Fluidizable material handling apparatus
BACKGROUND OF THE INVENTION 
     This invention relates to material handling apparatus and more particularly to a pallet molded of synthetic resin material or the like adapted to form part of a container for transporting, supporting, and storing a load of fine granular, particulate, powdered or other fluidizable material, and for fluidized unloading of the load from the container. 
     The pallet of this invention represents an improvement over the container disclosed in the coassigned U.S. Pat. No. 4,007,694, and commercially available from the assignee of this invention, Semi-Bulk Systems, Inc. of St. Louis, Mo. under their registered trademark AIR PALLET. The pallet disclosed in the above-noted patent is generally circular, as viewed from above, having a number of legs spaced for the entrance of the tines of a forklift from any of four directions. The pallet has a peripheral wall extending around the pallet and an upwardly facing deck supported by the peripheral wall for supporting the load. The deck slopes downwardly toward one side of the pallet and is adapted to have a porous diaphragm of cloth or the like secured thereto with the diaphragm covering the deck. An outlet opening is provided in the peripheral wall of this prior art pallet above the level of the deck at the lowest side thereof through which the powdered load may be discharged or unloaded. An inlet opening also extends through the peripheral wall for introducing compressed air into the space between the diaphragm and the deck. The compressed air flows upwardly through the porous diaphragm for fluidizing the powdered load bearing against the diaphragm. 
     The diaphragm of this prior art container was secured to the pallet by a spline held in place within a groove by means of staples driven into the pallet. The spline merely distributed the loading of the diaphragm to the staples. However, upon fluidizing the load in this prior pallet, the air pressure beneath the diaphragm would, on occasion, apply tension loading on the staples and pull them free of the pallet thereby releasing the diaphragm and preventing fluidization of the remaining portion of the load. When the diaphragm pulled loose, refurbishment of the pallet was required prior to reuse. 
     In many uses of the container of this invention, such as where the empty containers must be air transported or where the containers are used to contain toxic materials, it is desirable that essentially all of the material be emptied from the container during unloading thereby to minimize spilling of the material during handling of the empty containers. 
     The prior art container described in the above-mentioned patent had a tubular plastic film bag secured to its pallet. This bag was generally of the same diameter as the pallet (e.g., about 42 inches in diameter) and was of sufficient height to contain a desired quantity of powder (e.g., 500-4,000 pounds or more). The bag was typically attached to the peripheral wall of the pallet by means of a metal strap band on the outside of the bottom of the bag, tightened therearound and secured in place. Typically, this strapping band was of the well known type (nylon) used to band shipping containers commercially available from Signode Corporation of Chicago, Ill. and other companies. Upon pressurizing the interior of the bag during fluidized unloading of the load, the air pressure would, on occasion, pull the bag from between the strap and the pallet with the resultant loss of fluidization air and spillage of the powdered load. Although this rarely occurred, it was a serious problem when it did occur because the escaping powder often prevented resealing of the bag to the pallet and thus the load could not be fluidized for unloading and would continue spilling from the container. It was also recognized that because the pallet was preferably molded of synthetic resin material, it suffered from some degree of inherent dimensional instability and it would relax when a strap was tightly applied therearound. 
     It was also found that the pressure buildup within the container would reduce fluidizing air volume to merely equal the volume of powder and air discharge from the container thus limiting the degree of fluidization and the discharge of material from the container. 
     Due to the flow of material into the container during filling and due to the flow of air through the fluidized material and the flow of the fluidized material from the container during unloading, it has been found that a static electricity charge could build up on the container and pose a danger when handling potentially explosive or flammable materials or when unloading relatively safe materials in a hazardous environment (e.g., in a hydro carbon environment). 
     Still further, the discharge conduit on prior art containers would, on occasion, pull loose from the pallet during unloading or would not properly seal relative to the pallet with consequent leakage of the material during unloading. 
