Abstract:
Sifting apparatuses for stratifying raw material including a material feed-in device, a material support unit, a gas plenum, a discharge control mechanism, and a reservoir are described. The material support unit receives material from the material feed-in device and has a surface with a plurality of openings for a gaseous medium introduced from underneath the material support unit, thereby effecting loosening and stratification of the material into a layer of relatively heavier material, and a layer of relatively lighter material atop the relatively heavier material. The introduced gaseous medium originates in a pump, is collected in a pressurized reservoir, and is controlled by a metered valve prior to introduction to the material support unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION DATA 
       [0001]    This application is a Continuation-In-Part application based on U.S. patent application Ser. No. 14/855,418, filed Sep. 16, 2015, which claims priority to U.S. Provisional Patent Application No. 62/051,184, filed Sep. 16, 2014, both of which are incorporated herein by reference in their entireties. 
     
    
     FIELD 
       [0002]    This disclosure relates generally to sifting apparatuses and, more specifically, to sifting apparatuses for preparatory concentration of raw materials including, e.g., raw coal. 
       BACKGROUND 
       [0003]    Sifting or settling apparatuses generally include a material feed device, material support unit with holes through which flows a gaseous fluid, often gas guided by a plenum disposed underneath the material support unit, and a discharge control mechanism for controlling separated discharge of relatively heavier material and relatively lighter material. The inflowing pulsed gas operating to loosen the material fed onto the material support unit stratifies the material into layers of relatively lighter material atop of layers of relatively heavier material. An air sifting apparatus of this type is described, for example, in the publication Schubert “Aufbereitung fester mineralischer Rohstoffe”, Band II VEB Deutscher Verlag fuer Grundstoffindustrie, Leipzig, pages 89 and 90. 
         [0004]    Typically, sifting apparatuses, like the one described above, produce a less distinct separation between the heavier and lighter materials when compared with wet sifting machines. To achieve satisfactory sorting results according to the aforementioned apparatuses, traditionally multiple factors must be present including, for example, a large density difference between the components of the material. The material particles must be classified within a relatively narrow size range (i.e., within a narrowly defined kernel or grain size range), and the surfaces of the particles should be low in surface moisture, otherwise capillary retention forces hinder their relative movement. 
       SUMMARY 
       [0005]    Sifting apparatuses (“jigs”), whether wet or dry, operate according to two functions: they stratify and then separate. Improved stratification can be achieved when the volume, acceleration, and pulse frequency of the gas or air used in the jigging stroke are each achieved with relative independence. The inclusion of a pressurized reservoir has not been utilized in dry jigging, and thus rapid decompression of the gaseous medium occurs in the gas plenum during each jigging stroke. This disclosure provides sifting apparatuses that offer a solution to the challenge of providing a jig in which the acceleration of the jigging stroke can be improved without excessive pressure loss in the plenum or at the pump discharge point and without deleterious flow change across the material support unit, whereby a better stratification can be achieved and thus the separation will be enhanced, while shock to the gaseous pumping device is reduced. 
         [0006]    The solution to this challenge is principally comprised of providing a reservoir of sufficient size to accept gaseous flow from a pump to build a pressure and relatively large volume that will permit discharge of pulses of relatively smaller volumes as a controlled valve opens and closes, thereby causing flow of gas into the plenum, whereupon the pulsating gas flow is adjusted to a pulse strength sufficient to lift the particles of the material upward and, via the consequent varying distance of fall, thereby effect stratification of the material into relatively heavier material layers and relatively lighter material layers. 
         [0007]    One embodiment includes a sifting apparatus having a material support unit having a base with one or more apertures located therethrough; a plenum attached to an underside of the material support unit; a gas or air dispenser, such as a metering valve, that is attached to the plenum, which is in communication with the material support unit, and that provides a pulsating gaseous medium flow to the material support unit; a pump in communication with the dispenser, wherein the pump provides a pressurized medium; a reservoir that maintains a threshold pressure and that is positioned between the pump and the dispenser; and a discharge control mechanism in communication with the material support unit and operable to control discharge of a relatively heavier material. 
