Abstract:
In order to provide an improved multistage oil separator, in particular for the use with compressors in cryogenics, the oil separator includes a housing ( 10 ) having a gas inlet ( 18 ) and a gas outlet ( 20 ), and at least two filter elements ( 26, 28 ) arranged as a cascade in the housing between the gas inlet ( 18 ) and the gas outlet ( 20 ).

Description:
BACKGROUND 
     The invention relates to a multistage oil separator, particularly for use in compressors in cryotechnology. 
     In a cryo pump, helium will be condensed by a compressor to about 20-25 bar and, by subsequent expansion down to a pressure between about 1 and 8 bar, the helium will be cooled. For this purpose, the helium must have a high degree of purity. Condensation is typically performed by use of oil-sealed scroll compressors wherein parts of the oil will enter the helium. To avoid condensation or solidification, as much oil as technically feasible has to be separated. 
     To this end, use has been made heretofore of oil separators wherein oil is passed through one or a plurality of filter units. 
     It is an object of the invention to provide an improved oil separator. 
     SUMMARY 
     According to one aspect of the present invention, the oil separator is of a multi-stage configuration comprising a housing having a gas inlet and a gas outlet, at least two filter elements being arranged as a cascade in the housing between the gas inlet and the gas outlet. Arrangement of a plurality of filter elements in a common housing makes it possible to reduce the costs for the housing. 
     Preferably, for discharging the separated oil from the housing, an oil passage is provided at least between the last filter element of the cascade and the gas outlet, while the separated oil can be returned into the compressor system. In a vertical arrangement, the possibility exists that, under the effect of gravity, the separated oil will run down on the filter elements. In this regard, it is advantageous if an oil passage is formed in the housing near the filter element so that the oil running down on the filter element will creep in the direction of said oil passage. For catching the oil, an indentation can be formed in the housing which, in the manner of an eaves gutter, will guide the caught oil toward the oil passage. Preferably, at least one oil passage is provided behind each filter element. The oil passages can enter a common channel for returning the oil. 
     The filters can be fastened to a common housing flange wherein the return conveyance of the oil can be performed through the housing flange. Herein, the filter elements can be formed by the outer surfaces of cylindrical cartridges having differently sized diameters, at least two filter cartridges being located on a common longitudinal axis. In this case, there can be provided an arrangement of the two filter elements on a common axis on respectively mutually opposite sides of the housing flange, which is to say that, in a vertical arrangement of the filter cartridges, one filter element is attached standing on the flange and the other one is attached suspended from the flange. During the passage of the gas through the cylindrical filter element from the inside to the outside, the gas can be guided first via a channel through the flange into the interior of the smaller-diametered filter cartridge wherein the gas, after flowing through this filter element, can be guided via a further channel through the flange into the interior of the larger-diametered filter element. 
     By way of alternative, it is of particular advantage if at least two filter cartridges arranged on a common axis are placed on the same side of the housing flange so that the filter cartridges are inserted into each other. The smaller-diametered filter cartridge is preferably fully contained in the larger-diametered filter cartridge. The gas inlet into the housing can be guided into the interior of the filter cartridge through the housing flange, wherein the gas is flowing toward the outside through the filter elements on the same side of the housing flange in radial direction relative to the common axis. There can also be envisioned a combination of the arrangement of a plurality of mutually inserted filter elements on different sides of the housing, wherein the gas will first flow radially through the mutually inserted filter cartridges on one flange side and subsequently will flow radially through the mutually inserted filter cartridges on the other flange side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention will be explained in greater detail hereunder with reference to the FIGURE. The FIGURE shows a longitudinal sectional view of a multi-staged oil separator. 
     
    
    
     DETAILED DESCRIPTION 
     Said oil separator comprises a substantially cylindrical outer housing  10  having a housing flange  12  and a housing lid  14 . Housing lid  14  is provided as a cylindrical bell which is mounted on housing flange  12  and removably attached thereto. One end side of the cylindrical housing is formed by housing flange  12 , and the other, opposite end side is formed by a part of housing lid  14 . The substantially cylindrical housing  10  is configured with rotational symmetry relative to a longitudinal axis  16 . 
     In said housing flange  12 , a gas inlet  18  is formed in the region of longitudinal axis  16 . In the opposite end side formed by a part of housing lid  14 , a gas outlet  20  is formed in the region of longitudinal axis  16 . Longitudinal axis  16  is oriented vertically. 
     On flange  12 , within housing lid  14 , two filter cartridges  22 , 24  of substantially cylindrical shape are detachably fastened. The two filter cartridges  22 ,  24  are each formed with rotational symmetry relative to longitudinal axis  16 , the diameter of the inner filter cartridge  22  being smaller than the diameter of the outer filter cartridge  24 . The filter elements  26 , 28  are each formed by the cylindrical outer surface of the respective filter cartridge  22 , 24 . Each of the filter cartridges  22 , 24  is closed by a cartridge lid  30 , 32  on its end side opposite to flange  12 . The filter cartridges  22 , 24  are each fastened in an indentation  34 , 36  extending in an annular configuration about the longitudinal axis  16 . Filter element  26  is inserted into, and bonded to, the inner indentation  34 . In a corresponding manner, the outer filter element  28  is inserted into, and bonded to, the outer indentation  36 . 
     Between said indentations  34 , 36 , flange  12  is provided with an a continuous annular groove  38  having its center on the longitudinal axis  16 , said groove serving for catching the oil separated by filter element  26 . In a corresponding manner, a continuous annular groove  40  having its center on the longitudinal axis  16  is provided externally of indentation  36 , said groove serving for catching the oil separated by filter element  28 . At the bottom end of each groove  38 , 40 , a respective oil passage  42 , 44  is formed through flange  12 . The two oil passages enter a common channel, not shown in the FIGURE, through which the separated oil caught by the grooves  38 , 40  will be returned to the compressor system. 
     The gas to be cleansed will flow through the gas inlet  18  into the housing  10  and into the inner filter cartridge  22  and, from there, radially outward through the filter elements  26 , 28 . Subsequently, the gas will be directed from the housing lid  14  toward the gas outlet  20  through which the gas will leave the housing  10  again. While the gas is passing through the filter elements  26 , 28 , the filter elements  26 , 28  catch the separated oil. Under the influence of gravity, the separated oil will run along on the outer sides of the filter elements  26 , 28  towards the respective groove  38 , 40  and, via the groove  38 , 40 , will be guided toward the respective oil passage  42 , 44 . The filter cartridges  22 , 24  are located internally of the housing in the high-pressure region of the system so that, due to the pressure difference, the separated oil will be returned through the oil passages  42 , 44  in the direction toward the low pressure side of the system. 
     The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.