Patent Publication Number: US-2003230541-A1

Title: Vibratory screening machine with suction and pressure and method for screening a slurry

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003] The present invention relates to a vibratory screening machine and method for screening a slurry to withdraw liquid and fine particles therefrom and also cause coarse particles which are not withdrawn from the slurry to be relatively dry.  
       [0004] By way of background, in the oil drilling process, drilling mud is used for its conventional purposes of lubricating the drill and carrying drilled material to the surface. The combination of drilling mud and drilled material is a slurry of fine drilling mud solids, coarse drilled material particles and liquid. The primary liquid portion of the drilling mud may be oil or water, depending on whether the drilling mud is water-based or oil-based. It is desirable to recover the drilling mud for reuse because it can be expensive. It is also desirable to withdraw the liquid from the coarse drilled material particles so that the latter can be disposed of in an efficient manner.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005] It is accordingly the primary object of the present invention to provide a vibratory screening machine which withdraws liquid and fine material from a slurry feed which is being screened to thereby cause other particles which are not withdrawn from the slurry to be relatively dry.  
       [0006] Another object of the present invention is to provide a vibratory screening machine which effects screening of a slurry in an efficient manner.  
       [0007] A further object of the present invention is to provide an improved method of screening a slurry to efficiently withdraw liquid and fine particles therefrom and thus cause the remaining particles of the slurry to be relatively dry.  
       [0008] Yet another object of the present invention is to provide an improved four-way valve which is to be used in conjunction with a vibratory screening machine. Other objects and attendant advantages will readily be perceived hereafter.  
       [0009] The present invention relates to a vibratory screening machine comprising a frame, a vibratory motor on said frame, a bed on said frame, a chamber below said bed, and a source of suction and pressure in communication with said chamber.  
       [0010] The present invention also relates to a method of screening a slurry containing a mixture of fine and coarse particles and liquid comprising the steps of providing a vibratory screen, passing said mixture across said vibratory screen, applying suction on the opposite side of said vibratory screen from said mixture to draw liquid and fine particles from said mixture through said screen, and applying pneumatic pressure to said opposite side of said screen to dislodge particles which clogged said screen.  
       [0011] The present invention also relates to a method of screening a slurry containing a mixture of fine and coarse particles and liquid comprising the steps of providing a vibratory screen, vibrating said screen at a G force of between about 3 to 12 G&#39;s, passing a slurry containing a mixture of fine and coarse particles and liquid across said screen, and applying a suction only on the opposite side of said screen from said slurry to draw fine particles and liquid through said screen, and intermittently releasing said suction.  
       [0012] The various aspects of the present invention will readily be understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein: 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0013]FIG. 1 is a fragmentary side elevational view of the vibratory screening machine taken substantially in the direction of arrows  1 - 1  of FIG. 3 and showing primarily the movable frame;  
     [0014]FIG. 1A is a fragmentary end elevational view of the machine taken substantially in the direction of arrows  1 A- 1 A of FIG. 1;  
     [0015]FIG. 2 is a fragmentary side elevational view of the vibratory screening machine taken substantially in the direction of arrows  2 - 2  of FIG. 3;  
     [0016]FIG. 2A is a fragmentary perspective view of the structure of the side wall of the movable frame shown in FIG. 2;  
     [0017]FIG. 3 is an end elevational view of the vibratory screening machine taken substantially in the direction of arrows  3 - 3  of FIG. 1;  
     [0018]FIG. 3A is a fragmentary perspective view of the resilient connections between the stationary frame and the movable frame at the outlet end of the machine;  
     [0019]FIG. 4 is a view taken substantially in the direction of arrows  4 - 4  of FIG. 1 and showing various structural features of the movable frame including the screens;  
     [0020]FIG. 4A is a cross sectional view of the movable frame taken substantially along line  4 A- 4 A of FIG. 4;  
     [0021]FIG. 4B is a fragmentary perspective view of the flat screen at the outlet end of the movable frame;  
     [0022]FIG. 4C is a fragmentary perspective view of one of the undulating screens which is located at the slurry entry and central portions of the movable frame;  
     [0023]FIG. 4D is a fragmentary bottom plan view of the perforated frame of each of the screens showing the resilient plastic sealing bead on the periphery of the underside of the frame;  
     [0024]FIG. 5 is a plan view of the suction-pressure pan mounted on the underside of the machine to which the duckbill valves are attached, with this view being taken substantially in the direction of arrows  5 - 5  of FIG. 1 without showing anything other than the pan;  
     [0025]FIG. 6 is a fragmentary perspective enlarged view showing portions of the bed of the machine onto which the screens and the suction-pressure pan are attached;  
     [0026]FIG. 7A is a fragmentary end elevational view showing the flat screen which is mounted at the outlet end of the movable frame;  
     [0027]FIG. 7B is a fragmentary enlarged detail of the seal between the screen and the side of the movable frame;  
     [0028]FIG. 8 is an enlarged fragmentary cross sectional view taken substantially along line  8 - 8  of FIG. 1 and showing the connections between the suction-pressure pan and the sides of the movable frame;  
     [0029]FIG. 9 is an enlarged fragmentary view of the screen mounting and tensioning structure taken substantially in the direction of arrows  9 - 9  of FIG. 11;  
     [0030]FIG. 10 is a fragmentary enlarged view of the screen mounting and tensioning structure taken substantially in the direction of arrows  10 - 10  of FIG. 11;  
     [0031]FIG. 11 is an enlarged fragmentary cross sectional view taken substantially along line  11 - 11  of FIG. 1 and showing the screen tensioning members mounted on the sides of the movable frame of the machine;  
     [0032]FIG. 11A is a fragmentary enlarged view of the screen tensioner;  
