Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between runner portion and static part – Means to seal radial flow pump runner inlet from outlet
Reexamination Certificate
2000-01-12
2001-07-31
Kwon, John (Department: 3747)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between runner portion and static part
Means to seal radial flow pump runner inlet from outlet
C415S173100, C415S200000
Reexamination Certificate
active
06267555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to sheet metal casing for multistage pump and its manufacturing method, and particularly to a sheet metal casing for multistage submerged pump that has simple structure to facilitate fabrication and assembly at low cost, and has improved sealing and pumping efficiency.
2. Description of the Prior Art
Conventional multistage centrifugal pumps (such as submerged pumps) usually includes a plurality of casings with passages and impellers housed therein and mounted serially on a rotationable spindle for pumping fluid by adding pressure. The multistage pump made by casting in the past is heavy and bulky and has lower pump efficiency. It is generally replaced by sheet metal casing pump nowadays.
In the design of multistage sheet metal casing pump, the main considerations include: manufacturing and assembly cost, pump efficiency and passage design, pressure resistance, leakage prevention, etc. These factors are rarely totally met by conventional sheet metal casing multistage pump. For instance, European Pat. Application No. 81110541.0 discloses a sheet metal casing structure for multistage pump shown in FIG.
1
. It has a casing
11
made by punching and a partition member
12
to form a stage
2
for housing an impeller
3
and baffles
20
therein. The casing
11
has a curved portion
19
for engaging a front stage with a rear stage. At the juncture of the engagement, a seal ring
14
is provided. The dimension and precision of the curved portion
19
is difficult to control. When more than one stage being fastened axially, the positioning of the curved portion
19
is even more difficult and is prone to deform. The seal ring
14
tends to malfunction and result in leakage under pressure or vibration. Moreover there is no smooth passage inside the casing
11
and the impeller
13
. It is easy to produce turbulence around the front end
112
during pumping operation and result in lower pump efficiency. In short, it has the drawbacks of poor axial positioning, easy leaking and low pump efficiency.
FIG. 2
illustrates another prior art disclosed in U.S. Pat. No. 5,234,317. It has a pump casing
21
made by punching and pressing. The pump casing
21
has an end rim
211
formed in a U-shaped member for engaging securely with a next stage pump casing. However it has a smaller contact area (sealing surface). The end rim
211
is prone to deform and open outwardly under strong pumping pressure or vibration. Leaking is still not avoidable. Furthermore the pump casing
21
cannot be made by merely punching operation. It needs pressing operation to finish all the fabrication work required. The cost is higher. And there is also no smooth passage inside the casing and may result in turbulence and lower pump efficiency. When two stage pumps are connected, the connection portion forms an S-shaped structure. While it helps to prevent deformation and leakage, it increases production cost.
FIG. 3
shows a still another technique seen in the market place. The pump casing
4
includes a front outer shell
41
, a rear outer shell
42
, a front inner shell
43
, a rear inner shell
44
, a hub
46
, a front seal ring
47
and an impeller (not shown in the figure). The front outer shell
41
includes a front side ring
413
, an axial positioning ring
411
and a radial positioning ring
412
. The rear outer shell
42
includes an axial positioning end
421
and a radial positioning end
422
mating respectively with the rings
411
and
412
. The rear inner shell
44
has a positioning end
441
at the rear end.
For assembly of a single casing
4
, the vane
45
is firstly soldered to the front inner shell
43
. Then the front outer shell
41
, rear outer shell
42
, front inner shell
43
and rear inner shell
44
are assembled together (otherwise the inner shells
43
and
44
cannot be put into the outer shells
41
and
42
). Then circular soldering is made on the solder spots
48
around the outer shell.
For assembly of a multistage pump casing
4
, the positioning end
44
of a front casing
4
will be made contact with the front side ring
413
of a rear casing. The axial and radial positioning end
421
and
422
of the front casing will be made contact with the axial and radial positioning rings
411
and
412
which may couple with a seal ring to prevent leakage. The front and rear inner shells
43
and
44
have curved inside surface to smooth flow passage and enhance pump efficiency.
However there are still disadvantages in this technique, notably:
1. It has too many components and costs too much to produce. Eight components are required, including the front and rear outer shells
41
and
42
front and rear inner shells
43
and
44
, vane
45
, hub
46
, front seal ring
47
and the impeller. The molding cost and assembly time increase greatly. The hub
46
and front seal ring
47
also add to the cost.
2. It needs secondary machining that increases cost and production time. The axial and radial positioning ring
411
and
412
, and the axial and radial positioning end
421
and
422
need high precision machining work to get the accurate dimension for making the required connection. An usual punching operation cannot produce that kind of precision. The machining also unavoidably reduces shell thickness and weaken the structural strength.
3. The circular soldering of the solder spots
48
are much more expensive and time-consuming than conventional spot soldering. It also tends to produce notsightly casing and lower dimension accuracy. Positioning for assembly is more difficult. The soldering property and strength is difficult to control. A secondary machining is needed after the soldering and may reduce casing thickness.
The prior arts set forth above thus cannot totally meet all the design factors such as production and assembly costs, pump efficiency and passage streamline, pressure resistance, leak control and prevention, etc. There are still a lot of room for improvement.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a sheet metal casing for multistage pump and manufacturing method that has lower production and assembly cost, enhanced pressure resistance and improved leakage prevention.
The pump according to this invention consists of a plurality of pump unitsserially mounted on a rotationable spindle. Each pump unit includes a casing, an impeller and a hub. The casing includes an outer shell and an inner shell. The outer shell is integrally formed and includes a front end ring, a step positioning ring, an outer shell surface and a positioning end. The inner shell is located inside the outer shell and includes an inner end, an inner shell surface and a step positioning rim. The positioning rim and the outer shell surface form a holding space inside for holding a seal ring. When a plurality of casings are serially connected, the positioning end of a front casing may contact with the step positioning ring of a rear casing, and the positioning rim of the front casing may contact with front end ring of the rear casing for positioning the casings on the spindle and securing the seal ring in the closed holding space. The front end ring and the inner end are bent and extended forward and are parallel with the spindle with a gap formed therebetween to mate against inlet of the impeller. It also serves sealing function.
The manufacturing method of this invention includes more than one punching operation on a metal sheet to produce the front end ring, step positioning ring and outer shell surface. Then the inner shell is formed by more than one punching operation to form a front half and a rear half sections.
The front half section includes the inner end and about a half of the inner shell surface. The rear half section includes about a half of remaining inner shell surface and the positioning rim. Then the front half section, vane and rear half section are soldered serially to the outer shell. Finally a punching operation is performed on the outer shell to form the positioning end.
REFERENCES
Chien Huan-Jan
Kao Shu-Fen
Liaw Rong-Jau
Ou Pao-Yin
Dougherty & Troxell
Industrial Technology Research Institute
Kwon John
LandOfFree
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