U.S. patent application number 17/202607 was filed with the patent office on 2021-10-21 for centrifugal pump for conveying a fluid.
The applicant listed for this patent is Sulzer Management AG. Invention is credited to Daniele CIMMINO, Arnaldo RODRIGUES, Thomas WELSCHINGER, Marc WIDMER.
Application Number | 20210324862 17/202607 |
Document ID | / |
Family ID | 1000005479866 |
Filed Date | 2021-10-21 |
United States Patent
Application |
20210324862 |
Kind Code |
A1 |
WIDMER; Marc ; et
al. |
October 21, 2021 |
CENTRIFUGAL PUMP FOR CONVEYING A FLUID
Abstract
A centrifugal pump for conveying a fluid includes a pump
housing, an impeller to convey the fluid from an inlet to an
outlet, a shaft to rotate the impeller, a first sealing device to
seal the shaft at a suction side, a second sealing device to seal
the shaft at a discharge side, a balance drum connected to the
shaft between the impeller and the second sealing device, the
balance drum defining a front side facing the at least one impeller
and a back side facing the second sealing device, a relief passage
between the balance drum and a stationary part, a balance line
connecting the back side with the suction side, a discharge opening
arranged at the relief passage between the front side and the back
side, and a connecting line connecting the discharge opening with
the first sealing device.
Inventors: |
WIDMER; Marc; (Winterthur,
CH) ; RODRIGUES; Arnaldo; (Winterthur, CH) ;
CIMMINO; Daniele; (Figino, CH) ; WELSCHINGER;
Thomas; (Radolfzell, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sulzer Management AG |
Winterthur |
|
CH |
|
|
Family ID: |
1000005479866 |
Appl. No.: |
17/202607 |
Filed: |
March 16, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 29/043 20130101;
F04D 29/22 20130101; F04D 29/106 20130101; F04D 1/06 20130101; F04D
15/0022 20130101 |
International
Class: |
F04D 15/00 20060101
F04D015/00; F04D 1/06 20060101 F04D001/06; F04D 29/22 20060101
F04D029/22; F04D 29/10 20060101 F04D029/10; F04D 29/043 20060101
F04D029/043 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2020 |
EP |
20169858.6 |
Claims
1. A centrifugal pump for conveying a fluid, comprising: a pump
housing with an inlet at a suction side and an outlet at a
discharge side; at least one impeller configured to convey the
fluid from the inlet to the outlet; a shaft configured to rotate
the impeller about an axial direction; a first sealing device
configured to seal the shaft at the suction side; a second sealing
device configured to seal the shaft at the discharge side; a
balance drum fixedly connected to the shaft and arranged between
the at least one impeller and the second sealing device, the
balance drum defining a front side facing the at least one impeller
and a back side facing the second sealing device; a relief passage
disposed between the balance drum and a stationary part configured
to be stationary with respect to the pump housing, the relief
passage extending from the front side to the back side; a balance
line connecting the back side with the suction side; a discharge
opening arranged at the relief passage between the front side and
the back side; and a connecting line connecting the discharge
opening with the first sealing device.
2. The centrifugal pump in accordance with claim 1, wherein the
connecting line comprises at least one flow controller configured
to control the flow through the connecting line.
3. The centrifugal pump in accordance with claim 1, wherein the
connecting line comprises a first branch and a second branch, the
first branch connected with the first sealing device, and the
second branch connected with the second sealing device.
4. The centrifugal pump in accordance with claim 3, wherein the
first branch comprises a first flow controller configured to
control the flow through the first branch, and the second branch
comprises a second flow controller configured to control the flow
through the second branch.
5. The centrifugal pump in accordance with claim 3, wherein the
connecting line comprises a third branch, the third branch is
connected to the suction side.
6. The centrifugal pump in accordance with claim 5, wherein the
third branch comprises a third flow controller configured to
control the flow through the third branch.
7. The centrifugal pump in accordance with claim 6, wherein at
least one of the flow controllers is an adjustable valve.
8. The centrifugal pump in accordance with claim 2, wherein the at
least one flow controller includes a plurality of flow controllers
and each flow controller is an adjustable valve.
9. The centrifugal pump in accordance with claim 1, wherein the
first sealing device comprises a mechanical seal.