     [0033]FIG. 11B is a fragmentary cross sectional view taken crosswise of a vibratory screening machine showing a channel-type structure for mounting vibratory screens on the bed of the movable frame;  
     [0034]FIG. 12 is a fragmentary view taken substantially in the direction of arrows  12 - 12  of FIG. 11 and showing the manner in which the screen tensioning structure engages the frame of the screen;  
     [0035]FIG. 13 is a fragmentary enlarged side elevational view of the connection between a duckbill valve and the suction-pressure pan which mounts the duckbill valves;  
     [0036]FIG. 14 is an end elevational view of an undulating screen and its sealing relationship with the side of the movable frame;  
     [0037]FIG. 15 is a schematic plan view of the centrifugal blowers connected to the valve arrangements which are connected to the plurality of suction-pressure chambers of the movable frame;  
     [0038]FIG. 16 is a schematic view showing a valve of FIG. 15 in position to provide suction to a suction-pressure chamber;  
     [0039]FIG. 17 is a schematic view showing a valve of FIG. 15 in position to provide pressure to a suction-pressure chamber;  
     [0040]FIG. 18 is a side elevational view of a blower with a slide valve on the suction intake;  
     [0041]FIG. 19 is a schematic view of the slide valve of FIG. 18 in a partially closed position;  
     [0042]FIG. 20 is an exploded view of a four-way valve which is connected between each blower and its associated chamber;  
     [0043]FIG. 21 is a schematic block diagram showing the various operating components associated with the vibratory screening machine;  
     [0044]FIG. 22A is a flow chart showing the main program for operating the vibratory screening machine;  
     [0045]FIG. 22B is a flow chart showing the subroutine for operating the suction aspects relating to the operation of the vibratory screening machine;  
     [0046]FIG. 22C is a flow chart showing the subroutine for operating the ambient aspect relating to the operation of the vibratory screening machine; and  
     [0047]FIG. 22D is a flow chart showing the subroutine for operating the pressure aspect relating to the operation of the vibratory screening machine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0048] Summarizing briefly in advance, in the operation of the present vibratory screening machine and method, fine particles and liquid are withdrawn from a slurry which contains fine particles, coarse particles and liquid when chambers underneath the screen bed area are subjected to suction. The withdrawal of the liquid causes the coarse particles which are discharged from the machine to be desirably dry so that they can be disposed of without liquid which was withdrawn. In accordance with one method of the present invention the chambers are then subjected to pneumatic pressure which aids in forcing the fine particles and liquid out of the chambers and also tends to unclog materials from the screens. In accordance with another method of the present invention, one or more of the chambers are intermittently subjected to suction and release of suction while the machine is operating at a relatively high G force. The suction removes fine particles and liquid from the slurry, and the vibration at the high G force unclogs the screen.  
     [0049] The vibratory screening machine  10  of the present invention includes an outer stationary frame  11  and an inner movable or vibratory frame  12 . The outer stationary frame  11  (FIGS. 2 and 3) includes spaced upper elongated tubular members  13  and spaced lower elongated tubular members  14 . A pair of post-like members  15  extend upwardly from upper frame members  13  at the outlet end of the machine (FIG. 3) and they are connected by a cross member  17 . A slurry feeder  19 , shown in FIGS. 1 and 1A extends between the upper frame members  13  and lower frame members  14  at one end of the outer frame  11 , and it has its opposite sides connected thereto to support the sides of the frame members  13  and  14  in spaced relationship. In this respect, tubular members  12 ′ are suitably secured to frame members  13 , and bars  16  extend inwardly from tubular members  12 ′ and are welded to the sides  18  of feeder  19 . Frame member  16 ′ extends between the lower tubular members  14  of the outer stationary frame, and the lower portion of feeder  19  is secured thereto. The feeder does not contact the movable frame  12 . The feeder has an elongated opening which extends crosswise to the movable frame  12  to deposit slurry at the slurry inlet end of the machine. The feeder may be mounted in any suitable manner, and is not restricted to the manner shown. The lower frame members  14  are connected to each other by a cross member  20  (FIG. 3) at the opposite lower end of the outer frame  11 . The ends of each upper frame member  13  are connected to the ends of a lower frame member  14  by an elongated plate  21  (FIGS. 2 and 3) on each side of the machine. There are channel-like extensions  22  (FIG. 2) extending downwardly from each tubular member  14 . Flanges  23  at the bottom of each member  22  mount the stationary frame on a suitable base  24  by means of bolts. The stationary frame  11  of the vibratory screening machine  10  can take any other suitable form for mounting a movable frame inasmuch as the specific form described above is not at all critical, and frames of vibratory screening machines of various forms are well known in the art.  
     [0050] The movable or vibratory frame  12  is resiliently mounted on the stationary frame  11 . The movable frame  12  includes two plate-like sides  25  and  27  (FIGS. 1, 2 and  3 ) which extend for substantially the entire length and height of the movable frame. Channel members  29  (FIGS. 1, 3,  3 A and  4 ) are located at the outlet end  30  of the movable frame  12 , and channel members  31  are located at the slurry entry end of movable frame  12 . The tops of sides  25  and  27 , respectively, are bent over into flanges  32  and  33 , respectively (FIGS. 1, 2,  3 A,  4  and  8 ). A pair of resilient mounts  34  (FIGS. 3 and 3A) extend between a leg  28  (FIGS. 3 and 4) of each channel  29  of movable frame  12  and plate  21  of stationary outer frame  11  at each side of the outlet end of the machine (FIGS. 3 and 3A), and a like pair of resilient mounts (not shown) extend between each side  28 ′ (FIG. 4) of each channel member  31  and each plate  21  at entry portion of the machine to thereby resiliently mount the movable frame  12  on stationary frame  11 . There are a total of eight resilient mounts  34  between the stationary and movable frames. The resilient mounts  34  are substantially cylindrical members which have their opposite ends bolted to the members to which they are attached. The resilient mounting structure is well known in the art. It will be appreciated that other types of resilient mounts, such as springs, may be used, as is known.  