         [0008]    In accordance with embodiments of the jig, the pressure of the pulsating gas flow can also be adjusted by the proper selection of a pump, which will pressurize the reservoir. 
         [0009]    In a further aspect of the present disclosure, the reservoir of the sifting apparatus is placed vertically below the plenum. By doing so, an improved stratification of materials, as compared to traditional jigs, is achieved. Moreover, by placing the reservoir vertically below the plenum, turbulence and unexpected direction of pulsated air flows are reduced, thereby allowing the pulsated air to more evenly disperse under and through the material support unit. This creates a better and more consistent stratification of material, and subsequently an improvement in separation of materials as compared to traditional jigs. 
         [0010]    Yet a further aspect of the present disclosure relates to an interface detection detector capable of mimicking a particle at an interface between relatively high and relatively low density layers of materials caused by air jigging. The particle mimicking interface detection detector is physically configured to stably “float” in materials of the density it is mimicking. Moreover, the interface detection detector may have an adjustable weight so that a user can adjust the weight of the interface detection detector to allow the interface detection detector to mimic particles of a different density. By implementing the interface detection detector of the present disclosure, the depth of a selected density layer of particles is identified relative to the location of the material support device. Further, through standard automatic control systems, the depth of a selected density layer may be constantly maintained, and a user does not need to visually and continuously monitor and adjust an outflow of materials from the material support unit. Implementation of the interface detection detector also allows for a determination of an optimal separation density divergence prior in time and distance to a discharge control mechanism of the air jig, thereby producing a purer separated product. Furthermore, implementation of the interface detection detector of the present disclosure eliminates the need for using nuclear devices currently used with air jigs. 
         [0011]    Additional features and advantages of the present disclosure are described below. This disclosure may be readily utilized as a basis for modifying or designing other structures, systems, and processes for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent implementations do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The particular features and advantages of the present disclosure will be apparent from the detailed description set forth below in conjunction with the drawings in which like reference characters identify corresponding aspects throughout. 
           [0013]      FIG. 1  is a schematic side view of embodiments of a sifting apparatus of the present disclosure having a reservoir; 
           [0014]      FIG. 2  is a flow diagram of embodiments of using the sifting apparatuses of the present disclosure; 
           [0015]      FIG. 3  is a schematic side view of embodiments of another sifting apparatus of the present disclosure having a reservoir; 
           [0016]      FIG. 4  is a schematic side view of embodiments of another sifting apparatus of the present disclosure having a reservoir; 
           [0017]      FIG. 5  is a side view of an illustrative embodiment of an interface level detector according to the present disclosure; and 
           [0018]      FIG. 6  is a schematic side view of an interface level detector implemented in an embodiment of a sifting apparatus of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    As shown in  FIG. 1 , a sifting apparatus or jig  100  may include a pressure build up system including a pump  102  and reservoir  104 , a pressure release unit including a metering valve  106  and adjustable orifice  108 , a plenum  110 , a material support unit  112 , a discharge control mechanism  114 , a light product discharge channel  116 , a heavy product discharge channel  118 , a dust collection housing  120 , and a ducting  122  coupled to the dust collection housing  120 . As can be seen from  FIG. 1 , the arrangement of the pump  102 , the plenum  110 , and the reservoir  104  may be connected to or incorporated into other traditional gravity separators (e.g., having features such as, a material support unit  112 , a light product discharge channel  116 , a heavy product discharge channel  118 , and a dust collection housing  120 ). 
         [0020]    The pump  102 , which assists in producing a gas or air flow to the remainder of the jig  100 , may deliver gas or air at a relatively constant pressure to the reservoir  104 , for example. This embodiment may extend the life of the jig  100  due to the structure of the jig  100  reducing the vacillation of pressure from intermittent flow of gas through the adjustable orifice  108 . However, other embodiments may include variable or intermittent pressure being produced in the reservoir  104  by the pump  102 . 
