Abstract:
A turbine pump has a transition chamber ( 9 ), which separates a low-pressure section ( 1 B) from a high-pressure section ( 1 A) and into which an additional inlet port ( 5 ) opens. The chamber ( 9 ) is defined by a stator stage ( 10 ) consisting of a disc ( 11 ) with a peripheral edge ( 12 ), integral with said disc ( 11 ) and forming a spacer ring integrated into the stator stage, and with radial blades ( 17 ) joined with the disc ( 11 ) at both ends.

Description:
FIELD OF THE INVENTION 
     The present invention refers to high-vacuum pumps, and more particularly it concerns a turbine pump, in particular a turbomolecular pump, comprising a stator stage integrated with a spacer ring and located in correspondence of an intermediate inlet for a gas flowing in counter-current flow to the operating direction of the pump. 
     BACKGROUND OF THE INVENTION 
     Pumps with such an intermediate inlet are employed for example, in leak detectors. In leak detectors a test gas, usually helium, which enters a vessel to be tested or escapes therefrom because of leaks, is led to the intermediate inlet of the pump, then it flows in counter-current flow towards a gas detector, usually a mass spectrometer, connected to the low-pressure side of the pump. 
     Examples of such pumps are disclosed in U.S. Pat. No. 4,472,962 entitled “Low Pressure Leak-Detector” issued Sep. 25, 1984 and U.S. Pat. No. 5,585,548 entitled “Counterflow Leak-Detector Unit With A High-Vacuum Pump” issued Dec. 17, 1996. 
     The &#39;962 patent discloses a pump in which the intermediate inlet opens into an annular channel, formed in the pump housing and surrounding the rotor of an intermediate pumping stage. That pump requires a relatively high vacuum in the area where the test gas enters, a vacuum of the order of 10 −5  mbar, (1 mPa). 
     The &#39;548 patent discloses a pump in which the intermediate inlet opens into a transition chamber separating a group of low-pressure stages and a group of high-pressure stages. The chamber is limited upwards by a rotor impeller and downwards by a stator stage comprising a stationary disc, defining with the rotor shaft a constriction intended for providing a high detection sensitivity without any danger of the pressure in the test gas detector increasing to inadmissible levels. In an embodiment, the disc has a set of axially projecting strips. This pump does not require a relatively high vacuum in the inlet area of the test gas, where it tolerates pressures of the order of 0.1 mbar (10 Pa). 
     Therefore it is desirable to provide a pump with an intermediate inlet, exhibiting improved performance in terms of compression ratio and conductance of the test gas, such as helium, in order to increase the maximum pressure that can be tolerated at the intermediate port through which the test gas enters. 
     SUMMARY OF THE INVENTION 
     The present invention provides a pump where the transition chamber is limited by a stator stage integrated with a spacer ring and comprising a disc having a peripheral edge, integral with the disc and forming the spacer ring, and radial blades formed in a peripheral region of the disc and joined therewith at both a radially inner edge and a radially outer edge. 
    
    
     The above and other features of the present invention will become apparent from the following description of a preferred embodiment, given by way of non limiting example and shown in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematical cross-sectional view of a pump with an intermediate inlet, according to the present invention; 
     FIG. 2 is a perspective view of the stator stage located in correspondence with the intermediate inlet according to the present invention; 
     FIG. 3 is a plan view of the stator stage shown in FIG. 2; 
     FIG. 4 is a plan view showing the stator stage divided into two halves for allowing mounting on the rotor; 
     FIG. 5 is a cross-sectional view according to a plane passing through line A—A in FIG. 3; and 
     FIG. 6 is a cross-sectional view according to a plane passing through line B—B in FIG.  3 . 
     FIG. 7 is a schematical cross-sectional view of a pump with a plurality of stator stages located in correspondence with the intermediate inlets according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described in conjunction with an embodiment shown in FIG.  1 . 
     In FIG. 1, the turbomolecular pump generally designated  1 , has a housing  2  having a low-pressure inlet  3  that, in the application of the pump to a leak detector, is connected to the test gas detector, (not shown); a high-pressure outlet  4 , communicating with the atmosphere or a fore-pump; and an intermediate inlet  5  for the test gas, intended to flow in counter-current flow towards the detector. The turbomolecular pump  1  has multiple stages, each associated with a rotor impeller  6 , carried by a shaft  7 . Rotor impellers  6  cooperate with stator stages  8  arranged along the walls of housing  2 . Intermediate inlet  5  opens into a transition chamber  9 , separating a high-pressure pump section (the lower section), from a low-pressure pump section (the upper one). The two sections are designated  1 A and  1 B, respectively. Section  1 B is the section operating in counter-current flow in the application to a leak detector. 
     No rotor impeller is provided in correspondence with transition chamber  9  (therefore the pump has one pumping stage less than conventional pumps), and the chamber is limited upwards by a stator stage  10 . The remaining stator stages  8 , as well as rotor impellers  6 , are of a conventional type. 
     Referring to FIGS. 2 to  6 , stator stage  10  is a substantially cup-like member, comprising a disc  11  with a central bore  16  where rotor shaft  7  passes, and a side wall  12 , integral with disc  11  and acting as a spacer ring. Such a structure allows a precise location of stator stage  10  within transition chamber  9 . As shown in FIG. 4, stator stage  10  in effect comprises two identical portions  10 ′,  10 ″ that can be separated to allow mounting the stator about rotor shaft  7 . The two portions are obtained by cutting stator stage  10  along a diameter at the end of the manufacture. In FIG. 4, the elements in the two portions are designated by reference numerals with a prime or a double prime, respectively. 
     Side wall  12  axially projects from disc  11  at both sides thereof and, as shown in FIG. 1, its total height substantially corresponds with the spacing between the last stator stage  8  of low pressure section  1 B and the first stator stage  8  of high pressure section  1 A. Portion  12 A (FIG. 5) that, when the stator is mounted, is located on the side of high pressure pump section  1 A, is higher than the other portion and has a high-conductance opening  13  formed therein, which communicates with intermediate inlet  5 . Portion  12 B located on the low pressure side has instead an annular groove  14  housing a resilient ring  15  (FIG. 1) arranged to keep the two halves  10 ′,  10 ″ of stator stage  10  in contact. 
     A plurality of radial blades  17  is arranged along a peripheral portion of disc  11 . Said blades are regularly spaced along the circumference of disc  11  and are separated by channels  18  passing through the whole thickness of disc  11 . Blades  17  are joined with disc  11  not only at their radially inner edges, but also at their radially outer edges, where they end in correspondence of spacer ring  12 . Also the corresponding separation channels  18  are thus closed at both ends. 
     As clearly shown in FIG. 6, blades  17  form a very narrow angle with the plane of disc  11 , and adjacent blades  17  overlap, leaving very narrow channels therebetween, so that the stage is made optically opaque in the axial direction. In the embodiment shown, with eighteen blades, the angle is of about 10° and the separation channels have a constant thickness s of about 1 mm in the radial direction. Those values allow attaining, at stator stage  10 , a compression ratio of 2 for nitrogen and maintaining a molecular gas flow in the direction from inlet  3  to outlet  4  up to pressures as high as about 100 mtorr (1,333 Pa)—that is the pump can tolerate a pressure of 1,333 Pa in the transition chamber—without losing the compression capacity of the upper stages. 
     It is evident that the above description is given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention. In particular, the pump that is shown in FIG. 7 could include a plurality of stator stages made like stage  10 .