject to downward forces because of the combined weight of these constituent parts. Since such downward forces are generally greater than thrusts applied to the rotating assembly due to a pressure balance even though the direction of such thrusts is unstable, the rotating assembly is prevented from becoming unstable mechanically.

[0011] Since the motor comprises a canned motor, rotor chambers defined above and below the rotor have respective vertical axes and are cylindrical in shape, allowing the fluid therein to convect well. The fluid whose temperature has increased due to the heat radiated by the canned motor is thus prevented from being trapped somewhere in the rotor chambers. Specifically, the fluid whose temperature has increased and hence whose specific gravity has decreased flows into the upper rotor chamber, and is mixed with a main pump fluid flow through the upper pump unit for a heat exchange.

[0012] Any air which is trapped in the double-suction pump when it is primed can be removed in its entirety when an air vent plug that is positioned at the upper end of the pump is detached. The vertical pump is more effective in removing trapped air than horizontal pumps because the horizontal pumps require at least one air vent valve in each of the pump units on the respective opposite ends of the main shaft.

[0013] For draining the double-suction pump, the fluid in the pump can be removed when a drain plug on the lower end of the pump is detached. Since the fluid can fully be drained by gravity from the pump, the pump is free from the danger of cracking or breakage when frozen.

[0014] Radial bearings by which the main shaft is rotatably supported are not subject to the weight of the rotating assembly. Therefore, these radial bearings are substantially prevented from suffering localized wear especially when hydraulic radial loads are balanced on the radial bearings.

[0015] Inasmuch as thrust bearings which bear forces tending to displace the main shaft downwardly are disposed in the upper rotor chamber, the rotating assembly is supported in its upper region, and hence stable upon rotation.

[0016] A double-suction pump according to an embodiment of the present invention, which is suitable for use in applications under high suction pressure, is of relatively poor structural strength because of compressive loads imposed on the main shaft. However, such compressive loads are reduced by the weight of the rotating assembly below the thrust bearings as these thrust bearings are disposed in the upper rotor chamber.

[0017] An agitating impeller is positioned in the suction port of the upper impeller. The agitating impeller, when rotated, is effective in quickly eliminating an air lock which may possibly be caused by air trapped in the upper end of the pump due to cavitation or the like.

[0018] Openings and a communication hole that are defined in the main shaft allow the fluid being handled to convect well in the pump. The fluid flowing through the openings and the communication hole serves to cool the canned motor and also lubricates the bearings. When the rotating assembly rotates, air tends to collect around the main shaft because of the action of centrifugal separation under centrifugal forces, and such collected air would possibly prevent the bearings from being well lubricated. However, the openings and the communication hole in the main shaft draw and discharge such collected air to the upper impeller.

[0019] The upper and lower rotor chambers that are defined upwardly and downwardly, respectively, of the rotor occasionally tend to develop different pressure buildups therein. More specifically, the pressures in the upper and lower rotor chambers are determined by the pressures of the fluid discharged behind the impellers. The pressure-reducing action produced by the respective clearances behind the impellers differs between these impellers. The pressures in the upper and lower rotor chambers could be equalized if the fluid flowed in a sufficient amount between the upper and lower rotor chambers through the gap between the rotor and the stator. Actually, however, the rotor and the stator rotate at a very high relative speed relatively with each other with only a small gap left therebetween. Therefore, the amount of fluid that flows through the gap between the rotor and the stator is generally very small. For this reason, the upper and lower rotor chambers often are liable to develop different pressure buildups therein, as described above. Such different pressure buildups in the upper and lower rotor chambers apply different loads on the opposite axial ends of the rotor, generating thrust forces acting axially on the rotor. The thrust forces thus generated are unstable because they are affected by the clearances behind the impellers, tending to cause the rotating assembly to vibrate or suffer other drawbacks under the thrust forces. However, the openings and the communication hole in the main shaft are also effective in equalizing the pressures in the upper and lower rotor chambers, so that the rotating assembly is prevented from vibrating or suffering other drawbacks under the thrust forces.