         [0021]    The reservoir  104  stores air or gas supplied by the pump  102  and may have a pressure relief valve located thereon (not illustrated) for releasing excess pressure at or above a desired threshold. Such desired pressure threshold of the pressure release valve may be set by a user or may be determined according to the reservoir&#39;s  104  properties and capacity, for example. As illustrated, the reservoir  104  may be ovular in shape. However, the reservoir  104  may have any shape, size, and volume without deviating from the scope of the present disclosure. In further embodiments, the reservoir  104  may have a volume sufficient to reduce significant pressure drops in the reservoir  104  when a relatively smaller volume of air or gas is released to the rest of the jig  100 . 
         [0022]    The metering valve  106  allows for the flow of air or gas to the plenum  110  from the reservoir  104  and pump  102  to be controlled and adjusted. Also, a seal on the light material discharge or a gaslock similar to a star gate can be utilized to assist this. The metering valve  106  may be any device capable of adjusting and regulating gas flow (frequency of discharge and volume of gas) and may be controlled by various means such as electronically, wirelessly, Bluetooth, or direct user contact, for example. Proximate to the metering valve  106  may be an adjustable orifice  108  capable of regulating flow pressure or rate of the gas being released to the plenum  110 , thereby allowing for the control of the frequency and volume of pulsations into the gas plenum  110 . The adjustable orifice  108  may have outputs such as analog, digital, and audible, for example. Further, such outputs may be directly communicated to a user or may be indirectly communicated to a user through a computer. By providing relatively independent control of volume, pressure (i.e., acceleration of flow), and frequency of pulse using the adjustable orifice  108  and the metering valve  106 , stratification and control of stratification of material on the material support unit  112  is enhanced. By producing enhanced stratification, the separation of relatively heavy material (e.g., iron) from relatively light material (e.g., coal) is also enhanced, thereby producing a more efficient jig  100 . 
         [0023]    The plenum  110  is in fluidic communication with the reservoir  104 . As illustrated, the plenum  110  may have a conical shape, with a greater surface area located at the top of the plenum  110  and a smaller surface area located at the bottom of the plenum  110 . However, the plenum  110  may have any shape or size without deviating from the scope of the present disclosure. 
         [0024]    Also attached to the plenum  110  is the material support unit  112  that provides support for the heavy and light material mixture waiting to be stratified. A surface area upon which the material mixture is supported may include a plate or screen having holes there through. The material support unit  112  may be made of any material capable of supporting the material mixture, such as wood, metal, metal alloy, plastic, or any other material, for example. The material support unit  112  may also have any shape sufficient to encompass the material mixture. In one embodiment, the material support unit  112  may have a shape substantially similar, or identical, to that of the corresponding area of the plenum  110  upon which it couples. In other embodiments, the material support unit  112  may have a shape independent of the shape of the plenum  110 . 
         [0025]    The material support unit  112  also enhances the stratification of the material mixture by using movements such as rotation and pulsation, for example. The movement of the material support unit  112  may be provided by various means, including electronic, wireless, Bluetooth, or direct user contact, for example. The stratification of the material mixture is aided by a gaseous medium flow provided by the reservoir  104  and pump  102 . In an embodiment, a pulsating gaseous medium flow provided to the mixture material periodically lifts the material to promote stratification of the mixture into a “heavy” material layer and a “light” material layer located atop the heavy material layer without significantly segregating the materials toward the ends or sides of the material support unit  112 . In a further embodiment, the plenum  110  may produce a more constant gas flow through the openings of the material support unit  112  along with a pulsating air gas flow, overlaid on the constant air flow, the pulse impacting the material mixture on the material support unit  112 . As illustrated, the material support unit unit  112  may be located at an angle within the jig  100 . In other embodiments, the material support unit  112  may be oriented at different angles and orientations from that depicted in  FIG. 1 , including being directly or substantially horizontal, for example. 
