Note: Descriptions are shown in the official language in which they were submitted.
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CONCENTRIC MULTI-STAGE CENTRIFUGAL PUMP WITH START STAGE
Background of the Disclosure
This disclosure relates to a pump, and more particularly to a high speed
centrifugal pump, with the addition of a start stage. However, selective
details may
find application in related pump environments.
Centrifugal pumps are generally well known in the art. Generally speaking, an
axial inlet provides fluid to a rotating impeller. A first stage impeller is
driven by a
rotating drive shaft so that the first stage impeller imparts energy to the
fluid which
exits generally radially from the first stage. Typically, axially spaced
bearings are
disposed along an outer surface of the shaft to support the shaft and impeller
within
the pump housing. The impeller is located within a pumping cavity of the
housing
and seals are provided on front and rear faces of the impeller so that the
pressure
build-up from the rotating impeller is imparted to the fluid within the pump
cavity. A
stationary diffuser is provided at a radial outer location of the impeller and
receives
the fluid from the impeller. The diffuser converts high velocity fluid energy
into lower
velocity fluid energy thereby increasing the pressure of the fluid as the
fluid is
directed to a discharge passage.
Such centrifugal pumps are used in a wide variety of applications. One such
application is providing high pressure fuel flow to a jet engine, for example.
This
environment requires a minimal pump packaging volume, and also a minimal
weight.
Optimizing pump performance and particularly optimizing pump performance at
engine start-up in order to build the desired or required system pressure and
flow is
desired. However, once the start-up pressure and flow is established, it is
important
to limit the impact of the starting components on operation of the pump.
Therefore, a need exists for a compact package of a high-speed centrifugal
pump that also has reduced weight and satisfies start stage requirements for
the
system.
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Summary of the Disclosure
A centrifugal pump assembly includes a first pump stage, a second pump
stage independently rotatable relative to the first pump stage, and a drive
assembly
that rotates the first and second pump stages to a first speed and then
rotates the
second pump stage at a different speed than the first pump stage.
In one embodiment, the second pump stage becomes freely rotating at a
selectable operating condition.
The second impeller stage may rotate faster at start-up and then rotate at
approximately one-half of the speed of the first pump stage speed.
In one arrangement, the second pump stage rotates at a slower speed based
on a fluidic drive provided by the driven first stage speed.
A first pump stage is an inner impeller stage, and the second pump stage is
preferably a concentric, outer impeller stage.
The drive assembly includes a main drive shaft connected to and selectively
rotating the first pump stage.
The drive assembly includes a separate drive member for rotating the second
pump stage independently of the first pump stage.
In one arrangement, the separate drive member is an electric motor drive.
The electric motor drive many be concentrically located about the main drive
shaft and adapted to rotate the second pump stage at a different speed than
the
main drive shaft rotates the first pump stage.
Consequently, at start-up, the outer stage may rotate at a high speed to
increase the pressure.
After start-up, the second, outer stage rotates slower since the outer
impeller
stage is only fluidically coupled to the inner impeller stage.
A method of operating the centrifugal pump assembly includes providing first
and second pump stages. The method includes independently driving the first
and
second pump stages. .
Once start-up speed is attained, a positive drive for the second pump stage
may be turned off and the second pump stage allowed to freely rotate.
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In another arrangement, the concentric outer stage can be driven with not only
the fluidic drive but also the second, outer stage drive motor and continue to
drive the
second pump stage if so desired.
The driving step includes using an electric drive motor for rotating the
second
pump stage so that the first and second pump stages may be driven at different
speeds.
A primary benefit is a reduction in disk drag associated with the high speed
centrifugal pump using multiple stages.
Another benefit is associated with the minimal pump packaging volume, for
example by placing the first and second pump stages disposed in concentric
fashion.
Still another advantage resides in the reduced weight while providing for
start-
up.
Still other benefits and advantages of the present disclosure will become
apparent upon reading and understanding the following detailed description.
Brief Description of the Drawing
Figure 1 is a cross-sectional view of a preferred embodiment of the present
disclosure.
Detailed Description
As shown in Figure 1, a pump assembly, and more particularly a centrifugal
pump assembly 100, includes a housing 102 having an inlet 104 shown here as an
axial inlet that communicates with a pump cavity or chamber 106. Received in
the
pump chamber is a rotary pump 110 and specifically a multi-stage rotary pump
provided by a first or inner impeller stage 112 and a second or outer impeller
stage 114. The first stage is in fluid communication with the inlet so that an
axial
passage 116 receives the fluid from the inlet 104 and through rotation of the
inner
impeller stage, provides fluid at a higher pressure to radial outlet 118.
The inner impeller stage 112 is positively driven by a portion of the drive
assembly 120, and more particularly by drive shaft 122 that rotates the inner
impeller
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stage at a desired speed. Preferably the drive shaft 122 is supported and
axially
spaced locations by first and second bearings 124, 126 that support the drive
shaft
for relative rotation with respect to the housing 102. In addition, seals 128
are
typically provided and extend between the outer surface of the drive shaft and
an
inner wall of the passage in the housing that receives the drive shaft 122. In
addition,
a first impeller seal 140 is provided adjacent the inlet 104 and seals between
the
inner, front surface of the inner impeller stage 112 and the inlet 104 while a
second
or rear seal 142 is disposed along a rear surface or rear face of the inner
impeller
stage 112 and the housing 102. Thus, as the first impeller stage 112 is
rotated by
the drive shaft 122, fluid from the inlet 104 proceeds through passages 116 to
the
outlets 118.
