Abstract:
A pump includes a housing that contains a liquid, and a rotor including a plurality of blades extending radially from a shaft, and defining a conical space. A port member is disposed within the conical space. The port member defines an inlet port in communication with a low pressure region, a discharge port in communication with a high pressure region, and an anti-cavitation port in communication with a fluid supply having a pressure between the low and the high pressure regions. Each pair of adjacent blades cooperates with the liquid and the port member to enclose a variable volume bucket, wherein rotation of the rotor selectively positions a bucket in an inlet position adjacent the inlet port to draw in fluid, in an anti-cavitation position wherein the bucket is adjacent the anti-cavitation port and fluid is admitted into the bucket, and a discharge position wherein the bucket is positioned adjacent the discharge port to discharge fluid.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/115,408 filed Feb. 12, 2015, the contents of which are fully incorporated herein by reference pump. 
     
    
     BACKGROUND 
       [0002]    The disclosure concerns anti-cavitation constructions of a liquid ring pump. 
         [0003]    Liquid ring pumps and their operation are well known. In general liquid ring pumps utilize a liquid ring which, during operation, delimits a pumping chamber. The pumping chamber can comprise one or multiple lobes. A shaft rotates a rotor. The liquid ring is eccentric. During operation of the pump a radial inward surface of the liquid ring is radially spaced from the shaft at an intake zone to allow buckets formed by adjacent blades of the rotor to fill with gas entering the pump&#39;s pumping chamber through an inlet port. The inlet port is downstream of a pump head inlet. The buckets fill with gas as they sweep past the inlet port. An inlet port channel extends from the inlet port and provides a fluid connection between the pump head inlet and the inlet port. 
         [0004]    The radial inward surface of the liquid ring in a compression zone of the pump is oriented relative to the shaft to compress the gas in the buckets and force the gas through an outlet port which leads to an outlet of the pump. An outlet port channel extends from the outlet port and provides a fluid connection between the outlet port and the pump head outlet. 
         [0005]    The ring compresses the gas in the buckets because of its eccentric orientation. The orientation means the radially inward surface of the liquid ring has a much closer approach to the axis of the shaft in the radial direction along the compression zone as compared to its approach along the intake zone. 
         [0006]    During operation of the pump, sealing liquid is introduced into the buckets. The sealing liquid enters a bucket of the pump through a sealing liquid introduction port formed in the outer sidewall. A sealing liquid introduction channel extends to the sealing liquid introduction port and provides a fluid connection between a pump head sealing liquid inlet to the sealing liquid introduction port. The sealing liquid enters the buckets from the sealing liquid introduction port. The sealing liquid fills interstices and otherwise allows for proper operation of the pump such as replenishing the liquid forming the liquid ring. 
         [0007]    The sealing liquid in the bucket can cause cavitation of the blades and in particular at the base of a leading side of a trailing blade forming the bucket. To reduce the damage caused by cavitation, the art has used material resistant to cavitation. The art has also used diverters proximate the sealing liquid introduction port in the port member to reduce cavitation. U.S. Pat. No. 4,498,844, Bissell provides a comprehensive description of how a liquid ring pump having a conical or cylindrical port member operates and some of its basic structure and is hereby fully incorporated by reference. 
       SUMMARY 
       [0008]    An example of the invention is embodied by a liquid ring pump. The pump has a pump head. The pump head has a gas pump head inlet opening through an external portion of the pump head and has a gas intake channel in a portion of said pump head. The gas intake channel is open to the pump head gas inlet. The pump further has a pumping chamber housing forming a chamber. A rotor is in the chamber. The rotor has a plurality of blades which form a plurality of buckets. A port member is in a cavity formed said plurality blades. The port member has a first sidewall disposed around a second sidewall. A gas inlet port and a gas outlet port are formed in the first sidewall of the port member. The gas inlet port and gas outlet port are in the cavity. An anti-cavitation passage has a gas opening through an exterior facing surface of the first sidewall. The opening is in the cavity. The anti-cavitation passage has a gas entry which opens through a surface of said port member. The entry is outside of said buckets and the entry is separated from gas discharge from any of said buckets. The entry is separated from the pump head gas intake channel. The anti-cavitation passage opening is separated from said gas inlet port. 