10. The centrifugal pump in accordance with claim 1, wherein the
second sealing device comprises a mechanical seal.
11. The centrifugal pump in accordance with claim 1, wherein the
pump is a multistage pump and the at least one impeller includes a
plurality of impellers, and the impellers are arranged one after
another on the shaft.
12. The centrifugal pump in accordance with claim 11, wherein the
pump is a between-bearing pump.
13. The centrifugal pump in accordance with claim 11, further
comprising an outer barrel casing, in which the pump housing is
arranged.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to European Patent
Application No. 20169858.6, filed Apr. 16, 2020, the contents of
which are hereby incorporated herein by reference in their
entirety.
BACKGROUND
Field of the Invention
[0002] The invention relates to a centrifugal pump for conveying a
fluid.
Background Information
[0003] Conventional centrifugal pumps for conveying a fluid, for
example a liquid such as water, are used in many different
industries. Some examples are the oil and gas industry, the power
generation industry, the chemical industry, the water industry or
the pulp and paper industry. Centrifugal pumps generally have at
least one impeller and a shaft for rotating the impeller. The at
least one impeller can be configured for example as a radial
impeller or as an axial or semi-axial impeller or as a helicoaxial
impeller. Furthermore, the impeller can be configured as an open
impeller or as a closed impeller, where a shroud is provided on the
impeller, the shroud at least partially covering the vanes of the
impeller.
[0004] A centrifugal pump can be designed as a single stage pump
having only one impeller mounted to the shaft or as a multistage
pump comprising a plurality of impellers, wherein the impellers are
arranged in series on the shaft.
[0005] Many centrifugal pumps include at least one balancing device
for at least partially balancing the axial thrust that is generated
by the impeller(s) during operation of the pump. The balancing
device reduces the axial thrust that is acting on the axial bearing
or the thrust bearing. The balancing device can comprise a balance
drum for at least partially balancing the axial thrust that is
generated by the rotating impellers. The balance drum is fixedly
connected to the shaft of the pump in a torque proof manner.
Usually, the balance drum is arranged at the discharge side of the
pump between the last stage impeller and a shaft sealing device.
The balance drum defines a front side and a back side. The front
side is the side facing the last stage impeller. The back side is
the side facing the shaft sealing device. A relief passage is
disposed between the balance drum and a stationary part that is
stationary with respect to the pump housing. The back side is
usually connected to the suction side of the pump by a balance
line. During operation there is a leakage flow through the relief
passage from the front side along the balance drum to the back side
and from there through the balance line to the suction side. At the
front side of the balance drum the high pressure or the discharge
pressure prevails, and at the back side essentially the suction
pressure prevails. The pressure difference between the front side
and the back side results in a axial force or an axial thrust which
is directed in the opposite direction as the axial thrust generated
by the rotating impeller(s). Thus, the axial thrust that has to be
carried by the axial or thrust bearing is at least considerably
reduced. Of course, the leakage flow along the balance drum results
in a decrease of the hydraulic performance or efficiency of the
pump. Therefore, the relief passage is configured such, that the
leakage flow is as low as possible but still sufficient for
generating the axial thrust counteracting the axial thrust
generated by the impeller(s).
SUMMARY
[0006] A centrifugal pump generally has at least one shaft seal
device for sealing the shaft against a leakage of the fluid along
the shaft. In a so-called between-bearing design the rotating shaft
and all impellers are arranged between two shaft sealing devices,
which are typically arranged next to the bearings at the drive end
and at the non-drive end of the shaft, respectively.
[0007] The sealing devices can be configured for example as a
mechanical seal. Typically, a mechanical seal comprises a stator
and a rotor. The rotor is connected in a torque-proof manner with
the shaft of the pump and the stator is fixed with respect to the
pump housing such that the stator is secured against rotation.
During rotation of the shaft the rotor is in sliding contact with
the stator thus performing the sealing action. A liquid, e.g. the
fluid conveyed by the pump or any other lubricant is supplied to
the mechanical seal for generating a fluid film between the stator
and the rotor.
