Abstract:
An elbow fitting is used in a pneumatic product conveying system in which the fitting expands from the inlet pipe along the outer side of the elbow fitting to enable a layer of accumulated product particles to be formed so as to move at a lower velocity than the velocity of the incoming product stream while establishing a moving contact surface for deflecting incoming product particles toward the outlet pipe with a minimum of pressure resistance and product attrition. The accumulated product particles are discharged from the elbow fitting by incorporating a step in the outer surface of the elbow fitting to create a Bernoulli effect causing the accumulated product particles to enter the air flow after the incoming flow of product particles has ceased. The particles in the accumulated layer are replenished from the incoming flow during operation of the elbow fitting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/743,117, filed on Dec. 22, 2003, now U.S. Pat. No. 6,951,354. This application also claims domestic priority on U.S. Provisional Patent Application Ser. No. 60/567,954, filed May 4, 2004. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to pneumatic transport systems and, more particularly, to a fitting for pneumatic pipes to permit a change in direction of the material being conveyed therein. 
   Conveying solid particles injected into a high velocity stream of air contained within a pipe or tube is well known in industry. Dilute phase velocities often exceed sixty miles per hour and use up to one pound of air to move as much as five pounds of product per minute through the pipe. Typical air pressures for dilute phase systems will range from eight to twelve psig. High air velocity and low product particle population is accomplished with low pressure resistance, but greatly increased damage to the product particles being conveyed. Damage occurs in straight pipe sections, but is greatly increased whenever directional changes are imposed on the conveying system. 
   Dense phase systems move more product per pound of air, but travel at lower velocities and at higher pressures. Typically, system operating pressures will not exceed forty-five psig. Whether the conveying system is operating under dilute phase or dense phase, the product particles suffer considerable damage during transport, particularly when changes in direction are being used. To effect changes in direction elbow fittings having a radius as much as ten times the diameter of the pipe are used. Nevertheless, the combination of high velocity and centrifugal force does most of the damage, particularly on heat sensitive plastic compounds. 
   Elbow fittings used in pneumatic conveying systems typically suffer wear at the elbow curve in line with the product flow into the elbow fitting, whether the elbow fitting is a short radius elbow or a long radius sweep elbow fitting. Particles flowing into the elbow fitting impact the curved surface of the elbow and are redirected. The bouncing product particles create an area of turbulence that slows the speed of conveyance of the particles through the system, often causing plugging. Furthermore, the bouncing particles and the movement of the product particles around the outer surface of the elbow fitting generate friction, making the surface of the fitting warm to the touch. This heat can have a detrimental effect on the product being conveyed, particularly when the product is heat sensitive, such as plastic pellets on which the edges of the pellets will melt and adhere to the pipe. 
   One known attempt to overcome the problem of changing direction in a pneumatic conveying system is found in U.S. Pat. No. 4,387,914, issued to Hammertek Corporation on Jun. 14, 1983. In this Hammertek patent, the elbow fitting is formed with a vortex opening in substantial alignment with the incoming product stream from the straight section of pipe. The vortex section emulates a blocked “T” fitting by providing a chamber in which a loose ball of product particles slowly rotates to deflect incoming product without causing excessive wear on the fitting. 
   Another known attempt to overcome the aforementioned problems of changing directions in a pneumatic conveying system is taught in U.S. Pat. No. 5,288,111, issued to Waeschle Maschinenfabrik GmbvH on Feb. 22, 1994. IN the Waeschle patent, an angularly disposed baffle plate is positioned within an expanded elbow section that has a greater cross-sectional area than the cross-section of the pipe carrying the incoming product. The expanded elbow cross-section increases in size from the inlet pipe by expanding inwardly toward the inner elbow side. The outer elbow side of the expanding section defines a linear relationship with the inlet pipe to direct the stream of product particles into engagement with the baffle plate that is oriented at between 55 and 65 degrees with respect to the axis of the inlet pipe. Accordingly, the expanded elbow cross-section is not intended to provide a flow of material along the outer side of the elbow fitting. Excessive wear on the baffle plate is, therefore, incurred due to the direct impact with the incoming product stream. 
