Abstract:
An oil rotary vacuum pump of mechanical type is filled with a requested amount of oil at the end of the manufacturing process, then it is stored and then shipped to the user, letting the user avoid an operation of introducing the proper amount of oil into the pump. The oil leakage is prevented by securing the suction and/or exhaust ports of the pump, which are sealed by means of a removable sealing member, for instance by means of a membrane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/118,863, filed Apr. 29, 2005 now U.S. Pat. No. 7,588,426, which is incorporated by reference herein by its entirety. 
     This application is a divisional of U.S. patent application Ser. No. 11/118,863, filed Apr. 29, 2005, titled OIL ROTARY VACUUM PUMP AND MANUFACTURING METHOD THEREOF, now issued on Sep. 15, 2009 as U.S. Pat. No. 7,588,426, which claims Paris Convention priority of Italian Patent Application No. TO2004A000268 filed Apr. 30, 2004, the complete disclosures of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an oil rotary vacuum pump of mechanical type and to a method of manufacturing such pump. 
     Oil rotary pumps of mechanical type are generally used to obtain low vacuum conditions, in a pressure range from atmospheric pressure to about 10 −1  Pa. 
     Typical mechanical pumps include a casing, having a suction port and an exhaust port, within which a stator is provided defining a cylindrical chamber housing an eccentric circular rotor equipped with spring-loaded radial vanes. Said pumps are immersed into an oil bath, which has to cool down and lubricate the pump and isolate the pump from the outside environment. 
     Pumps of such kind are known for instance from the U.S. Pat. No. 6,019,585 “Oil-Sealed Vane-Type Rotary Vacuum Pump With Oil Feed” and the GB Patent Application No.2151091A “Electric Drive for Oil Sealed Sliding Vane Rotary Vacuum Pump.” 
     According to the prior art, manufactured pumps are stored and subsequently shipped to the user without oil inside them. Thus, it is up to the user, who often has no skill in the art, to introduce the proper amount of oil into the pump prior to the first use. 
     It is clear that such a way of proceeding has a serious drawback: indeed, if the user does not perform the oil filling of the pump properly, severe risks of damaging the pump are encountered, in particular because of seizure of the moving parts due to the lack or insufficiency of lubricant. 
     Therefore, it is an object of the present invention to obviate the above-identified drawback, by providing an oil rotary pump of mechanical type, which can be filled with the proper amount of oil at the end of the manufacturing process and shipped to the user in such conditions. 
     It is another object of the present invention to provide an oil rotary pump of mechanical type already containing the proper amount of oil, which pump can be stored for any period of time and subsequently shipped to the user without any risk of the oil coming out or undergoing degradation. 
     SUMMARY OF THE INVENTION 
     The above-identified and other objects are achieved by means of an oil rotary vacuum pump of mechanical type according to the invention, as described herein. 
     According to one embodiment, an oil rotary vacuum pump ofmechanical type includes a first casing; an oil bath disposed within said first casing; a second casing having a chamber therein, said second casing located within said first casing immersing into said oil bath; a suction port for introducing a gas into said chamber via a suction duct; a rotor located in said chamber and arranged to compress a gas present in said chamber; an exhaust port for discharging the gas from said chamber via an exhaust duct; and a removable sealing member closing said suction and/or exhaust ports when said pump is in a non-operative mode prior to first use of said pump. 
     The sealing member may include a membrane having a thin film composition subject to tearing without producing fragments thereof on application of a pressure difference across the membrane. 
     Due to the sealing of the suction and exhaust ports in the pump by suitable membranes, oil which is introduced into the pump cannot come out during storage and shipping operations, so that the end user receives the pump already containing the proper amount of oil. 
     Advantageously, the methods employed in order to apply these membranes to the respective ports are chosen so that the membranes can be easily removed by the user before starting the pump operations. 
     Moreover, the material and the thickness of the membranes are chosen so that, even if the user forgot to remove the membranes from the ports before using the pump, said membranes tear when the pump is started, leaving the ports free without damaging the components of the pump or of devices connected thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some non-limiting exemplary embodiments of the pump according to the invention will be described in more detail hereinafter, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective schematic view of the oil rotary mechanical vacuum pump according to the present invention; 
         FIG. 2  is a schematic cross-sectional view of the vacuum pump shown in  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional view of a detail of  FIG. 1 , concerning the suction/exhaust port of the pump according to the present invention; 
         FIG. 4  is a schematic cross-sectional view of the detail shown in  FIG. 3 ; 
         FIG. 5  is a schematic cross-sectional view of the detail shown in  FIG. 3 , according to an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a mechanical oil pump ( 100 ) according to the invention comprises an external casing  1  in which an internal casing  2 , having a cylindrical chamber  7  formed therein, is tightly arranged. The chamber  7  houses a cylindrical rotor  9 , driven into rotation by a motor  110  connected to pump  100 . The rotor  9  has an axis parallel to the axis of cylindrical chamber  7 , but eccentrically located relative to the chamber axis. One or more radially movable radial vanes  11  (two vanes in the embodiment shown) are mounted onto rotor  9  and are kept against the wall of chamber  7  by means of springs  13 . 
