Abstract:
The seed distribution tower of an air seeder splits a single, primary stream of conveying air and seeds into a plurality of secondary streams for delivery to openers that deposit the seeds into the ground as the seeder advances. As seeds enter the head of the tower in an upward vertical direction through an inlet at the bottom of the head, they are scattered 360° in a horizontal direction by an inverted, overhead distribution cone. The inlet through which the seeds enter the distribution head has an eased configuration to reduce turbulence and promote laminar flow within the head during the dramatic transition from vertical to horizontal movement. Sensitive components such as tram line valves, solenoid actuators, and blockage sensors are protectively housed within the interior of the distribution head to avoid exposure to hostile environmental elements.

Description:
TECHNICAL FIELD 
     The present invention relates to air seeders and, more particularly, to improvements in the way in which a primary stream of air and seeds from a bulk source of supply on the machine is divided into a multiplicity of secondary streams for conveyance to individual openers that deposit the seeds into the ground as the machine advances. 
     BACKGROUND AND SUMMARY 
     It is well known in the farm equipment industry to meter seeds or other particulate materials from bulk supply hoppers on the seeder into one or more airstreams that transport the seeds to a corresponding number of distribution towers, where each primary stream of air and seeds is divided into a number of secondary streams. The secondary streams are then directed to openers on the machine that deposit the seeds into the ground as the seeder advances. 
     It is also well known to temporarily shut off one or more of the hoses that carry the secondary streams so that the corresponding opener does not deposit any seeds, thereby creating a plant-free row in the field sometimes known as a tram line. Valves and electrically energized valve actuators of various types have been employed to carry out this function. In addition, electronic sensors have typically been provided on the secondary hoses to detect whether seeds are in fact passing through the hoses as anticipated. However, seeders necessarily operate in relatively harsh environments, and in the past the sensitive valves, actuators and sensors have been subject to malfunction and premature wear due to excessive exposure to such hostile conditions. 
     As the primary stream of air and seeds enters the distribution head of the tower through an inlet in the bottom of the head, the seeds are subjected to an abrupt right angle change in direction as they are split into secondary streams and exit the head horizontally. In prior towers, a significant amount of turbulence has been created at this location that can adversely affect the output rate of the tower and may damage the seeds. 
     Accordingly, the present invention provides a seed distribution tower wherein sensitive devices such as tram line valves, actuators and/or sensors are protectively housed within the interior of the distribution head of the tower, away from harsh environmental elements that could damage or ruin the devices. In another aspect of the present invention, the distribution head of a seed distribution tower is provided with an internal plenum configured to reduce turbulence and promote more laminar flow as the primary stream splits into secondary streams and transitions from vertical to horizontal movement, thereby increasing the flow rate through the tower and reducing seed damage. An eased inlet into the bottom of the plenum from the conduit eliminates the squared off corner of prior designs to assist the incoming air and seeds in making a smooth transition. In one embodiment, the eased inlet comprises an opening in the floor of the plenum and a raised rim around such opening, preferably arcuate in transverse cross-section, An inverted overhead cone projects down from the top wall of the plenum in concentric relationship with the inlet to cooperate in transitioning and splitting primary stream. Other embodiments include a beveled opening into the plenum having either substantially flat or rounded sloping sidewalls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a left, front perspective view of a cultivation air seeder utilizing seed distribution towers in accordance with the principles of the present invention; 
         FIG. 2  is a left side elevational view of the seeder; 
         FIG. 3  is an enlarged left front perspective view of one of the distribution towers of the seeder with the secondary distribution hoses removed for clarity; 
         FIG. 4  is an enlarged, fragmentary bottom perspective view of the tower with parts broken away to reveal details of construction; 
         FIG. 5  is a fragmentary exploded view of the tower; 
         FIG. 6  is a top plan view of the tower; 
         FIG. 7  is a fragmentary vertical cross-sectional view through the upper end of the tower taken substantially along line  7 - 7  of  FIG. 6 ; 
         FIG. 8  is an enlarged, fragmentary vertical cross-sectional view through the tower taken substantially along line  8 - 8  of  FIG. 6 ; 
         FIG. 9  is an enlarged front perspective cross-sectional view of one of the blockage sensors of the tower; 
         FIG. 10  is a top perspective view of the lower disc of the stacked assembly of parts comprising the distribution head of the tower; 
         FIG. 11  is an enlarged, fragmentary cross-sectional view through part of the lower disc illustrating details of construction; 
         FIG. 12  is a bottom perspective view of the lower disc; 
         FIG. 13  is a bottom perspective view of the top disc of the stacked assembly of parts comprising the distribution head of the tower; 
         FIG. 14  is a top perspective view of the top disc; 
         FIG. 15  is a top perspective view of the inspection plate of the distribution head; 
         FIG. 16  is a bottom perspective view of the inspection plate, illustrating the attached transition cone in cross-section; 
         FIG. 17  is a fragmentary, vertical cross-sectional view through an alternative embodiment of the tower illustrating another form of eased transition inlet into the distribution head; and 
         FIG. 18  is a fragmentary, vertical cross-sectional view through another alternative embodiment of the tower illustrating a further form of eased transition inlet. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is susceptible of embodiment in many different forms. While the drawings illustrate, and the specification describes, certain specific embodiments of the invention, it is to be understood that such disclosure is by way of example only. The principles of the present invention are not limited to the particular disclosed embodiments. 