[0020] Since partition walls which are positioned inside the outer cylinder separate a suction pressure region from a discharge pressure region in the pump. These partition walls put limitations on the axial position of the pump suction or discharge port of the pump. Because of the positional limitations, the pump discharge port is relatively high in one of the embodiments of the present invention. The relatively high discharge opening of the pump often presents a serious problem for the user of the pump. According to another embodiment, the discharge case is mounted on the outer cylinder over the discharge window, and the discharge case defines a pump discharge port which is positioned lower than the discharge window. Consequently, the height of the pump discharge port of the pump according to the other embodiment is relatively low.

[0021] The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 

FIG. 1 is a vertical cross-sectional view of a full-circumferential-flow double-suction pump according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II - II of FIG. 1;

FIG. 3 is a vertical cross-sectional view of a full-circumferential-flow double-suction pump according to another embodiment of the present invention;

FIG. 4 is a cross-sectional view taken along line IV - IV of FIG. 3;

FIG. 5 is a vertical cross-sectional view of a full-circumferential-flow double-suction pump according to still another embodiment of the present invention; and

FIG. 6 is a cross-sectional view taken along line VI - VI of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Like or corresponding parts are denoted by like or corresponding reference numerals throughout views.

[0024] FIGS. 1 and 2 show a vertical cross-sectional view of a full-circumferential-flow double-suction pump according to an embodiment of the present invention.

[0025] The full-circumferential-flow double-suction pump shown in FIGS. 1 and 2, which comprises a vertical pump, has a canned motor 6 housed centrally in a pump casing 1. As shown in FIG. 1, the canned motor 6 includes a main shaft 7 supporting on its opposite ends respective pairs of lower impellers 8A, 9A and upper impellers 8B, 9B each having a suction port which opens axially outwardly. An agitating impeller 105 is fixedly disposed in the suction port of the upper impeller 8B. The lower impellers 8A, 9A belong to a lower pump unit, and the upper impellers 8B, 9B and the agitating impeller 105 belong to an upper pump unit.

[0026] The pump casing 1 comprises an outer cylinder 2 (see FIG. 2) of sheet stainless steel and a pair of upper and lower end covers 63A, 63B of sheet stainless steel joined to respective axial ends of the outer cylinder 2 by upper flanges 51, 52 and lower flanges 53, 54. The lower flange 54 has an integral leg 54a by which the full-circumferential-flow double-suction pump is vertically supported on a floor. The upper end cover 63A has a removable air vent plug 100 disposed as an air vent valve centrally thereon in vertical alignment with the main shaft 7. The lower end cover 63B has a drain pipe 101 having a horizontally open end on which a removable drain plug 102 is mounted.

[0027] The canned motor 6 comprises a stator 13, a cylindrical outer motor frame 14 fitted over the stator 13, a pair of side frame plates 15, 16 welded respectively to open ends of the outer motor frame 14, and a can 17 fitted in the stator 13 and welded to the side frame plates 15, 16. The canned motor 6 also has a rotor 18 rotatably housed in the can 17 in radial alignment with the stator 13 and shrink-fitted over the main shaft 7. The outer motor frame 14 and the outer cylinder 2 jointly define an annular flow passage 40 therebetween.

[0028] The main shaft 7 has a pair of axially spaced openings 7a, 7b positioned axially one on each side of the canned motor 6 and opening at an outer circumferential surface thereof, and a communication hole 7c defined axially in the main shaft 7 and interconnecting the openings 7a, 7b. The communication hole 7c has a lower end opening at the lower end of the main shaft 7. The openings 7a, 7b and the communication hole 7c provides fluid communication between an upper rotor chamber 107 which is defined above the rotor 18 in the canned motor 6 and a lower rotor chamber 108 which is defined below the rotor 18 in the canned motor 6.

[0029] As shown in FIG. 2, a terminal case 20 is fixed to an outer circumferential surface of the outer motor frame 14 and also to the outer cylinder 2. The canned motor 6 and the outer cylinder 2 are integrally fixed to each other by the terminal case 20 and a plurality of stays 43 fixedly positioned between the canned motor 6 and the outer cylinder 2.