     SUMMARY OF THE INVENTION 
     Among the several objects and features of the present invention may be noted the provision of a material handling container or pallet adapted to support a load of granular, particulate, powder, or other fluidizable material and adapted to fluidize the load for efficient and rapid discharge of substantially all the load from the container leaving little residue therewithin; the provision of such a pallet having a porous diaphragm secured thereto in such manner that the diaphragm may be readily installed and yet can resist being pulled from the pallet by air pressure during fluidization of the load; the provision of such a pallet which substantially uniformly fluidizes the load therewithin; the provision of such a pallet which may have a plastic film or other flexible bag readily secured thereto for containing the load, the bag being secured to the pallet in such manner that the bag resists being pulled from the pallet during fluidization of the load and that the bag is effectively sealed relative to the pallet to prevent leakage of the load; the provision of such a pallet in which the bag may be readily secured to the pallet without damage to the bag or the pallet and with a minimum amount of labor required; the provision of such a pallet in which the air pressure within the container during fluidized unloading is maintained within a predetermined pressure range for maintaining the structure and shape of the fluidized contents in the otherwise flexible container without restricting air flow and for minimizing the possibility that the bag may be pulled from the pallet; the provision of such a pallet of a container which is safe in handling materials which may explode or ignite when exposed to open static electricity sparks; the provision of a probe for such a container which may be readily and effectively sealed and secured relative to the discharge opening of the container; and the provision of such a container which is of rugged and economical construction, and which may be repeatedly reused with a minimum amount of refurbishment. 
     Briefly, a material handling container or pallet of this invention for supporting a load of granular, particulate or powdered material and for pneumatically fluidized unloading of the load from the pallet includes pallet base having a plurality of legs engageable with the ground for supporting the pallet and the load carried thereby, the legs being spaced for accommodating the tines of a forklift vehicle to facilitate forklift transport of the pallet and the load. The pallet further includes an upwardly facing deck for supporting the load, the deck sloping downwardly toward one side of the pallet, and a peripheral wall extending around the pallet joining the upper deck and the legs. A porous diaphragm overlies the deck and defines a plenum between the diaphragm and the deck. An inlet is provided in the pallet for the introduction of air under pressure into the plenum for fluidizing the load bearing on the porous diaphragm. An outlet is provided which extends through the peripheral wall of the pallet for providing communication between the space above the porous diaphragm and the exterior of the pallet, the inner end of the outlet being disposed at the above-mentioned one side of the pallet adjacent the lowermost portion of the deck being generally flush with the deck, and angling downwardly from its inner end below the level of the deck whereby the fluidized load flows down the inclined deck toward the inner end of the outlet and thence down the outlet. 
     In another embodiment of the material handling container or pallet of this invention, generally similar to that described above, means is provided for securing the diaphragm to the pallet. This securing means comprises an upwardly facing groove in the deck of the pallet under the outer margin of the diaphragm, and an elongate spline or retainer of relatively stiff material having a plurality of teeth on one side thereof. The spline is insertable into the groove along with the diaphragm so that the teeth engage the diaphragm and bear against one side wall of the groove, and with the other side of the spline bearing against the other side of the wall of the groove whereby upon introduction of compressed air into the penum for fluidizing the load with resultant pressurization of the diaphragm and application of tension loading to the diaphragm, the spline self-locks in the groove and securely holds the diaphragm in place on the deck. 
     In still another embodiment of the container of this invention generally similar to the containers above described, means is provided for sealably securing the bag to the pallet and for preventing air pressure from within the bag present during fluidization of the load from pulling the bag from the pallet. The pallet has a continuous, outwardly projecting flange around its peripheral wall and the bag has its lower end folded on itself to form a hem and a cord is disposed within the hem, the hem fitting over the outside of the flange. The means securing the bag to the pallet comprises a hoop clamp which fits over the flange on the outside of the hem. The clamp includes means for circumferentially tightening the clamp on the hem and on the pallet for sealingly clamping the bag to the pallet whereby upon pressurization of the bag during fluidization of the load and upon the bag being pulled upwardly by the air pressure therewithin, the cord engages the clamp and prevents the bag from slipping relative to the clamp and to the pallet. 
     In still another variation of a container of this invention, means is provided for venting the container (as defined by the bag) and for maintaining an air pressure within the storage space within a predetermined pressure range during fluidization of the load. 
