Abstract:
An eccentric screw pump for delivering fluid and/or granular media. The pump body of the eccentric screw pump includes an inlet region, a pump unit and an outlet region. A drive unit is assigned to the inlet region. The pump unit includes a rotor and a stator, wherein the rotor moves eccentrically in the stator. The inlet region constitutes the suction side and the outlet region constitutes the pressure side of the eccentric screw pump. A bypass connection with at least one safety valve is assigned to the eccentric screw pump in order to take up and return back-flowing medium between the pressure side and the suction side of the eccentric screw pump. The bypass connection and the safety valve may also be integrated into the pump body of the eccentric screw pump.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an eccentric screw pump for delivering liquid and/or granular media and the use of such an eccentric screw pump. 
       BACKGROUND OF THE INVENTION 
       [0002]    Eccentric screw pumps are pumps for delivering a plurality of media, in particular viscous, highly viscous and abrasive media such as for example sludges, manure, crude oil and greases. Eccentric screw pumps known from the prior art comprise a rotor and a stator, wherein the rotor is accommodated in the stator and moves eccentrically in the stator. The stator is constituted by a housing with a helically coiled inner side. As a result of the motion of the rotor and mutual contact, meandering delivery spaces are formed between stator and rotor, by means of which liquid media can be transported along the stator. The rotor performs an eccentric rotary motion around the stator axis or around the longitudinal axis of the eccentric screw pump. The outer screw, i.e. the stator, has the form of a double thread, whilst the rotor screw is only single thread. Eccentric screw pumps are particularly well suited for the delivery of water, crude oil and a plurality of other liquids. The shape of the delivery spaces is constant during the motion of the rotor inside the stator, so that the delivered medium is not squashed. With a suitable design, not only fluids but also solids can be delivered with eccentric screw pumps. 
         [0003]    An excess pressure may arise in the eccentric screw pump during the delivery of certain media. For this application, eccentric screw pumps require at least one safety device against excess pressure. This is solved in the prior art by disposing a connection line between the inlet flange of the suction side of the pump body and the discharge flange of the pressure side. The connection line is an external pipeline and/or hose line into which an overflow or safety valve is integrated. 
         [0004]    A drawback with the described prior art is that the connection line represents an external attachment to the eccentric screw pump. On account of the necessary design height, therefore, the space requirement for the eccentric screw pump is increased. In addition, there is an increased risk of external attachments being damaged by moving loads. The requirement for safety devices against excess pressure has hitherto prevented the use of eccentric screw pumps in certain areas of application. For example, the use of eccentric screw pumps in boreholes could be advantageous. However, the space is limited here by the diameter of the borehole. In addition, there is the risk of an external pipeline on the eccentric screw pump being damaged when the eccentric screw pump is inserted into the borehole. 
         [0005]    The problem of the invention, therefore, is to make available an eccentric screw pump with at least one safety device against excess pressure, which is characterised by a simple and uncomplicated design and in particular does not exhibit the aforementioned drawbacks of the prior art. 
       SUMMARY OF THE INVENTION 
       [0006]    The above problem is solved by an eccentric screw in accordance with the invention. 
         [0007]    The invention relates to an eccentric screw pump for delivering fluids and/or granular media, in particular viscous, highly viscous and abrasive media. An eccentric screw pump comprises a pump body and a drive unit. The pump body is split up into an inlet region with an inlet connecting piece, a pump unit and an outlet region with an outlet connecting piece. The inlet connecting piece and the outlet connecting piece comprise standardised flanges for connection with further pipe sections for delivering the pumped medium. 
         [0008]    The pump unit is constituted by a rotor and a stator. The stator is constituted by a housing with a helically coiled inner side. The rotor is constituted as a kind of round threaded screw and moves eccentrically in the interior of the stator, as a result of which the delivery chambers constituted between the rotor and the stator are mobile in the delivery direction. 