[0008] A sealing device such as a mechanical seal requires cooling
for removing the heat from the sealing device, as well as flushing
to keep particles away from the sealing elements. Therefore a
certain flow is required for cooling and flushing. It is a known
measure that the flow required to flush and to cool the sealing
devices is extracted either at or near the outlet of the pump or at
an intermediate stage of the pump. This required flow for flushing
the sealing devices causes additional losses which reduces the
efficiency of the pump.
[0009] Nowadays many applications strived for the most efficient
use of the pump. It is desirable to have the highest possible ratio
of the power, especially the hydraulic power, delivered by the pump
to the power needed for driving the pump. This desire is mainly
based upon an increased awareness of environment protection and a
responsible dealing with the available resources as well as on the
increasing costs of energy.
[0010] It is therefore an object of the invention to propose a
centrifugal pump for conveying a fluid, having a high efficiency
without a reduction in the operating safety of the pump.
[0011] The subject matter of the invention satisfying these objects
is characterized by the features described herein.
[0012] Thus, according to an embodiment of the invention, a
centrifugal pump for conveying a fluid is proposed, comprising a
pump housing with an inlet at a suction side and an outlet at a
discharge side, at least one impeller for conveying the fluid from
the inlet to the outlet, a shaft for rotating the impeller about an
axial direction, a first sealing device for sealing the shaft at
the suction side, a second sealing device for sealing the shaft at
the discharge side, a balance drum fixedly connected to the shaft
and arranged between the at least one impeller and the second
sealing device, wherein the balance drum defines a front side
facing the at least one impeller and a back side facing the second
sealing device, wherein a relief passage is disposed between the
balance drum and a stationary part configured to be stationary with
respect to the pump housing, wherein the relief passage extends
from the front side to the back side, wherein a balance line is
provided connecting the back side with the suction side, wherein a
discharge opening is arranged at the relief passage between the
front side and the back side, and wherein a connecting line is
provided for connecting the discharge opening with the first
sealing device.
[0013] Thus, a part of the flow passing through the relief passage
along the balance drum is guided away from the relief passage
through the connecting line to the first sealing device and used
for flushing and cooling the first sealing device. Therefore, there
is no need to extract an additional flow of the fluid e.g. at the
discharge side or at an intermediate stage of the pump. This
results in an increase of the efficiency of the pump, because only
the unavoidable leakage flow through the relief passage is used for
flushing the first sealing device. There is no need for an
additional take-off of pressurized fluid in order to flush the
first sealing device.
[0014] At the first sealing device, or in the first seal
housing/chamber, respectively, a pressure prevails that is at most
slightly higher than the suction pressure at the suction side of
the pump. The pressure at the discharge opening in the relief
passage is considerably higher than the suction pressure. Therefore
the flow of fluid in the connecting line is directed towards the
first sealing device and can be used for flushing the first sealing
device.
[0015] Preferably, the connecting line comprises at least one flow
control element for controlling the flow through the connecting
line. This has the advantage that the volumetric flow for flushing
the first sealing device can be adjusted. The flow control element
can be, for example, a valve or an orifice.
[0016] In order to make the pump even more efficient it is
preferred that the connecting line comprises a first branch and a
second branch, wherein the first branch is connected with the first
sealing device, and the second branch is connected with the second
sealing device. Thus, the flow discharged from the relief passage
through the discharge opening and the connecting line is
additionally used to also flush the second sealing device.
[0017] According to a preferred configuration, the first branch
comprises a first flow control element for controlling the flow
through the first branch, and the second branch comprises a second
flow control element for controlling the flow through the second
branch. By this measure both the flow to the first sealing device
and the flow to the second sealing device can be controlled.
[0018] Furthermore, it is preferred that the connecting line
comprises a third branch, wherein the third branch is connected to
the suction side. The third branch can be connected for example to
the inlet of the pump or to the balance line or to a suction tank
being in fluid communication with the inlet of the pump. By the
third branch, the flow extracted from the relief passage can be
routed directly back to the suction side, i.e. without passing
through one of the sealing devices, for example if the extracted
flow exceeds the required flow for the sealing devices or if the
pressure requires an adjustment. The third branch is particularly
advantageous to adjust the leakage flow through the relief
passage.
[0019] Preferably, the third branch comprises a third flow control
element for controlling the flow through the third branch.
