Pump shell for multistage metal working pump

Details Pump shell for multistage metal working pump Pump shell for multistage metal working pump

2000-08-23

2002-08-27

Verdier, Christopher (Department: 3745)

Rotary kinetic fluid motors or pumps

With shaft connected fluid force subjected thrust balancing...

C415S172100, C415S199200, C415S200000, C415S214100, C415S215100

Reexamination Certificate

active

06439835

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved pump shell for a multistage metal working pump and particularly to a pump shell consisting of a plurality of pump shell units housed in a hollow cylindrical casing, each pump shell unit has an inner shell and an impeller, the inner shell has a novel positioning, and sealing structure to form a simple pump shell structure that may be made easily at low cost, and provide smooth fluid guiding with less turbulence and improved sealing.
2. Description of the Prior Art
Conventional multistage centrifugal pumps (such as submersible pumps, or also called as water-sunken pumps) mostly have a plurality of pump shell units and impellers stacked in series along a shaft. The shaft rotates the impellers against the pump shell and generates centrifugal force for fluid to flow in the passage through the pump shells. Traditionally, multistage pumps are made by casting. They are heavy, bulky, brittle, have low strength and lower pumping efficiency. Hence contemporary multistage pumps are increasing made by high strength and low weight metal working pumps.
The design consideration of a metal working pump usually includes cost of production and assembly, pumping efficiency, flow guide design, pressure resistance, sealing effect, and etc. Conventional metal working pumps seldom can totally make all of aforesaid factors to the optimum level.
For instance, EU Patent application No. 81110541 suggests a pump shell design shown in FIG.
1
. It has a casing
11
made by a metal working process. Inside the casing
11
, there are partition members
12
to form multistages
2
desired. Each stage
2
of the casing
11
includes an impeller
3
and baffles
20
. The casing
11
of a stage
2
has a curved portion
19
formed in the circumference at a rear rim
111
for engaging with a front end of inner side
112
of an adjacent stage and to form an annular space therebetwen to squeeze a seal ring
14
therein. While it makes assembly of a multi stage pump easier, the fabrication of the curved portion
19
and front end
112
cannot always reach the precision required, and may result in not precise engagement between the two stages. Pumping thrust force and vibration may also cause deformation of the rim
111
and make the seal ring
14
become not effective for sealing function. Furthermore inside the casing
11
, there is no smooth fluid guide in the fluid passage between the impeller
3
and baffles
20
and may induce turbulence at the front end of the impeller and result in poor pumping efficiency. Hence it has the disadvantages of poor axial alignment, poor sealing and lower pumping efficiency.
FIG. 2
shows another prior art of metal working pump disclosed in U.S. Pat. No. 5,234,317 which has a pump casing
21
made by pressing and stamping. The pump casing
21
has a U-shaped end rim
211
for engaging with another end of an adjacent stage pump casing. As the sealing area between the end rim
211
and another end is relatively small, the sealing effect is not good when subject to great pumping pressure or vibration. Furthermore, the casing
21
should be made by hydraulic or oil pressing, its cost is higher. And there is also no smooth fluid passage between the impeller and the baffles. It also is prone to produce turbulence and result in lower pumping efficiency.
FIG. 3
shows a further prior art of a metal working pump casing now available in the market place. It has a metal working shell
4
consisted of a front outer shell
41
, a rear outer shell
42
, a front inner shell
43
, a rear inner shell
44
, a diffuser
45
, an impeller hub
46
, a front seal ring
47
and an impeller (not shown in the figure). The front outer shell
41
has a front end plate
413
, an indent axial holding side
411
and a radial holding side
412
. The rear outer shell
42
has radial holding ends
421
and
422
for engaging respectively with the axial and radial sides
411
and
412
of an adjacent pump shell, and a holding end
441
for making contact with the front end plate
413
of the adjacent pump shell. The positioning and sealing effect is simpler and more effective. The curved inner portion of the front and rear inner shell
43
and
44
also may produce more streamline fluid flow and offers improved pumping efficiency. However it still has the following disadvantages:
1. Too many components. As shown in
FIG. 3
, the pump casing
4
has a total of eight components, including the front and rear outer shells
43
,
44
, diffuser
45
, impeller hub
46
, front seal ring
47
and impeller. It needs more molds and fabrication processes to produce. The cost becomes much higher. It also takes more assembly time and becomes more expensive.
2. It needs more precise machining. The engagement and sealing function between the holding ends
421
,
422
and holding sides
411
,
412
need more precise dimensions which cannot be made by conventional stamping or pressing operation. Extra machining work should be done. It increases production time and cost. The machining also makes the pump shell thinner and may reduce pump shell strength.
3. The front shells
41
,
43
and rear shells
42
,
44
should be joined by circular soldering at circular solder points
48
. It costs much higher than spot soldering. Circular soldering also produces a not smooth or sightly appearance and inaccurate dimensions. It makes assembly more difficult. The soldering portion may temper material strength and needs extra machining work to reach dimension desired, and may result in a thinner pump shell and lower strength.
There are many other prior arts being disclosed, such as U.S. Pat. Nos. 4,877,372, 5,082,425, 5,344,678, 5,425,618, 5,201,848, 5,133,639, EU Pat. No. 0 492 575A1, 0 257 358A2, Pct No. WO 94/23211, DE Pat. No. 44 46 193C2. All of the above prior arts have some drawbacks and cannot fully satisfy the aforesaid design considerations such as production and assembly cost, enhanced flow passage and pumping efficiency, better pressure resistance and more effective sealing.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved metal working pump shell for a multistage pump that has a fewer number of components, may be made and assembled at a lower cost, has strong pressure resistance and improved sealing.
It is another object of this invention to provide an improved metal working pump shell that may be used for a pump with a floatable impeller. The pump shell according to this invention includes a plurality of pump shell units stacked in series on a rotatable shaft. Each pump unit includes at least a hollow inner shell, an impeller, a sealing ring and a diffuser. The rotating shaft rotates the impeller in the shell for drawing fluid from an impeller inlet and discharging fluid to another pump unit at another stage.
The inner shell has an inner end which has one side fixedly engaged with the diffuser, an inner shell side formed with a curved connection with the inner end, and a step and taper holding end to form a curved connection with the inner shell side. Fluid flows into the impeller through an inlet at the holding end, passing around the curved connection of the inner shell side and through the outlet of the diffuser to be discharged into another impeller of the next adjacent pump unit. More than one pump unit is housed inside a hollow cylindrical casing.
The inner end may attach from its outside surface a holding ring which forms a sealing flange at one end to make a close engagement with the holding end of the next stage pump unit so that two pump units may be aligned and assembled easily and accurately. The holding end, and inner end and casing form a close compartment to hold and squeeze the seal ring therein for preventing leaking.
The impeller is floatable and has a rear wall mounted on an impeller hub and a front wall with an impeller front thrust ring attached thereon. The impeller hub has an impeller metal working member soldering with the rear wall of the impeller and an impeller plastic member mountin

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