Patent Publication Number: US-2019195234-A1

Title: Pump assemblies with sealing

Description:
CROSS-REFERENCE OF RELATED APPLICATION 
     This application is a Section 371 National Stage Application of International Application No. PCT/GB2017/052384, filed Aug. 14, 2017, and published as WO 2018/042150 A1 on Mar. 8, 2018, the content of which is hereby incorporated by reference in its entirety and which claims priority of British Application No. 1614816.5, filed Sep. 1, 2016. 
    
    
     FIELD 
     The invention relates to pump assemblies with sealing and particularly, but not exclusively to pump casing assemblies of turbomolecular vacuum pumps. 
     BACKGROUND 
     Pumps such as vacuum pumps may comprise parts that are fitted together with an intermediate seal to prevent fluid leakage between the two parts. For example, a vacuum pump may comprise two body parts that are joined to form a casing assembly. One of the body parts may have an end face that is recessed to receive a seal that is fitted between the two body parts to prevent gas leakage between them. The seal is typically an O-ring that sits in the recess and is engaged by a sealing face provided on the other of the two body parts. The two body parts may be secured to one another by one or more clamps or by a plurality of bolts or studs passing through suitable holes provided in, for example, flanges provided on the body parts. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
     SUMMARY 
     The invention provides a pump casing assembly as specified in claim  1 . 
     The invention also includes a pump casing assembly comprising: 
     a first body part defining a hollow interior having a first longitudinal axis and having a first end face that defines a recess to receive a seal, said recess defining a sealing surface; 
     a second body part defining a hollow interior having a second longitudinal axis and having a first end face facing said first end face of the first body part and defining a sealing surface; and 
     a seal disposed in said recess in sealing engagement with the respective sealing surfaces of said first and second body parts, 
     wherein said first and second longitudinal axes define a lengthways direction of the pump casing assembly, 
     wherein said second body part defines at least one projection extending beyond said sealing surface of the second body part in said lengthways direction so as to be disposed in said recess alongside said seal, and 
     wherein said recess defines a register surface and said projection defines a register face engaging said register surface to align said first and second body parts. 
     The invention also includes a pump assembly comprising a first part, a second part and a seal disposed between said first and second parts, said first part having a first face that defines a recess to receive said seal and said second part having a first face disposed opposite said first face of said first part and defining a first sealing surface engaged by said seal and a projection extending beyond said first sealing surface into said recess. 
     The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following disclosure, reference will be made to the drawings, in which: 
         FIG. 1  is a side elevation view of a turbomolecular vacuum pump; 
         FIG. 2  is a schematic section view through a portion of the turbomolecular vacuum pump of  FIG. 1 ; 
         FIG. 3  is an enlargement of the circled portion of  FIG. 2 ; and 
         FIG. 4  is a schematic comparison of a modification of the casing assembly shown in  FIGS. 2 and 3  and a conventional casing assembly. 
     
    
    