     [0051] In FIG. 2A the bracing structure is shown for plate-like side  27  of the movable frame, and, while not described, side  25  of the movable frame possesses substantially identical mirror image bracing structure. In this respect, a series of parallel plate-like ribs  35  are welded to the outside of plate  27  and they extend from upper flange  33  to lower flange  37  (FIGS. 2 and 2A) which is formed at the bottom of plate side  27 . An identical flange  37 ′ (FIGS. 1 and 8) is located at the lower end of side plate  25  of movable frame. Flanges  37  and  37 ′ are in mirror image relationship (FIG. 8). Flange  37 ′ terminates at an upturned lip  39 ′ (FIGS. 1 and 8) and a mirror image lip  39  (FIGS. 2 and 8) is associated with flange  37 . Plate-like ribs  40  are welded to side  27  and they extend from upper flange  32  to plate-like ribs  41  which are welded at their lower ends to ribs  35 . As can be seen from FIG. 1, side  25  of the movable frame has bracing structure which is the substantial mirror image of the bracing structure described above relative to frame side  27 , and the various elements are designated with primed numerals corresponding to the unprimed numerals of frame side  27 .  
     [0052] Vibratory motors  42  have their opposite ends securely bolted to bases  43  (FIGS. 1, 2,  4  and  4 A) which extend upwardly from sides  25  and  27  of the movable frame. In this respect, side plates  44  and  45  have their bottom edges welded to frame sides  25  and  27 , respectively. Ribs  47 ,  49 ,  50  and  51  are welded to side plate  44  (FIG. 1), and ribs  52 ,  53 ,  54  and  55  are welded to side plate  45  (FIG. 2). The ribs of plates  44  and  45  extend between bases  43  and the top flanges  32  and  33  of frame sides  25  and  27 , respectively.  
     [0053] As can be seen from FIG. 4A, plate  45  to which base  43  is attached has internal plate-like ribs  57 ,  59 ,  60  and  61 , and plate  44  on the opposite side of movable frame  12  has mirror image ribs (not shown). It is also to be noted that plate  45  has a lower portion  62  and this lower portion is welded to the inside surface of movable frame side  27 . Mirror image structure (not shown) is associated with motor-supporting plate  44 .  
     [0054] At this point it is to be noted that the general structure of the outer frame  11  and the inner frame  12  thus far described are exemplary of well-known prior outer and inner frames of vibratory screening machines. However, it will be appreciated that other inner and outer frame structures can be utilized provided that they incorporate modifications which are required to produce the suction-pressure aspects of the present invention.  
     [0055] In accordance with the present invention, the movable frame  12  has been structured so as to contain a plurality of suction-pressure chambers  73 ,  74  and  75  underneath the screen bed so that the screens thereon can be alternately subjected to suction to thereby draw liquid and fine particles from a slurry being screened and thereafter be subjected to pneumatic pressure for the dual purpose of both (1) aiding in emptying the suction-pressure chambers of the liquid and fine particles which pass through the screens and (2) also blowing out material which clogs the screens. In the foregoing respect, the opposite ends of major ribs  63  (FIGS. 4, 4A and  6 ) are welded to frame sides  25  and  27 . Minor ribs  64  also have their opposite ends welded to frame sides  25  and  27 . A plate  65  (FIGS. 4 and 4A) has its opposite ends welded to frame sides  25  and  27  at the outlet end of the screen bed. A plate  67  (FIGS. 4 and 4A) has its opposite ends welded to plates  25  and  27  at the slurry entry end of the screen bed. Stringers  69  extend lengthwise at equally spaced intervals between plates  65  and  67  and they are received in notched portions  70  of major ribs  63  and slots  71  of minor ribs  64 . Channel-shaped plastic caps  72  are mounted on stringers  69 , as is known in the art.  
     [0056] The three suction-pressure chambers  73 ,  74  and  75  (FIGS. 1, 2 and  4 A) are produced by bolting a pan  77  (FIGS. 4A and 5) to the ribs  63  and frame sides  25  and  27  and plates  65  and  67  of movable frame  12 . Pan  77  includes flange edge portions  79 ,  80 ,  81  and  82  which lie in a single plane. They also include central strip-like portions  83  and  84  which also lie in the same plane. Spaced perforations  85  (FIG. 5) are provided in the foregoing flange members  79 ,  80 ,  81  and  82  and in central strip-like portions  83  and  84 . The central strip portions  83  and  84 , which lie in the same plane with the flange members, are bolted to flanges  87  of major ribs  63  by bolts such as  90 ′. The flange  80  of pan  77  (FIG. 8) is bolted to flange  37 ′ of frame side  25  by a plurality of bolts  90 ′ which extend through the perforations  85 . Flange  79  of pan  77  is bolted to flange  37  of frame side  27  by bolts  90 ′ also. The flange edge  81  of pan  77  is bolted to flange  89  of plate  65  (FIG. 4A), and flange  82  of pan  77  is bolted to flange  91  of plate  67 . Suitable gaskets or sealants  90  (FIG. 8) are provided between all of the flanges  79 ,  80 ,  81  and  82  of the pan  77  and the flanges  37 ′ and  37  of side walls  25  and  27 , respectively, and the flanges  89  and  91  of plates  65  and  67 , respectively. Also, suitable gaskets or sealants are provided between central strips  83  and  84  of pan  77  and flanges  87  of ribs  63  to thereby provide fluid-tight connections between pan  71  and side walls  25  and  27  and ribs  63  and plates  65  and  67 .  