     In still another embodiment of this invention similar to those described above, the bag is specified to be made of an electrically conductive material and means is provided for electrically grounding the bag thereby to minimize the buildup of static electric charges on the bag. 
     Further in accordance with this invention, a probe is provided which is adapted to be removably inserted into the outlet opening of the pallet and sealed relative thereto. The probe includes a tubular body, an outwardly protruding shoulder extending circumferentially around the body, a ring slidable axially on the body toward and away from the shoulder, deformable seal means disposed around the body between the shoulder and ring, and lever means manually movable between a release position in which the seal means is substantially free of compression and a seal position in which the seal means is compressed between the ring and the shoulder for effecting outward expansion of the seal means so as to sealingly engage the walls of the pallet discharge opening. 
     Other objects and features of this invention will be in part apparent and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a material handling container or pallet of this invention for fluidized unloading of fluidizable material; 
     FIG. 2 is an enlarged plan view of the pallet base of the container of this invention illustrating a discharge outlet for the fluidized load, an air inlet, an air distribution network in the upwardly facing deck of the pallet, and a porous diaphragm overlying the deck; 
     FIG. 3 is an enlarged cross-sectional view taken along line 3--3 of FIG. 2 showing the discharge outlet of the container; 
     FIG. 4 is an enlarged cross-sectional view taken along line 4--4 of FIG. 2 illustrating means in accordance with this invention for securing the diaphragm to the pallet and means for securing the bag to the pallet; 
     FIG. 5 is an enlarged side elevational view with parts broken of a valve of this invention for venting the container and for maintaining the pressure of the fluidizing air within the container within a predetermined pressure range during fluidization of the load; 
     FIG. 6 is an enlarged view of a probe of this invention for being releasably and sealingly secured within the discharge opening of the pallet, the probe being shown in its sealed position; 
     FIG. 7 is an enlarged side elevational view of the clamp of this invention for clamping the bag to the pallet; 
     FIG. 8 is a view taken along line 8--8 of FIG. 4 illustrating a spline for securing the diaphragm in place on the pallet; and 
     FIG. 9 is a view similar to FIG. 4 illustrating a modification of the container of this invention incorporating an electrically conductive liner within the bag; 
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, a container of this invention for transporting, storing, and unloading a load of powder, granular, particulate or other fluidized material is indicated in its entirety at reference character 1 and is shown to include a one-piece pallet base 3, preferably molded of a suitable synthetic resin material (e.g., polyethylene or nylon), and a tubular bag 5 or other enclosure secured to the pallet for defining a storage space therewithin in which a load of fluidizable material is contained. The pallet includes a plurality of legs 7 (for example, 12 legs) engageable with the ground for supporting the container and the load therewithin, the legs being spaced to receive the lifting tines (not shown) of a forklift so that the loaded containers may be readily moved about. The bag may be of any suitable material, such as a limp coated fabric, or other air impervious limp sheet material, but it is preferably of a tough, strong plastic film as will be hereinafter specified. As indicated in FIG. 1, circumferential straps 9 may be optionally installed around the bag during or after filling to provide additional circumferential support for the bag. The quantity of material constituting a load may vary greatly depending on the material and container size. In many instances, the container of this invention is used primarily to transport and store so-called &#34;semi-bulk&#34; quantities of material (i.e., more than a bag full but less than a truck or railroad car full of fluidizable material). 
     As is best shown in FIGS. 1 and 3, pallet 3 includes an outer, generally vertical peripheral wall 11 defining the outside of the pallet. An outwardly projecting, continuous flange 13 extends around the pallet at the top of wall 11 for purposes as will appear. The pallet further includes a generally planar load supporting deck 15 inclined downwardly toward one side of the pallet relative to the lower ends of legs 7. As is shown in the drawings, pallet 3 is preferably a hollow, unitary molded plastic structure and is preferably fabricated by well known rotational molding techniques. It will be understood, however, that the number in which pallet 3 is fabricated and specific details of its structure may be varied significantly and still be within the scope of this invention. As disclosed in the above-discussed co-assigned U.S. Pat. No. 4,007,694, the load supporting deck 15 of the present invention is preferably spaced from supports formed within the pallet and is flexible or deformable under the weight of the load supported thereby so as to deflect downwardly thereby to rest on supports so that the weight of the load is transferred to legs 7 and so that the deck need not resist the entire weight of the load supported thereby. 