         [0026]    As illustrated, the light product discharge channel  116  is attached to the material support unit  112 , proximate the discharge control mechanism  114 . However, it should be appreciated that the light product discharge channel  116  may be attached to the the plenum  110  at an area downstream from the material support unit  112 , or another location of the jig  100  where heavy materials cannot access after separation. Located proximate to the material support unit  112  and the light product discharge channel  116  is the discharge control mechanism  114 . The discharge control mechanism  114  allows for the adjustable selection or control of heavy material capable of passing through the discharge control mechanism  114  and the light product discharge channel  116 . The discharge control mechanism  114  may be controlled by any sufficient means, such as electronically, wirelessly, Bluetooth, or by direct user contact, for example. Further, the discharge control mechanism  114  may include devices capable of determining densities of material, such as a nuclear sensor, X-ray sensor, optical sensor, or any other sensor capable of determining densities, for example. The discharge control mechanism  114  may also include a device capable of determining thicknesses of material, such as, for example, a mechanical sensor. The discharge control mechanism  114  may also be configured to direct the heavy material to a location separate from the light product discharge channel  116 , such as the heavy product discharge channel  118 . In an embodiment, the discharge control mechanism  114  may include a device capable of automatically controlling discharge of the heavy material. 
         [0027]    As illustrated, the heavy product discharge channel  118  is located below the discharge control mechanism  114 , proximate to the material support unit  112 . However, it should be appreciated that the heavy product discharge channel  118  may be located elsewhere on the jig  100 . For example, the heavy product discharge channel  118  may be attached to the plenum  110  (e.g., at a bottom of the plenum  110 ), directly on the material support unit  112 , etc. 
         [0028]    A dust collection housing  120 , which manages the amount of dust released by the jig  100 , may be attached to the material support unit  112  by fasteners such as screws, clamps, snaps, epoxies, resins, and seals, for example. Specific embodiments of the system may or may not have a dust collection housing  120 . The dust collection housing  120  may be conical in shape, as illustrated in  FIG. 1 , or may be any other shape sufficient to trap dust. 
         [0029]    A material feed-in device (not illustrated) may be proximate to the material support unit  112 , and also may be proximate to the dust collection housing  120 . In a further embodiment, the material feed-in device may be removably attached to the dust collection housing  120 . The material feed-in device provides for replenishment of the material mixture to the material support unit  112 . In so doing, the material feed-in device may provide the material mixture in uniform or substantially uniform dosages, or may also provide the material variably. Such manner of replenishment may be calculated according to volume, density, or weight of the material mixture, for example. In yet another embodiment, the material feed-in device may include a volume adjustment device. 
         [0030]    As seen in  FIG. 2 , a method  200  of using a jig according to the present disclosure is depicted. At block  202  the material support unit is supplied with a material mixture containing at least one relatively heavier material and at least one relatively lighter material. This supplying of the material mixture may occur directly or may occur through the use of a material feed-in. Supplying of the material mixture may occur at a uniform rate or may occur in variable dosages based on, for example, volume, density, and/or mass of the material mixture. 
         [0031]    At block  204  pressure is generated in the reservoir by using the pump. The pressure generated in the pump may be set by a user of the jig, or may be determined based on the physical characteristics of the reservoir and pumping power of the pump. At block  206  the material mixture located on the material support unit may be stratified. Such stratification may occur through the use of movements such as rotation, pulsation, and/or vibration of the material support unit, for example. At block  208  gas may be released from the reservoir to the material support unit. Such release of gas may be constant, or variable, or intermittent. 
         [0032]    In one embodiment, the release of gas from the reservoir may include releasing the entirety of the pressure, built up in the reservoir, all at once. In other embodiments of the present disclosure, the gas stored in the reservoir may be released gradually so that there always remains some pressure buildup within the reservoir. In yet another embodiment, the release of pressure from the reservoir may include releasing a constant gas flow along with a pulsating gas flow overlaid on the constant gas flow, for pulses to impact the material mixture on the material support unit. 