     [0057] As can be visualized from FIG. 4A, chamber  73  is bounded by the lower portions of side walls  25  and  27  and rib  63  and plate  67 . Chamber  74  is bounded by the lower portions of side plates  25  and  27  and spaced ribs  63 . Chamber  75  is bounded by the lower portions of side plates  25  and  27  and rib  63  and plate  65 . Also chamber  73  is bounded by the four sides  92  and  93  of pan  77  and the bottom portion  94  of pan  77  which has ducts  95  extending downwardly therefrom. Chamber  74  is also bounded by formed bottom wall  97  which has ducts  99  extending downwardly therefrom. Chamber  75  is also bounded by bottom wall  100  which has ducts  101  extending downwardly therefrom. Thus, the chambers  73 ,  74  and  75  are sealed from each other by the above-described structure. At this point it is to be noted that the reason bottom walls  97  and  100  of pan  77  are shaped as they are is to allow spaces  102  and  103  (FIGS. 1 and 4A) between the sides  25  and  27  of the movable frame, for other structure of the vibratory screening machine, namely, shafts (not shown) connected to the stationary frame  11  which have to extend through those spaces and which are used for tilting the movable frame  12 . However, since these portions of the vibratory screening machine are totally unrelated to the subject matter of the present invention, they are not shown. It will be appreciated that the pan can take any desired shape consistent with the structure of the machine, and it is not restricted to the shape shown.  
     [0058] The bed of the movable frame includes the following structure. Laid crosswise to the stringers  69  are plastic strips  104  (FIGS. 4 and 6) which are suitably bolted to strips  105  welded to stringers  69  (FIG. 6). Plastic strips  107  (FIGS. 4 and 6) are bolted to flanges  109  (FIG. 6) which are welded to side plates  27  and  25 , respectively, of the movable frame. Also, plastic strips  110  and  111  (FIGS. 4, 4A and  6 ) are bolted to flanges  112  and  113  of plates  65  and  67  (FIG. 4A), respectively. Plastic strips  107  extend for substantially the entire length of the screen bed between plastic strips  110  and  111 . Plastic strips  104 ,  110  and  111  extend for substantially the entire width of the screen bed between plastic strips  107 . The upper surfaces of plastic strips  104 ,  110  and  117  are curved downwardly, and these strips along with strips  107  lie in the same arc. The above-described plastic strips  104 ,  107 ,  110  and  111  constitute the portion of the screen bed to which screens are placed in sealing relationship. The additional portions of the screen bed which engage the screens in supporting relationship are the plastic caps  72 .  
     [0059] A plurality of screening screens is mounted on the screen bed and the edges on their undersides are positioned in substantially sealing relationship with plastic strips  107 ,  104 ,  110  and  111 . More specifically, there are two undulating screens  112  (FIGS. 4, 4C and  14 ) positioned in sealing relationship with the bed of the movable frame above chambers  73  and  74 . In this respect, one undulating screen is located above chamber  73  and it has its edges in sealing engagement with strips  104 ,  107  and  111 . The central undulating screen is located above chamber  74  and it has its edges in sealing engagement with strips  104  and  107 . A planar screen  113  (FIGS. 4 and 4B) is positioned over chamber  75  with its edges in sealing relationship with strips  107 ,  104  and  110  at the discharge end of the screen bed. In the foregoing respects, as can be noted from FIGS. 4 and 4D the screens of undulating screens  112  are mounted on perforated plates  114 . The planar screen is also mounted on a perforated plate  114 . A perforated plate of this type is fragmentarily shown in FIG. 4D. Its underside has a resilient flexible plastic bead  115  on its entire periphery. Therefore, the plastic bead  115  of plate  114  of the planar screen  113  provides sealing contact with plastic strips  107 ,  104  and  110 . The plastic strip  115  on perforated plate  114  of the central undulating screen  112  provides sealing engagement with portions of plastic strip  107  and plastic strips  104 . The edges of perforated plate  114  of undulating screen  112  provide sealing engagement with plastic strips  107 ,  104  and  111 . While the above description has referred to two undulating screens and one planar screen, it will be appreciated that there can be any desired mix of the foregoing screens or the screens can be all undulating or all planar. It will be appreciated that other types of seals can be used instead of seal  115 , including but not limited to gaskets between plate  114  and the bed of the machine.  
     [0060] Insofar as pertinent here, the undulating screens  112  have one or more layers of undulating screening material  117  with their troughs  119  (FIG. 4C) bonded to the perforated plate  114 . Undulating screens of this type are known in the art, and are shown in U.S. Pat. No. 5,958,236 which may be referred to for relevant information and is incorporated herein by reference. Planar screen  113  has a plurality of flat layers of screen material  120  bonded to a perforated plate  114 . A screen of this type is known in the art and shown in U.S. Pat. No. 4,575,421 which may be referred to for relevant information and is incorporated herein by reference. The undulating screens  112  are placed in end-to-end relationship and the planar screen  113  is placed in abutting relationship with an edge of the central undulating screen  112 .  