         [0009]    The inlet region of the eccentric screw pump forms the suction side and the outlet region of the eccentric screw pump forms the pressure side. A bypass connection with at least one safety valve is disposed between the pressure side and the suction side. Said bypass line serves for the uptake and return of back-flowing medium between the pressure side and the suction side of the eccentric screw pump, in order to prevent an uncontrolled excess pressure from building up inside the eccentric screw pump. An excess pressure has to be reduced in a controlled manner in order to hinder or prevent damage to the eccentric screw pump. 
         [0010]    According to the invention, the bypass connection and the safety valve are integrated into the pump body of the eccentric screw pump. In particular, the bypass connection and the safety valve are integrated in the region of the pump unit into the pump body of the eccentric screw pump. 
         [0011]    According to a first preferred embodiment of the invention, the stator comprises an additional casing. In particular, the stator is disposed in a casing tube, wherein the stator has an outer circumference which is smaller than the inner circumference of the casing tube, so that an intermediate space is formed between the stator and the casing tube. Said intermediate space is in fluidic connection with the respective internal spaces of the inlet region and the outlet region and constitutes the bypass connection. Furthermore, at least one safety valve is assigned to the intermediate space. When an excess pressure builds up on the pressure side of the eccentric screw pump, part of the delivered medium is conveyed as a return flow via the intermediate space back into the inlet region of the pump body and the excess pressure is thus reduced. 
         [0012]    According to a second preferred embodiment of the invention, the stator is disposed in a stator sleeve. The inner circumference of the stator sleeve broadly corresponds to the outer circumference of the stator, so that the stator sleeve lies with its inner circumference extensively over its surface area against the outer circumference of the stator. At least one connection line parallel to the longitudinal axis of the eccentric screw pump is constituted between the stator and the stator sleeve. The connection line is in fluidic connection via first and second connections with the respective internal spaces of the inlet region and the outlet region and constitutes the bypass connection. The first and second connections are in particular bores in the housing of the pump body, in particular in the regions in which the outlet and inlet region each border on the pump unit. Furthermore, at least one safety valve is assigned to the at least one connection line. When an excess pressure builds up on the pressure side of the eccentric screw pump, part of the delivered medium is conveyed as a return flow via the at least one connection line back into the inlet region of the pump body. 
         [0013]    The at least one connection line between the stator and the stator sleeve is constituted for example by a continuous recess in the external lateral surface of the stator parallel to the longitudinal axis of the eccentric screw pump. For example, a continuous groove is constituted on the external lateral surface. The recess extends along a length of the stator, in particular along the entire length of the stator. 
         [0014]    According to a third preferred embodiment of the invention, the rotor comprises a hollow space along its rotor longitudinal axis. The hollow space can for example be a through-bore through the rotor along the rotor longitudinal axis. Alternatively, the hollow space can already be integrated into the rotor during production, whereby the latter is already cast correspondingly hollow or is moulded hollow by means of another suitable process. The hollow space of the rotor is in fluidic connection with the respective internal spaces of the inlet region and the outlet region and constitutes the bypass connection. At least one safety valve is assigned to the hollow space. When an excess pressure builds up on the pressure side of the eccentric screw pump, part of the delivered medium is conveyed as a return flow via the internal hollow space of the rotor back into the inlet region of the pump body. 
         [0015]    According to a fourth preferred embodiment of the invention, the eccentric screw pump comprises a stator with at least one return flow channel. The return flow channel is constituted parallel to the longitudinal axis of the eccentric screw pump along the stator length. The at least one return flow channel is in fluidic connection with the respective internal spaces of the inlet region and the outlet region and constitutes the bypass connection. 
         [0016]    The return flow channel is constituted in particular in a region between an inner thread pitch of the stator and the external lateral surface of the stator. The return flow channel does not comprise any open connection to the inner thread pitch of the stator and/or to the external lateral surface of the stator. This means that the return flow channel is constituted in the stator material. 