[0020] According to a preferred design at least one of the flow
control elements is configured as an adjustable valve.
[0021] For many embodiments it is advantageous that each flow
control element is configured as an adjustable valve.
[0022] Preferably, the first sealing device comprises a mechanical
seal.
[0023] It is also preferred that the second sealing device
comprises a mechanical seal.
[0024] According to a preferred embodiment the pump is configured
as a multistage pump having a plurality of impellers, wherein the
impellers are arranged one after another on the shaft.
[0025] Furthermore, it is preferred that the pump is configured as
a between-bearing pump.
[0026] In particular, the pump can be configured as a barrel type
pump comprising an outer barrel casing, in which the pump housing
is arranged.
[0027] Further advantageous measures and embodiments of the
invention will become apparent from the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention will be explained in more detail hereinafter
with reference to the drawings.
[0029] FIG. 1 is a schematic cross-sectional view of an embodiment
of a centrifugal pump according to the invention, and
[0030] FIG. 2 is a cross-sectional view illustrating a
configuration of the balance drum and the connecting line.
DETAILED DESCRIPTION
[0031] FIG. 1 shows a schematic cross-sectional view of an
embodiment of a centrifugal pump according to the invention, which
is designated in its entity with reference numeral 1. The pump 1 is
designed as a centrifugal pump for conveying a fluid, for example a
liquid such as water.
[0032] The centrifugal pump 1 comprises a pump housing 2 having an
inlet 3 and an outlet 4 for the fluid to be conveyed. The inlet 3
is arranged at a suction side S, where a suction pressure prevails,
and the outlet 4 is arranged at a discharge side D, where a
discharge pressure prevails. The suction pressure is also referred
to as low pressure, and the discharge pressure is also referred to
as high pressure. The centrifugal pump 1 further comprises at least
one impeller 5, 51 for conveying the fluid from the inlet 3 to the
outlet 4 as indicated by the dashed arrows without reference
numerals, as well as a shaft 6 for rotating each impeller 5, 51
about an axial direction A. The axial direction A is defined by the
axis of the shaft 6. Each impeller 5, 51 is mounted to the shaft 6
in a torque proof manner. The shaft 6 has a drive end 61, which can
be connected to a drive unit (not shown) for driving the rotation
of the shaft 6 about the axial direction. The drive unit can
comprise, for example, an electric motor. The other end of the
shaft 6 is referred to as non-drive end 62.
[0033] In the following description reference is made by way of
example to an embodiment, which is suited for many applications,
namely that the centrifugal pump 1 is configured as a multistage
pump 1 having a plurality of impellers 5, 51, wherein the impellers
5, 51 are arranged one after another on the shaft 6. The reference
numeral 51 designates the last stage impeller 51, which is the
impeller 51 closest to the outlet 4. The last stage impeller 51
pressurizes the fluid to the discharge pressure. The embodiment
shown in FIG. 1 has nine stages, which has to be understood
exemplary. The plurality of impellers 5, 51 can be arranged in an
in-line configuration as shown in FIG. 1 or in a back-to-back
configuration.
[0034] The multistage centrifugal pump 1 shown in FIG. 1 is
designed as a horizontal pump, meaning that during operation the
shaft 6 is extending horizontally, i.e. the axial direction A is
perpendicular to the direction of gravity. In particular, the
centrifugal pump 1 shown in FIG. 1 can be designed as a horizontal
barrel casing multistage pump 1, i.e. as a double-casing pump. The
multistage pump 1 can be designed, for example, as a pump 1 of the
pump type BB5 according to API 610. When configured as a BB5 type
pump, the centrifugal pump 1 comprises an outer barrel casing 100,
in which the pump housing 2 is arranged.
[0035] It has to be understood that the invention is not restricted
to this type of centrifugal pump 1. In other embodiments, the
centrifugal pump can be configured without an outer barrel casing,
for example as a BB4 type pump, or as an axially split multistage
pump, or as a single stage pump, or as a vertical pump, meaning
that during operation the shaft 6 is extending in the vertical
direction, which is the direction of gravity, or as any other type
of centrifugal pump.