     [0061] The perforated plate  114  of the undulating screens  112  is bent up at  121  (FIG. 4C). A filler of epoxy  122  is located between the bent-up edge  123  of the screening material  117  and the flange  121 , both of which extend for the entire width of the screen. A flexible plastic wiper  124  is mounted as shown in FIGS. 4C and 14 wherein a slotted portion  126  thereof straddles the upper edge of flange  121  and a side of slotted portion  126  is embedded in the epoxy. The wiper  124  thus makes a sealing engagement between the entire side of the screen and the frame wall  25 . The wiper  124  deters slurry from bypassing the screen and also effectively acts as a supplemental seal between the screen and the bed of the machine along the side wall of the machine. An analogous wiper support construction is provided in mirror image relationship on the opposite side of the screen and seals that side of the screen to the opposite wall  27  of the frame.  
     [0062] The planar screen  113  (FIG. 4B) has shell  125  of epoxy overlying foam material for the entire width of the screen, and the shell  125  includes a blocked off end at  129  and at the opposite end of shell  125  to provide fluid-tight connections between plate  114 , flange  130  of plate  114  and shell  125 . A flexible plastic wiper  131  is mounted on the upper edge of flange  130  and is bonded to the edge  132  of epoxy  125  and the upper edge of flange  130 . The wiper  131  deters slurry from bypassing the screen and also effectively acts as a supplemental seal between the screen and the bed of the machine along the side wall of the machine. An analogous wiper support construction is provided in mirror image relationship on the opposite side of the screen, as can be visualized from FIG. 11. Thus, the wipers, such as  131 , on the edges of planar screen  113  will provide sealing engagement with the side walls  25  and  27  of the movable frame for the entire width of the screen.  
     [0063] In the present instance, both the undulating screens  112  and the planar screen  113  are mounted on the screen bed by toothed tensioning members  133  and  134  on side walls  25  and  27 , respectively (FIGS. 9, 10 and  11 ). In this respect, the toothed tensioning members  133  (FIGS. 4A, 9 and  11 ) are bolted to side wall  25  by bolts  135 . A plurality of toothed tensioning members  134 , equal in number to tensioning members  133 , are movably mounted toward and away from side wall  27  by means of cam-operated tensioners  137  (FIG. 2) mounted on side wall  27 . In FIGS. 11 and 11A the tensioner  137  is shown in more detail. It is mounted on frame side  27 , and it includes a cam base  138  fixedly secured to frame side  27 . The cam base  138  has two cam tracks  138 ′, each of which has a low point  139 ′ spaced 180 degrees apart, each gradually leading to two high points  140 ′ spaced 180 degrees apart. A cam follower nut  141 ′ (FIG. 11) is rotatably secured to the end of shaft  139  of toothed member  134 . Cam follower nut  141 ′ has two cam follower legs  142 ′ (only one shown) spaced 180 degrees apart. When the cam follower legs  142 ′ are on the two low points  139 ′, shaft  139  extends inwardly from side  27  more than when the cam follower legs  142 ′ are rotated with nut  141 ′ to the high points  140 ′. When the cam follower nut is rotated to move cam follower legs  142 ′ to high points  140 ′, shaft  139  will be caused to move to the right in FIG. 11 to pull toothed tensioning member  134  to the right to tension the screen mounted between toothed members  133  and  134 . When it is desired to loosen a screen to remove it from the machine, the nut  141 ′ is rotated in the opposite direction to cause the cam follower legs  142 ′ to return to the low points  139 ′ of cam  138 ′. A cylindrical housing  146 , shown only in FIG. 11A, surrounds the structure shown in FIG. 11 to shield it from extraneous matter. As noted in FIG. 4A, there are two toothed tensioning members  133  associated with each screen. There are a like number of toothed tensioning members  134  also associated with each screen. Toothed tensioner members and cam-operated tensioners are known in the art.  
     [0064] Each perforated plate  114  is mounted in the following manner. Each perforated plate  114  (FIG. 12) is mounted on teeth  141  of two adjacent fixed toothed tensioning members  133  such that the teeth  141  enter the perforations closest to the edge of the plate. The teeth  143  of two adjacent movable members  134  are inserted in the perforations such as  144  of the perforated plate  114  at the opposite side of the plate from perforations  142 . In the undulating screens  112  (FIG. 4C) the teeth  143  enter the perforations  144  to the left of the bent-up edge  123  (FIG. 14), and the teeth  141  enter the perforations  142  in the opposite edge of the screen in an analogous manner. In the planar screens  113  (FIG. 4B) the teeth  143  enter the foam material within epoxy shell  125  and displace it. The teeth  141  enter the foam material on the opposite side of the plate  114  and displace it. Thereafter, the teeth  143  are moved to their solid line position of FIG. 12 from their dotted line position by the operation of tensioners  137 , to thereby tension the screen and cause the teeth  141  of fixed toothed member  133  to engage the edges  142  of the perforations on which they are located. When the toothed tensioning members  134  move toward and away from frame side  27 , they are supported by plates  146  (FIGS. 10 and 11) welded to frame side  27 . The undersides of inverted T-shaped members  148  on each toothed tensioning member  134  slide on the top surfaces of plates  146 . When all the screens are fully tensioned, the sealing strips  115  on the underside of the screens will engage the adjacent plastic strips such as  104 ,  107 ,  110  and  111  on the screen bed and also cause the wipers  124  and  131  on the opposite edges of the screens to engage the side walls  25  and  27  of the movable frame.  