     DETAILED DESCRIPTION 
     In this specification the words ‘first’ and ‘second’ are used in connection with certain parts. It is to be understood that unless otherwise stated, these words are used purely as a means of identification and do not provide any indication of a number of parts or of precedence of the parts. 
     Referring to  FIGS. 1 and 2 , an example of a pump in the form of a turbomolecular vacuum pump  10  comprises a casing assembly  12  with sealing in the form of a seal  14 , The casing assembly  12  comprises a first body part  16  and a second body part  18 . The seal  14  is disposed between the first and second body parts  16 ,  18 . In use of the turbomolecular vacuum pump  10 , the seal  14  prevents gas from leaking between the body parts  16 ,  18 . The casing assembly  12  may include a third body part  20  mounted on the second body part  18 . The third body part  20  may, for example, house control electronics, a user interface and a power inlet. The casing assembly  12  may be provided with an inlet port  22 , a backing port  24 , a purge port  26 , an interstage port  28  and a vent port  30 . The inlet port  22  may be defined by a flange  32 . The flange  32  may be an ISO063 flange or an ISO100 flange via which the turbomolecular vacuum pump  10  may be clamped to a body or a piece of equipment that is to be evacuated. It is to be understood that the inlet end of the turbomolecular vacuum pump  10  does not have to the take the form of an ISO flange and different end configurations or designs may be used according to the intended use of the pump. Furthermore, it is not essential that the inlet port  22  is provided at an end of the casing assembly  12 , which may be closed at both ends. 
     Referring to  FIG. 2 , the first body part  16  may comprise a generally annular wall  38  that defines a hollow interior  40  and has a longitudinal axis, or centre line,  42 . The second body part  18  may comprise a generally annular wall  44  that defines a hollow interior  46  and has a longitudinal axis, or centre line  48 . The first and second body parts  16 ,  18  may house a rotor shaft  50 . The axis of rotation of the rotor shaft  50  may be coaxial with the longitudinal axes  42 ,  48 . The second body part  18  may house a first pumping mechanism comprising a plurality of stator blades  52  and a plurality of interleaving rotor blades  54 . The stator blades  50  may be fixed to the second body part  18  and the rotor blades  52  may be fixed to the rotor shaft  50 . The first body part  16  may house a second pumping mechanism  56  and an electric motor  58  that is operable to drive the rotor shaft  50 . The second pumping mechanism  56  may, be a Holweck drag mechanism. It will be understood that the positioning of the second pumping mechanism  56  within the first body part  16  as shown in  FIG. 2  is not essential and that a part of the second pumping mechanism may be housed in the second body part  18 . It will also be understood that in some examples the second pumping mechanism may be omitted or different pumping mechanisms such as a Gaede mechanism, Siegbahn mechanism or an aerodynamic pumping mechanism comprising a regenerative mechanism may be included as a second pumping mechanism. 
     As best seen in  FIG. 3 , the first body part  16  has a first end face that defines a recess  60  that receives the seal  14 . The second body part  18  has a first end face that is disposed opposite the first end face of the first body part  16  and defines a first sealing face  62  that is engaged by the seal  14  and a projection  64  that extends into the recess  60  beyond the first sealing surface  62 . With respect to the longitudinal axis  48 , the projection  64  may be disposed radially outwardly of the first sealing surface  6 : 2  so as to surround the first sealing surface. The first sealing surface  62  may be an annular surface and the projection  64  may extend continuously around a circumference of the annular surface. The projection  64  may have a height that is less than the height of the seal  14  and may be disposed in the recess  60  in side by side relation with the seal. 
     The recess  60  may define a second sealing surface  66  that is disposed opposite the first sealing surface  62  and is engaged by the seal  14 . Although not essential, in the illustrated example the first and second sealing surfaces  62 ,  66  are planar surfaces disposed in parallel spaced apart relationship. The first and second sealing surfaces  62 ,  66  may be disposed perpendicular to the longitudinal axes  42 ,  48  of the first and second body parts  16 ,  18 . The recess  60  may define a register surface  68  that extends transverse to the second sealing surface  62  and the projection  64  may define a register face  70  that engages the register surface  68  to locate the second body part  18  relative to the first body part  16 . The register surface  68  and register face  70  may be configured to locate the second body part  18  relative to the first body part  14  such that the longitudinal axes  42 ,  48  are aligned. The register surface  68  may extend perpendicular to the second sealing surface  66  and parallel to the longitudinal axis  42  of the first body part  16 . The register face  70  may extend perpendicular to the first sealing surface  62  and parallel to the longitudinal axis  48 . At least one of the register surface  68  and register face  70  may comprise an annular surface extending continuously about the respective longitudinal axis  42 ,  48 . 