[0036] The centrifugal pump 1 comprises bearings on both sides of
the plurality of impellers 5, 51 (with respect to the axial
direction A), i.e. the centrifugal pump 1 is designed as a
between-bearing pump. A first radial bearing 81, a second radial
bearing 82 and an axial bearing 83 are provided for supporting the
shaft 6. The first radial bearing 81 is arranged adjacent to the
drive end 61 of the shaft 6. The second radial bearing 82 is
arranged adjacent or at the non-drive end 62 of the shaft 6. The
axial bearing 83 is arranged between the plurality of impellers 5,
51 and the first radial bearing 81 adjacent to the first radial
bearing 81. The bearings 81, 82, 83 are configured to support the
shaft 6 both in the axial direction A and in a radial direction,
which is a direction perpendicular to the axial direction A. The
radial bearings 81 and 82 are supporting the shaft 6 with respect
to the radial direction, and the axial bearing 83 is supporting the
shaft 6 with respect to the axial direction A. The first radial
bearing 81 and the axial bearing 83 are arranged such that the
first radial bearing 81 is closer to the drive end 61 of the shaft
6. Of course, it is also possible to exchange the position of the
first radial bearing 81 and the axial bearing 83, i.e. to arrange
the first radial bearing 81 between the axial bearing 83 and the
plurality of impellers 5, 51, so that the axial bearing 83 is
closer to the drive end 61 of the shaft 6.
[0037] A radial bearing, such as the first or the second radial
bearing 81 or 82 is also referred to as a "journal bearing" and an
axial bearing, such as the axial bearing 83, is also referred to as
an "thrust bearing". The first radial bearing 81 and the axial
bearing 83 can be configured as separate bearings as shown in FIG.
1, but it is also possible that the first radial bearing 81 and the
axial bearing 83 are configured as a single combined radial and
axial bearing supporting the shaft both in radial and in axial
direction.
[0038] The second radial bearing 82 supports the shaft 6 in the
radial direction. In the embodiment shown in FIG. 1, there is no
axial bearing provided at the non-drive end 62 of the pump shaft 6.
Of course, in other embodiments it is also possible that an axial
bearing for the shaft 6 is provided at the non-drive end 62. In
embodiments, where an axial bearing is provided at the non-drive
end 62, a second axial bearing can be provided at the drive end 61
or the drive end 61 can be configured without an axial bearing.
[0039] The centrifugal pump 1 further comprises two sealing
devices, namely a first sealing device 91 for sealing the shaft 6
at the suction side S and a second sealing device 92 for sealing
the shaft 6 at the discharge side D. With respect to the axial
direction A the first sealing device 91 is arranged between the
plurality of impellers 5 an the second radial bearing 82, and the
second sealing device 92 is arranged between the last stage
impeller 51 and the axial pump bearing 83. Both sealing devices 91,
92 seal the shaft 6 against a leakage of the fluid along the shaft
6 e.g. into the environment. Furthermore, by the sealing devices 91
and 92 the fluid can be prevented from entering the bearings 81,
82, 83. Preferably each sealing device 91, 92 comprises a
mechanical seal. Mechanical seals are well-known in the art in many
different embodiments and therefore require no detailed
explanation. In principle, a mechanical seal is a seal for a
rotating shaft 6 and comprises a rotor fixed to the shaft 6 and
rotating with the shaft 6, as well as a stationary stator fixed
with respect to the pump housing 2. During operation the rotor and
the stator are sliding along each other--usually with a liquid as
lubricant there between--for providing a sealing action to prevent
the fluid from escaping to the environment or entering the bearings
81, 82, 83. In many embodiments a separate bearing isolator is
provided which prevents liquids or solids to enter the bearings 81,
82, 83. In such embodiments where separate bearing isolators are
provided, the sealing devices 91, 92, e.g. the mechanical seals
prevent the fluid from leaking into the environment.
[0040] The centrifugal pump 1 further comprises a balance drum 7
for at least partially balancing the axial thrust that is generated
by the impellers 5, 51 during operation of the centrifugal pump 1.
The balance drum 7 is fixedly connected to the shaft 6 in a torque
proof manner. The balance drum 7 is arranged at the discharge side
D between the last stage impeller 51 and the second sealing device
92. The balance drum 7 defines a front side 71 and a back side 72.
The front side 71 is the side facing the last stage impeller 51.