     [0065] In FIG. 11B another well-known screen construction and tensioner arrangement is shown. In such an arrangement a screen  136  includes a screen  135 ′ mounted on a plate  137 ′, and the edges of the plate are bent up into channels  138 ′. The sides  25  and  27  have plates  139 ′ secured thereto, and bolts  140 ′ extend therethrough and through channel members which engage screen channels  138 ′ and tension the screen when the bolts are tightened. The tensioning also causes the central portions of the screen to bear on stringers  141 ′ and the edges of the plate  137 ′ to rest on plastic strips  107  which are bolted to flanges  109 . It will be appreciated that other tensioning structures can also be used including but not limited to pretensioned screen arrangements.  
     [0066] A plurality of duckbill valves  145  (FIGS. 1, 2 and  13 ) have upper cylindrical openings  147  which are mounted on cylindrical ducts  95  associated with chamber  73 . The mounting is effected by means of ring clamps  149 . As is well understood in the art, duckbill valves  145  are fabricated from resilient material such as rubber or resilient plastic and they have spaced lips  150  at their lower edges which will remain closed when the valve is subjected to suction but will be forced open when they are subjected to pneumatic pressure. A plurality of duckbill valves  151  are mounted on ducts  99  of chamber  74 . A plurality of duckbill valves  152  are mounted on ducts  101  of chamber  75 .  
     [0067] Structure is provided for supplying each of chambers  73 ,  74  and  75  alternately with suction and pressure (FIGS. 1, 3,  15 ,  16  and  17 ). In this respect, a plurality of centrifugal blowers  154  is provided having suction inlets  155  and pressure outlets  157 . A four-way valve  159  is connected to each blower  154 . In this respect each blower has a conduit  160  which connects the four-way valve  159  to suction conduit  155  of the blower, and a conduit  161  connects the blower pressure outlet  157  to the four-way valve. When the vane  162  of a four-way valve  159  is in the position shown in FIG. 16, the chamber such as  73 ,  74  and  75  will be subjected to suction because the air flow will be from the suction-pressure chamber through duct  166  leading from the chamber, duct  163  of the four-way valve, the four-way valve, duct  164  of the four-way valve and into suction inlet  155  of the blower  154 . The suction will cause fine particulate material and liquid to be withdrawn from the slurry and deposited in chambers  73 ,  74  and  75  while the coarse material will not pass through the screens and it will be dried. At the same time the pressure duct  157  will be in communication with the four-way valve  159  through conduit  161  which is mounted on duct  165 , and the pressure produced by blower  154  will be discharged from duct  167  of the four-way valve. When a chamber  73 ,  74  or  75  is subjected to pressure, the four-way valve  159  has its vane  162  in the position shown in FIG. 17 so that pressure will be supplied from blower duct  157  to conduit  161  and duct  165 , through valve  159  and into duct  166  leading to the chamber. When the valve  159  is in the position of FIG. 17, air will be supplied to the blower through duct  167  of valve  159 , through valve  159 , through conduit  160  and suction inlet  155 . The providing of pneumatic pressure to chambers  73 ,  74  and  75  will aid in forcing the fine material and liquid out of the chambers through the duckbill valves. Also, the pneumatic pressure will tend to unclog the screens.  
     [0068] In the operation of the machine  10  under conditions of suction and pressure, the maximum suction was at six inches of water and the maximum pressure was at six inches of water. However, it will be appreciated that the suction and pressure may vary depending on the nature of the slurry which is being screened. Also, while three chambers have been shown as being capable of having suction and pressure applied to all of them simultaneously, it will be appreciated that only one or two of the chambers may have the suction and pressure applied thereto depending on the nature of the slurry. Screens of  175  mesh have been used in tests. However, the screens may range between about  38  and  325  mesh depending on the nature of the slurry.  
     [0069] In FIGS. 18 and 19 a slide valve  192  is shown mounted on blower  154 . The plate  192  fits slidably between a pair of plates  193  and  194  which are mounted on suction inlet  155 . As can be seen in FIG. 18 the slide valve is in a fully opened position and in FIG. 19 the slide valve is in a partially closed position. By this arrangement the amount of air flowing through each blower  154  and each chamber  73 ,  74  or  75  can be varied as may be desired for different installations.  
     [0070] In FIG. 1 the rims  167  are shown to which conduits  166  are connected. It will be appreciated that the conduits can be connected in any suitable manner. The rims  167  are perforated, and mating perforated plates at the ends of conduits  166  are bolted to plates  167 . It will be appreciated that the various conduits may be connected to the various ducts in any suitable manner, including but not limited to ring clamps of the type shown in FIG. 13.  