   Other deflector plate elbow fittings for pneumatic conveying systems are taught in U.S. Pat. No. 4,595,319, issued to Richard H. Cook for Cubeco, Inc. on Jun. 17, 1986; and in U.S. Pat. No. 4,733,889, issued to Edwin L. Haines for The Goodyear Tire and Rubber Company on Mar. 29, 1988. Both patents provide for an expanded elbow cross-section in conjunction with the obliquely arranged deflector plate or corresponding linear deflecting portion of the elbow outer side. In U.S. Pat. No. 4,606,556, issued to Robert E. Metzger for Fuller Company on Aug. 19, 1986, a stepped deflector plate is positioned at the outer elbow side to provide for a reduced wear elbow fitting. As the steps or ribs wear, the extra thickness of the material will permit a longer life for the fitting. In U.S. Pat. No. 4,995,645, issued to Josef Pausch for General Resource Corporation on Feb. 26, 1991, an open expanded area at the impact zone for the incoming particles is provided to create an accumulation of product in alignment with the incoming stream of product particles. The elbow section is expanded with a flare at 15 degrees to provide improved product flow after impacting the accumulated material. 
   In U.S. Pat. No. 5,024,466, issued to Gregory R. Brotz on Jun. 18, 1991, the elbow fitting is formed with an expanded box section at the outer elbow side in which a screen is positioned to engage product particles. The expanded box section is coupled to a vacuum system to hold particles against the screen member to form an accumulation area of product into which the incoming product particles impact. The captured product particles are retained against the screen until worn sufficiently to be replaced by other product particles. While the structure of the Brotz patent provides a layer of product to absorb the impact of incoming product particles and thus reduce wear on the outer side of the elbow, the Brotz apparatus does not contemplate a moving flow of material along the outer elbow side. 
   Accordingly, it would be desirable to provide an elbow fitting for use in pneumatic conveying or transport systems to improve wear characteristics on the outer elbow side of the fitting and to improve the flow characteristics for product moving through the fitting and that would be operable to affect a clean-out of product particles from the elbow fitting when the flow of particles through the elbow fitting has halted. 
   SUMMARY OF THE INVENTION 
   It is an object of this invention to overcome the aforementioned disadvantages of the known prior art by providing an elbow fitting for use in pneumatic conveying systems. 
   It is another object of this invention to provide a fitting for making directional changes in the flow path of a pneumatic product conveying system. 
   It is a feature of this invention that the elbow fitting expands along the outer side of the fitting to provide an accumulation layer of product particles. 
   It is an advantage of this invention that the incoming product particles impact into a slower moving accumulation layer along the outer side of the elbow fitting. 
   It is still another object of this invention to provide an elbow fitting for use in a dense phase pneumatic conveying system without utilizing a deflector plate for engaging the incoming stream of product particles. 
   It is yet another object of this invention to provide an elbow fitting that will experience a minimum of wear from engagement with an incoming stream of product particles in a pneumatic conveying system. 
   It is another advantage of this invention that the impact of incoming product particles is absorbed without causing substantial wear on a structural component of the elbow fitting. 
   It is another feature of this invention that the accumulation layer of product particles moves along the outer side of the elbow fitting at a slower velocity than the velocity of the incoming particle stream. 
   It is still another feature of this invention that the moving accumulation layer of product on the outer side of the elbow fitting continually provides a fresh impact zone for incoming product particles. 
   It is yet another advantage of this invention that product particles in the moving accumulation layer of product is not subjected to excessive wear from impact by incoming particles because of the movement of the accumulation layer, thus minimizing the creation of impact dust in the product stream. 
   It is yet another feature of this invention that the elbow structure expands along the outer side of the elbow fitting from the inlet pipe and contracts along the outer side of the elbow fitting to the outlet pipe. 