     With initial reference to  FIGS. 1 and 2 , an exemplary air seeder that may incorporate a seed distribution tower in accordance with the present invention is broadly denoted by the numeral  10  and is provided with a mobile chassis or frame  12  having a tongue  14  and hitch structure  16  for connecting seeder  10  to a suitable towing tractor or other vehicle (not shown). A number of ground-engaging wheels  18  are disposed across the rear of frame  12  to support the frame for over-the-ground travel. In the exemplary disclosed embodiment, seeder  10  comprises a cultivation air seeder and is thus provided with a set of cultivation tools  20  on frame  12  ahead of wheels  18 . It will be appreciated, however, that the principles of the present invention may be readily employed on many different types of air seeders and are not limited to use with a cultivation air seeder. A row of openers  22  of any suitable construction well known to those skilled in the art is supported across the rear of frame  12  behind wheels  18 . In the illustrated embodiment, seeder  10  comprises a three-section machine, such that frame  12  has a main frame section  24  and pair of left and right wing frame sections  25 ,  26  respectively, although the number of frame sections is not of importance insofar as the principles of the present invention are concerned. When applied to various parts of the machine, the terms “left” and “right” are utilized as if the machine were being viewed from the rear, looking forwardly. 
     Seeder  10  further comprises a hopper  28  supported on main frame section  24  for holding a supply of seeds and/or fertilizer or other particulate materials to be distributed to openers  22 . Although the illustrated embodiment of the invention will be described in connection with the holding and distribution of seeds by hopper  28 , it will be appreciated that the principles of the present invention are not limited to seeds and may, in fact, be utilized in connection with many different kinds of particulate materials. 
     A meter  30  at the bottom of hopper  28  may be utilized to dispense seeds at a metered rate into one or more conduits  32  that transport the metered seeds within an airstream toward the rear of the machine. One or more distribution towers  34  in accordance with the present invention are coupled with conduits  32  downstream from meter  30  for the purpose of dividing each primary stream of seeds into a multiplicity of secondary streams that flow to the openers  22  through hoses  35  (only a limited number being shown in the interest of clarity). A blower  36  adjacent the lower front end of hopper  28  supplies the transporting air for conduits  32  and the secondary hoses  35 . 
     Hopper  28  may be constructed in a variety of different shapes and sizes, and from a variety of different materials. In the illustrated embodiment, hopper  28  is constructed from sheet metal and is covered on three sides by an ornamental facing  29  of molded ABS plastic or the like, which is the subject of related application Ser. No. 13/157,856 titled “Cultivation Air Seeder With Visually Enhanced Seed Hopper”, assigned to the assignee of the present invention. 
     Each of the towers  34  includes an upright pipe or conduit  38  fixed to frame  12  and connected at its lower end to the conduit  32  from hopper  28 . Conduit  38  may be provided with a multitude of exterior dimples  40  that form corresponding interior projections disposed to be impinged by seeds in the moving primary stream to aid in scattering the seeds as they approach the upper end of conduit  38 . A generally flat, circular distribution head  42  is secured to the upper end of conduit  38  for splitting the primary stream into the secondary streams and transitioning the direction of seed flow from generally vertical to generally horizontal. 
     With reference to  FIG. 7 , in general terms distribution head  42  has an exterior  44  and a hollow interior  46 . Interior  46  includes a plenum  48  that communicates with the upper end of conduit  38  via an eased inlet  49  that in one embodiment comprises (in part) a circular opening  50  in a floor  52  of plenum  48 . Opening  50  surrounds the upper end of conduit  38  and is coaxially aligned therewith. 
