US20080232954A1

US20080232954A1 - Vacuum system for conveying a high amount of supplemental liquid

Info

Publication number: US20080232954A1
Application number: US11/755,157
Authority: US
Inventors: Rudi Dittmar
Original assignee: Gardner Denver Deutschland GmbH
Current assignee: Gardner Denver Deutschland GmbH
Priority date: 2007-03-20
Filing date: 2007-05-30
Publication date: 2008-09-25
Also published as: DE102007013872A1; ITMI20071529A1; CN101270765A

Abstract

A pump apparatus for conveying a gas-liquid mixture comprises a first pump (7) for conveying gas with a first pump chamber (28) and a first impeller (33), a second pump (11) for conveying liquid with a second pump chamber (36) and a second impeller (41), and a drive device (2) with a rotary-driveable drive shaft (4) for driving the pumps (7, 1 1), the drive shaft (4) being connected to both impellers (33, 41).

Description

The present application claims foreign priority from DE Application 102007013872.7 filed Mar. 20, 2007.

FIELD

The invention relates to a pump apparatus for producing a vacuum while simultaneously conveying liquids.

BACKGROUND

Liquid ring pumps are widely used for producing a vacuum. These pumps convey gas in a highly efficient manner. However, it is a disadvantage that they are only restrictedly suitable for conveying liquids. If the ratio by volume between the liquid to be conveyed and the gas to be conveyed exceeds a value of approximately 5%, there ensue gravitational phenomena, noise disturbance and an extreme mechanical strain on the pump components leading to blockage, motor overload or damage to the pump.
The use of a second separate pump for conveying liquids entails an increased spatial requirement, is unfavourable in terms of energy and is associated with high operating and fixed costs.

SUMMARY OF THE DISCLOSURE

The object of the invention is therefore to provide a pump apparatus for producing a vacuum while simultaneously conveying liquids.
This object is achieved by the features of claim 1. The invention forms a single-phase combination of a vacuum pump and a pump for conveying liquid. The pump apparatus according to the invention is particularly compact, it provides an efficiency which is higher by up to 30% than a liquid-conveying liquid ring pump of a comparable size, it does not require any additional control elements and it protects the vacuum pump against overloading due to an excessive amount of liquid to be conveyed. Other advantages of the invention are provided. Features and details of the invention are provided in the description of two embodiments with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective view of a pump apparatus according to one embodiment,

FIG. 2 a front view of the pump apparatus according to FIG. 1,

FIG. 3 a side view of the pump apparatus according to FIG. 1,

FIG. 4 a plan view of the pump apparatus according to FIG. 1,

FIG. 5 a longitudinal section through the pump chambers of the pump apparatus according to FIG. 1,

FIG. 6 a schematic view of the flow sequences during operation of the pump apparatus according to FIG. 1, and

FIG. 7 a schematic view of the flow sequences during operation of the pump apparatus according to a second embodiment.