     [0071] In FIG. 20 an exploded view of a preferred four-way valve  159  is shown. The valve includes a substantially square base  170  on which the lower end of housing  171  of substantially square cross section is mounted. Four cylindrical ducts  163 ,  164 ,  165  and  167  extend outwardly from housing  171 . A perforated cylinder  172  is mounted within housing  171  and it has four strip-like divider members  173  having their inner edges  174  bonded, as by welding, to cylinder  172 . Each divider  173  is located between two adjacent series of four circular openings  175 . In this respect there are four vertical rows of openings  175  with each row containing four circular openings which communicate with the inside of cylinder  172 . In its assembled position, the outer edges  177  of dividers  173  are in sealing engagement with the corners  179  of housing  171 . The centers of each vertical row of apertures  175  are spaced 90 degrees apart, and the dividers  173  are also spaced 90 degrees apart. The dividers  173  are spaced 45 degrees from the centers of the apertures  175 . The vane  162  is mounted on a shaft  180 , the opposite ends of which are rotatably mounted in caps  181 . The lower cap  181  is received in bore  182  in base  170 . The upper cap  181  is received in cylindrical portion  183  of cap  184  which is mounted on housing  171  through ring  185  which is mounted on the upper end of housing  171 . The shaft  180  extends through bore  187  in cap  181  and also extends through bore  189  in cap  183  and is received in double acting pneumatic actuator  190  which has internal mechanism to pivot shaft  180  to move vane  162  back and forth an amount of 90 degrees to cause vane  162  to move between the positions shown in FIGS. 16 and 17. Actuator  190  has two conduits  186  coupled thereto which in turn are coupled to a solenoid valve  188  which controls the flow of compressed air from conduit  196  to conduits  186 , as discussed in detail hereafter. Alternately, shaft  180  can be pivoted manually by forming its top into a non-circular shape and applying a handle or wrench thereto, thereby eliminating the need for an actuator  190 . Vane  162  has suitable wipers  191  on opposite edges thereof which gauge the inside of cylinder  172  in fluid-tight relationship. As can be visualized from FIGS. 16 and 17 in each of the two positions of vane  162 , it causes communication between two adjacent vertical series of apertures  175  of cylinder  172 .  
     [0072] The valve  159  has been designed so that the total area of four apertures in a vertical row equals the total cross sectional area of a conduit, such as  165  or  167 . In addition, the volume between a pair of dividers  173  and the outside of cylinder  172  and the side of housing  171  between adjacent dividers  173  has a volume which is at least as great as the volume which will not throttle the air passing through the valve between two adjacent ducts such as  165  and  167 . The foregoing parameters will permit the necessary air flow through the valve  159  without unnecessarily throttling it. As noted above, the reason for the vertical cylinder  172  with the four sets vertical apertures therein, is so that the footprint of base  170  occupies a relatively small area so as to be extremely well adaptable for use on offshore drilling rigs where floor space is at a premium. However, it will be appreciated that in areas where floor space is not at a premium, any suitable four-way valve which functions in the manner described above relative to FIGS.  15 - 17  can be used.  
     [0073] In accordance with another method of the present invention, a slurry containing a mixture of fine and coarse particles and liquid can be screened by alternating the application of periods of suction and release of suction to the one or more chambers. The foregoing has been effected by the use of a blower  154  with a valve such as  159  by merely disconnecting conduit  161  from valve duct  165  so that the latter is open to the atmosphere. It is believed that the release of suction causes the chamber to return to full atmospheric pressure because the chamber is open to the atmosphere through the valve  159  and duct  165  and also through the screen. However, it is possible that some residual suction may have remained in the chamber if the period of release of suction has been very small. If only one chamber is to be subjected to suction, it is preferably the chamber at the exit end of the machine, namely, chamber  75 . In a test, the suction which has been applied to a single chamber at the exit end of the machine has been up to ten inches of water, and it has generally been about six inches of water. The foregoing was effected with a  175  mesh screen, although, as stated above, the screen mesh can be anywhere between about  38  and  325  mesh, depending on the nature of the slurry which is being screened. In the test, the suction was applied for periods of four seconds and there were intermittent releases of suction for periods of one second. It is believed that the suction was completely released during the period of one second, but it may have been reduced to a lesser value, considering the short release period. In a test, both the flat screen and an undulating screen were used at the exit end of the machine above chamber  75 . It was observed that the undulating screen performed better because it channeled the material lengthwise in rows whereas the flat screen permitted the material to drift slightly to the sides of the machine. The screens were vibrated at approximately 6½ G&#39;s, and it was observed that this relatively high vibratory force kept the screen above chamber  75  very clean. However, it is believed that the G force can be between about 3 to 12 G&#39;s depending on the capability of the screens to withstand the higher G forces. However, preferably the G force could be between 5 to 9 G&#39;s and most preferably between 6 to 8 G&#39;s. Generally the G force should be in excess of 6 G&#39;s for good anticlogging operation of the screens. The periods of suction and the release of suction can be effected by the use of a programmable logic controller (PLC) which controls the shifting of the valve  159 . In the operation of the vibratory screening machine under suction and release of suction conditions only, as described above, the weight of the liquid and fine particles which were pulled into the chamber opened the duckbill valves to release the liquid and fines therefrom when the liquid and fines reached a predetermined depth above the valves. It is possible to use a different system for applying suction to a chamber, namely, by intermittently applying a greater suction and a lesser suction by intermittently venting the chamber to produce periods of lesser suction.  
     [0074] In FIG. 21 a block diagram is shown which illustrates the operation of the entire system. At the operator interface the operator enters the mode of operation of the system, preferably by means of a key pad or mouse. Broadly, the system permits the operation of all the chambers  73 ,  74  and  75  by suction and pressure, or permits the operation of all of the chambers by suction and ambient or only under ambient conditions when the blowers  154  are not in operation. Also with suitable expansion of the PLC, the system will permit each chamber of the group to be operated independently of the others either by suction and pressure, or by suction and ambient, or only by ambient. Also, the time of application of the periods of suction, ambient or pressure may be varied for each chamber.  