         [0017]    At least one safety valve is assigned to the return flow channel. When an excess pressure builds up on the pressure side of the eccentric screw pump, part of the delivered medium is conveyed as a return flow via the at least one return flow channel of the stator back into the inlet region of the pump body. The at least one return flow channel is preferably cast in the stator during production. Alternatively, the at least one return flow channel can also be formed subsequently after the production of the stator. 
         [0018]    According to an embodiment of the invention, the safety valve is disposed inside the return flow channel, preferably in a region between the inlet region and the pump unit. According to an alternative embodiment, the safety valve is integrated into the outlet region of the pump body. Provision is made here such that an outlet opening of the safety valve emerges into a return flow channel via a first connection. A plurality of return flow channels and a plurality of correspondingly disposed safety valves can also be used in this embodiment. When an excess pressure builds up on the pressure side of the eccentric screw pump, part of the delivered medium is conveyed as a return flow via the at least one return flow channel of the stator back into the inlet region of the pump body. 
         [0019]    The safety valve for preventing an inadmissible pressure rise inside the eccentric screw pump can be a spring-loaded safety valve, a weight-loaded safety valve or a medium-loaded safety valve. Preferably, the safety valve is an overflow valve for releasing pressure from the interior of the eccentric screw pump when inadmissible excess pressure occurs inside the closed system. 
         [0020]    A previously described eccentric screw pump according to the invention can be used in particular for the delivery of fluid and/or granular media in a borehole. Such an eccentric screw pump can generally be used whenever the development of excess pressure is to be expected, for example on account of the medium to be delivered. 
         [0021]    As a result of the integration of the return flow circuit with the safety or overflow valve in the pump body of the eccentric screw pump, its structure remains compact. In particular, the integrated return flow circuit generally does not lead to an increase in the size of the pump body of the eccentric screw pump. 
         [0022]    The integration of a return flow circuit is possible not only for eccentric screw pumps with a stator made from an elastomer. It is just as conceivable to integrate, in a comparable way, a return flow circuit in a so-called stepwise vortex pump. A stepwise vortex pump is described for example in US 2008/0050249 A1. In contrast with the eccentric screw pump, this pump does not comprise a stator made of rubber, which can be attacked by the delivered medium, for example during the pumping of petroleum or suchlike. Instead, the pump is constituted stepwise, comprises only corrosion-resistant metal components and operates in a centralized manner. Vibrations in the system can thus be eliminated, the pump can operate at raised temperatures and can be constituted smaller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Examples of embodiment of the invention and its advantages are explained in greater detail below with the aid of the appended figures. The size ratios of the individual elements with respect to one another in the figures do not always correspond to the actual size ratios, since some forms are represented simplified and other forms magnified compared to other elements for the sake of better clarity. 
           [0024]      FIG. 1  shows an eccentric screw pump with a conventionally known bypass line according to the prior art. 
           [0025]      FIG. 2  shows an eccentric screw pump according to the invention. 
           [0026]      FIG. 3  shows a detail of an eccentric screw pump according to the invention. 
           [0027]      FIG. 4  shows a second embodiment of an eccentric screw pump according to the invention. 
           [0028]      FIG. 5  shows a third embodiment of an eccentric screw pump according to the invention. 
           [0029]      FIG. 6  shows a fourth embodiment of an eccentric screw pump according to the invention. 
           [0030]      FIG. 7  shows a fifth embodiment of an eccentric screw pump according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Identical reference numbers are used for identical or identically acting elements of the invention. Furthermore, for the sake of clarity, only reference numbers that are required for the description of the given figure are represented in the individual figures. The represented embodiments only represent examples as to how the device according to the invention can be constituted and do not represent a conclusive limitation. 
         [0032]      FIG. 1  shows an eccentric screw pump  1  with a conventionally known external bypass line  2  according to the prior art. Eccentric screw pump  1  comprises a pump body  3  with an inlet region  4 , a pump unit  5  and an outlet region  6 . Inlet region  4  forms suction side S of eccentric screw pump  1  and outlet region  6  forms pressure side D of eccentric screw pump  1 . Pump unit  5  comprises an eccentric screw conveyor, the so-called rotor  8 , which rotates in a stator  7  with a helically coiled inner side thereby forming meandering delivery spaces  14 . Rotor  8  is connected to drive unit  12 , which connects rotor  8  to a drive shaft  13  by means of a coupling rod  9  disposed in the inlet region of pump body  3 . Located between the latter are links  10 ,  11  for the connection of and power transmission between drive unit  12  and rotor  8 . 