DETAILED DESCRIPTION

One embodiment of the invention is described hereinafter with reference to FIGS. 1 to 5. A pump apparatus 1 includes a drive device configured as a motor 2 with a drive shaft 4 oriented along the axis of rotation 3, a motor housing 5 and a base 6. The pump apparatus 1 also includes a first pump 7 for producing a vacuum with a first suction connecting piece 8 and a first outlet connecting piece 9, as well as a first pump housing 10. The first pump 7 is configured in particular as a liquid ring pump.
Furthermore, the pump apparatus 1 includes a second pump 11 for conveying liquid with a second suction connecting piece 12, a second outlet connecting piece 13 and a second pump housing 14. The second pump 11 is configured as a side channel pump and is self-priming. However, the second pump 11 may also be configured as any other pump which is suitable for conveying liquids.
Finally, the pump apparatus 1 includes a first supply line 15 with a first liquid separator 16, a first discharge line 17 for further conveying gas with a second liquid separator 18, a second supply line 19 as well as a second discharge line 20 for further conveying liquid.
In more detail, the first supply line 15 is connected to the first suction connecting piece 8 via a first supply line flange 21. The first supply line 15 has a controllable inlet 44 for supplying operational liquid to the first pump 7. The first discharge line 17 is connected to the first outlet connecting piece 9 via a first discharge line flange 22. The second supply line 19 is connected to the second suction connecting piece 12 by a second supply line flange 23 and the second discharge line 20 is connected to the second outlet connecting piece 13 by a second discharge line flange 24. Finally, the end of the second supply line 19, opposite the second suction connecting piece 12, is connected to the first liquid separator 16 via a first separator flange 25.
The second discharge line 20 is T-shaped and is connected to the second liquid separator 18 via a connecting piece 26 which forms one arm of the T-shaped piece. All the flange connections 21, 22, 23, 24, 25 and 27 are configured to be gas-tight and, in particular, liquid-tight. Moreover, the pump apparatus 1 has a main supply line 45 and a gas discharge line 46. The main supply line 45 opens on the pump side into the first liquid separator 16. The gas discharge line 46 opens on the pump side into the second liquid separator 18.
The liquid separators 16, 18 are configured as gravity separators. They may also be formed by a simple pipe which allows the pump apparatus 1 to be constructed in a particularly economical manner.
The first pump housing 10 is configured substantially in the shape of a hollow cylinder. It is positioned eccentrically to the drive shaft 4. The second pump housing 14 is also configured to be substantially in the shape of a hollow cylinder and is positioned concentrically to the drive shaft 4.
The first pump 7 has a first pump chamber 28 which is outwardly sealed off in a gas and liquid-tight manner from the first pump housing 10 over its periphery as well as on its side facing the motor 2. On the side remote from the motor 2, the first pump chamber 28 is delimited by a first cover plate 29 belonging to the first pump housing 10. The first cover plate 19 has a first suction opening 30, a first outlet opening 31 and a first connection opening 32. In this arrangement, the first suction connecting piece 8 is connected in terms of flow with the first suction opening 30. The first outlet connecting piece 9 is connected in terms of flow with the first outlet opening 31. On the side, remote from the first pump chamber 28, of the first cover plate 29, the pressure and the suction sides of the first pump 7 are separated by a partition wall (not shown in the figures).
The first pump chamber 28 is positioned eccentrically to the drive shaft 4. The drive shaft 4 is guided through the first pump chamber 28 and is sealed off from the first pump housing 10 and from the first cover plate 29. A first impeller 33 is positioned on the drive shaft 4 in the first pump chamber 28. The first impeller 33 sits in particular in a “floating” manner on the drive shaft 4. On the side, facing the motor 2, of the first pump housing 10, the passage of the drive shaft 4 through the housing 10 is sealed by a seal 34, configured as a sliding ring seal.
The first cover plate 29 is sealed peripherally by an O ring 35 from the first pump housing 10 and the second pump housing 14.
The second pump housing 14 adjoins the side, remote from the motor 2, of the first pump housing 10 in the direction of the axis of rotation 3. This arrangement allows the pump apparatus 1 to be constructed in a particularly compact manner.
The diameter of the drive shaft 4 tapers slightly in the region of the first cover plate 29.
The second pump 11 has a second pump chamber 36. The second pump chamber 36 is substantially delimited on its side facing the motor 2 by a partition wall 37 formed integrally with the second pump housing 14. The second pump chamber 36 is delimited peripherally by the second pump housing 14. On its side opposite the partition wall 37 in the direction of the axis of rotation 3, the second pump chamber 36 is delimited by a cover shield 38 which belongs to the second pump housing 14 and is connected to the second pump housing 14 in a gas and liquid-tight manner. The cover shield 38 has a seat 39 for receiving the end of the drive shaft 4 remote from the motor 2. The drive shaft 4 may be mounted in the seat 39 by a bearing (not shown in the figures). The cover shield 38 also has on its side facing the motor 2 a channel-type annular groove which forms a side channel 40 and is part of the second pump chamber 36. To avoid undesirable vortex formations, it is provided that the outer boundary wall of the side channel 3 is configured so as to align with the inner wall of the second pump housing 14. The side channel 40 has a break in the peripheral direction. A second impeller 41 is mounted on the drive shaft 4 in the second pump chamber 36. Said second impeller 41 sits in a closely sliding manner on the drive shaft 4. To avoid tolerance problems, it is configured to be self-adjusting in the axial direction of the drive shaft 4.
The second suction connecting piece 12 and the second outlet connecting piece 13 are connected in terms of flow with the second pump chamber 36. The partition wall 37 has a second connection opening 42. The first connection opening 32, the second connection opening 42 and a connection line 43 form a throughflow connection 47 between the outer region of the first pump chamber 28 and the second pump chamber 36. The connection line 43 is configured, for example, as a cast channel.
The first pump housing 10 and the second pump housing 14 are made of grey cast iron, the impellers 33, 34 are made of bronze and the drive shaft 4 is made of stainless steel to prevent cavitational damage and corrosion. Provision is also made for the impellers 33, 41 and the housings 10, 14 to be made of stainless steel for certain applications. Alternative materials are possible, depending on the determined use of the pump apparatus 1.