         [0033]    In operation and use, the sifting apparatus or arrangement may operate similar to other sifting apparatuses (e.g., a gravity separator) or with other sifting apparatuses. Material to be handled is fed onto a support device e.g., through a funnel, which can perform the dosing preparation of the material. Gas or air introduced constantly flows upwardly through the support device from below so as to effect a base fluidization which contributes to a loosening of the material layer lying on the material support device. The loosened material layer exhibits a reduced resistance than would be exhibited by a material layer on the material bed support device which had not been subjected to a constant air or gas flow. As a result of this sifting movement, the layers of the material bed sort themselves into the relatively heavier material layer and the relatively lighter material layer. 
         [0034]      FIG. 3  illustrates a further sifting apparatus  300  having a reservoir  104  according to the present disclosure. It should be appreciated that the sifting apparatus  300  of  FIG. 3  may include all or substantially all of the components discussed with respect to the sifting apparatus  100  of  FIG. 1 . It should also be appreciated that the components of the sifting apparatus  100  may be implemented within the sifting apparatus  300  in similar or identical configurations/orientations, unless explicitly differentiated herein below. 
         [0035]    The sifting apparatus  300  may include a dust collection housing  120  configured to manage an amount of dust released by the sifting apparatus  300 . The dust collection housing  120  may have any shape that allows the dust collection housing  120  to prevent dust from being released from the sifting apparatus  300  into the surrounding environment. The dust collection housing  120  may be attached to the material support unit  112  by fasteners such as screws, clamps, snaps, epoxies, resins, and seals, for example. Additionally, ducting  122  may be attached to the dust collection housing  120 . The sifting apparatus  300  may also include a material feed-in unit/device (not illustrated in  FIG. 3 ). 
         [0036]    The material support unit  112  may include a sloped surface, offset from horizontal, upon which material mixtures are separated into relatively “light” and relatively “heavy” materials. As described herein, pulsated air causes light materials (i.e., less dense materials) to rise in the material mixture, thereby generating a light material layer atop of a heavy material (i.e., more dense material) layer. 
         [0037]    The slope of the material support unit  112  directs materials thereon to a discharge control mechanism  114 . The discharge control mechanism  114  allows for the adjustable selection or control of heavy material capable of passing through the discharge control mechanism  114  and the heavy product discharge channel  118 . Consequently, the discharge control mechanism  114  also controls the amount of light material that passes to the light product discharge channel  116 . For example, by decreasing the amount of heavy materials allowed to pass to the heavy product discharge channel  118 , the more materials build up on the material support unit  112 , and consequently the more products are released through the light product discharge channel  116 , and vice versa. The discharge control mechanism  114  can be a movable bed, a star gate, a clam shell, a drag conveyor, a lifting wheel, a bottom gate, a vibrating plate, a vibrating screen, or like mechanism. For example, when the discharge control mechanism  114  is a rotary (e.g., star gate) device, the faster the rotary device spins, the more heavy material is moved through the discharge control mechanism  114  to the heavy product discharge channel  118 , and vice versa. 
         [0038]    Located below the material support unit  112  is a plenum  110  configured to provide the material support unit  112  with a pulsated medium of gas or air. The plenum  110  may be directly or indirectly coupled to a bottom portion of the material support unit  112 . The plenum  110  may have a shape that enables the plenum  110  to evenly distribute air to the material support unit  112 . For example, the plenum  110  may have a conical shape, with a “large” opening of the plenum  110  being proximate to the material support unit  112  and a “small” opening of the plenum  110  being distal from the material support unit  112 . 