         [0033]    Medium M to be delivered passes via inlet flange  15  of inlet region  4  into eccentric screw pump  1 , is transported by meandering delivery spaces  14  in delivery direction Fr through the pump unit and is pumped out of eccentric screw pump  1  via outlet flange  16  of outlet region  6 . Bypass line  2  with a safety valve  20 , for example with an overflow valve  21 , is disposed between outlet flange  16  and inlet flange  15  by means of suitable connection means  17 ,  18 . In particular, overflow valve  21  is disposed directly on a connection means  17  which is assigned to outlet flange  16 . Bypass line  2  extends parallel to pump body  3  between overflow valve  21  and connection means  18  which is assigned to inlet flange  15 . 
         [0034]    With the represented safety circuit, when an excess pressure builds up on the pressure side of eccentric screw pump  1 , part of delivered medium M is conveyed as return flow M R  back to inlet flange  15  and onward into inlet region  4  of pump body  3 . 
         [0035]      FIG. 2  shows an eccentric screw pump  30 - 1  according to the invention. In the latter, at least one overflow valve  40  is integrated into pump body  3 . In particular, stator  7  is surrounded by a casing tube  45 . The housing of pump body  3  comprises in outlet region  5  a first connection  46  to casing tube  45 , so that the internal space of outlet region  5  has a fluidic connection to a hollow space  43  constituted between casing tube  45  and stator  7 . Furthermore, the housing of pump body  3  comprises in inlet region  4  a second connection to casing tube  45 , so that the internal space of inlet region  4  has a fluidic connection to hollow space  43  constituted between casing tube  45  and stator  7 . A return flow channel between casing tube  45  and the external lateral surface of stator  7  is thus constituted, through which part of medium M R  can flow from pressure side D back to suction side S of eccentric screw pump  30 - 1  when an excess pressure occurs inside eccentric screw pump  30 - 1 . Back-flowing medium M R  emerges into inlet region  4  of pump body  3  and is then delivered again in delivery direction FR through eccentric screw pump  30 - 1 . 
         [0036]    One or more overflow valves  40  for limiting the delivery pressure of eccentric screw pump  30 - 1  are also disposed in hollow space  43  or in the two connections  47  between hollow space  43  and the interior of pump body  3  in inlet region  4 , the outlet of said overflow valves emerging into the interior of pump body  3  in inlet region  4 . The arrangement of overflow valve  40  in hollow space  43  is represented in detail in  FIG. 3 . 
         [0037]      FIG. 4  shows an eccentric screw pump  30 - 2  according to the invention. In the case of the latter, at least one overflow valve  40  is integrated into pump body  3 . In particular, stator  7 - 2  is surrounded by a stator sleeve  50 . A connection line  52  parallel to longitudinal axis L of eccentric screw pump  30 - 2  is constituted at least in sections between stator  7 - 2  and stator sleeve  50 . Connection line  52  comprises, at the pressure-side end of eccentric screw pump  30 - 2 , a first connection  55  to the interior of eccentric screw pump  30 - 2  in outlet region  6 . Furthermore, connection line  52  comprises, at the suction-side end of eccentric screw pump  30 - 2 , a second connection  56  to the interior of eccentric screw pump  30 - 2  in inlet region  4 . First connection  55 , connection line  52  and second connection  56  form a return flow channel, through which part of medium M R  can flow from pressure side D back to suction side S of eccentric screw pump  30 - 2  when an excess pressure occurs inside eccentric screw pump  30 - 2 . Back-flowing medium M R  emerges into inlet region  4  of pump body  3  and is then delivered again in delivery direction FR through eccentric screw pump  30 - 2 . 