     A series of outlets  54  within interior  46  extend circumferentially about the outer periphery of plenum  48  in communication therewith and are arranged on generally horizontal axes that project radially outwardly from the central axis of opening  50 , in the nature of spokes of a wheel. A corresponding number of elbow fittings  56  are disposed around the exterior  44  of head  42  and are coupled with corresponding outlets  54 . Fittings  56  are configured to attach to the corresponding secondary hoses that lead to the openers  22 . 
     Distribution head  42  is adapted to facilitate tram line farming wherein one or more of the outlets  54  may be selectively closed off to prevent the delivery of seeds to the opener corresponding to the closed outlet. In the illustrated embodiment, distribution head  42  is adapted for selectively closing off a maximum of two diametrically opposed outlets  54 , although there may be a smaller or greater number of such closable outlets without departing from the principles of the present invention. To carry out such closing function, a valve  58  ( FIGS. 5 ,  7 ) is located within the interior  46  of head  42  at the radially inner end of each closable outlet  54  (only one such valve being illustrated), adjacent the outer periphery of plenum  48 . Valve  58  is adapted to be actuated between a closed position blocking communication between plenum  48  and outlet  54 , and an open position permitting such communication. Thus, when valve  58  is closed, seeds transitioning from conduit  38  to outlets  54  are not permitted to enter closed outlet  54  such that no seeds are delivered to the opener  22  for that particular closed outlet. Seeds that would otherwise enter the closed outlet  54  are thus deflected back into plenum  48  for random and even distribution to the unblocked outlets  54 . 
     In the particular embodiment disclosed in the drawings, valve  58  is a flapper valve that opens and closes by pivoting about a transverse axis, although valve  58  could take a variety of different forms without departing from the principles of the present invention. Valve  58  has a generally rectangular flapper  60  that stands generally upright when in the closed position and lies down generally horizontally when in the open position. A transversely extending pivot rod  62  is fixed to flapper  60  across its lower end and is rotatably retained within the floor  52  of plenum  48  to define the axis of pivoting movement. 
     An operating arm  64  is fixed to rod  62  and projects downwardly therefrom through floor  52  where it is operably coupled with a solenoid actuator  66  housed within a chamber  68  beneath floor  52 , but still within the interior  46  of distribution head  42 . Solenoid  66  has a stem  70  that is retracted when flapper  60  is in the closed position and extended when flapper  60  is in the open position. In a preferred embodiment, stem  70  retracts when solenoid  66  is energized, thus closing the outlet, but stem  70  is not spring-loaded such that when solenoid  66  is in a deenergized condition the pressure of a secondary stream seeking to leave plenum  48  freely pivots flapper  60  to its open position, which pulls stem  70  out to an extended position. Arm  64  is connected to stem  70  by a transverse pin  72 , and an elongated slot  74  in arm  64  receives pin  72  so as to accommodate the fact that arm  64  swings arcuately while stem moves linearly. Solenoid  66  has an electrical conductor  75  that connects solenoid  66  with a source of electrical potential, including a controller (not shown). A connector  77  may be provided at a distal end of conductor  75  to facilitate such connection. 
     Each of the outlets  54  includes a sensor  76  ( FIGS. 5 ,  7 ,  9 ) for detecting the movement or non-movement of seeds through outlet  54 . Each sensor  76  is disposed within the interior  46  of distribution head  72  in association with the outlet  54 , rather than being located on the exterior  44  of the head. In the exemplary embodiment shown in the drawings, each sensor  76  is constructed to serve as part of the outlet  54  with which it is associated. In this respect, a main portion of each sensor  76  comprises a tube  78  having a central passage  80 , an inboard end  82 , and an outboard end  84 . Inboard end  82  is closest to plenum  48 , while outboard end  84  receives the fitting  56 . 