[0030] The outer cylinder 2 has a pair of suction windows 2a, 2b defined therein closely to the respective opposite axial ends thereof. The suction windows 2a, 2b are connected to each other by a suction case 55 which is fixed to an outer circumferential surface of the outer cylinder 2. The suction case 55 has a pump suction port 55a projecting radially outwardly and supporting a suction flange 56 fixed thereto.

[0031] A case 77 is welded to an outer circumferential surface of the outer cylinder 2. The case 77 houses therein a frequency converter 76 which is electrically connected to the stator 13 by power supply cables through the terminal case 20.

[0032] The outer cylinder 2 houses a pair of axially spaced inner casings 65 disposed respectively in the opposite axial ends thereof and housing the respective pairs of lower impellers 8A, 9A and upper impellers 8B, 9B. The inner casings 65 comprise respective upper and lower cylindrical members 65a and respective upper and lower end covers 65b which are joined to each other, thereby making up substantially cylindrical containers. The upper and lower cylindrical members 65a have inner ends held against the outer cylinder 2 by respective resilient seal members 75. The upper and lower end covers 65b which are secured to the respective axially outer ends of the cylindrical members 65a have respective suction openings 65c defined centrally therein in communication with the suction ports of the impellers 8A, 8B. The agitating impeller 105 which is fixedly disposed in the suction port of the upper impeller 8B is also disposed in the suction opening 65c in the upper end cover 65b. The resilient seal members 75 serve to prevent a fluid that is discharged from the impellers 9A, 9B from flowing back to the suction side of the impellers 8A, 8B, respectively.

[0033] The inner casings 65 are connected to the respective side frame plates 15, 16 by bolts 66. The inner casings 65 house therein respective pairs of axially spaced holders 46 which hold respective liner rings 45, respective return guide vanes 47 positioned between the holders 46 for guiding a fluid discharged from the impellers 8A, 8B toward the impellers 9A, 9B, and respective guide devices 48 positioned radially outwardly of the impellers 9A, 9B for guiding the fluid discharged radially outwardly from the impellers 9A, 9B to flow axially in the annular flow passage 40 between the outer motor frame 14 and the outer cylinder 2.

[0034] As shown in FIGS. 1 and 2, the outer cylinder 2 has a discharge window 2c defined in its circumferential wall. A discharge nozzle 68 is mounted on the outer cylinder 2 and projects radially outwardly in registry with the discharge window 2c, the discharge nozzle 68 supporting a discharge flange 69 fixed thereto. The discharge window 2c is positioned in diametrically opposite relationship to the pump suction port 55a.

[0035] As shown in FIG. 1, the main shaft 7 is rotatably supported in the side frame plates 15, 16 by a pair of axially spaced bearing assemblies. One of the bearing assemblies, which is positioned closely below the upper impellers 8B, 9B, includes a bearing bracket 21 supporting a radial bearing 22 and a stationary thrust bearing 23 that is positioned above and adjacent to the radial bearing 22. The radial bearing 22 has an end face serving as a stationary thrust sliding member. The bearing assembly also includes a rotatable thrust bearing 24 as a rotatable thrust sliding member and a rotatable thrust bearing 25 which are positioned one on each side of the radial bearing 22 and the stationary thrust bearing 23. The rotatable thrust bearing 24 is fixed to a thrust disk 26 mounted on the main shaft 7, and the rotatable thrust bearing 25 is fixed to a thrust disk 27 mounted on the main shaft 7.

[0036] The bearing bracket 21 is inserted in a socket in the side frame plate 16 through a resilient O-ring 29. The bearing bracket 21 is axially held against the side frame plate 16 through a resilient gasket 30. The radial bearing 22 is slidably mounted on a sleeve 31 which is mounted on the main shaft 7.