         [0039]    The sifting apparatus  300  additionally includes a pressure release unit configured to release pressure from the reservoir  104  to the plenum  110 , resulting in the pulsated air experienced by the material support unit  112 . The pressure release unit includes the metering valve  106  and adjustable orifice  108 . The metering valve  106  may be a flutter valve that intermittently pulsates air (i.e., releases air from the reservoir  104 ) into the plenum  110 . The metering valve  106 , and optionally the adjustable orifice  108 , may be located directly below the plenum  110 , between the reservoir  104  and the plenum  110 . For example, the metering valve  106  may be centrally locate below the plenum  110  so a single vertical axis extends through both the plenum  110  and the metering valve  106 . By placing the metering valve  106  below the material support unit  112  (i.e., below the plenum  110 ), an even distribution of air to the material support unit  112  is achieved, thereby resulting in greater separation as compared to traditional air sifting apparatuses. 
         [0040]    The adjustable orifice  108  is configured to regulate flow pressure and/or rate of the gas/air released to the plenum  110  by the metering valve  106 . This allows a user, or a computing device configured to control the metering valve  106 , to manipulate the metering valve  106  to control the frequency and volume of pulsations of gas into the plenum  110 . 
         [0041]    Several benefits arise from placing the metering valve  106  vertically below the plenum  110  (i.e., vertically below the material support unit  112 ). For example, an increased stratification and separation of materials as compared to traditional air sifting apparatuses/jigs is achieved. Moreover, turbulence and unexpected direction of pulsated air flows are reduced, thereby allowing the pulsated air to more evenly disperse under and through the material support unit  112 . 
         [0042]    The sifting apparatus  300  further includes a pressure build up system including the pump  102  and the reservoir  104 . The reservoir  104  of the sifting apparatus  300  may be located vertically beneath the plenum  110  (e.g., a vertical axis may extend through the reservoir  104  and the plenum  110 , or exterior edges of the reservoir  104  are vertically in line with exterior-most edges of the plenum  110 ). By pumping air into the reservoir  104 , a constant or substantially constant pressure is maintained for the pump  102  to work against. This results in less stress on the bearing of the air pump  102 . 
         [0043]      FIG. 4  illustrates yet another sifting apparatus  400  of the present disclosure. The sifting apparatus  400  may include all or substantially all of the components discussed with respect to the sifting apparatus  300  of  FIG. 3 . It should also be appreciated that the components of the sifting apparatus  300  may be implemented within the sifting apparatus  400  in similar or identical configurations/orientations, unless explicitly differentiated herein below. 
         [0044]    The sifting apparatus  400  includes a material feed-in device  402  configured to replenish a material mixture to the material support unit  112 . For example, the material feed-in device  402  may provide the material mixture in uniform or substantially uniform dosages, or may provide the material mixture variably. Replenishment of material mixture by the material feed-in device  402  may be calculated according to volume, density, or weight of the material mixture, for example. 
         [0045]    The material feed-in device  402  is located proximate to the material support unit  112 . For example, an outlet of the material feed-in device  402  may be located above the material support unit  112  such that materials released by the material feed-in device  402  are provided to a top/elevated portion of the material support unit  112 . Alternatively, an outlet of the material feed-in device  402  may be located horizontally with respect to the material support unit  112 . In this example, materials released by the material feed-in device  402  are provided to a side portion of the material support unit  112 . 
         [0046]    The sifting apparatus  400  may include more than one plenum  110 . When one plenum  110  is implemented (as illustrated in  FIGS. 1 and 3 ), a top portion of the plenum  110  may correspond or substantially correspond in size and/or shape to a bottom of the material support unit  112 . When more than one plenum  110  is implemented (as illustrated in  FIG. 4 ), top portions of the plenums  110 , collectively, may correspond or substantially correspond in size and/or shape to a bottom of the material support unit  112 . By configuring the plenums  110  as such, the plenums  110  are able to distribute air to all or nearly all of an underside of the material support unit  112 . 
         [0047]    Moreover, when more than one plenum  110  is implemented, the plenums  110  may be horizontally located with respect to each other (i.e., the plenums  110  may be located side-by-side as illustrated in  FIG. 4 ). When more than one plenum  110  is implemented, the plenums  110  may be equal or substantially equal in size and/or shape, or the plenums  110  may have unequal sizes and/or shapes. Alternatively, the plenums  110  may be vertically located with respect to each other. 