   It is another feature of this invention that the expansion in depth of the outer side of the elbow fitting is accomplished through the formation of a step forming a sharp drop in the outer surface of the elbow fitting. 
   It is another advantage of this invention that the step in the outer side of the elbow fitting creates a Bernoulli Effect to cause accumulated product particles to re-enter the air flow stream through the elbow fitting after the incoming flow of product particles has ceased. 
   It is still another feature of this invention that locating the expansion and contraction of the elbow fitting along the outer side of the fitting provides for the creation of an accumulation layer while permitting the accumulation layer to re-enter the product stream at the outlet pipe. 
   It is still a further advantage of this invention that the expanded structure of the elbow fitting establishes a slowly moving accumulation layer of product along the outer side of the elbow fitting. 
   It is still another advantage of this invention that the slowly moving accumulation layer of product minimizes wear on the outer side of the elbow fitting. 
   It is yet another feature of this invention that the shape of the elbow fitting provides an ideal aerodynamic shape for the flow of air and product through the fitting. 
   It is yet another advantage of this invention that heat generated from friction along the outer side of the elbow fitting is minimal and eliminates the melting of plastic particles from engagement with the elbow fitting. 
   It is a further advantage of this invention that the moving accumulation layer of product is uniformly distributed over an expanded triangular fitting configuration to provide a resultant reflective force upwardly toward the outlet pipe at approximately 90 degrees. 
   It is yet a further feature of this invention that the expanded portion of the elbow fitting forms a triangular shape. 
   It is still a further advantage of this invention that the elbow fitting provides a directional change for a pneumatic product conveying system with minimum pressure resistance and product attrition. 
   It is still another advantage of this invention that the reduction in resistance results in lower energy requirement for imposing a change in direction for the flow of product through a pneumatic transport system. 
   It is still another feature of this invention that the expanded shape for the outer side of the elbow fitting utilizes gravity and Bernoulli&#39;s Law to reduce the velocity of the accumulated product layer. 
   It is yet a further feature of this invention to provide an elbow fitting configuration that can be utilized to create either a 90 degree directional change or a 45 degree direction change for the product stream. 
   It is yet another advantage of this invention that the step feature of the elbow fitting creates an effective clean-out of the elbow fitting after the incoming product flow has ceased. 
   It is yet another object of this invention to provide an elbow fitting for pneumatic product conveying systems that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
   These and other objects, features and advantages are accomplished according to the instant invention by providing an elbow fitting for use in a pneumatic product conveying system in which the fitting expands from the inlet pipe along the outer side of the elbow fitting to enable a layer of accumulated product particles to be formed so as to move at a lower velocity than the velocity of the incoming product stream while establishing a moving contact surface for deflecting incoming product particles toward the outlet pipe with a minimum of pressure resistance and product attrition. The accumulated product particles are discharged from the elbow fitting by incorporating a step in the outer surface of the elbow fitting to create a Bernoulli effect causing the accumulated product particles to enter the air flow after the incoming flow of product particles has ceased. The particles in the accumulated layer are replenished from the incoming flow during operation of the elbow fitting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of a 90 degree elbow fitting having a step feature incorporating the principles of the instant invention; 
       FIG. 2  is an elevational view of the elbow fitting depicted in  FIG. 1 , looking into the inlet portion of the fitting; 
       FIG. 3  is an elevational view of the elbow fitting depicted in  FIG. 1 , looking into the outlet portion of the fitting; 
       FIG. 4  is a side elevational view of the elbow fitting depicted in  FIG. 1 ; 
       FIG. 5  is a cross-sectional view of the elbow fitting depicted in  FIG. 1  taken along the centerline axis of the fitting, corresponding to lines  5 - 5  of  FIG. 3 ; 