[0037] The other bearing assembly, which is positioned closely above the lower impellers 8A, 9A, includes a bearing bracket 32 supporting a radial bearing 33 that is slidably mounted on a sleeve 34 which is mounted on the main shaft 7. The sleeve 34 is axially held against a washer 35 which is fixed to the lower end of the main shaft 7 through the impeller 9A, the sleeve 42, and the impeller 8A by a screw and nuts 36. The bearing bracket 32 is inserted in a socket in the side frame plate 15 through a resilient O-ring 37. The bearing bracket 32 is axially held against the side frame plate 15.

[0038] Operation of the full-circumferential-flow double-suction pump shown in FIGS. 1 and 2 will be described below.

[0039] A fluid which is drawn in through the pump suction port 55a is divided into two flows in the suction case 55, and the fluid flows are introduced through the respective suction windows 2a, 2b into the pump units. The fluid flows that have entered the pump units through the suction openings 65c are pressurized by the impellers 8A, 9A and 8B, 9B. While passing through the guide devices 48, the fluid flows discharged from the impellers 9A, 9B change their direction from the radially outward direction to the axial direction. Thereafter, the fluid flows are introduced into the annular flow passage 40 defined between the canned motor 6 and the motor frame 14. In the annular flow passage 40, the fluid flows are merged into a fluid flow which is discharged from the discharge window 2c through the discharge nozzle 68.

[0040] The full-circumferential-flow double-suction pump shown in FIGS. 1 and 2 offers various advantages as described below.

[0041] The annular flow passage 40 is defined around the stator 13, and the respective pairs of lower impellers 8A, 9A and upper impellers 8B, 9B are mounted respectively on the lower and upper ends of the main shaft 7. With this arrangement, the full-circumferential-flow double-suction pump is constructed as a vertical pump which requires a smaller installation space than horizontal pumps.

[0042] The main shaft 7, the rotor 18, the impellers 8A, 9A and 8B, 9B, and associated components jointly make up a rotating assembly. The rotating assembly is subject to downward forces because of the combined weight of these constituent parts. Since such downward forces are generally greater than thrusts applied to the rotating assembly due to a pressure balance even though the direction of such thrusts is unstable, the rotating assembly is prevented from becoming unstable mechanically.

[0043] In the canned motor 6, the rotor chambers 107, 108 have respective vertical axes and are cylindrical in shape, allowing the fluid therein to convect well. The fluid whose temperature has increased due to the heat radiated by the canned motor 6 is thus prevented from being trapped somewhere in the rotor chambers 107, 108. Specifically, the fluid whose temperature has increased and hence whose specific gravity has decreased flows into the upper rotor chamber 107, and is mixed with the main pump fluid flow through the upper pump unit for a heat exchange.

[0044] Any air which is trapped in the full-circumferential-flow double-suction pump when it is primed can be removed in its entirety when the air vent plug 100 that is positioned at the upper end of the pump is detached. The vertical pump is more effective in removing trapped air than horizontal pumps because the horizontal pumps require at least one air vent valve in each of the pump units on the respective opposite ends of the main shaft. For draining the full-circumferential-flow double-suction pump, the fluid in the pump can be removed when the drain plug 102 on the lower end of the pump is detached. Since the fluid can fully be drained by gravity from the pump, the pump is free from the danger of cracking or breakage when frozen.

[0045] The radial bearings 22, 33 are not subject to the weight of the rotating assembly. Therefore, these radial bearings 22, 33 are substantially prevented from suffering localized wear especially when hydraulic radial loads are balanced on the radial bearings 22, 33.

[0046] Inasmuch as the thrust bearings 23, 24, 25 are disposed in the upper rotor chamber 107, the rotating assembly is supported in its upper region, and hence the rotating assembly is stable upon rotation.

[0047] The agitating impeller 105 is positioned in the suction port of the upper impeller 8B which communicates with the suction opening 65c. The agitating impeller 105, when rotated, is effective in quickly eliminating an air lock which may possibly be caused by air trapped in the upper end of the pump due to cavitation or the like.

