Abstract:
Method and apparatus for pneumatically conveying granular resin material and controlling such conveyance includes a sensor associated with granular plastic resin material receiver with the sensing vacuum level thereat and a microprocessor adjusting vacuum pump speed based on vacuum level sensed at the receiver.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims the benefit of the priority of U.S. provisional patent application Ser. No. 62/131,935 filed 12 Mar. 2015. The priority is claimed under 35 USC 119 and 35 USC 120. 
         [0002]    This patent application is a 35 USC 120 continuation-in-part of co-pending U.S. patent application Ser. No. 14/185,016 filed 20 Feb. 2014 in the name of Stephen B. Maguire and entitled “Air Flow Regulator,” published 20 Aug. 2015 as United Stated Patent Publication 2015/0232287 A1, the priority of which is claimed under 35 USC 120. 
         [0003]    This patent application is also a 35 USC 120 continuation-in-part of co-pending U.S. patent application Ser. No. 14/574,561 filed 18 Dec. 2014 in the name of Stephen B. Maguire and entitled “Resin Delivery System With Air Flow Regulator,” published 20 Aug. 2015 as United States patent publication 2015/0231801 A1, the priority of which is claimed under 35 USC 120. 
         [0004]    This patent application is further a 35 USC 120 continuation-in-part of co-pending U.S. patent application Ser. No. 14/593,010 filed 9 Jan. 2015 in the name of Stephen B. Maguire and entitled “Air Flow Limiter with Closed/Open Sensing,” published 20 Aug. 2015 as United States patent publication 2015/0232289 A1, the priority of which is claimed under 35 USC 120. 
         [0005]    This patent application is yet further a 35 USC 120 continuation-in-part of co-pending U.S. patent application Ser. No. 14/602,784 filed 22 Jan. 2015 in the name of Stephen B. Maguire and entitled “Method and Apparatus For Resin Delivery With Adjustable Air Flow Limiter,” published 20 Aug. 2015 as United States patent publication 2015/0232290 A1, the priority of which is claimed under 35 USC 120. 
         [0006]    This patent application is still further a 35 USC 120 continuation-in-part of co-pending U.S. patent application Ser. No. 14/804,404 filed 21 Jul. 2015 in the name of Stephen B. Maguire and entitled “Vacuum Powered Resin Loading System Without Central Control,” published 12 Nov. 2015 as United States patent publication 2015/0321806 A1, the priority of which is claimed under 35 USC 120. 
         [0007]    The disclosures of all the foregoing patent publications are hereby incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0008]    Not applicable—this invention was conceived and developed entirely using private source funding; this patent application is being filed and paid for entirely by private source funding. 
       BACKGROUND OF THE INVENTION 
       [0009]    This invention relates to manufacture of plastic articles and more particularly relates to pneumatic conveyance and processing of plastic resin pellets prior to molding or extrusion of those pellets into a finished or semi-finished plastic product. 
         [0010]    In this patent application, injection and compression molding presses and extruders are collectively referred to as “process machines.” 
         [0011]    The plastics industry is very diversified; there are thousands of different products, hundreds of materials, and dozens of processes, and all are very different from one another. The only thing all these share in common is that the source material is some type of plastic. 
         [0012]    Equipment sold to this industry is, therefore, very diversified in design. Plastics factories have multiple process machines, sometimes several hundred in one location. Virtually all plastics fabricating operations require that each process machine, namely a molding press or an extruder, be supplied automatically with the required raw resin material on a continuous basis. This resin may be supplied in large boxes called “Gaylords”, in fiber drums, in 50 pound bags, or more typically may be delivered by bulk truck or rail car, with the resin material then being transferred in bulk into storage silos. In all cases the resin material must be further distributed throughout the plant to the process machines. For that reason a great deal of design and capital expense is devoted to the automatic distribution of the raw resin material throughout the plant. 
         [0013]    These resin distribution systems, more commonly referred to as “Loading Systems”, must deal with many variables. One set of variables includes the type, shape, size and consistency of the granular material. 
         [0014]    Resin pellets, nominally about ⅛ inch in size, come in various shapes, with round, square, and cylindrical being the most common. 
         [0015]    Flowing resin powder is also an option, and very fine but free flowing resin pellets and other granular materials may be conveyed as well. 
         [0016]    The design variables to be considered for each customer include:
       1. Type of resin being conveyed.   2. Size and consistency of the resin pellets.   3. Distances the resin pellets are to be conveyed.   4. Variability of these distances from shortest to longest.   5. Acceptable range for velocity of resin material travel through the lines.   6. Throughput rate of resin required for each machine.   7. Total throughput rate of resin for the entire plant.   8. Excess capacity performance margin so a molding or extrusion process is not interrupted by short term loading issues.   9. Loss of resin material from or at the supply so that only air is being pulled, thereby reducing system vacuum levels and reducing overall design throughput.   10. Loading sequence, or priority, when multiple receiver stations call for material.   11. Detecting problems and alarm conditions.   12. Proper air to material ratio for resin conveying.   13. Detecting plugged lines due to poor resin flow or over feeding of resin material.   14. Dust condition and filter requirements.   15. Reliability.   16. Serviceability.   17. Ease of use.   18. Cost   19. Vacuum pump type, namely positive displacement, regenerative, and others.   20. Vacuum pump horsepower and rated CFM capacity as well as vacuum levels.       