     Details of the sensor  76  are illustrated in  FIG. 9 . In the illustrated embodiment, each sensor  76  comprises an optical sensor, although a variety of other types of sensors could be utilized, such as, for example, an audio sensor, a pressure sensor, or an impact sensor. Accordingly, the tube  78  of each sensor  76  carries a pair of photo cells  86 ,  88  arranged in diametrically opposed locations on tube  78  for transmitting a light beam across passage  80 . One of the cells is a sender and the other is a receiver. Breaking of the light beam by moving seeds is utilized to confirm the fact that seeds are indeed being dispensed through the outlet. A clear lens  85  covers cell  86 , while a clear lens  87  covers cell  88 . A protective cup  90  surrounds tube  78  and the photo cells  86 ,  88  and contains a pair of circuit boards  89 ,  89   a  embedded within potting material  91 , the boards  89 ,  89   a  being connected with cells  86 ,  88 . Suitable boards  89 ,  89   a  are available from DICKEY-john Corporation of Auburn, Ill. as the VIGILENSE brand blockage sensor. An electrical conductor  92  is connected to boards  89 ,  89   a  and is located within chamber  68  below floor  52 . Each conductor  92  has a connector  94  at its distal end for connecting sensors  76  with an appropriate control system of the machine. 
     With reference to  FIG. 4 , the conductors  92  from sensors  76  and the conductor(s)  75  from solenoid(s)  66  lead generally radially inwardly from sensors  76  and solenoid(s)  66  toward conduit  38  and pass downwardly through a number of holes  96  in a circular, horizontal plate  98  that forms the bottom of distribution head  42 . Plate  98  is welded or otherwise rigidly affixed to the upper end of conduit  38  and cooperates with the floor  52  of plenum  48  to define the chamber  68  within which the solenoids  66  are located. A bowl-shaped housing  100  is attached to the bottom of plate  98  and has an opening  102  that receives and clears the conduit  38 . Housing  100  thus defines a protected compartment  104  immediately below the bottom of distribution head  42  within which electrical hardware such as portions of conductors  75 ,  92  and connectors  77 ,  94  may be disposed. Leads  106  forming part of the control system of the seeder may be routed upwardly through opening  102  and joined with the connectors  77 ,  94  within compartment  104 . 
     Plenum  48  has a top wall  108  ( FIG. 7 ) that is specially configured to cause the incoming primary stream of air and seeds to effectually transition from vertical to horizontal and split into the desired secondary streams. In this respect top wall  108  is provided with an inverted, centrally disposed transition cone  110  that is coaxial with conduit  38  and opening  50 . Preferably, the cone  110  is so sized that its tip  112  projects downwardly into and slightly beyond opening  50 , terminating within the upper end of conduit  38 . Preferably also, the periphery  114  of cone  110  is parabolic in cross-section. 
     To provide additional guidance and smoothing for the air and seeds as they enter plenum  48  from conduit  38 , the inlet  49  is constructed in the nature of an eased inlet so as to soften what would otherwise be a sharp, right angle corner or edge encountered by the air and seeds during their transition. In one embodiment, the eased inlet  49  comprises the planar opening  50  in floor  52  and a raised rim  116  around opening  50 . Preferably, rim  116  is transversely rounded such that its upwardly facing surface  116   a  is arcuate. Rounded surface  116   a  is not necessarily concentric with the parabolic periphery  114  of cone  110  and is preferably a complex curve having a plurality of radii of curvature. 
     With reference to  FIGS. 5-8  and  10 - 16 , each distribution head  42  may advantageously be constructed from a stacked assembly of parts. Plate  98  may serve as the support for the stack inasmuch as plate  98  is rigidly affixed to conduit  38 . A first or lower disc  118 , preferably molded from a relatively hard, rubber-like material such as poured urethane, overlies plate  98  and is attached thereto by a plurality of bolts  120  (see also  FIG. 7 ). Disc  118  has an annular, central collar  122  ( FIGS. 11 ,  12 ) that projects downwardly from the underside of rim  116  and encircles the upper end of conduit  38 . Collar  122  is coaxial with opening  50  and is slightly larger in internal diameter than opening  50  so as to define an undercut below rim  116  that rests upon the uppermost edge of conduit  38 . A circular web portion  124  projects outwardly from collar  122  at the base of rim  116  so as to present floor  52  of plenum  48  on the upper face of web  124  and the top of chamber  68  on the bottom face of web  124 . A series of circumferentially spaced apart, radially extending ribs  126  interconnect web  124  with an outermost, annular wall  128  that is spaced radially outwardly from the outer circumferential edge of web  124  so as to present a circumferential series of voids  130  between ribs  126 . Outer wall  128  has a flat bottom edge  128   a  that lies flatly against plate  98 . At two diametrically opposed locations, the bottom side of web  124  is provided with a recessed, radially extending seat  129  that matingly receives the body of a solenoid  66 . A transversely extending slot  131  near the radially inner end of seat  129  serves the dual functions of a pivot seat for the rod  62  of flapper  60  and clearance for operating arm  64 . 