         [0009]    The port member can further have a sealing liquid introduction port which opens through the first sidewall. A sealing liquid introduction channel in said port member is open to the sealing liquid introduction port. The sealing liquid introduction channel comprises walls which each extend along a first axis in a direction away from the first sidewall exterior surface towards the central axis of the port member. The walls also each extend along a second axis in a direction away a second open end of the port member towards a first open end of the port member. Each wall, along its second axis, is angled relative to a plane passing through an area of the sealing liquid introduction port opening through the first sidewall. The plane extends along the central axis and is parallel thereto. The angle is preferably 10 degrees±2 degrees. The area of the sealing liquid introduction port opening through the first sidewall can have a rim which comprises a chamfered surface. A sealing liquid diverter can be proximate the introduction port. 
         [0010]    Accordingly summarized even further, the port member in the cavity of the rotor of the liquid ring pump has the anti-cavitation passage. The passage has a gas opening through an exterior facing surface of the first sidewall of the port member. The opening is in the cavity. The gas entry of the ant-cavitation passage opens through the surface of said port member. The entry is outside of buckets formed by blades of the rotor and is separated from the gas discharge from any of said buckets. The entry is separated from the pump head gas intake channel of the liquid ring pump. The anti-cavitation passage opening is separated from said gas inlet port. The sealing liquid introduction port opens through the first sidewall. The sealing liquid introduction channel opens to the sealing liquid introduction port and has walls angled relative to a plane passing through an area of the sealing liquid introduction port opening through the first sidewall. The plane extends along a central axis and is parallel thereto. 
         [0011]    The following detailed description and above summary and the accompanying drawing figures that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The present invention is delimited by the appended claims. The description, therefore, is not to be taken in a limiting sense and shall not limit the scope of equivalents to the invention. 
         [0012]    In one aspect, a liquid ring pump includes a pump head having an inlet opening, an outlet opening, and an anti-cavitation opening, a pump housing coupled to the pump head and defining a chamber that is substantially enclosed by the pump housing and the pump head, and a rotor at least partially disposed in the chamber. A port member is disposed in the chamber and positioned adjacent the rotor. The port member includes a wall that defines an inlet port, a discharge port, and an anti-cavitation port each separate from the others. A plurality of blades is arranged around a rotational axis of the rotor, wherein each pair of adjacent blades partially define a bucket therebetween. Each bucket rotates from a first position in which the bucket is positioned between the discharge port and the inlet port, to a second position in which the bucket is in fluid communication with the inlet port to draw fluid into the bucket, to a third position in which the bucket is in fluid communication with the anti-cavitation port to admit fluid, to a fourth position in which the bucket is in fluid communication with the anti-cavitation port and the discharge port, and to a fifth position in which the bucket is in fluid communication with the discharge port to discharge the fluid within the bucket. 
         [0013]    In another aspect, a liquid ring pump includes a pump housing defining a chamber that is substantially enclosed and that contains a quantity of liquid, and a rotor at least partially disposed in the chamber and including a shaft supported for rotation about a rotational axis and a plurality of blades extending radially from the shaft, the plurality of blades defining a conical interior space. A port member is disposed at least partially within the conical interior space. The port member defines an inlet port in fluid communication with a low pressure region, a discharge port in fluid communication with a high pressure region, and an anti-cavitation port in fluid communication with a fluid supply having a pressure between the low pressure region and the high pressure region. The plurality of blades is arranged such that each pair of adjacent blades cooperates with the liquid and the port member to substantially enclose and define a variable volume bucket, wherein rotation of the rotor selectively positions a first bucket of the plurality of buckets in an inlet position adjacent the inlet port to draw low pressure fluid into the bucket, in an anti-cavitation position wherein the bucket is adjacent the anti-cavitation port and fluid is admitted into the first bucket, and a discharge position wherein the first bucket is positioned adjacent the discharge port to discharge fluid from the bucket to the high pressure region. 