 
         [0037]    In all of these areas, system designers look to find improved methods and solutions whenever possible. 
         [0038]    One of the most important considerations is to hold a correct velocity during conveyance for the conveyed resin material. The type of resin material dictates the target conveying speed. To maximize the resin material transfer rate, a high conveying speed is preferred, and air speed in any case must be sufficient to keep the resin pellets suspended and moving in the air stream. But velocity must be limited so as not to damage the pellets. Hard brittle pellets can fracture and break when conveyed, resulting in excessive dust. 
         [0039]    Softer pellets can skid along the conduit walls, causing “angel hair” as a result of the plastic resin melting at the point of high speed contact with the conduit wall; this leaves a thin film on the wall. Strings of very thin “angel hair” accumulate, effectively reducing diameter of the conduit and causing problems in the system. 
         [0040]    Air speed and resin conveying velocity are directly related to pump capacity (rated in Cubic Feet per Minute, abbreviated as “CFM”) and horsepower, as well as conveying line diameter. There is always a correct velocity “range” for each type of resin material. It is a design challenge to assure that the resin material is conveyed within the correct velocity range. 
         [0041]    Conveying distances affect system design. Conveying over short distances requires a less powerful vacuum source then over longer distances. Systems are generally sized to produce the best compromise for material velocity between the shortest and longest conveying distance. 
         [0042]    Required conveying rate usually dictates line size (conduit diameter), and this in turn dictates the CFM required to maintain correct velocity in a given diameter conduit. This means different conduit sizes in the same system can be a problem if one vacuum pump is to draw air and resin through several different diameter conveying lines. Pumps have known CFM ratings. Pulling air through a small conduit will result in higher velocity flow than pulling the same CFM through a larger conduit. 
         [0043]    Excessive velocity can damage pellets. 
         [0044]    The type of vacuum pump to be selected is important. Regenerative blowers deliver wide ranging CFM depending on vacuum level. Positive displacement type pumps deliver high vacuum levels, and have a flatter CFM curve over their vacuum range. Regenerative blowers are quieter and generally cost less. Positive displacement blowers may require sound enclosures and tend to cost more, but are generally more reliable and more forgiving as respecting dust in the air. 
         [0045]    The simplest systems use a fixed speed motor to drive the vacuum pump, and a single size conveying line to serve all receivers regardless of conveying distance, conveying rate requirement, or the material being conveyed. 
         [0046]    VFD (Variable Frequency Drive) motors allow vacuum pumps to operate at different speeds, and therefore at different CFM rates, with the vacuum pump pulling different vacuum levels depending on preset information about each receiver being served. 
         [0047]    The addition of a SCFM (Standard Cubic Feet per Minute) limiter in the air flow line allows oversized vacuum pumps to be used without risk of conveying at excessive velocity. SCFM limiters restrict air flow to a preset SCFM. This maintains the desired SCFM air flow at the inlet, which is critical for proper conveying in a given size conveying line. 
       DESCRIPTION OF THE PRIOR ART 
       [0048]    Current resin central loading systems concerned with conveying granular plastic resin pellets from a storage area for molding or extrusion typically include a vacuum pump or pumps and multiple receivers. 
         [0049]    In some systems, with many receivers, several small pumps are used. 
         [0050]    It would be less expensive to use only one, or fewer, larger pumps. However, a larger pump may draw too much air with resulting damage to the material being conveyed. While a larger pump could load several receivers at once, there is a risk that an “open” line, namely a line pulling only air, and no resin material, would cause the vacuum to drop too much, and no resin would load. Also, when only one receiver is loading resin, air velocity might be too high, again with a risk of damaging the resin. 
         [0051]    Nevertheless, in facilities that fabricate plastic products by molding or extrusion, it is common to use such vacuum loading systems to pneumatically convey pellets of thermoplastic resin, prior to molding or extrusion of those pellets into a finished or semi-finished product. The plastic resin pellets are typically purchased in 50 pound bags, 200 pound drums, or 1,000 pound containers commonly referred to as “Gaylords.” 
         [0052]    A common approach for conveying plastic resin pellets from a storage location to a process machine, which approach is often used in larger facilities, is to install a central vacuum pump or even several vacuum pumps, connected by common vacuum lines to multiple “receivers.” 
         [0053]    Vacuum pumps connected to the vacuum lines draw vacuum, namely air at pressure slightly below atmospheric, as the vacuum pump sucks air through the “vacuum” line. The suction moves large quantities of air which carries thermoplastic resin pellets through the “vacuum” line. 