       FIG. 6  is an elevational view of an alternative embodiment of the elbow fitting similar to that of  FIG. 3 , but incorporating an attachment flange for connection of the elbow fitting to an outlet pipe for a pneumatic product conveying system; 
       FIG. 7  is a side elevational view of the elbow fitting depicted in  FIG. 6 ; and 
       FIG. 8  is a cross-sectional view of the elbow fitting taken along the centerline axis of the fitting, corresponding to lines  8 - 8  of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1-5 , a 90 degree elbow fitting for use in a pneumatic product conveying system, and incorporating the principles of the instant invention, can best be seen. The elbow fitting  10  is to be connected to a conventional inlet pipe  12  and an outlet pipe  13  to provide a directional change for the path of travel of the product within the pipes  12 ,  13 . While the instant invention is intended for use with dilute phase pneumatic systems, an elbow fitting  10  incorporating the principles of the instant invention can also be utilized with dense phase pneumatic systems. Typically, dense phase pneumatic systems fill the pipe with product particles and inject a sufficient amount of air to effect movement of the product through the pipe  12 ,  13 . Accordingly, a substantial amount of product particles are being moved at a significant velocity through the pipes  12 ,  13 . Changing directions typically results in wear from the product particles rubbing against the inside of the fitting, which also creates heat from friction that can melt plastic particles being conveyed through the pneumatic system. 
   The elbow fitting  10  is preferably formed from a durable metallic material, such as steel or, preferably, stainless steel, and includes an inlet portion  16  and an outlet portion  17 , each of which are sized to mate with the inlet pipe  12  and the outlet pipe  13  in a known manner, such as through a known compression coupling (not shown). Between the inlet portion  16  and the outlet portion  17 , the elbow fitting  10  includes an inlet transition section  18  and similar outlet transition section  19  connected, respectively, to the inlet portion  16  and the outlet portion  17 . Lastly, a curved expanded section  15  interconnects the inlet and outlet transition sections  18 ,  19 . 
   The inlet and outlet transition sections  18 ,  19  transcend between a circular cross-section of the inlet and outlet portions  16 ,  17  and a generally triangular cross-sectional configuration of the curved expanded portion  15 . The triangular shape of the curved expanded portion  15  generally carries through the curved expanded portion  15 , except as required to curve from one direction to another at the apex  21  of the curved expanded portion  15 . Preferably, the triangular shape of the triangular cross-section of the curved expanded portion  15 , as is best seen in  FIG. 2 , has three curved apexes  26  connected with the adjacent apex  26  by a linear portion, one of which defines a bottom portion  27  having a width greater than the diameter of the inlet and outlet portions  16 ,  17 . 
   Looking at the cross-sectional view through the centerline axis of the elbow fitting  10 , as depicted in  FIG. 3 , it can be seen that the inner side  21  of the elbow fitting  10  continues linearly from the inlet pipe  12  through a curved area  24  to another linear run to the outlet pipe  13 . The outer side  25  of the elbow fitting  10  provides an expanded cross-section area for the elbow fitting  10  by extending downwardly through the inlet transition portion  18  from the inlet portion  16  to the curved expanded portion  15 . 
   The law of gravity and centrifugal force will urge product particles outwardly into this expanded area  30  to provide a slurry layer of accumulated particles along the outer side  25  of the curved expanded portion  15  of the elbow fitting  10 . Due to the expanded cross-sectional area of the curved expanded portion  15 , Bernoulli&#39;s Law requires that the velocity of the product particles will be slowed, as compared to the velocity of the product particles traveling through the circular inlet portion  16 . This layer of accumulated particles, represented by dashed line  29 , provides a moving impact zone for the incoming particles exiting the inlet portion  16 , which can then be deflected upwardly toward the outlet pipe  13  to effect a change of direction for the product being conveyed. 
   The slowly moving layer  29  of accumulated product particles along the outer side  25  of the curved expanded section  15  also prevents an elevation of the temperature of the fitting  10  that would be normally attributable to friction from the impact of the incoming particles against the outer side of the fitting  10 . As a result, the particles will not be damaged by the elevation in temperature. 