     Referring particularly to  FIGS. 10 and 11 , the top edge  128   b  of outer wall  128  is scalloped to present a series of equally circumferentially spaced semi-circular notches  132  configured to complementally receive the semi-circular bottom parts of the inner end of fittings  56 . The ribs  126  are thicker in a vertical dimension than web  124  so as to project upwardly beyond the plane of web  124  on the top side of disc  118  and downwardly below the plane of web  124  on the bottom side of disc  118 . On the top side of disc  118  ribs  126  taper toward a radially innermost tip  134  that stops short of opening  50  and rim  116  to define the radially outer margin of plenum  46 . Adjacent pairs of the tips  134  also define the entry end of outlets  54 , and it will be noted that the flapper  60  is located at such entry end of its outlet  54 . Spaced radially outwardly from tips  134  and at the radially inner extremity of the voids  130  are semi-circular, concave saddles  136  configured to matingly receive locating rings  138  ( FIGS. 7 ,  9 ) on the exterior of sensor tubes  78 . 
     A second or top disc  140  ( FIGS. 13 ,  14 ) is stacked on top of lower disc  118  and is preferably molded from the same relatively hard rubber material (such as poured urethane) as lower disc  118 . Top disc  140  has the same outer diameter as lower disc  118 , but is provided with a significantly larger central opening  142  that is coaxial with opening  50 . An annular web portion  144  surrounds opening  142  and is connected to an outermost annular wall  146  by a series of circumferentially spaced apart, radially extending ribs  148 . Voids  150  are defined between adjacent ones of the ribs  148 . 
     The top side of disc  140  is flat ( FIG. 14 ), except for a shallow annular valley  151  between opening  142  and voids  150 , but its bottom side ( FIG. 13 ) is configured to cooperate with lower disc  118  in defining portions of the outlets  54  and means for locating and confining the sensors  76 . To this end, on the bottom side of disc  140  web  144  is dished out to present a recessed annulus  152 , and ribs  148  continue inwardly across annulus  152  to the edge of opening  142 . Thus, ribs  144  on the bottom side of top disc  140  are configured substantially the same as ribs  126  on the top side of bottom disc  118  and are disposed in vertical registration therewith. Consequently, the stacked ribs  126  and  148  cooperate to define the side boundaries of outlets  54  for the width of web  144 , while the annulus  152  defines the top boundary of the outlets  54  over that same radial width. When a valve  58  is in its closed position, flapper  60  thereof traverses substantially the entire vertical height of the outlet  54  between floor  52  and annulus  152 . 
     Outer wall  146  is scalloped along its lower edge in the same manner as the upper edge of lower disc  118 . Thus, a series of semi-circular notches  154  are defined in the lower edge  146   a  of wall  146  that register with corresponding notches  132  in lower disc  118 . Notches  132  and  154  thus cooperate to matingly receive and retain the inner end of corresponding elbow fittings  56 . The top portions of cups  90  of sensors  76  are received within the voids  150 , while semi-circular saddles  156  at the radially inner ends of voids  150  register with corresponding saddles  136  on lower disc  118  to receive and confine the locating rings  138  on tubes  78  of sensors  76 . 
     An annular top plate  158  ( FIGS. 5 ,  7 ) having the same outer diameter as discs  118  and  140  overlies top disc  140 . A plurality of long bolts  159  near the outer periphery of plate  158  pass downwardly through plate  158 , top disc  140 , bottom disc  118 , and support plate  98  to clamp such parts together in a sandwich-like assembly. Housing  100  is attached to support plate  98  by a series of screws  160  ( FIG. 7 ) that pass upwardly through an outmost circumferential flange  162  around housing  100 . Cover plate  158  is provided with a number of upwardly projecting, externally threaded studs  164  ( FIGS. 5 ,  8 ) for a purpose hereinafter explained in more detail. The heads of studs  164  project downwardly from the bottom side of cover plate  158  and are received within valley  151  to avoid interference with top disc  140 . 