     Pallet 3 of this invention further has an outlet opening, generally indicated at 19, at the side of the pallet adjacent the lowermost edge of inclined deck 15 extending from the space above the deck through peripheral wall 11 for the discharge of material within the container. This discharge opening is defined by conduit walls 21 through the peripheral wall. The outlet is adjacent the lowermost portion of deck 15 and is generally flush with the deck and angles downwardly from its inner end below the level of the deck toward the inlet end of the outlet and thence down and out of the container via the outlet. The pallet further includes a second opening constituting an inlet 23 for the introduction of compressed air or other gas for fluidizing the load in a manner that will appear. 
     Pallet 3 further includes a porous diaphragm 25 overlying deck 15 with a space between the diaphragm and the deck constituting a plenum chamber 27. Compressed air or other gas introduced via inlet 23 enters the plenum and passes through the porous diaphragm so as to fluidize the load of fluidizable material within bag 5 bearing on the diaphragm. In accordance with this invention, deck 15 includes a plurality of upwardly facing open grooves or channels constituting an air distribution network, as generally indicated at 29, for substantially uniformly distributing air pressure within plenum 27 beneath diaphragm 25 to facilitate uniform fluidization of the load over the entire working area of the diaphragm. This air distribution network includes a main air channel 31 in communication with air inlet 23. The main air channel extends around the outer margin of deck 15 and, as shown in FIG. 2, the outer margin of diaphragm 25 overlies the main air channel and an outer circumferential retainer groove 33. The air distribution network still further includes a plurality of secondary air channels 35 radiating from a common point of locus P and intersecting the main air channel 31 at substantially equal intervals therealong. The air distribution network includes a plurality of tertiary air channels 37, these tertiary air channels being shown to be curvilinear and to intersect the secondary air channels 35. The common point P is located adjacent outlet opening 19 and the secondary air channels 35 radiate therefrom. The common point P is also shown to be the common center of the curvilinear tertiary air channels 37. Main air channel 31 is of a depth substantially greater than the secondary air channels and the other air channels are so sized relative to one another as to facilitate equal distribution of air pressure from one channel to another, especially upon initial introduction of compressed air into plenum 27 when the diaphragm is pushed down under the weight of the load against deck 15. 
     In accordance with this invention, improved means is provided for rapidly and securely fastening diaphragm 25 to the pallet in such manner as to prevent the diaphragm from becoming dislodged or partially dislodged from pallet 3 during fluidization of the load due to air pressure beneath the diaphragm from pulling it from the pallet. As previously mentioned, the outer margins of the diaphragm overlie retainer groove 33 which extends continuously around the outer perimeter of deck 15 and which outlines opening 19 (see FIG. 2). An elongate retainer spline 39 of a relatively stiff material (e.g., stainless steel or the like) having a series of serrated teeth 41 on one side thereof is inserted down into groove 33 along with diaphragm 25, with one side (i.e., teeth 41) bearing against one side face (i.e., the inner side face toward the center of deck 15) of groove 33 and with the other side of the spline bearing against the other side face of the groove. As best shown in FIG. 4, spline 39 is crimped along its entire length so that it has a generally flattened V-shaped configuration when viewed in cross-section. The spline includes base portion 42 on one side of the crimp, and teeth 41 project outwardly from the other side of the crimp (see FIG. 8). Teeth 41 are generally triangular when viewed in plan and may, for example, have a length of about 0.25 inches (0.63 cm.). Spline 39 may, for example, have about 5 teeth per inch (2 teeth per cm.). The spline further includes tabs 43 extending outwardly from the outer edge of base portion 42. These tabs may, for example, be spaced on one inch (2.5 cm.) centers and be about 3/32 inches (0.24 cm.) long. Spline 39 is inserted into groove 33 with teeth 41 pointing downwardly and toward the inner generally vertical wall of the groove with base portion 42 being parallel to and bearing against the outer generally vertical wall of the groove. Thus, the tips of teeth 41 uniformly engage the diaphragm and hold it firmly against the inner wall (bottom inner corner) of the groove. Staples 44 are preferably driven into the outer wall of groove 33 so as to engage selected tabs 43 for holding the spline in place in the groove. Upon introduction of the fluidized air into plenum 27, the air pressure acting against the diaphragm will tend to pull the diaphragm upwardly out of the groove. However, as the diaphragm begins to move