[0048] The openings 7a, 7b and the communication hole 7c that are defined in the main shaft 7 allow the fluid being handled to convect well in the pump. The fluid flowing through the openings 7a, 7b and the communication hole 7c serves to cool the canned motor 6 and also lubricates the bearings. When the rotating assembly rotates, air tends to collect around the main shaft 7 because of the action of centrifugal separation under centrifugal forces, and such collected air would possibly prevent the bearings from being well lubricated. However, the openings 7a, 7b and the communication hole 7c in the main shaft 7 draw and discharge such collected air to the upper impellers 8B, 9B.

[0049] The upper and lower rotor chambers 107, 108 that are defined upwardly and downwardly, respectively, of the rotor 18 occasionally tend to develop different pressure buildups therein. More specifically, the pressures in the upper and lower rotor chambers 107, 108 are determined by the pressures of the fluid discharged behind the impellers 8A, 9A and 8B, 9B. The pressure-reducing action produced by the respective clearances behind the impellers 8A, 9A and 8B, 9B differs between these impellers 8A, 9A and 8B, 9B. The pressures in the upper and lower rotor chambers 107, 108 could be equalized if the fluid flowed in a sufficient amount between the upper and lower rotor chambers 107, 108 through the gap between the rotor 18 and the stator 13. Actually, however, the rotor 18 and the stator 13 rotate at a very high relative speed relatively with each other with only a small gap left therebetween. Therefore, the amount of fluid that flows through the gap between the rotor 18 and the stator 13 is generally very small. For this reason, the upper and lower rotor chambers 107, 108 often are liable to develop different pressure buildups therein, as described above. Such different pressure buildups in the upper and lower rotor chambers 107, 108 apply different loads on the opposite axial ends of the rotor 18, generating thrust forces acting axially on the rotor 18. The thrust forces thus generated are unstable because they are affected by the clearances behind the impellers 8A, 9A and 8B, 9B, tending to cause the rotating assembly to vibrate or suffer other drawbacks under the thrust forces. However, the openings 7a, 7b and the communication hole 7c in the main shaft 7 are also effective in equalizing the pressures in the upper and lower rotor chambers 107, 108, so that the rotating assembly is prevented from vibrating or suffering other drawbacks under the thrust forces.

[0050] The vertical double-suction pump in this embodiment is susceptible to an air lock in its upper pump unit. However, even when an air lock is produced in the upper pump unit, since the fluid discharged from the lower pump unit flows back into the upper pump unit, the air lock that is produced in the upper pump unit is removed by the fluid from the lower pump unit. Actually, therefore, no problem will arise even if the agitating impeller 105 is dispensed with.

[0051] FIGS. 3 and 4 show a full-circumferential-flow double-suction pump according to another embodiment of the present invention.

[0052] The full-circumferential-flow double-suction pump shown in FIGS. 3 and 4 differs from the full-circumferential-flow double-suction pump shown in FIGS. 1 and 2 in that a discharge case 110 is mounted on the outer cylinder 2 over the discharge window 2c and has a pump discharge port defined therein, and a discharge nozzle 111 is connected to the discharge case 110, with a discharge flange 112 fixedly mounted on the discharge nozzle 111. The discharge nozzle 111 is positioned lower than the discharge window 2c. Other structural details of the full-circumferential-flow double-suction pump shown in FIGS. 3 and 4 are the same as those of the full-circumferential-flow double-suction pump shown in FIGS. 1 and 2.

[0053] The inner casings 65 and the seal members 75 which are positioned inside the outer cylinder 2 serve as partition walls which separate a suction pressure region from a discharge pressure region in the pump. These partition walls put limitations on the axial position of the pump suction or discharge port of the pump. Because of the positional limitations, the pump discharge port, which is provided by the discharge nozzle 68 in the embodiment shown in FIGS. 1 and 2, is relatively high in the embodiment shown in FIGS. 1 and 2. The relatively high pump discharge port of the pump often presents a serious problem for the user of the pump. According to this embodiment, the discharge case 110 is mounted on the outer cylinder 2 over the discharge window 2c, and the discharge case 111 defines a pump discharge port which is positioned lower than the discharge window 2c. Consequently, the height of the discharge opening of the pump shown in FIGS. 3 and 4 is relatively low.