     Transition cone  110  is provided with a relatively thick, circular base  110   a  ( FIGS. 5 ,  7 ,  16 ) that is slightly smaller in diameter than opening  142  in top disc 140 . The thickness of base  110   a  is substantially the same as the combined thickness of top disc  140  and cover plate  158 . Cone  110  is affixed to an inspection plate  166  ( FIGS. 5 ,  7 ,  15 ,  16 ) by a series of screws  168 , and inspection plate  166  has a nominal diameter that is greater than opening  142 . Accordingly, inspection plate  166  and cone  110  comprise an assembled unit wherein cone  110  fits within opening  142  and plate  166  overlaps the inner margin of top plate  158  to limit the depth of insertion of cone  110  into opening  142 . Manifestly, this also establishes the working position of cone tip  112  with respect to rim  116 , opening  50 , and the upper end of conduit  38 . 
     The unit that comprises cone  110  and inspection plate  166  may be conveniently installed and removed utilizing a handle  170  on the top of inspection plate  166 . The peripheral edge of inspection plate  166  is configured to present four hooks  172  that open in a clockwise-facing direction and are sized to receive the studs  164  on top plate  158  when cone  110  is inserted into opening  142 , inspection plate  166  is brought into abutting engagement with top plate  158 , and inspection plate  166  is then rotated a short distance in a clockwise direction utilizing handle  170 . A set of four internally threaded knobs  174  receive the externally threaded studs  164  for the purpose of releasably retaining inspection plate  166  on the studs  164 . When knobs  174  are threaded downwardly on studs  164  to tightly bear against inspection plate  166 , inspection plate  166  and cone  110  are held securely in place. Conversely, when knobs  174  are slightly backed off from a tight condition, inspection plate  166  and cone  110  may be slightly rotated in a counterclockwise direction to disengage hooks  172  from studs  164  and then lifted up and away from top plate  158  to provide inspection and access to the interior  46  of distribution head  42  via opening  142 . 
     It should be apparent from the foregoing description that a distribution tower constructed in accordance with the principles of towers  34  provides a number of distinct advantages. Instead of being exposed to hostile environmental elements, critical and sensitive components associated with tower  34  are protectively contained within the interior  46  of distribution head  42 . For example, tram line valves  58  are disposed within plenum  48 , rather than on the exterior  44  of head  42  or elsewhere. Similarly, the solenoid actuators  66  for valves  58  are contained within the chamber  68  between support plate  98  and floor  52  of plenum  48 . 
     In addition, sensors  76  are associated with outlets  54  inboard of elbow fittings  56  and are covered at the top and bottom by top plate  164  and support plate  98 . Much of the conductors associated with sensors  76  and solenoids  66  are disposed within chamber  68 , while that which extends below distribution head  42  is protectively received within compartment  104  of housing  100 . The connectors between the conductors and leads are likewise well protected within compartment  104 . While it is thus desirable that most of such sensitive components and hardware be contained within the interior  46  of distribution head  42 , it is within the scope of the present invention to have less than all of such components so located. 
     It will be noted that as the primary stream of air and seeds passes upwardly through conduit  38  and the eased inlet  49  into the plenum  48 , such stream encounters the downwardly projecting distribution cone  110 . The parabolic periphery  114  of cone  110  gently splits the primary stream and disperses the seeds and air 360° into secondary streams that enter the outlets  54  on their way to the openers  22 . In the first embodiment, raised rim  116  around opening  50  gently guides the seeds and air into plenum  48  while avoiding the presence of sharp corners that could otherwise cause turbulence and disruption of the flow. Consequently, it has been found that the flow rate through distribution head  42  is increased compared to prior constructions wherein rim  116  is lacking. Thus, significant operating efficiencies and improved performance are obtained. 
     Alternative Embodiments 
     In a first alternative embodiment illustrated in  FIG. 17 , the tower  500  has an eased inlet  49   a  that comprises a beveled opening  502  into plenum  48 . Beveled opening  502  has outwardly flaring sloping sidewalls  504  that are substantially flat. The periphery of transition cone  506  in this embodiment is illustrated as being straight rather than parabolic, but a parabolic construction would also be effective. 
     In a second alternative embodiment illustrated in  FIG. 18 , the tower  600  has an eased inlet  49   b  that comprises a beveled opening  602  of slightly different construction than beveled opening  502  of tower  500 . In tower  600 , the beveled opening  602  has gently convexly rounded, outwardly flaring sidewalls  604 . Also, transition cone  606  in tower  600  has a parabolic, rather than straight, sidewall. Both of these alternative designs for the eased inlet can be expected to provide superior outcomes compared to the sharp-cornered prior art inlets. 
     The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as it pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.