upwardly out of the groove, teeth 41 which protrude at least partially through the diaphragm, move along with the diaphragm and thus more fully penetrate the diaphragm (if they have not already done so) and further are caused to dig into the plastic material constituting the inner wall of the groove. The outer edge of base portion 42 and staples 44 engaging tabs 43 constitute a fulcrum about which the spline rotates. The rotation of the spline about this fulcrum is indicated by the arrows in FIg. 4. In this manner, the spline self-locks in the groove and the application of additional tension loading to the diaphragm tends to cause the teeth to grip even more securely and thus effectively resists tension loading of the diaphragm. It will be appreciated that staples 44 are primarily for acting as a fixed fulcrum or pivot for the upper edge of the base portion as well as for holding the spline in the groove prior to the application of fluidizing air pressure to the diaphragm and that the staples are substantially free of tension loading which might tend to pull them from the pallet while the diaphragm resists the pressure force. The staples are primarily subjected to shear loading which does not tend to pull them from the pallet. 
     It has been found that a spline having the approximate dimensions as indicated above effectively and efficiently fastens a variety of types of diaphragms from relatively heavy canvas to a fine ripstop nylon or parachute nylon. It has also been found that the spline arrangement described above is effective in securing multiple plies of cloth constituting the diaphragm and it has been still further found that the teeth do not cut or penetrate through the diaphragm to such a degree as to degrade its strength. This method of attachment causes the diaphragm to form an air seal at the inside of groove 33 so that the small holes made in the diaphragm by the spline teeth are outside this air seal and do not leak any substantial quantity of fluidizing air. As shown in the drawings, spline 39 is substantially continuous along the length of groove 33, but it will be understood that a series of shorter lengths of the spline could be placed intermittently around the diaphragm in the groove. It will be noted that a diametric groove 33&#39; is provided in deck 15 for receiving a spline 39 so as to secure the center of diaphragm 25 to the deck thereby to reduce the total force on the peripheral spline. 
     As previously mentioned, container 1 includes bag 5 which is removably and sealably secured to pallet 3. Bag 5, as heretofore described, is an elongate tubular sleeve of a tough, strong plastic film or the like. Specifically, in certain applications, plastic coated fabric film such as is commercially available from the Van Leer Plastics, Inc. of Houston, Texas under their trademark VALERON, may be used. It will be understood, however, that a variety of different films and bag configurations may be used in conjunction with the container of this invention depending on the quantity of product to be contained in the bag, the characteristics (i.e., density, toxicity, etc.) of the product, the number of desired reuses of the container, and other parameters. 
     In accordance with this invention, a split hoop clamp, as is generally indicated at 45, is provided for releasably and sealably fastening bag 5 to pallet 3 so as to substantially eliminate the tendency of the bag to be pulled free of the pallet during fluidization of the load due to air pressure within the bag, and to substantially eliminate leakage of the product between the bag and the pallet. As shown in FIG. 4, pallet 3 is formed to have the above-mentioned continuous flange 13 extending circumferentially therearound. By way of example, flange 13 has a heighth of approximately 3/4 inches (1.9 cm.) and extends radially outwardly from peripheral wall 11 approximately 1/4inch (0.63 cm.). In accordance with this invention, the bottom margin of tubular bag 5 is folded back on its outside face so as to form a hem 47 (see FIG. 4). A cord 49, such as a stretchable elastomeric ring, a fiber rope, or the like, is placed inside the hem below flange 13. It will be noted that the double ply of the hem extends up above flange 13. Clamp 45 is shown to comprise a hoop 51 of an electrically conductive metal, such as mild steel or the like, which is generally channel-shaped in cross section (see FIG. 4) having a web 53 adapted to be generally parallel to and to be cooperable with the outer face of flange 13 thereby to clamp bag 5 relative to the pallet. The clamp further has upper and lower flanges 55a, 55b. The outer edges of these flanges are preferably bent back on themselves so as to protect the bag from being cut or otherwise damaged by the strap. It will be understood, the lower margin of a bag 5 containing an unfluidized load of fluidizable material has a tendency to droop down over the outside of clamp 51. In accordance with this invention, flange 55a of hoop clamp 51 positively holds the bag on flange 13 of the pallet and positively prevents the weight of the fluidizable material in the bag from pushing or pulling the bag and hoop clamp 51 off the pallet. 
