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:
[0001]    The present application claims foreign priority from DE Application 102007013872.7 filed Mar. 20, 2007. 
       FIELD  
       [0002]    The invention relates to a pump apparatus for producing a vacuum while simultaneously conveying liquids. 
       BACKGROUND  
       [0003]    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. 
         [0004]    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  
       [0005]    The object of the invention is therefore to provide a pump apparatus for producing a vacuum while simultaneously conveying liquids. 
         [0006]    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  
         [0007]      FIG. 1  a perspective view of a pump apparatus according to one embodiment, 
           [0008]      FIG. 2  a front view of the pump apparatus according to  FIG. 1 , 
           [0009]      FIG. 3  a side view of the pump apparatus according to  FIG. 1 , 
           [0010]      FIG. 4  a plan view of the pump apparatus according to  FIG. 1 , 
           [0011]      FIG. 5  a longitudinal section through the pump chambers of the pump apparatus according to  FIG. 1 , 
           [0012]      FIG. 6  a schematic view of the flow sequences during operation of the pump apparatus according to  FIG. 1 , and 
           [0013]      FIG. 7  a schematic view of the flow sequences during operation of the pump apparatus according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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 . 
         [0018]    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 . 
         [0019]    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. 
         [0020]    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 . 
         [0021]    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). 
         [0022]    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. 
         [0023]    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 . 
         [0024]    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. 
         [0025]    The diameter of the drive shaft  4  tapers slightly in the region of the first cover plate  29 . 
         [0026]    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 . 
         [0027]    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. 
         [0028]    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 . 
         [0029]    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. 
         [0030]    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 &gt;p s . 
         [0031]    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 . 
         [0032]    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 . 
         [0033]    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. 
         [0034]    The same pressure p D  prevails 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 D  in 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 . 
         [0035]    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. 
         [0036]    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. 
         [0037]    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.