The back side 72 is the side facing the second sealing device 92.
The balance drum 7 is surrounded by a stationary part 21, so that a
relief passage 73 is formed between the radially outer surface of
the balance drum 7 and the stationary part 21. The stationary part
21 is configured to be stationary with respect to the pump housing
2. The relief passage 73 forms an annular gap between the outer
surface of the balance drum 7 and the stationary part 21 and
extends from the front side 71 to the back side 72. The front side
71 is in fluid communication with the outlet 4, so that the axial
surface of the balance drum 7 facing the front side 71 is exposed
essentially to the discharge pressure prevailing at the outlet 4
during operation of the pump 1. Of course, due to smaller pressure
losses caused by the fluid communication between the outlet 4 and
the balance drum 7 the pressure prevailing at the axial surface of
the balance drum 7 facing the front side 71 can be somewhat smaller
than the discharge pressure. However, the considerably larger
pressure drop takes place over the balance drum 7. At the back side
72 a chamber 74 is provided, which is connected by a balance line
10 with the suction side S, e.g. with the inlet 3. The pressure in
the chamber 74 at the back side 72 is somewhat larger than the
suction pressure due to the pressure drop over the balance line 10
but considerably smaller than the discharge pressure.
[0041] Since the front side 71 is exposed essentially to the
discharge pressure at the outlet 4 a pressure drop exists over the
balance drum 7 resulting in a force that is directed to the right
side according to the representation in FIG. 1 and therewith
counteracts the axial thrust generated by the impellers 5, 51
during operation of the pump 1.
[0042] The balance line 10 recirculates the fluid from the chamber
74 at the back side 72 to the suction side S. A part of the
pressurized fluid passes from the front side 71 through the relief
passage 73 to the back side 72, enters the balance line 10 and is
recirculated to the suction side S of the centrifugal pump 1. The
balance line 10 constitutes a flow connection between the back side
72 and the suction side S at the pump inlet 3. The balance line 10
can be arranged--as shown in FIG. 1--outside the pump housing 2 and
inside the barrel casing 100. In other embodiments the balance line
10 can be designed as internal line completely extending within the
pump housing 2. In still other embodiments the balance line can be
arranged outside the barrel casing 100.
[0043] According to the invention, a discharge opening 70 is
arranged at the relief passage 73 between the front side 71 and the
back side 72 and a connecting line 40 connects the discharge
opening 70 with the first sealing device 91. Thus, a part of the
flow passing through the relief passage 73 enters the connecting
line 40 through the discharge opening 70 and is guided to the first
sealing device 91 for flushing and cooling the first sealing device
91. Due to the location of the discharge opening 70 between the
front side 71 and the back side 72 the pressure at the discharge
opening 70 is an intermediate pressure, which is smaller than the
discharge pressure at the outlet 4 of the pump 1 and larger than
the pressure in the chamber 74 at the back side 72 that is a bit
larger than the suction pressure at the suction side S of the
centrifugal pump 1. The pressure in the first sealing device 91,
e.g. the pressure in the sealing chamber of the mechanical seal, is
at most slightly higher than the suction pressure, so that this
pressure in the first sealing device 91 is considerably lower than
the intermediate pressure prevailing at the discharge opening 70.
Thus, the flow discharged through the connecting line 40 can be
used for flushing the first sealing device 91 in order to cool the
first sealing device 91 down and to keep particles away from the
sealing elements of the first sealing device 91. During operation
of the centrifugal pump 1 a volume of the pumped fluid is
constantly extracted from the relief passage 72, guided through the
connecting line 40 and injected into the first sealing device 91
for flushing. Consequently, there is no need to extract pressurized
fluid at any other location e.g. from the outlet 4 or at an
intermediate stage of the pump 1 for flushing the first sealing
device 91. Only a part of the unavoidable leakage flow through the
relief passage 73 along the balance drum 7 is used for flushing the
first sealing device 91. Therefore, the efficiency of the
centrifugal pump 1 is enhanced.
[0044] Referring now to FIG. 2 some preferred measures and variants
are explained, each of which can be realized in particular in the
embodiment shown in FIG. 1. Since it is sufficient for the
understanding, in FIG. 2 only one impeller is shown, which can be
for example the only impeller of a single stage pump or the last
stage impeller 51 of a multistage pump.