The operation of the pump apparatus 1 can be understood with reference to FIG. 6. Although the flow sequences during operation of the pump apparatus 1 are shown schematically in FIG. 6, they have been given the reference numerals of the respectively associated constructive elements of the pump apparatus 1 in order to make these sequences more readily comprehensible.
A liquid-gas mixture is drawn up by suction through the main supply line 45 from a process chamber 48. A pressure Ps prevails in the main supply line 45. The liquid, drawn up by suction, collects in the bottom of the first liquid separator 16 due to gravity, as a result of which the liquid-gas mixture is at least partly separated into its two components of liquid and gas. The gas which may contain a residual amount of liquid, is then drawn up by suction via the first supply line 15 by the first pump 7 into the first pump chamber 28 via the first suction connecting piece 8. The rotation of the first impeller 33 driven by the motor 2 via the drive shaft 4 forces the operational liquid in the first pump chamber 28 of the first pump 7 onto the peripheral boundary of the first pump chamber 28 away from the axis of rotation 3 due to the centrifugal force. Consequently, the operational liquid of the first pump 7 forms a liquid ring in the outer region of the first pump chamber 28. This results in chambers which are sealed in a gas-tight manner and are delimited by the liquid ring on the one hand and by the first impeller 33 on the other hand. The volume of the chambers changes periodically during rotation of the first impeller 33 about the axis of rotation 3 due to the eccentric arrangement of the first pump chamber 28 in respect of the drive shaft 4. The periodical change in volume is associated with a periodic fluctuation in pressure. Positioned in the region in which the chambers have the lowest volume and thus the highest pressure is the first outlet opening 31, through which the gas leaves the first pump 7 with a pressure p_D>p_s.
The residual process liquid or operational liquid of the pump present in the gas after passing through the first pump 7 is separated from the gas in the second liquid separator 8, before the gas is further conveyed through the gas discharge line 46. The liquid separated in the second liquid separator 18 is introduced into the second discharge line 20 via the connection piece 26 and is there further conveyed together with the liquid discharged from the second pump 11.
The liquid separated in the first liquid separator 16 is drawn up by suction into the second pump chamber 36 through the second suction connecting piece 12 by the second pump 11 via the second supply line 19. The second impeller 41 of the second pump 11 is driven by the same drive shaft 4 as the first impeller 33 of the first pump 7. The first pump 7 and the second pump 11 thus have a common drive shaft 4. The combination of the first pump 7 configured as a liquid ring pump and of the second pump 11 configured as a side channel pump is thus produced in a very compact, space-saving manner. After passing through the second pump 11, the conveyed liquid is guided into the second discharge line 20 through the second outlet connecting piece 13 and is further conveyed into and through said second discharge line 20.
Separating the liquid-gas mixture into a liquid fraction and a gas fraction in the first liquid separator 16 prevents the instantaneous liquid volume flow, drawn up by suction by the liquid ring pump, from exceeding a maximally admissible value of approximately 5% of the gas volume flow conveyed by the liquid ring pump. This ensures that the liquid ring pump always operates in a cavitation-free manner, irrespective of the amount of liquid to be conveyed. This means that damage to the pump components and overload of the motor 2 is avoided. At the same time, the pump apparatus 1 achieves an efficiency which is up to 30% higher than a liquid ring pump of a comparable size which also conveys a liquid.
The same pressure p_Dprevails in the second discharge line 20 as in the first discharge line 17. A pressure in the second discharge line 20 other than the pressure p_Din the first discharge line 17 is possible in principle, although it may lead to disturbing pressure compensation phenomena in the second liquid separator 18 and on both pressure sides of the pumps 7, 11.
Liquid from the liquid ring in the first pump chamber 28 may flow into the second pump chamber 36 through the connection 47. This eliminates the risk of the side channel pump running dry.
A complex, fully effective seal of the shaft between the two pump chambers 28, 36 is unnecessary, since the differences in pressure between the two pump chambers 28, 36 are marginal. A narrow gap seal thus suffices. A combination of liquid ring pump and side channel pump is particularly advantageous, since no specific control mechanism is required to operate the liquid-conveying second pump 11 due to the conveying characteristic of a side channel pump, compared, for example, to a centrifugal pump.
Another embodiment of the pump apparatus 1 is described hereinafter with reference to FIG. 7. The fundamental difference from the first embodiment is that two separate supply lines 15, 19 are provided instead of the main supply line 45 for drawing up by suction a liquid-gas mixture and a first liquid separator 16 for separating the conveyed liquid from the conveyed gas. The first supply line 15 is mainly used for conveying gas, the first pump 7 configured as a liquid ring pump ensuring that a vacuum is maintained in the process chamber 48. The second pump 11 configured as a self-priming pump, in particular as a side channel pump, conveys the liquid in the process chamber 48 using the second supply line 19. The throughflow connection 47 between the first pump 7 and the second pump 11 makes it possible to prevent the side channel pump from running dry where there is a small amount of liquid and thus prevents possible damage to the seal.

Claims

1. The pump apparatus for conveying a gas-liquid mixture comprising

a. a first pump for conveying gas having

i. a first pump chamber and

ii. a first impeller,

b. a second pump for conveying liquid having

i. a second pump chamber and

ii. a second impeller, and

c. a drive device with a rotary-driveable drive shaft for driving the pumps,

d. the drive shaft being connected to both impellers.

2. The pump apparatus according to claim 1, wherein the first pump is configured as a liquid ring pump.

3. The pump apparatus according to claim 1, wherein the second pump is self-priming.

4. The pump apparatus according to claim 1, wherein the second pump is configured as a side channel pump.

5. The pump apparatus according to claim 1, further comprising at least one liquid separator provided for separating the conveyed liquid from the conveyed gas.

6. The pump apparatus according to claim 5, wherein the at least one liquid separator is positioned on the suction side with respect to the pumps.

7. The pump apparatus according to claims 6, further comprising a second liquid separator positioned on the outlet side.

8. The pump apparatus according to claim 7, wherein at least one of said separators is configured as a gravity separator.