[0054] FIGS. 5 and 6 show a full-circumferential-flow double-suction pump according to still another embodiment of the present invention.

[0055] The full-circumferential-flow double-suction pump shown in FIGS. 5 and 6, which comprises a vertical pump, has a canned motor 6 housed centrally in a pump casing 1. As shown in FIG. 5, the canned motor 6 includes a main shaft 7 supporting on its opposite ends respective pairs of lower impellers 8C, 9C and upper impellers 8D, 9D each having a suction port which opens axially inwardly. The lower impellers 8C, 9C belong to a lower pump unit, and the upper impellers 8D, 9D and the agitating impeller 105 belong to an upper pump unit.

[0056] The pump casing 1 comprises an outer cylinder 2 (see FIG. 6) of sheet stainless steel and a pair of upper and lower end covers 63A, 63B of sheet stainless steel joined to respective axial ends of the outer cylinder 2 by upper flanges 51, 52 and lower flanges 53, 54. The lower flange 54 has an integral leg 54a by which the full-circumferential-flow double-suction pump is vertically supported on a floor. The upper end cover 63A has a removable air vent plug 100 disposed as an air vent valve centrally thereon in vertical alignment with the main shaft 7. The lower end cover 63B has a drain pipe 101 having a horizontally open end on which a removable drain plug 102 is removably mounted.

[0057] The canned motor 6 is of a structure which is essentially identical to the canned motor 6 in the embodiment shown in FIG. 1. In the canned motor 6 shown in FIG. 5, the side frame plates 15, 16 have respective fluid guides 80 which have radial fluid passages.

[0058] The outer cylinder 2 houses a pair of axially spaced substantially cylindrical inner casings 85 of unitary structure disposed respectively in the opposite axial ends thereof and housing the respective pairs of lower impellers 8C, 9C and upper impellers 8D, 9D. The inner casings 85 have axial inner ends fitted over and fixed to the respective fluid guides 80. The inner casings 85 have inner ends held against the outer cylinder 2 by respective resilient seal members 75 which serve to prevent a fluid that is discharged by the impellers 9C, 9D from leaking back to a suction side of the impellers 8C, 8D. Stays 87 are interposed between the axially outer ends of the inner casings 85 and the covers 63A, 63B. The inner casings 85 have respective discharge openings 85a defined centrally in their axially outer ends.

[0059] The inner casings 85 house therein respective pairs of axially spaced holders 46 which hold respective liner rings 45, respective return guide vanes 47 positioned between the holders 46 for guiding a fluid discharged from the impellers 8C, 8D toward the impellers 9C, 9D, and respective return guide vanes 48 positioned axially outwardly of the impellers 9C, 9D for guiding the fluid discharged from the impellers 9A, 9B to flow radially inwardly.

[0060] As shown in FIGS. 5 and 6, the outer cylinder 2 has a pump suction port 2e defined in its circumferential wall, and a radially outwardly projecting suction nozzle 89 is mounted on the outer cylinder 2 over the pump suction port 2e in registry with the pump suction port 2e, the suction nozzle 89 supporting a suction flange 90 fixed thereto. The outer cylinder 2 also has a pair of axially spaced discharge windows 2f, 2g defined in its circumferential wall near the respective axial ends thereof and interconnected by a discharge case 91 which is mounted on the outer cylinder 2. The discharge case 91 has a pump discharge port 91a, and a discharge nozzle 92 is mounted on the discharge case 91 and projects radially outwardly in registry with the pump discharge port 91a, the discharge nozzle 92 supporting a discharge flange 93 fixed thereto. The pump discharge port 91a is positioned in diametrically opposite relationship to the pump suction port 2e. Other structural details of the full-circumferential-flow double-suction pump shown in FIGS. 5 and 6 are the same as those of the full-circumferential-flow double-suction pump shown in FIGS. 1 and 2.