         [0048]    As illustrated and described, each metering valve  106  has a single corresponding adjustable orifice  108 . Yet, one skilled in the art should appreciate that each metering valve  106  may have more than one corresponding adjustable orifice  108  without departing from the scope of the present disclosure. Additionally, as illustrated, each plenum  110  of the sifting apparatus  300  may have a single corresponding metering valve  106  and adjustable orifice  108 . However, it should be appreciated that each plenum  110  may have more than one corresponding metering valve  106  and/or adjustable orifice  108  without departing from the scope of the present disclosure. 
         [0049]    Moreover, the sifting apparatus  400  may have more than one metering valve  106 . Each metering valve  106  may provide an equal or substantially equal amount and/or magnitude of gaseous flow (i.e., pulsating and/or steady stream flow) to the material support unit  112 . Alternatively, each metering valve  106  may provide a different amount and/or magnitude of gaseous flow to the material support unit  112 . Additionally, some of the metering valves  106  may provide a steady stream of gaseous material to the material support unit  112  while other metering valves  106  provide a pulsating gaseous material to the material support unit  112 . 
         [0050]    As illustrated and described, each metering valve  106  has a single corresponding adjustable orifice  108 . However, one skilled in the art should appreciate that each metering valve  106  may have more than one corresponding adjustable orifice  108  without departing from the scope of the present disclosure. Additionally, as illustrated, each plenum  110  of the sifting apparatuses of the present disclosure may have a single corresponding metering valve  106  and adjustable orifice  108 . However, it should be appreciated that each plenum  110  may have more than one corresponding metering valve  106  and/or adjustable orifice  108  without departing from the scope of the present disclosure. 
         [0051]    Efficient stratification of materials is obtainable by the sifting apparatuses of the present disclosure by balancing the frequency, amplitude, and acceleration of each jigging stroke of the sifting apparatus. By placing the metering valve  106  (and optionally the reservoir  104 ) below the material support unit  112 , the metering valve  106  is able to provide relatively independent control of the acceleration of each jigging stroke received by the material on the material support unit  112 . Accordingly, air sifting apparatuses of the present disclosure can provide a greater mass of air to the material support unit  112  as compared to traditional air jigs. For example, the air sifting apparatuses of the present disclosure are capable of achieving pressures from two (2) to greater than ten (10) times that of traditional air jigs. Moreover, to allow large, relatively high density materials to fall from a higher layer to a lower layer of mixed sized and density materials, it may be beneficial to expand a bed of mixed materials to cover a surface area larger than that allowed for by traditional material support units. 
         [0052]    To further enhance the efficiency of separation of mixed size and density materials, a relatively high density layer may be maintained on the material support unit  112 . By maintaining a reserve layer of relatively high density materials, relatively low density materials are prevented from being misplaced with the relatively high density materials (i.e., relatively low density materials are prevented from entering the heavy product discharge channel  118 , which, in beneficial implementations, would receive little to no relatively low density materials). If relatively high density materials are withdrawn from the material support unit  112  (via the heavy product discharge channel  118 ) in direct proportion to the amount of relatively high density materials provided to the material support unit  112  by the material feed-in device  402 , a relatively constant layer of relatively high density materials may be maintained on the material support unit  112 . 
         [0053]    As illustrated in  FIGS. 1, 3, and 4 , the light product discharge channel  116  mates to the material support unit  112  directly above where the discharge control mechanism  114  mates to the material support unit  112 . When the material mixture is separated into light materials and heavy materials, there exists an interface/split-point between the light materials and heavy materials. In order for the maximum amount of light materials to be directed to the light product discharge channel  116 , the interface between the light materials and heavy materials should be configured between or substantially between the light product discharge channel  116  and the discharge control mechanism  114  (illustrated as dashed line A-A). 