     The first end face of the first body part  16  may additionally define an annular surface  72  disposed perpendicular to the longitudinal axis  42  of the first body part  16 . The annular surface  72  may be disposed radially outwardly of the recess  60  to form a seat for an annular surface  74  that is defined by the first end face of the second body part  18 . The annular surface  74  may be disposed radially outwardly of the projection  64  so as to be disposed opposite the annular surface  72  perpendicular to the longitudinal axis  48  and parallel to the annular surface  72 . In the illustrated example, the end of the annular wall  38  disposed remote from the recess  60  and annular surface  72  is closed by a plate or other suitable body so that when the first body part  16  is secured to the second body part  18 , the hollow interiors  40 ,  46  define a sealed enclosure accessible via the ports  22 - 30 . In addition to the rotor shaft  50 , first and second pumping mechanisms  52 - 56  and electric motor  58 , the hollow interiors  40 ,  46  may house associated parts (not illustrated) such as rotor shaft bearings and their associated lubrication system. The first and second body parts  16 ,  18  may be secured to one another by means of bolts or studs extending along through-holes provided in one of the annular walls  38 ,  44  to engage in threaded apertures provided in the other. In other examples, the first and second body parts  16 ,  18  may be secured to one another by clamps or by studs or bolts received in apertures provided in flanges or lugs provided on the outer sides of the first and second body parts.  16 ,  18   
     As best seen in  FIG. 3 , the side face  76  of the projection  64  adjoining the first sealing surface  62  may be configured such that in cross section the projection tapers so as to have a first thickness adjacent the first sealing surface and a second thickness at its tip that is less than the first thickness. The side face  76  may have an arcuate profile. 
     Advantageously the projection  64  may protect the first sealing surface  62  against damage during assembly and transport of the second body part  18 . For example, if the second body part  18  is placed on a supporting surface such as a work bench with the first sealing surface  62  face down, the projection  64  seats on the supporting surface and supports the second body part so that the first sealing surface does not contact the supporting surface. This avoids potential damage to the first sealing surface  62  that may arise from contact with the supporting surface objects lying on the supporting surface. 
       FIG. 4  provides a comparison between a prior art casing assembly P and a casing assembly  112  that is a modification of the casing assembly  12  shown in  FIGS. 2 and 3 . In the casing assembly  12  shown in  FIGS. 2 and 3 , the register face  70  of the second body part  16  is defined solely by the projection  64 . In the casing assembly  112  illustrated by  FIG. 4 , the projection  64  is a constituent part of a register face  70 . An advantage provided by the casing assembly  112  when compared with the conventional casing assembly P is that since the projection  64  defines a part of the register face  70 , it is possible to obtain a register face that has the same height X as the prior art register face  70 P of the conventional casing assembly while reducing the overall height, or length, of the casing assembly by a height Y corresponding to the height of the projection  64 . It will be understood that the same advantage is obtainable with the casing assembly  12  shown in  FIGS. 2 and 3 . In that example, the register face  70  defined by the projection  64  is disposed within the recess  60  alongside the seal  14  and does not add to the overall height of the casing assembly  12 . 
     In the illustrated examples, the pump casing assembly comprises two body parts  16 ,  18  secured to one another with a seal  14  clamped between respective end faces of the body parts, an auxiliary body part  20  and a plate to close an end of the first body part. It will be understood that this is purely an example of a pump casing assembly utilising the invention and that many other configurations are possible. For example, a pump casing assembly may comprise three or more body parts comprising annular walls secured to one another in series with respective seals between them. In some examples, both ends of the pump casing assembly may be closed by respective end plates or the like. In other examples, one or both body parts may comprise an integral end wall. The skilled person will understand that the invention may be utilised in all such configurations of pump casing assembly and in many others not described herein. 
     In the illustrated examples the projection  64  is an annular member encircling the first sealing surface  62 . It is to be understood that this is not essential and that a plurality of discrete projections may be provided. For example, three projections may be disposed about the first sealing surface at, for example, intervals of 120° to define a tripod arrangement for supporting the second body part  18 . In other examples a larger number of projections may be provided to form a castellated wall surrounding the first sealing surface  62 . 
     The illustrated examples the pump casing assembly with sealing is for a turbomolecular vacuum pump. It will be understood that the invention is not limited to this application. For example, the invention may be applied to pump casing assemblies generally. The invention may also be applied to other pump assemblies in which the ends of two parts are clamped to one another with a seal between them. 
     Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.