Multi-stage pump device

Details Multi-stage pump device Multi-stage pump device

2000-03-30

2001-10-23

Walberg, Teresa (Department: 3742)

Pumps

Successive stages

C417S248000

Reexamination Certificate

active

06305910

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to a multi-stage pump device which is used for feeding working fluid under pressure.
2. Description of the Related Art
A multi-stage pump device is shown in
FIG. 4
as a pump device related to this invention. The multistage pump device shown in
FIG. 4
comprises pump devices A, B, C, and D arranged in line to form a four stage pump device. Each pump device A, B, C, and D is firmly secured by a support frame
15
. A casing
10
of the pump device A and a casing
20
of the pump device B are provided with a flange
12
and a flange
13
, respectively. The flange
12
and the flange
13
are sealed by sealing means and firmly connected by a fastening belt
14
.
The working fluid fed by the pump device A flows through a passage provided in the flange
12
and flows into the pump device B through a passage provided in the flange
13
of the pump device B. The working fluid thus flows into the pump B, and further flows into the pump device C through passage similarly provided in the flange (not numbered) of pump device C. As explained above, by arranging a plurality of pump devices in line, a high degree of vacuum can be obtained if used in a vacuum pump device, for instance.
In the conventional multi-stage pump device, however, each pump device is firmly secured by the supporting frame
15
. Therefore stress occurs in the connecting area between the flange
12
and the flange
13
due to the thermal expansion of the casing
10
and the casing
20
, respectively, by the rise of the temperature in the pump while the pump device is working. The stress may deform the casings
10
,
20
, and such deformation partially loads the bearings provided in the casings
10
,
20
and shortens a life span of the bearings.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved multi-stage pump device overcoming the foregoing drawbacks and including a plurality of pump devices connected in line to perform a multi-stage operation.
According to a first aspect of the present invention, the above and other objects are achieved by a multi-stage pump device comprising a plurality of pump devices, each of the pump devices having a pump portion feeding working fluid under pressure, and a connecting portion provided between at least two of the pump devices, through which working fluid pumped by the respective pump devices passes, wherein the connecting portion is expandable in a direction of the length thereof, and wherein the connecting portion is provided with a sealing structure to prevent a leakage of the working fluid.
According to the first aspect of the present invention, the ability of the connecting portion to expand makes it possible to reduce the transfer of heating stress to a casing of each pump device while the pump devices are in operation. Therefore, bearings provided in the casings of the pump devices may not receive the partial load which is often caused by the deformation of the casing by the heat stress. Thus, the working life span of the pump device of this invention can be extended.
According to a second aspect of the present invention, the above and other objects are achieved by a multi-stage pump device comprising a plurality of pump devices, each of the pump devices having a pump portion feeding working fluid under pressure, and a bellows provided between at least two of the pump devices, through which working fluid pumped by the respective pump devices passes.
According to the second aspect of the present invention, the deformation of the bellows makes it possible to reduce the transfer of heating stress to a casing of each pump device while the pump devices are in operation. Therefore, bearings provided in the casings of the pump devices may not receive the partial load which is often caused by the deformation of the casing by the heat stress. Thus, the working life span of the pump device of this invention can be extended.


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