         [0054]    Traditionally, a user would control operation of the discharge control mechanism  114  to control the level of the interface within the material support unit  112 . For example, if the interface was too high in the material support unit  112 , the discharge control mechanism  114  would be manually changed to increase the rate at which heavy material is allowed to pass through the discharge control mechanism  114 , and vice versa. 
         [0055]      FIG. 5  of the present disclosure illustrates an interface level detector  500  that allows a level of the interface between “light” and “heavy” materials to be automatically determined and manipulated without user interaction (e.g., via computer). By determining a location of the interface level detector  500  within the material support unit  112 , the discharge control mechanism  114  may be automatically controlled to control the interface between the heavy and light materials. The interface level detector  500  mimics a particle of relatively high density due to weight(s) placed within or on the interface level detector  500 . By adding or subtracting weight from the interface level detector  500 , the interface level detector  500  may reside at any density strata. Once a density strata is identified as being composed of particles similar in density to particles mimicked by the interface level detector  500 , it is only necessary to measure the location of the interface level device  500  relative to a weir or other fixed point on the material support unit  112  at the discharge end of the air sifting apparatus. Through common measurement techniques any displacement of the interface level detector  500  can be used as a control signal to actuate the discharge control mechanism  114  to discharge an appropriate amount of heavy materials from the material support unit  112 . If the feed material contains a greater portion of high density particles, the interface level detector  500  will rise within the material support unit  112  as material is added to and moved through the material support unit  112 . The corollary is also true. If less high density particles are delivered to the air sifting apparatus, the interface level detector  500  will fall within the material support unit  112  as material is added to and moved through the material support unit  112 . 
         [0056]    The discharge control mechanism  114  is operable with the interface level detector  500  to automatically withdraw relatively high density materials from the material support unit  112  in direct proportion to the amount of relatively high density materials provided to the material support unit  112  by the material feed-in unit  402 . For example, when it is detected that the interface level detector  500  has risen above a desired/threshold location within the material support unit  112 , the discharge control mechanism  114  is automatically engaged to release heavy products through the heavy product discharge channel  118  at a greater rate until the interface level detector  500  relocates to the desired location. Contrarily, when it is detected that the interface level detector  500  has fallen below a desired location within the material support unit  112 , the discharge control mechanism  114  is automatically engaged to reduce or stop the release of heavy products through the heavy product discharge channel  118  until the interface level detector  500  relocates to the desired location. 
         [0057]    The interface level detector  500  may be made of glass, metal, plastic, or other like solid material. The interface level detector  500 , as illustrated, has a bulbous exterior shape into which weight is placed. However, one skilled in the art should appreciate that the interface level detector  500  may have other shapes without departing from the scope of the present disclosure. Illustrative weights include bearings or like solid materials having known weights, for example. By implementing the illustrated interface level detector  500 , a nuclear density detection device, which is typically used with air sifting apparatuses, may be omitted. The illustrated interface level detector  500  also enables the air sifting apparatus to achieve a discharge system identical to those used in traditional wet jigging apparatuses. 
         [0058]      FIG. 6  illustrates the interface level detector  500  as it would be implemented within the material support unit  112  of a sifting apparatus. The interface level detector  500  includes an end  602  that couples to an end  604  of an arm  606  within the material support unit  112 . The ends  602 / 604  of the interface level detector  500  and arm  606  may couple via threads, male/female members, friction, etc. The arm  606  connects to a weir or other fixed point on the material support unit  112 . As materials are moved through the material support unit  112 , measurements of the displacement of the interface level detector  500  are taken and used to determine the speed at which the discharge control mechanism  114  should operate, as described herein above with respect to  FIG. 5 . As illustrated, movement of the interface level detector  500  within the material support unit  112  is determined by measuring displacement of the arm  606 . However, one skilled in the art should appreciate that the location of the interface level detector  500  within the material support unit  112  may be determined using non-lever techniques. For example, movement of the interface level detector  500  may be determined using infrared measurements, sonic measurements, magnetic techniques, etc. 
         [0059]    The present disclosure is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.