     Still further in accordance with this invention, the outer face of flange 13 may optionally have a layer of compressible foam material 56 adhered thereto. This foam material is shown to be about as wide as flange 13 and to have a thickness of about 1/8 inch (0.31 cm.). The foam layer is disposed between the double plies of hem 47 and flange 13 so as to constitute a compressible surface against which the bag hem may be compressed and sealed. This foam takes up dimensional variances in the pallet and in the clamp and enables a leak-tight seal to be made within a relatively wide band of dimensional tolerances. 
     Hoop clamp 51 further includes a tension connector, as generally indicated at 57, for adjustably drawing the ends of the clamp together and for securely clamping bag 5 on pallet 3. As shown in FIG. 7 tension connector 57 comprises a pair of upper and lower tubular barrels 59a, 59b, respectively, secured to each end of the split hoop clamp for receiving upper and lower bolts 61a, 61b. By tightening the bolts, the hoop may be tightened a desired amount within the limits of bolts 61a, 61b. By selectively tightening either the upper or lower bolts somewhat more than the other, the upper and lower edges of the clamp may be adjusted independently of one another so as to vary the degree to which the upper and lower portion of the clamp grips the bag. The hoop further includes a resilient tongue 63 of relatively thin gauge stainless steel or the like which is secured to one end of the hoop clamp and which extends beneath the other end of the hoop clamp to protect the bag from damage (i.e., from being torn) as the hoop is tightened. While tension connector 57 has been herein described as a bolt tightening arrangement, other types of tensioning devices, such as overcenter buckles and the like, may be used. 
     In accordance with the above-described bag securing means of this invention, as fluidizing air enters bag 5 from plenum 27 through diaphragm 25 and as air pressure within the bag builds up so as to exert vertical tension force on the bag (thereby maintaining its shape in a semi-rigid manner) which would tend to pull it away from deck 15, any slippage of the bag relative to the hoop clamp is prevented by cord 49 after the cord comes into contact with the bottom flange 55b of the hoop clamp. Thus, the securing arrangement for the bag of this invention can be said to be self-locking and to thus positively prevent the bag from being pulled off the pallet during fluidized unloading. 
     After filling bag 3 with product, the upper margin or mouth of the bag is twisted or otherwise drawn shut so as to at least partially close off the mouth of the bag. As has been heretofore conventional, a length of plastic tubing 65 or the like constituting a vent for the bag is inserted in the constricted mouth of the bag and the bag is clamped, as by means of a wire tie 67 or the like so as to releasably close and seal the mouth of the bag with respect to the vent tube (see FIG. 1). Vent conduit 65, discharge outlet 19, and compressed air inlet 23 may be capped by suitable plastic caps or plugs (not shown) inserted therein so as to seal the load within container 1. Thus, upon unloading the container, the plugs are removed from the discharge outlet, the fluidizing air inlet and from the bag vent tube. 
     As the fluidizing air enters the bag from plenum through porous diaphragm 25, it is vented from the bag via vent tube 65 after it has flowed through the product within the bag. As heretofore mentioned, the degree of fluidization of the product or material within bag 5 may vary, depending on the quantity of product in the bag, as the product is unloaded. Also, the pressure within the bag may occasionally decrease or increase as the product is intermittently discharged from the bag. In certain instances, an increase in air pressure within the bag will pull the bag free of the pallet. In other instances, a decrease in pressure within the bag below a specified level will cause an erect bag to lose rigidity and to permit the load to shift so as to cause the container to tip. 