     Gas is sucked through suction port  3  and enters, through a suction duct  5 , chamber  7 , where it is pushed by the vanes, and hence compressed. Subsequently, gas is released through an exhaust duct  15  ending at a corresponding exhaust port  17 . 
     External casing  1  is filled with a suitable amount of oil, such that the second, tightly arranged casing  2  is immersed into an oil bath  19  acting as cooling and lubricating fluid. In a known manner, pump  100  is indeed manufactured so that a certain amount of oil can penetrate into chamber  7  and form a thin film ensuring tightness between vanes  11  of rotor  9  and the wall of chamber  7 . 
     Advantageously, according to the invention, at the end of the manufacturing process, the proper amount of oil is introduced into external casing  1 , through a proper introduction port  12  sealed by a plug  10 , in order to form oil bath  19 , and suction and exhaust ports  3 ,  17  are sealed by means of a pair of membranes  21 ,  23  for the subsequent storage and shipping operations. 
     As better shown in  FIG. 3 , the membranes  21 ,  23  can be applied to the respective suction and exhaust ports  3  and  17  by gluing, so that a portion  21   a ,  23   a  of each membrane  21 ,  23  is made to adhere to outer surface  3   a ,  17   a  of port  3 ,  17 , respectively, through a layer  25   a ,  27   a  of a proper adhesive, thereby sealing said port  3 ,  17 . 
     In the alternative, according to the embodiment shown in  FIG. 4 , a portion  21   b ,  23   b  of said membranes  21 ,  23  is made to adhere to rim  3   b ,  17   b  of port  3 ,  17 , respectively, through a layer  25   b ,  27   b  of said adhesive. 
     In both embodiments described, the adhesive  25   a ,  27   a  or  25   b ,  27   b  is selected so that it ensures a perfect tightness of said membranes  21 ,  23  on said ports  3 ,  17 , while allowing an easy and complete removal of said membranes  21 ,  23  by the operator when the pump  100  is to be used. 
     Turning to  FIG. 5 , an alternative embodiment of the invention is shown. According to this embodiment, a flange  29  is applied to the suction and exhaust ports  3  and  17  of pump  100  and is kept in register with the respective port  3 ,  17  by means of a centering ring  31  and a ring gasket  33 . The flange  29  can be kept pressed against the respective port  3 ,  17  by a locking nut  35  during the storage and shipping steps, and subsequently removed when the pump  100  is to be used. 
     According to this embodiment, membranes  21 ,  23  are applied to the centering ring  31  and not directly to suction or exhaust port  3 ,  17 . More particularly, a peripheral portion  21   c ,  23   c  of each membrane  21 ,  23  can be made to adhere to the inner surface of centering ring  31 . 
     This second embodiment entails important advantages. 
     First, membranes  21 ,  23  could be secured to centering ring  31  even in a non-removable manner, since the ring  31  will be removed together with the respective membrane  21 ,  23  before starting the pump  100 . Consequently, any conventional technique (gluing, welding, crimping, etc.) could be used for securing the membranes  21 ,  23  to the respective centering ring  31 . 
     Second, said membranes  21 ,  23  do not undergo any deterioration when they are removed from suction and exhaust ports  3 ,  17 , and therefore they can be used again in case of a possible further storage and/or shipping, by simply applying again the respective centering ring  31  and the respective flange  29  on each port  3 ,  17 . 
     In general manner, these membranes  21 ,  23  are made as very thin films, so that a moderate pressure difference is enough to tear them. In this way, even if the user forgot to remove them before starting pump  100 , when starting the pump  100  the pressure exerted on said membranes  21 ,  23  because of rotor  7  being driven into rotation would be enough to make them tear, thus leaving ports  3 ,  17  of pump  100  unobstructed and without producing fragments that could damage the pump  100 . 
     It is clear that the vacuum pump according to the invention attains the desired objects, in that it lets the user avoid the delicate operation of introducing the proper amount of oil into the pump when first starting the same pump. 
     Moreover, the provision of sealing membranes on the suction and/or exhaust ports of the pump according to the invention allows storing the pump for any time period and then shipping it without risks of oil leakage and consequent soiling of the pump or its packing.