         [0014]    In yet another aspect, a method of reducing cavitation in a liquid ring pump includes defining a plurality of buckets between adjacent blades of a rotor, forming a liquid ring around the blades, the liquid ring and the blades cooperating to enclose each of the buckets such that as the buckets rotate about a rotational axis the volume within each bucket varies as a result of movement of the liquid ring with respect to the rotor, and rotating a first of the plurality of buckets to a closed position wherein the bucket is substantially sealed and the volume of the bucket is at a minimum volume. The method also includes rotating the first of the plurality of buckets to an intake position in which the bucket is in fluid communication with an inlet port, maintaining fluid communication between the first bucket and the inlet port during further rotation of the bucket during which the liquid ring moves radially away from the rotational axis with respect to the first bucket to expand the volume of the first bucket and draw fluid into the volume via the inlet port, and rotating the first of the plurality of buckets to an anti-cavitation position wherein an anti-cavitation port is in fluid communication with the first bucket. The method further includes admitting a flow of fluid into the first bucket via the anti-cavitation port to increase the pressure within the first bucket, rotating the bucket to a full discharge position in which the first bucket is in fluid communication with a discharge port and is not in fluid communication with the anti-cavitation port, and maintaining fluid communication between the first bucket and the discharge port during further rotation of the first bucket during which the liquid ring moves radially toward the rotational axis with respect to the first bucket to reduce the volume of the first bucket and discharge fluid from the volume via the discharge port. 
         [0015]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1 a    is a side schematic irregular view of a liquid ring pump illustrating features of the invention; the schematic shows a port member in a cavity of a rotor; the rotor is in a housing, and the housing is coupled to a pump head. 
           [0017]      FIG. 1 b    is a side schematic view of a liquid ring pump illustrating the location of a gas inlet port relative to a pump head, rotors and housing of a liquid ring pump which embodies the features of the present invention. 
           [0018]      FIG. 1 c    is a side schematic view of a liquid ring pump illustrating the location of a gas discharge port relative to a pump head, rotors and housing of a liquid ring pump which embodies the features of the present invention. 
           [0019]      FIG. 2  is a front schematic view of a port member and a rotor of a liquid ring pump embodying features of the present invention. 
           [0020]      FIG. 3  is a sectional view of the port member shown in  FIG. 2 ; the section is taken along the central axis of the port member. 
           [0021]      FIG. 4  is a front schematic view of the port member shown in  FIG. 2  illustrating certain angles. 
           [0022]      FIG. 5  is a side view of the port member shown in  FIG. 4  illustrating the inner diameter of the second sidewall of the port member. 
           [0023]      FIG. 6  is a rear schematic view of the port member of  FIG. 4  in combination with a pump head of the liquid ring pump embodying features of the present invention. 
           [0024]      FIG. 7  is a rear isometric view of the port member of  FIG. 4 . 
           [0025]      FIG. 8  is a side isometric view of the port member of  FIG. 4 . 
           [0026]      FIG. 9  is a side isometric view of the port member of  FIG. 4  different from the side view in  FIG. 8 . 
       
    
    
       [0027]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
       DETAILED DESCRIPTION 
       [0028]    As illustrated in Fig. la, a liquid ring pump  10  includes a chamber  14  formed by a pumping chamber housing  16 . A rotor  18  in the pumping chamber to pump the gas  20  has a plurality of blades  18   a  which are arranged around a central area of the rotor. More particularly they are arranged circumferentially about the rotor&#39;s central axis  18   b.  The blades  18   a  are equidistantly spaced from each other. Between each pair of adjacent blades is a space which can be called a bucket  18   c.  There is a plurality of buckets  18   c  arranged around the rotor central axis  18   b.  Each bucket  18   c,  when the liquid ring pump is operating at its running speed, forms a separate sealed bucket  18   c  sealed by liquid of a liquid ring  22 . The sealed bucket  18   c  has a void space (volume) which expands and contracts depending on the angular orientation of the bucket  18   c  relative to an inner surface  22   a  of the rotating liquid ring  22  in the chamber. The inner surface  22   a  of the liquid ring delimits a radial inner boundary of the liquid ring  22  and forms a radial outer boundary of a respective sealed bucket  18   c.  The radial inward boundary of each sealed bucket  18   c  is formed by an exterior facing surface  24   a  of a second sidewall  24  of a port member  26 . Each sealed bucket can be called a compressible fluid chamber. 