[0045] FIG. 2 shows a cross-sectional view illustrating a
configuration of the balance drum 7 and the connecting line 40. The
connecting line 40 as well as the balance line 10 are at least
partially represented as single lines in FIG. 2, wherein the
direction of flow through the particular line is indicated by the
arrows without reference numeral. The Fluid flowing through the
pump 1 is indicated by the dashed arrows without reference
numeral.
[0046] Preferably, the connecting line 40 comprises at least one
flow control element, namely a first flow control element (flow
controller) 45, for controlling the flow through the connecting
line 40 into the first sealing device 91. The first flow control
element 45 can be designed as a throttle or as a orifice or as a
valve such as a flow control valve or any other adjustable valve.
With the first flow control element 45 the flushing volumetric flow
injected into the first sealing device 91 can be adjusted.
[0047] As a further advantageous measure the connecting line 40 can
comprise a first branch 41 and a second branch 42, wherein the
first branch 41 is connected with the first sealing device 91, and
the second branch 42 is connected with the second sealing device
92. If the first flow control element 45 is provided in this
design, the first flow control element 45 is arranged in the first
branch 41.
[0048] Flushing both the first sealing device 91 and the second
sealing device 92 with the flow extracted from the relief passage
73 through the discharge opening 70 still increases the efficiency
of the centrifugal pump 1, because there is no need to extract the
flow for flushing the second sealing device 92 at any other
location of the centrifugal pump than at the discharge opening 70
in the relief passage 73. Since the second sealing device 92 faces
the chamber 74 at the back side 72 of the balance drum 7, the
pressure at or in the second sealing device 92 is at most as high
as the pressure at the back side 72, i.e. only slightly higher than
the suction pressure. Thus, the pressure in the second sealing
device 92, e.g. the pressure in the sealing chamber of the
mechanical seal of the second sealing device 92, is considerably
lower than the intermediate pressure at the discharge opening 70.
Thus, the flow taken from the discharge opening 70 and guided
through the connecting line 40 can be injected into the second
sealing device 92.
[0049] Preferably, the second branch 42 of the connecting line 40
comprises a second flow control element (flow controller) 46, for
controlling the flow through the second branch 42 into the second
sealing device 92. The second flow control element 46 can be
designed as a throttle or as a orifice or as a valve such as a flow
control valve or any other adjustable valve. With the second flow
control element 46 the flushing volumetric flow injected into the
second sealing device 92 can be adjusted.
[0050] It is a further preferred measure that the connecting line
40 comprises a third branch 43, wherein the third branch 43 is
connected to the suction side S. Thus, a part of the flow
discharged from the relief passage 73 through the discharge opening
70 can be directly recirculated to the suction side S without
passing through any of the sealing devices 91, 92. The third branch
43 can be connected for example to the inlet 3 of the centrifugal
pump 1 or to a tank, from which the fluid is supplied to the inlet
3 of the centrifugal pump 1. Furthermore, it is also possible, that
the third branch 43 leads into the balance line 10.
[0051] Optionally, the third branch 43 of the connecting line 40
comprises a third flow control element (flow controller) 47, for
controlling the flow through the third branch 43 leading to the
suction side S. The third flow control element 47 can be designed
as a throttle or as a orifice or as a valve such as a flow control
valve or any other adjustable valve.
[0052] It has to be noted that the preferred measures, in
particular those explained referring to FIG. 2, do not have to be
realized all together. Each of the measures can be realized
independently from the other measures. In addition, all
combinations of specific measures can be realized.
[0053] The centrifugal pump 1 renders possible to control and to
adjust the balancing flow passing through the relief passage 72 and
the balance line 10, i.e. the flow that is recirculated through the
balance line 10 can be adjusted. Said adjustment can be realized by
regulating the flow passing through the discharge opening 70 into
the connecting line 40. Thus, by controlling the flow through the
connecting line 40 the balance flow recirculated to the suction
side S can be adjusted. This is in particular advantageous for such
embodiments of the centrifugal pump 1, that are designed for high
to very high discharge pressures and a low discharge flow.
* * * * *