Patent Publication Number: US-2005121640-A1

Title: Flow control device for fluids

Description:
TECHNICAL FIELD  
      The present invention relates to a flow control device for fluids.  
      The present invention relates more particularly to a flow control device for fluids of the type comprising a duct having a predetermined inner port and a shutter member for the port mounted to move within the duct.  
     BACKGROUND ART  
      Control devices of the type described above, although universally used, are not normally very suited for use in cases in which it is necessary to control, with a relatively high degree of precision, the flow of fluid through the above-mentioned port when the shutter member assumes positions close to a position of total closure of the port, since relatively small displacements of the moving shutter member from its closed position generally cause relatively high variations of the flow of fluid through the port controlled by the moving shutter member.  
     DISCLOSURE OF THE INVENTION  
      The object of the present invention is to provide a duct for the passage of fluids, which is free from the drawbacks described above and which is at the same time easy and economic to produce.  
      The present invention relates to a flow control device for fluids, the control device comprising a duct having a predetermined inner port, and a shutter member for the port mounted to move within the duct, characterised in that it comprises, on each side of the moving shutter member, a fixed shutter member for the port, each fixed shutter member being limited by an inner surface having a predetermined shape and the fixed shutter members being adapted to cooperate with the moving shutter member to define a hydraulic resistance varying according to a predetermined law which is a function of this shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described below in further detail, with reference to the accompanying drawings, which show a number of non-limiting embodiments, and in which:  
       FIG. 1  is an axial section through a preferred embodiment of the control device of the present invention;  
       FIG. 2  is a cross-section along the line II-II of  FIG. 1 ;  
       FIGS. 3 and 4  show, in axial section, two further embodiments of the control device of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      In  FIGS. 1 and 2 , a flow control device for fluids is shown overall by  1  and comprises a duct  2  and a moving shutter member  3  housed in the duct  2  at the location of its annular seat  4  and adapted to be displaced with respect to the seat  4  in order to vary the working flow section of a fluid through a port  4   a  formed by this seat  4 .  
      The duct  2  comprises two cylindrical portions  5 , shown respectively by  5   a  and  5   b , having substantially identical inner diameters and disposed upstream and downstream respectively of the seat  4 . The portions  5  are connected together at the location of respective flanges  6  in contact with one another along a transverse median plane  7  of the seat  4  and have respective longitudinal axes  8   a  and  8   b  which are parallel to one another and perpendicular to the transverse median plane  7 , both lie in the plane of  FIG. 1  and are disposed at a predetermined distance D from one another with the longitudinal axis  8   a  disposed, in  FIG. 1 , above the longitudinal axis  8   b . Following the offset position of the two portions  5 , the union between these two portions  5  at the location of the transverse median plane  7  defines two shoulders  9 , shown respectively by  9   a  and  9   b , of half-moon shape, respectively facing the portion  5   a  and the portion  5   b , which are subsequently made frustoconical, with opposing conicity, by means of internal working and overall form the seat  4 . Each shoulder  9  has two opposite ends, at which the width of the shoulder  9  is reduced to zero, disposed on a same longitudinal median plane  10  extending longitudinally along the entire duct  2 , perpendicular to the plane of  FIG. 1  and equidistant from the longitudinal axes Ba and  8   b.    
      The intersection between the planes  7  and  10  defines the axis of rotation  11  of a butterfly shutter  12  forming part of the shutter member  3 , which further comprises a pin  13  rigid with the butterfly shutter  12  and coaxial with the axis of rotation  11 . The pin  13  comprises two portions mounted idly through respective substantially radial holes  14  obtained through the wall of the duct  2  coaxially with the axis of rotation  11  and a control portion  15  disposed externally to the duct  2 . The butterfly shutter  12  comprises two flanges  16 , shown respectively by  16   a  and  16   b , which are substantially cylindrical, intersect with one another along a plane passing through the axis of rotation  11 , and have respective parallel axes which are disposed coaxially with the longitudinal axes  8   a  and  8   b  respectively when the butterfly shutter  12  is in a position parallel to the transverse median plane  7  and closing the port  4   a  (shown in continuous lines in  FIG. 1 ).  
      Part of the outer lateral surface of each flange  16  is defined by a frustoconical surface  17  which is complementary with the frustoconical surface of the relative shoulder  9  and is coupled in a leak-tight manner with the relative shoulder  9  when the butterfly shutter  12  is in its closed position.  
      The device  1  further comprises two fixed shutter members  18 , shown respectively by  18   a  and  18   b , which cooperate with the butterfly shutter  12  in order to close off the port  4   a  and are respectively disposed within the portions  5   a  and  5   b  and on opposite sides of the longitudinal median plane  10 . Each fixed shutter member  18  forms a single piece with the respective portion  5 .  
      Each fixed shutter member  18  has a semi-cylindrical inner surface  19  which is concave and coaxial with the respective longitudinal axis  8  and which is traversed by a plurality of axial grooves  20  of substantially triangular section with their vertices facing the exterior of the duct  2 , and is limited, on the side facing the butterfly shutter  12 , by a concave end surface  21  which intersects the grooves  20 . Each concave end surface  21  has a shape substantially complementary with a respective part of a convex surface  22  of a rotational solid generated by the rotation of the butterfly shutter  12  about the axis of rotation  11 . In particular, the points A of the convex surface  22  arranged along a same generatrix of this convex surface  22  are disposed at a relatively small and constant distance from respective corresponding points B of the concave end surface  21 .  
      In operation, during a first part of the rotation of the butterfly shutter  12  about the axis of rotation  11  from its rest position in contact with the seat  4 , the outer profile of each flange  16  is maintained at a substantially constant and relatively small (normally of the order of some tenths of a millimetre) distance from the relative end surface  21  allowing the passage, through the port  4   a , substantially only of the fluid passing through that part of each end section of each groove  20  which is gradually exposed by the butterfly shutter  12 . Since the section of each groove  20  is triangular with its vertex facing outwards, the free port through which the fluid may flow increases in a relatively modest way with the variation of the angle of opening of the butterfly shutter  12  when the outer profile of each flange  16  of the butterfly shutter  12  remains facing the relative end surface  21  allowing the control device  1  to control, with relatively high precision, the flow of fluid through the port  4   a  at relatively small opening angles from the above-mentioned closed position.  
      The variant shown in  FIG. 3  relates to a control device  23  similar to the control device  1 , whose members bear the same reference numerals as corresponding members of the control device  1 .  
      The control device  23  differs from the control device  1  substantially only in that, in the control device  23 , each end surface  21  is shaped as a parabolic or elliptical crown such that the points A arranged along a same generatrix of the convex surface  22  are disposed, with respect to the corresponding points B of the end surface  21 , at distances that are relatively small but that grow as the distance of the points A from the transverse median plane  7  increases.  
      The variant shown in  FIG. 4  is completely identical to the variant shown in  FIG. 3 , from which it differs only in that, in the variant of  FIG. 4 , the grooves  20  are omitted.  
      According to a variant which is not shown, each fixed shutter member  18  does not form a single piece with the respective portion  5 , but is disposed within the respective portion  5  and in contact with an inner surface of this respective portion  5 .