         [0029]    Each rotor blade  18   a  has a first free end  18   d  which extends in a radial direction relative to the central axis of the rotor. Each rotor blade has a second free end  18   e  extending in an axial direction relative to the rotor central axis  18   b.  Each second free end  18   e  is either inclined or parallel relative to the rotor central axis  18   b.  In the present example they are inclined. Each blade&#39;s first and second free ends intersect with each other. The second free ends form a cavity  19 . The rotor is fixedly connected to a shaft  28 . The shaft extends through the cavity  19  and through a shaft receiving aperture  18   g  formed by a hub  18   h  of the rotor  18 . 
         [0030]    The port member  26  is in the cavity  19 . The port member  26  has a first sidewall  30  in the cavity  19 . The first sidewall  30  is elongated in a first direction. The first direction is a direction away from a first open end  26   a  of the port member towards a second open end of the port member  26   b.  The first sidewall  30  extends in the first direction and is between the first open end  26   a  and second open end  26   b.  The first sidewall  30  is an outer sidewall and can be called a port wall. The first sidewall is disposed around the second sidewall  24 . The second sidewall  24  is an inner sidewall. The inner sidewall  24  forms a shaft receiving hollow  24   b.  The shaft  28  extends into the hollow  24   b.    
         [0031]    The port member  26  has a gas inlet port  32  and a gas discharge port  36  formed in the first sidewall  30 . The gas inlet port  32  opens through the first sidewall  30 . The gas discharge port  36  opens through the first sidewall  30 . The inlet port  32  and discharge port  36  each has a respective beginning end  33 ,  37 . Each respective beginning end  33 ,  37  is spaced, in the circumferential direction from a respective closing end  34 ,  38 . The beginning end  37  of the discharge port is spaced from the closing end  38  of the gas discharge port. The beginning end  33  of the gas inlet is spaced from the closing end  34  of the gas inlet port. The beginning ends  33 ,  37  of the inlet port and gas discharge port each comprise a beginning edge and the closing ends  34 ,  38  of the gas inlet port and gas outlet port each comprise a closing edge. A portion of an interior surface  30   a  of the first sidewall  30  delimits in a second direction a gas inlet port channel  35  (shown in  FIG. 7 ). The second direction is a direction going outward in a radial direction from the central axis of the port member. The gas inlet port channel  35  extends from and opens through the first open end  26   a  of the port member to the gas inlet port  32 . The gas inlet port  32  is open to the gas inlet port channel  35 . The gas inlet port channel  35  provides a gas flow connection between a gas intake channel  42  in the pump head  44  and the gas inlet port  32 . The gas inlet port channel  35  is open to the gas intake channel  42  in the pump head. The pump head gas intake channel  42  is open to a pump head inlet  43 . The pump head inlet  43  opens into the pump head  44 . 
         [0032]    A portion of the interior surface  30   a  of the first sidewall  30  delimits in the second direction a gas discharge channel  39 . The gas discharge channel  39  extends from the outlet port to and through the first end  26   a  of the port member  26 . The gas discharge port  36  is open to the gas discharge channel  39 . The gas discharge channel  39  provides a gas flow connection to a gas discharge channel  45  in the pump head. The pump head gas discharge channel  45  is open to port member gas discharge channel  39 . The pump head gas discharge channel  45  is open to a pump head gas outlet  46 . The gas outlet  46  opens out of the pump head. 