     [0075] As the system is shown in FIG. 21, the mode of operation will apply identically to each of the three chambers  73 ,  74  and  75 . When the system is to operate by suction and pressure, the system is set up as shown in FIG. 15 wherein all conduits  161  are connected between the blowers  154  and the four-way valves  159  as shown. The main program (FIG. 22A) is started, and this energizes the decision blocks  200 ,  201  and  202  for the three subroutines A, B and C, respectively. Subroutines A, B and C are dependent on the input of the operator. Subroutine A relates to the application of suction to the chambers; subroutine B relates to the application of ambient to the chambers; and subroutine C relates to the application of pressure to the chambers.  
     [0076] When the system is to operate with simultaneous alternate applications of suction and pressure to all of the chambers, the following procedure is followed. Subroutine A (FIG. 22B) is executed in the following manner. Timer setting for the period of suction is determined in the “Change Timer Setting” block. After it is set, the PLC sends out a signal to cause the suction to be applied to each chamber upon the start of the suction timer. In this respect, the signal is applied to each solenoid valve  188  associated with each valve  159 . The signal causes each solenoid valve  188  to cause flow of compressed air from conduit  196  to the proper conduit  186  to shift the double acting pneumatic actuator  190  to shift its associated valve  159  to apply suction to each chamber  73 ,  74  and  75 . After the timer has finished in accordance with the timer setting, the subroutine A will return back to the main program. After the return of subroutine A to the main program, the subroutine B (FIG. 22C) relating to the placement of the chambers in communication with the ambient is initiated if there is to be this mode of operation. However, when the system is operating under suction and pressure, there is no placement of the chambers in communication with the ambient, and therefore then the decision block therein on the main program is bypassed to subroutine C. When subroutine C (FIG. 22D) is executed, the Change Timer Setting block sets up the period of time that pressure will be applied to the chambers  73 ,  74  and  75  and thereafter the pressure timer is started. Therefore the signal is sent out from the PLC to each solenoid valve  188  associated with valve  159 . The signal causes each solenoid valve to cause the flow of compressed air from the conduit  196  to the proper conduit  186  to shift the double acting pneumatic actuator  190  to shift its associated valve  159  to supply pressure to each chamber  73 ,  74  and  75 , and the pressure is applied for the period that the timer is in operation. Thereafter, the subroutine C returns to the main program. Thereafter, the above-described series of executions are repeated.  
     [0077] As described above, when the system is set up as shown in FIG. 15, each of the chambers  73 ,  74  and  75  is treated identically by the alternate application of suction and pressure, in accordance with the above-described intelligence provided by the above-described system.  
     [0078] There are certain circumstances in which it will be desirable to operate the system by the simultaneous identical alternate application of suction and ambient to the three chambers. When this is desired, the conduit  161  is disconnected from between each of the pressure outlets of blowers  154  and each of the valves  159  so that the duct  165  (FIGS. 16 and 17) of each valve  159  previously in communication with the pressure outlet of each of the blowers is now open to the atmosphere. It will be appreciated that ambient may be effected in other ways, for example, by actuating a valve in each conduit  161  which routes the pressure to the atmosphere and opens the duct  165  of valve  159  to the atmosphere, or in any other suitable manner.  
     [0079] In order to alternately apply suction and ambient to each of the chambers  73 ,  74  and  75 , the operator will input the mode of operation at the operator interface by means of a key pad or mouse to actuate the subroutine A in the above-described manner. Thereafter, the subroutine B relating to the application of ambient to the chambers will be actuated and this will set the timer setting for subroutine B to determine the length of time of exposure of each of the chambers to the ambient through each valve  159 . Thereafter, the ambient period for each chamber will be started when a signal is sent from the PLC to the solenoid valve  188  associated with each double acting pneumatic cylinder  190 , to actuate each valve  159  in the above described manner to place valve  159  in the position of FIG. 17, and the length of time will exist until the timer has finished, and thereafter there is a return to the main program wherein the entire sequence of subroutine A and subroutine B is repeated. The decision block  202  on the main program relating to pressure subroutine C will be bypassed when the operation is under suction and ambient.  
     [0080] The above description has shown how the four-way valves  159  can be actuated to provide identical simultaneous operation to each of the chambers  73 ,  74  and  75 . However, it will be appreciated that each of the three chambers can be operated separately so that, for example, chamber  73  may not be subjected to suction or pressure and chamber  74  may be subjected only to suction and pressure and chamber  75  may be subjected to suction and ambient. The foregoing can be achieved by having three separate decision blocks of the type shown in the main program of FIG. 22A for each of the chambers and three separate subroutines A, B and C associated with each group of decision blocks. Thus, there will be three groups of three decision blocks, that is, one group of three decision blocks for each chamber and three subroutines for each decision block. Thus, there will be nine decision blocks and three subroutines A, three subroutines B and three subroutines C. If the foregoing is effected, there can be any desired type of operation applied to each of the three chambers. For example, it may be desirable to have the first two chambers  73  and  74  operating strictly by suction and pressure and have the exit chamber  75  operating by suction and ambient. Alternately, it may be desirable to operate one chamber under suction and pressure and the two of the other chambers by suction and ambient. Still alternately, it may be desirable to operate one chamber by suction and pressure, another chamber by suction and ambient and the third chamber without suction and pressure.  
     [0081] In addition to all of the foregoing, whether all chambers are being operated identically or differently, the periods of application of the suction, pressure or ambient may be varied by the operator through the PLC.  
     [0082] While the above description has been directed primarily to the recovery of drilling mud and drying coarse material, it will be appreciated that the above described machine and method can be used in any application where it is desired to separate fine material and liquid from a slurry and also dry the non-separated material.  
     [0083] While preferred embodiments of the present invention have been disclosed, it will be appreciated that it is not limited thereto but may be otherwise embodied within the scope of the following claims.