     In accordance with this invention, a vent valve, as generally indicated at 69, is connected to a vent valve conduit 71 which is sealably connected to vent tube 65 for venting the fluidizing air from within bag 5. Thus, vent valve 69 constitutes means for venting the fluidizing air from the bag and for maintaining air pressure within the bag within a predetermined range during fluidization of the load so as to hold the bag erect and to prevent pressure within the bag from pulling it from the pallet during fluidization of the bag. Vent valve 69 comprises a body 73 having an inlet 75 connected to vent conduit 71 and an outlet 77 with a damper or flapper valve member 79 pivotally mounted offcenter between the inlet and outlet. A counterbalancing crank arm 81 rotates with the flapper valve member and carries a counterbalancing weight 83 for biasing the flapper valve member toward its closed position in which it substantially blocks the flow of fluidizing air from the bag. Since valve member 79 is pivotally mounted offcenter, air pressure from within the bag tends to cause the flapper valve member to pivot or rotate relative to body 73 from its closed position toward its opening position against the bias of counterbalancing weight 83. The counterweight 83 being positioned to reduce its closing bias on the valve member 79 as the valve member 79 moves through a succession of positions from the flow blocking closed position to the fully open position. Thus, by adjusting the position of counterbalancing weight 83 along the length of crank arm 81, vent valve 69 can be selectively adjusted to maintain air pressure within the bag within a selected pressure range so as to insure proper fluidization of the load within the bag, to prevent the build up of excessive air pressure within the bag, and to maintain a sufficient pressure within the bag to hold the bag erect thus preventing the load from shifting as the load is discharged therefrom. This pressure range may, for example, vary between 2 and 40 inches (5 and 100 cm.) of water. It will be understood that means other than weight 83, such as a spring, may be used to counterbalance valve member 79 against opening under the influence of fluidizing air pressure within the bag. 
     As previously mentioned, fluidized product from within bag 5 is discharged from the container via outlet 19. As was conventional in prior art containers, such as disclosed in the above-mentioned coassigned U.S. Pat. No. 4,007,694, the discharge conduit or hose was removably inserted into the discharge opening of the pallet so that the product discharged therefrom could be conveyed to a remote location, such as to a hopper, an eductor, or the like. Heretofore, the discharge conduit of these prior art containers had a probe which was forcibly inserted into the pallet discharge opening so as to be frictionally sealed and held in place on the pallet. However, due to dimensional variances of the pallet discharge opening, due to inadvertant bumping of the discharge conduit, and due to air pressure within the discharge opening, the prior art probes would, on occasion, become dislodged from the pallet with consequent spillage of the product and termination of unloading from the container. 
     In accordance with this invention, a probe, as generally indicated at 85, is provided for insertion into and for being positively and sealingly connected to outlet opening 19 of pallet 3 of this invention so as to receive the material being discharged from the pallet. A conduit or hose 87 is secured to probe 85 for conveying the discharged material from the pallet. The probe has a tubular body 89 of circular cross section and has an outwardly extending flange 91 adjacent the outlet end of the body with the surface of the flange facing away from the end of the body constituting a shoulder 93. As shown in FIG. 6, shoulder 93 is preferably undercut for purposes as will appear. An expandible seal 95 of hard rubber, plastic or the like is positioned on the body behind shoulder 93. A compression ring 96 is located on body 89 behind the seal and is axially movable on the body between a retracted position (not shown) in which it is substantially clear of seal 95 and in which the seal is substantially free of compression and a position (as shown in FIG. 6) in which the ring compresses the seal between itself and shoulder 93 thereby to cause the seal to expand radially outwardly into firm gripping and sealing engagement with walls 21 defining outlet 19 of pallet 3. It will be understood that the seal fits into the undercut of shoulder 93 to hold the seal as it is compressed thereagainst. As shown in FIG. 6, the seal extends past the inner surface of peripheral wall 11 so that upon being compressed, it engages the walls of the outlet and bulges out on the inside of the peripheral wall to a diameter larger than the outlet thereby to positively prevent the probe from being withdrawn from the opening. With the seal frictionally engaging walls 21 of outlet 19, the probe firmly engages the pallet and thus prevents inadvertent removal of the probe from the pallet and the probe is effectively sealed relative to the pallet so as to prevent leakage of product from the outlet 19 during unloading. The probe further includes a handle 97 joining two cam levers 99a, 99b on opposite sides of body 89, the cam levers being pivotally secured to the body as indicated at 100. Each of the cam levers has a respective rotary cam 101a or 101b adjacent its pivotal connection. These cams cammingly engage the rear face of compression ring 96 opposite seal 95 and cause the ring to move axially along the body member toward shoulder 93 so as to move the ring toward its compression position. Handle 97 and cam levers 99a, 99b constitute manually operable means for compressing and releasing seal 95. 