         [0033]    The port member  26  has an anti-cavitation passage  50  (shown in  FIGS. 6 and 7 ) comprising a gas opening  51  which opens through an exterior surface  30   b  of the first sidewall  30 . The anti-cavitation gas opening  51  is an exit for the anti-cavitation passage. The anti-cavitation passage gas opening  51  is in gas flow connection with a gas entry  52  of the anti-cavitation passage  50 . The gas entry  52  is in the port member  26 . The gas entry  52  is not in receiving flow connection or receiving gas discharge connection with any bucket  18   c  in the chamber  14 . The entry  52  is outside of the buckets  18   c.  The gas entry  52  is in flow connection with a gas supply channel  56 . It is open to the gas supply channel  56 . The gas supply channel is outside of said pumping chamber. It can extend through the pump head  44 . The gas supply channel  56  is not open to the pump head gas inlet  43  or pump head intake channel  42 . It is separated from, including fluidly separated from, the pump head gas intake channel  42  and pump head inlet  43 . The gas supply channel  56  receives gas from a source external to the pumping chamber and the pump head. The gas supply channel  56  and the anti-cavitation passage  50  are continuous. The anti-cavitation passage is not open to the gas inlet port channel  35  or gas inlet port  32 . The anti-cavitation passage is separated from, including fluidly separated from items  35 ,  32 . The gas source for the gas supply channel  56  can be ambient air in the environment surrounding the chamber  14  and pump head  44 . Further details of the anti-cavitation passage are explained in more detail below. 
         [0034]    The port member  26  also has a sealing liquid introduction port  60  which opens through the first sidewall  30 . The sealing liquid introduction port  60  is oriented in the circumferential direction of rotation of the rotor between the closing end  34  of the gas inlet port  32  and the beginning end  37  of the gas discharge port  36 . The sealing liquid introduction port  60  is open to a sealing liquid introduction channel  61  of the port member  26 . The sealing liquid introduction channel  61  provides a flow connection to a sealing liquid supply channel  62 . The sealing liquid introduction channel  61  is open to the sealing liquid supply channel  62 . The sealing liquid supply channel  62  can extend through the pump and in particular the pump head. The sealing liquid introduction channel  61  of the port member comprises walls  63  which extend in a direction away from the first sidewall exterior surface  30   b  towards the central axis  40  of the port member. The walls are connected with the second sidewall  24  and the first sidewall  30 . The sealing liquid introduction channel  61  opens through the second sidewall  24  and is open to the shaft  28 . The sealing liquid introduction channel  61  extends from and opens through the first open end  26   a  of the port member to the sealing liquid introduction port  60 . The sealing liquid  21  enters the buckets  18   c  from the sealing liquid introduction port  60  as the buckets  18   c  sweep past the sealing liquid introduction port in the circumferential direction of rotation. The sealing liquid fills interstices and otherwise allows for proper operation of the pump. 
         [0035]    In operation, a sealed bucket  18   c  rotates to a position K (as shown in  FIG. 2 ) wherein it is in a gas flow receiving connection with said anti-cavitation exit  51 . In the position K the sealed bucket is open to the anti-cavitation exit  51 . The exit  51  opens into the sealed bucket  18   c . The bucket when in the position K is in a gas flow discharge connection with said gas discharge port  36 . The bucket  18   c  is open to the gas discharge port  36 . In the position K the bucket is not in a gas flow receiving connection with said gas inlet port  32  or gas inlet port channel  35 . It is not open to the gas inlet port  32  or gas inlet channel  35 . It has swept completely past the gas inlet port  32 . In the position K it is not open to the sealing liquid introduction port  60 . At least a portion of the bucket is circumferentially between the closing end  34  of said gas inlet port and the beginning end  37  of said gas discharge port. When the bucket is in the position K the external supply of gas has entered the anti-cavitation passage  50  through the entry  52  without having first flowed through the gas inlet port  32 . The gas in the anti-cavitation passage is passing through said anti-cavitation opening  51  into said sealed bucket  18   c  without having first passed through the gas inlet port  32 . The flow into the bucket increases the volume of gas and pressure in the bucket. Thus the bucket in the position K has an increased gas volume and increased gas pressure from gas received from said anti-cavitation passage  50 . The gas received from said passage is from the external gas source. The gas is received without said gas first passing through the gas inlet port  32 . 