Also received within the pump chamber 106 is the second or outer impeller
stage 114. Preferably, the outer impeller stage 114 is concentrically located
relative
to the inner impeller stage 112. That is, a radially extending passage 144
receives
fluid from the outlet 118 of the inner impeller stage, and imparts additional
energy
from the outer impeller stage 114 before the fluid exits and communicates with
a
stationary diffuser 150 that leads to discharge passage 152. The outer
impeller
stage 114 includes a recess 154 dimensioned to closely receive the outer
radial
dimension of the inner impeller stage 112. An axially extending portion of the
outer
impeller stage has a first portion 156 that is received in the pump chamber in
radially
spaced location relative to the inlet end of the inner impeller stage. The
first axial
portion 156 is supported by an outer stage bearing 158 that supports the outer
impeller stage for relative rotation with respect to the housing 102. In
addition, seal
160 is interposed between the first axial portion 156 and an inner surface
that defines
the pump chamber in the housing. Similarly, a second axial portion 162 extends
rearwardly and is supported by a second outer stage bearing 164 and receives a
seal
166 between the second axial portion and the pump housing 102.
A second portion of the drive assembly 120 is provided by an outer stage drive
motor 180 which is in this particular instance is an electric drive motor.
This drive
motor 180 provides for positive independent driving movement of the outer
impeller
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stage 114 relative to the inner impeller stage 112. There are situations where
it is
desirable to use the drive motor 180 to positively drive the outer impeller
stage 114 at
a different speed than the inner impeller stage. Of course, one skilled in the
art will
also appreciate that the inner and outer impeller stages 112, 114 could be
driven at
the same speed if so desired. By using an independent outer stage drive motor
180,
the outer stage can be positively driven or rotated at a fast speed at start-
up in order
to build a desired pressure. Once the desired pressure is reached, then one of
two
actions can be taken. First, the outer stage drive motor 180 can be turned off
so that
the outer impeller stage rotates freely and the drive energy imposed on the
outer
stage is provided by a fluid coupling fluidic forces provided by the driven
inner
impeller stage 112. Under such an arrangement, the inner impeller stage 112
may
be rotating at a first speed N1 while the outer stage may be rotating at a
reduced,
second rotational speed N2. Typically, N2 is approximately one-half the
rotational
speed of N1. Thus, the electric motor drive 180 is capable of being switched
on for
starting and then turned off for normal operation of the outer impeller stage
114.
During low inner impeller stage drive speed operation, such as engine
starting, the
electric drive motor 180 that drives the outer impeller stage 114 builds the
required
system pressure and flow. Once sufficient engine speed is attained to permit
the
impeller stage to produce the required system pressure, the electric drive
motor 180
may be switched off. Thereafter, the outer stage 114 is allowed to act as a
free
rotating disk, and driven only by the fluidic coupling provided by fluid
rotation caused
by the inner impeller stage 112 and thereby improves the operating efficiency
of the
pump 100.
In other instances, it may be desired to control the rotational speed of the
outer stage 114 by using both the fluid coupling and the outer stage drive
motor 180.
In such instances, the outer impeller stage 114 is rotated faster or slower
than the
inner impeller stage, however, optimized pump performance can be controlled
through selective, independent drive of the outer impeller stage.
By locating the outer impeller stage 114 in concentric relation with the inner
impeller stage 112, the fluid is first pressurized by the inner impeller
stage, exits
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outlet 118, and is fed to inlet of the radial passage 144 of the outer
impeller stage.
Upon exiting the outer impeller stage, the energized fluid enters the
stationary
diffuser and ultimately reaches the discharge or outlet of the fluid pump.
The concentric arrangement provides for a compact package of a high speed
centrifugal pump that includes a start stage. In addition, by independently
driving the
inner and outer impeller stages, reduced impeller fluid friction drag due to a
free
rotating disk action during normal operation is achieved. Likewise, there is
an
increased ability to receive flow at the stationary radial diffuser and shape
the diffuser
pressure recovery characteristics due to lower outer stage rotational speed.
As a
result, pump performance can be optimized relative to the ratio of impeller
drive
speeds (i.e., N1 vs. N2). Further, pump performance can be optimized via the
ratio
of pressure rise from each impeller stage. All of this is achieved in a pump
package
volume that is minimized and a multistage pump that has a reduced weight while
still
incorporating a start stage.
The disclosure has been described with reference to the preferred
embodiments. Modifications and alterations will occur to others upon reading
and
understanding this specification. It is intended to include all such
modifications and
alterations in so far as they come within the scope of the appended claims or
the
equivalents thereof.
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COMPONENT NUMBER PART
100 centrifugal pump assembly
102 Housing
104 inlet (axial)
106 pump chamber/cavity
110 rotary pump
112 1 s /inner impeller stage
114 2" /outer impeller stage
116 axial passage
118 radial outlet
120 driver assembly
122 drive shaft
124 first bearing
126 second bearing
128 seals
140 front seal
142 rear seal
144 radial passage
150 Diffuser
152 Discharge
154 recess
156 first axial portion
158 outer stage bearing
160 first front seal
162 second axial portion
164 outer stage bearing
166 second/rear seal
180 I outer stage drive motor
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