[0061] The full-circumferential-flow double-suction pump shown in FIGS. 5 and 6 operates as follows:
   A fluid drawn in from the pump suction port 2e is divided into two flows in the annular flow passage 40, and the fluid flows are introduced through the respective guides 80 into the impellers 8C, 8D. The fluid flows are then discharged from the impellers 8C, 8D, and introduced through the respective guide vanes 47 into the impellers 9C, 9D. After pressurized by the impellers 9C, 9D, the fluid flows are guided by the return guide vanes 48 and then discharged from the respective discharge openings 85a of the inner casings 85. The fluid flows discharged from the discharge openings 85a pass through the respective discharge windows 2f, 2g in the outer cylinder 2 into the discharge case 91 where the fluid flows are merged with each other. The fluid in the discharge case 91 is thereafter discharged from the pump discharge port 91a and the discharge nozzle 92.

[0062] The full-circumferential-flow double-suction pump shown in FIGS. 5 and 6 offers the same advantages as those of the full-circumferential-flow double-suction pump shown in FIGS. 1 and 2. The full-circumferential-flow double-suction pump shown in FIGS. 5 and 6, which is suitable for use in applications under high suction pressure, is of relatively poor structural strength because of compressive loads imposed on the main shaft 7. However, such compressive loads are reduced by the weight of the rotating assembly below the thrust bearings 23, 24, 25 as these thrust bearings are disposed in the upper rotor chamber 107.

[0063] Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Claims

1. A vertical double-suction pump comprising:
   an outer cylinder;
   a motor housed in said outer cylinder, said motor having a stator and a rotor rotatably disposed in said stator, said outer cylinder defining a flow passage between said outer cylinder and said motor;
   a main shaft supporting said rotor and extending substantially vertically; and
   a pair of upper and lower impellers mounted respectively on upper and lower ends of said main shaft.

2. The vertical double-suction pump according to claim 1, wherein said motor comprises a canned motor including self-lubricated slide bearings, said main shaft being rotatably supported by said self-lubricated slide bearings.

3. The vertical double-suction pump according to claim 1 or 2, further comprising an upper rotor chamber defined above said rotor, and a thrust bearing housed in said upper rotor chamber for receiving a thrust force which is directed downwardly.

4. The vertical double-suction pump according to claim 1 or 2, further comprising an agitating impeller disposed above said upper impeller.

5. The vertical double-suction pump according to claim 1, wherein said main shaft has a pair of axially spaced openings defined therein and opening at an outer surface thereof, and a communication hole defined axially in the main shaft and interconnecting said openings.

6. The vertical double-suction pump according to claim 5, wherein said motor is positioned axially between said openings.

7. The vertical double-suction pump according to claim 5 or 6, further comprising a pair of rotor chambers defined above and below said rotor, said openings being positioned in said rotor chambers, respectively.

8. A full-circumferential-flow pump comprising:
   an outer cylinder having a suction window and a discharge window;
   a motor housed in said outer cylinder, said motor having a stator and a rotor rotatably disposed in said stator, said outer cylinder defining an annular space between said outer cylinder and said motor;
   a main shaft supporting said rotor;
   a pump unit having an impeller mounted on an end of said main shaft;
   a suction case mounted on said outer cylinder and having a pump suction port for introducing a fluid through said suction window into said annular space; and
   a discharge case mounted on said outer cylinder and having a pump discharge port for discharging a fluid through said discharge window.

9. The full-circumferential-flow pump according to claim 8, wherein said motor comprises a canned motor including self-lubricated slide bearings, said main shaft being rotatably supported by said self-lubricated slide bearings.

10. The full-circumferential-flow pump according to claim 8 or 9, further comprising an upper rotor chamber defined above said rotor, and a thrust bearing housed in said upper rotor chamber for receiving a thrust force which is directed downwardly.

11. The full-circumferential-flow pump according to claim 8 or 9, further comprising an agitating impeller disposed above said upper impeller.

Drawing