   The curved expanded section  15  is preferably formed with a curved outer side  25 , or for the sake of manufacturing convenience may be formed from a pair of linear portions  36 ,  37  interconnected by a curved portion  39 . The linear portions  36 ,  37  are not perpendicular but are disposed through an angular deflection of approximately 100 degrees, which is at approximately 80 degrees to the line of the incoming product stream through the inlet pipe  12 . Since the layer  29  of accumulated product particles along the outer side  25  serves to deflect incoming particles toward the outlet pipe  13 , the outer side  25  does not need to function as a deflector plate that needs to be disposed at 55 to 65 degrees with respect to the axis of the inlet pipe  12 . 
   The outlet transition section  19  provides a smooth transition from the triangular shape of the curved expanded portion  15  to the circular shape of the outlet portion  17 . Thus, the layer  29  of accumulated product particles is directed back into the outlet pipe  13  to provide a continuous flow of particles through the elbow fitting, including the moving accumulated layer  29  along the outer side  25  of the fitting. 
   As can be seen in  FIGS. 6-8 , this configuration for an elbow fitting can be provided with a conventional mounting flange  40  having a series of apertures for deployment of fasteners for attaching the elbow fitting  10  to the inlet and outlet pipes  12 ,  13  which are correspondingly equipped. One skilled in the art will also recognize that the elbow fitting can be formed to affect a 45 degree deflection of the product particles, instead of the 90 degree elbow depicted in the drawings. 
   While the elbow fitting  10  described above is particularly suitable for use in either dense phase or dilute phase pneumatic product transport systems, one skilled in the art will recognize that the same principles for effecting a directional change for slurry product transport systems also apply. The elbow fitting  10  described above provides a lower resistance to effecting directional changes in the flow of product particles through the system. As a result, the energy required to effect directional changes is lower than known long radius elbows. Damage to the product being conveyed due to frictional losses and impact, as is known for long radius elbow fittings, will be significantly reduced. Accordingly, superior results with lower energy costs are associated with the instant invention. 
   The downward expansion of the outer surface  25  of the elbow fitting  10  is preferably accomplished through a sharp step  35  at the inlet transition portion  18 . The step  35  has a slope angle, as is best seen in  FIGS. 4 and 7 , which is substantially greater than the slope angle of the inlet portion, which is at a nominal zero angle, and the slope angle of the bottom member  27  of the curved expanded portion  15 , which is at approximately 10 degrees. The formation of the step  35  creates a Bernoulli effect that allows the layer of accumulated product particles to be formed along the outer surface of the curved expanded portion  15 , but creates pressure differentials with the halting of the incoming flow of product particles into the elbow fitting  10  that draw the particles from the accumulated layer  29  into the air flow through the elbow fitting  10 . Thus, when the pneumatic conveying system stops conveying product particles, the final flow of air through the system to clean product particles out of the system will effectively clean the particles from the elbow fitting as well. 
   Without the formation of the step  35 , it is believed that the stream of air entering the inlet portion  16  to purge the fitting  10  of remaining product particles would pass over the accumulated solids along the bottom floor  36  of the outer expanded surface  25  and strike the back wall  33  of the fitting  10  causing a high pressure condition on the surface of the accumulated solids, preventing them from purging from the fitting  10 . 
   By modifying the bottom surface  25  of the fitting  10  to extend the bottom inlet portion  16  along the line of the expected accumulated layer  29  while opening the sides of the fitting  10  outwardly to form the curved expanded portion  15  to a point at which the sharp drop or step  35  could be incorporated, the purge air flow was directed upwardly into the main air flow entering the fitting  10  through the inlet  16 . The result is a reduction in pressure and the creation of pressure differentials relative to the accumulated particles  29  permitting them to be purged back into the main air flow and discharged from the fitting  10 . The incorporation of the sharp drop or step  35  into the bottom surface of the fitting  10  improves purge performance substantially. 
   It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.