         [0036]    The area of the sealing liquid introduction port  60  opening through the first side wall is delimited by a rim  65 . The rim comprises a chamfered surface. The chamfered surface is seamless with the first sidewall and part of the first sidewall  30 . The surface can be a continuous perimeter. The surface delimits at least one half of the perimeter&#39;s length. The sealing liquid introduction channel  61  is open to the shaft  28 . The walls  63  of the sealing liquid introduction channel are angled relative to a plane  67  passing through the area of the sealing inlet port opening through the first side wall and more particularly the area opening through the external surface  30   b  of the first sidewall. The plane passing through extends along the central axis  40  of the port member and is parallel thereto. The walls are each angled in a direction going away from a first end of the wall distal the first end  26   a  to a second end of the wall proximate the first end  26   a.  Thus a shortest straight line extending from the first end of the wall to the second end of the wall is angled relative to the plane  67 . The walls, along the line, are each angled 10 degrees±2 relative to the plane. The walls along an axis extending along the line area angled relative to the plane in the same amount. The walls can be considered to have been rotated 10 degrees±2 degrees in the circumferential direction of rotation from a prior position relative to the plane. In the prior position, in the direction from the first end to the second end, the walls extend parallel to the plane. The angled walls  63  lesson the pressure drop in the bucket because the angled walls direct the sealing liquid through the sealing liquid introduction port at an angle relative to the plane  67 . The angled flow lessons the velocity of the sealing liquid thus increasing the pressure in the bucket. The chamfered rim  65  operates on the same principal. 
         [0037]    Proximate the sealing liquid introduction port  60  is a diverter  69  having an interference orientation to a flow of the sealing liquid  21 . The interference is before the liquid passes through the sealing liquid introduction port  60 . The diverter  69  breaks up the sealing liquid  21  thus decreasing the velocity of the liquid running along a leading surface of a trailing blade delimiting the bucket as it sweeps past the sealing liquid introduction port. The resulting decrease in velocity increases the pressure in the bucket and thus lessons the pressure drop in the bucket and thus the cavitation at the base of the leading surface of the trailing blade. 
         [0038]    In more detail, the anti-cavitation passage  50  comprises a channel having a first portion  53  and a second portion  55 . The first portion comprises the gas entry  52  to the anti-cavitation passage of the port member. The gas entry  52  opens through a surface of the port member  26 . The surface can be a face surface at the first open end  26   a  of the port member. The face surface faces the pump head  44  when the port member  26  is connected to the pump head. The gas entry is configured to couple to the gas supply channel  56 . The first portion extends in the first direction. The first portion does not open though the interior facing surface  30   a  of the first sidewall  30 . It does not open into the gas inlet port channel  35  or discharge channel  39 . It extends in the first direction within additional structure  71  of the port member  26 . The structure  71  is between interior surface  24   c  of said second side wall  24  and said exterior surface  30   b  of said first sidewall  30 . The additional structure can be considered a portion of the first sidewall  30  having increased thickness in a direction away from the exterior surface of first sidewall towards the central axis of the port member. The direction comprises a radial direction away from the first sidewall exterior surface towards the central axis of the port member. The structure can be a portion which extends from the first sidewall  30  to the second sidewall  24 . The structure can delimit the gas discharge channel  39  in a circumferential direction opposite the direction of rotation. The additional structure  71  has a length measured in a direction going away from the first open end  26   a  of the port member towards the second open end  26   b  of the port member along the central axis less than a length of the gas discharge port  36  measured along the central axis. The length of the gas discharge port  36  is measured from a first end  73  of the opening of the discharge port  36  through the exterior surface  30   b  most proximate the port member first end  26   a  to a second end  75  of the opening of the discharge port  36  most distal the port member first end  26   a.  The length of the additional structure is at least 1.5 and more preferably about 2 times the length of the gas discharge port. 