         [0038]    One or more overflow valves  40  for limiting the delivery pressure are disposed inside connection line  52  or between connection line  52  and second connection  56  on suction side S of eccentric screw pump  30 - 2 . 
         [0039]      FIG. 5  shows a third embodiment of an eccentric screw pump  30 - 3  according to the invention. A rotor  8 - 3  constituted at least partially hollow is used here. Rotor  8 - 3  comprises a hollow space  60 , which extends along rotor longitudinal axis L R . Furthermore, rotor  8 - 3  at its drive end comprises connection bores  62  between the external lateral surface of rotor  8 - 3  and hollow space bore  60 , for producing a fluidic connection between hollow space  60  and the interior of pump body  3  in inlet region  5  of eccentric screw pump  30 - 3 . An overflow valve  40  is also integrated into hollow space  60 . Hollow space  60  of rotor  8 - 3  and connection bores  62  form a return flow channel, through which part of medium M R  can flow from pressure side D back to suction side S of eccentric screw pump  30 - 3  when an excess pressure occurs inside eccentric screw pump  30 - 3 . Back-flowing medium M R  emerges into inlet region  4  of pump body  3  and is then delivered again in delivery direction FR through eccentric screw pump  30 - 3 . 
         [0040]      FIG. 6  shows a fourth embodiment of an eccentric screw pump  30 - 4  according to the invention. The employed stator  7 - 4  comprises here cast-in return flow channels  65  parallel to rotor longitudinal axis LR, which form a fluidic connection to the interior of pump body  3  in outlet region  6  and to the interior of pump body  3  in inlet region  4 . Part of medium M R  flows through return flow channels  65 , in which at least one overflow valve  40  can be disposed in each case, from pressure side D back to suction side S of eccentric screw pump  30 - 4  when an excess pressure occurs inside eccentric screw pump  30 - 4 . Back-flowing medium M R  emerges into inlet region  4  of pump body  3  and is then delivered again in delivery direction FR through eccentric screw pump  30 - 4 . 
         [0041]    Overflow valve  40  can also be integrated and disposed in the pump body in such a way that medium M R  flowing back through return flow channels  65  of stator  7 - 4  flows through overflow valve  40  before it emerges into inlet region  4  of pump body  3 . 
         [0042]      FIG. 7  shows a fifth embodiment of an eccentric screw pump  30 - 5  according to the invention. Stator  7 - 5  also comprises here cast-in return flow channels  65 . The latter have a fluidic connection via first and second connections  66 ,  67  in each case to the interior of pump body  3  in outlet region  6  and to the interior of pump body  3  in inlet region  4 . In this embodiment, overflow valve  40 * is integrated around the pressure connecting piece into outlet region  6  of pump body  3 . The outlet opening of overflow valve  40 * emerges into one or more first connections  66  and therefore into one or more of cast-in return flow channels  65 . 
         [0043]    The invention has been described by reference to a preferred embodiment. A person skilled in the art can however imagine that modifications or changes to the invention can be made without thereby departing from the scope of protection of the following claims. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
         
           
               1  eccentric screw pump 
               2  external bypass line 
               3  pump body 
               4  inlet region 
               5  pump unit 
               6  outlet region 
               7  stator 
               8  rotor 
               9  coupling rod 
               10  link 
               11  link 
               12  drive unit 
               13  drive shaft 
               14  delivery space 
               15  inlet flange 
               16  outlet flange 
               20  safety valve 
               21  overflow valve 
               30  eccentric screw pump 
               40  overflow valve 
               43  hollow space 
               44  return flow circuit 
               45  casing tube 
               46  first connection 
               47  second connection 
               50  stator sleeve 
               52  connection line 
               55  first connection 
               56  second connection 
               60  hollow space 
               62  connection bore 
               65  cast-in return flow channel 
               66  first connection 
               67  second connection 
             D pressure side 
             FR delivery direction 
             L longitudinal axis 
             M medium 
             M R  back-flowing medium 
             S suction side