     Probe 85 may optionally include an air tube 103 for directing air into the fluidizable material as it flows into outlet 19 from within bag 5 thereby to insure that the material will continue to flow through the outlet and will not bridge or jam in the outlet. This discharge air tube is shown to comprise a tubular member extending endwise from the top of the probe from the inside of body 89. The tubular member extends into the probe body and has external connections 105 thereon so that an air line (not shown) from a compressed air source may be connected thereto. Thus, in operation compressed air may be directed through air tube 103 and discharged into the powder within outlet 19 thereby to breakup and to keep the powdered material flowing through the outlet. Compressed air for air tube 103 may optionally be applied by a bypass from the fluidizing air line adapted to be inserted in inlet 23. 
     As heretofore mentioned, in handling certain products which pose a risk of explosion or fire, or in handling relatively safe materials in a hazardous environment (such as in a hydrocarbon environment in a chemical plant or the like) it is necessary that the container 1 of this invention be properly grounded so as to lessen the danger of the discharge of static electricity which could cause an explosion or fire. In accordance with this invention, bag 5 may be made electrically conductive either by placing an electrically conductive liner 107 inside bag 3 or by providing an electrically conductive coating 109 on the inside surface of the bag. For example, liner 107 may be of an electrically conductive plastic film such as is commercially available from the 3M Company of Minneapolis, Minn. under their registered trademark VELOSTAT. As shown in FIG. 9, liner 107 is placed inside bag 5 so as to form a multi-ply bag and the liner and the bag are folded up to form hem 47&#39;. Clamp 45 contacts liner 107 to make good electrical contact therewith. The plastic film constituting bag 5 may be made electrically conductive by electrodepositing a layer of aluminum or other electrically conductive metal on one face (the inside face) of bag 5 so as to constitute coating 109 (see FIG. 4). Such coating of plastic film is commercially available from the above-noted supplier of bag 5. 
     In forming hem 47 at the bottom margin of the bag, the electrically conductive inner face 109 of the bag faces outwardly when folded to form the hem and thus the electrically conductive metallic hoop clamp makes good electrical contact with the conductive surface of the bag around its entire bottom portion. Regardless of whether an electrically conductive bag or a liner 107 is used, a grounding wire 111 (as shown in FIG. 1) is clipped onto clamp 45 thereby to electrically ground the bag during filling, unloading, and other operations so as to dissipate static electric charges on the bag. 
     Still further in accordance with this invention, it is sometimes necessary to electrically ground vent conduit 71 and discharge conduit 87 so as to further prevent the discharge of static electricity. These conduits may be made of electrically conductive hose material, such as is commercially available from the 3M Company under their registered trademark VELOSTAT. Of course, these electrically conductive conduits may be properly grounded by connecting grounding wires (not shown) to the conduits. Thus, the entire container 1 of this invention may be effectively and readily grounded. 
     In handling potentially explosive or flammable materials, it may be desirable to fluidize the material during unloading with a gas other than air. For example, an inert or chemically inactive gas, such as nitrogen or the like, may be used in place of compressed air thereby to even further diminish any likelihood of fire or explosion during unloading. 
     It will be understood that an outlet for the discharge or vacuum withdrawal of fluidizable material within container 3 may be provided by inserting a tube (not shown) into bag 5 from the top and sucking on this tube. Of course, this withdrawal tube is sealed relative to the bag and the bag is vented to the atmosphere. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.