         [0039]    The second portion  55  of the channel comprises the opening (exit)  51  of the passage  50 . The first portion  53  opens into the second portion  55 . The second portion does not open through the interior surface  30   a  of the first sidewall. The first and second portions are in gas flow connection and continuous with each other. 
         [0040]    The anti-cavitation passage does not open through the interior surface  30   a  of the first sidewall  30 . It does not open into the inlet port  32  or inlet port channel  35 . Excepting the entry, it does not open through a surface of the additional structure  71 . The passage  50  is separated from, including fluidly separated from, the gas inlet port  32 , gas inlet port channel  35 , gas discharge port  36  and gas discharge channel  39 . A bucket  18   c,  when in position K, can couple exit  51  to the discharge port  36 . 
         [0041]    As shown in  FIGS. 8 and 9 , the opening  51 (more particularly the midpoint of the opening  51 ) of the anti-cavitation passage  50  is an axial distance X from the first open end  26   a . The axial distance is measured along the central axis of the port member  26 . The distance X is greater than the axial distance Y from the first end  26   a  of the port member  26  to an end  77  of the gas inlet port  32  most proximate the first open end  26   a  of the port member. Preferably the distance is minimized. The distance Y is measured along the central axis of the port member. The distance X is less than the axial distance Z from the first end  26   a  of the port member to an end  79  of the gas inlet port  32  most distal the first end  26   a  of port member  26 . Again the distance Z is measured along the central axis of the port member. With reference to  FIG. 2 , the opening  51 (more particularly the midpoint of the opening  51 ), in the circumferential direction of rotation, is A degrees from the closing end  34  of the gas inlet port  32 . It is B degrees from the beginning end  37  of the gas discharge port  36 . Preferably A is greater than B. Preferably A is 2 times B±0.2. In the shown example A is 66 degrees±5 degrees and B is 32 degrees±5 degrees. 
         [0042]    The diverter has a first length from one end to an opposite end measured in the circumferential direction preferably the same as or about the same as the width of the sealing liquid introduction channel measured in the circumferential direction at the rim of the sealing liquid introduction port  60  opening through the exterior surface  30   b  of the first sidewall  30 . The length should be at least the 0.5 times the width of the sealing liquid introduction port. The diverter should have a closest distance d measured along a radius of the central axis of the port member. The distance d should be greater than the inner radius r of the second sidewall. The distance d is about 1.22 times r±0.02. 
         [0043]    A surface  81  of a filling  82  delimits said anti-cavitation passage  50  and thus said passage is open to said surface  81  of said filling. The surface  81  thus forms a surface of said passage. The filling  82  can be a plug. The filling  82  fills at least a portion of a channel  85 . The channel  85  having the filling  82  is in the additional structure  71 . Exclusive of the filling  82 , the channel  85  has an opening  85   a  which opens into said ant-cavitation passage  50  from said additional structure. The filling  82  fills the opening. The channel  85  also has an opening  85   b  through the surface of the additional structure. This opening  85   b  is not filled. The channel  85  is a locating channel provided in connection with providing the anti-cavitation passage  50 . 
         [0044]    In a preferred operating mode, the pump  10  operates as a vacuum pump that produces a low absolute pressure (high vacuum pressure) at the inlet  32  and discharges the pumped fluid at a higher absolute pressure (e.g., atmospheric pressure) at the discharge  36 . During some operating conditions, the pressure within the bucket as it passes the inlet  32  closing end  34  is lower than the vapor pressure of the liquid that forms the liquid ring. This condition can result in boiling (i.e., the formation of bubbles) of the liquid. Sudden exposure of this boiling liquid to a high pressure region (such as atmospheric pressure at the discharge  36 ) can cause the sudden collapse (implosion) of the bubbles which can cause cavitation. 
         [0045]    With reference to  FIG. 2 , the operation of the pump including the anti-cavitation device is best understood.  FIG. 2  illustrates multiple positions of buckets delineated by several radial broken lines. Each bucket rotates through multiple positions with positions G, H, I, J, K, and L being identified for description. A bucket begins its rotational cycle in position G. In this position, the bucket is closed to both the discharge opening  36  and the inlet opening  32  and is rotating in a clockwise direction as shown in  FIG. 2 . In position G, the liquid ring is at or near its closest approach to the shaft such that the volume of the bucket is at or near its minimum. Further rotation positions the bucket in position H. In this position, the bucket is open to the inlet opening  32  and the volume of the bucket is increasing as the liquid ring recedes from the shaft. The increasing volume draws fluid into the increasing volume. Further rotation positions the bucket in position I. In this position, the bucket is again closed to both the inlet  32  and the discharge  36 . In addition, in position I, the liquid ring is at or near its maximum distance from the rotor such that the volume of the bucket is at or near its maximum. It is at position I where the bucket is at its lowest pressure (highest vacuum pressure) and the formation of bubbles is most likely. Continued rotation positions the bucket in location “J”. As the bucket approaches this position, the liquid ring is moving toward the shaft to reduce the volume and increase the pressure within the bucket. Once in position “J”, the bucket is open to the anti-cavitation opening  51 . The anti-cavitation opening  51  is fluidly coupled to a source of relative high pressure (e.g., atmospheric pressure) and admits a volume of high pressure fluid into the bucket. The anti-cavitation opening  51  or the fluid path is sized to control the quantity of fluid admitted into the bucket to slowly increase the pressure in the bucket. The bucket then rotates to position K where it is open to both the anti-cavitation opening  51  and the discharge opening  36 . At this point fluid is free to enter the bucket to increase the pressure to atmospheric pressure. The bucket eventually rotates to position L where the volume is substantially at atmospheric pressure and the volume is reducing as the liquid ring moves closer to the shaft and the bucket volume is reduced. Finally, the bucket returns to position G and the process begins again. The admission of high pressure fluid via the anti-cavitation inlet prior to exposing the bucket to the discharge  36  allows for a more gradual increase in the pressure within the bucket which allows any bubbles to dissipate more slowly, thereby reducing the likelihood of cavitation damage. 
         [0046]    To manufacture the port member  26  the first sidewall  30  and the second sidewall  24  of said port member  26  are provided. The gas inlet port  32  and gas discharge port  36  are provided in the first sidewall  30 . The sealing liquid introduction port  60  is provided in the first sidewall  30 . The sealing liquid channel  61  has the walls  63  angled relative to the plane  67 . The additional structure  71  is provided to extend a length less than the length of the discharge port  36 . The above features can be provided by way of casting in combination with machining. 
         [0047]    The first portion  53  of the channel of the anti-cavitation passage is provided in the additional structure  71  to have the entry  52  into the anti-cavitation passage. The locating channel  85  is provided in the additional structure  71  to open into the first portion  53  and to open through a surface of the additional structure  71 . The second portion  55  of the channel is provided to have the opening  51  of the anti-cavitation passage  50  and to open into the first portion  53 . The opening  85   a  of the locating channel open to the first portion  53  is filled with filling  82 . The first  53  and second portion  55  and location channel  85  are machined into the port member  26  after it has been cast or otherwise formed. 
         [0048]    The pump  10  can have a chamber housing  16  that has a circular inner surface delimiting a chamber  14 . In this case the compressor package is a single lobe design having a single intake zone and compression zone. The pump could be a multiple lobe design. In this case the working chamber housing  16  would have an oval inner surface delimiting an oval chamber  14 . The chamber would have two intake zones and two compression zones in an alternating pattern. The two intake zones would be on opposite ends of the minor axis of the oval and the two compression zones would be on opposite ends of the major axis. 
         [0049]    The term gas as use herein is broad enough to include, without limitation, ambient air, fluids in a gaseous state other than ambient air, mixtures of gases, other than ambient air, with ambient air and/or non-ambient gases, and mixtures of incompressible and compressible fluids, vaporized liquids mixed with ambient air; and vaporized liquids. 
         [0050]    Various features and advantages of the invention are set forth in the following claims.