         [0054]    An alternative is to use positive pressure produced by a blower or the exhaust from a vacuum pump. With such an approach, the positive pressure results in a movement of substantial amounts of air which may be used to carry the plastic resin pellets. However, the vacuum approach of drawing or sucking or pulling pellets through the system conduit(s) is preferable to the positive pressure approach of pushing the resin pellets through the system conduit(s). 
         [0055]    In practice, vacuum pumps are preferred and vacuum lines are desirable in part because power requirements to create the required vacuum necessary to draw plastic resin pellets through the lines are lower than the power requirements if the plastic resin pellets are pushed through the lines by a blower or by the exhaust side of a vacuum pump. When vacuum is used, the static pressure within the line may be not much less than atmospheric. When positive pressure is used, the dynamic pressure of the air flowing through the line must be relatively high in order to move an adequate quantity of plastic resin pellets. 
         [0056]    As used herein, and in light of the foregoing explanation, the terms “vacuum pump” and “blower” are used interchangeably. 
         [0057]    When one or more central vacuum pumps are connected to multiple receivers, a receiver is typically located over each temporary storage hopper, in which the plastic resin pellets are temporarily stored before being molded or extruded. A temporary storage hopper is typically associated with each process machine. 
         [0058]    In current practice, the receiver is connected by a control wire to a central control system. The control system works by selectively opening a vacuum valve located in each receiver, allowing one or several vacuum pumps to work in sequence drawing “vacuum”, i.e. below atmospheric pressure air, to carry the pellets among and to multiple receivers as individual ones of the receivers, positioned over individual hoppers associated with individual process machines, require additional plastic resin pellets. The receiver for a given hopper-process machine combination is actuated by opening the vacuum valve located in or near the receiver, causing the receiver to supply plastic resin pellets by gravity feed into the hopper from where the pellets may be fed further by gravity downwardly into the associated process machine. 
         [0059]    Large, high capacity industrial vacuum pumps are reliable and are suited to heavy duty industrial use. Large, high capacity vacuum pumps allow long conveying distances for the plastic resin pellets. Currently available large capacity vacuum pumps permit plastic resin pellets to be conveyed over distances of 200 feet or more using vacuum drawn by the pump. Use of such high capacity vacuum pumps results in a big rush of below atmospheric pressure air through the line, carrying the plastic resin pellets over a long distance. The vacuum pump speed is not modulated; the vacuum pump is either “on” or “off.” As a result, when the pump is operating, “vacuum”, more accurately “air”, is drawn at a fixed rate by the vacuum pump through the system. 
         [0060]    Operators of plastic manufacturing facilities prefer to buy plastic resin pellets in bulk, in rail cars or tanker trucks. Bulk purchases result in cost savings. Plastic resin pellets delivered in bulk are typically pumped into large silos for storage. In a large manufacturing facility, the distance from a plastic resin pellet storage silo to a process machine may be several hundred feet, or more. Accordingly, when plastic resin pellets are purchased in bulk, a central vacuum-powered conveying system, powered by one or more large, high capacity industrial vacuum pumps, is a necessity. 
         [0061]    Typically, large central plastic resin pellet conveying systems have one or more vacuum pumps, each typically being from 5 to 20 horsepower. These central systems include central controls connected by wire to each receiver associated with each process machine in the facility. Typically eight, sixteen, thirty-two or sixty-four receivers, each associated with a process machine, may be connected to and served by the central plastic resin pellet vacuum conveying system. Of course, the higher the number of receivers served by the system, the higher the cost. The central control is connected by wire to each receiver and is used to signal when a receiver is empty and therefore needs and should receive granular resin material. The central control, wired to each receiver, does not measure vacuum level at the receiver and is not in any way used to moderate or modulate operation of the vacuum pump. 
         [0062]    A factor to be considered in designing such a system is the speed of the plastic resin pellets as they flow through a conduit as the plastic resin pellets are carried by the moving air stream drawn by the vacuum pump. If air flow is too slow, the plastic resin pellets fall out of the air stream and lie on the bottom of the conduit, with resulting risk of clogging the conduit. If air flow is too fast, the plastic resin pellets can skid along the conduit surface. In such case, harder, more brittle plastic resin pellets may be damaged, resulting in dust within the conduit, which when drawn into the vacuum pump can damage the vacuum pump and render the system inoperative. Softer plastic resin pellets heat up and can melt from friction when contacting the conduit interior surface. This results in “angel hair”—long, wispy-thin strands of plastic film which eventually clog the conduit and cause the system to shut down. 
         [0063]    For these reasons, pneumatic plastic resin pellet conveying systems must be designed to produce desired, reasonable conveying speeds for the plastic resin pellets. 
         [0064]    Currently, conveying speed of the plastic resin pellets is most often controlled by controlling air flow, measured in cubic feet per minute, and varying the desired and designed cubic feet per minute based on conduit diameter, with a larger diameter conduit requiring more cubic feet per minute of air flow to maintain proper air flow speed through the conduit. Controlling air flow, measured in cubic feet per minute, is conventionally done by specifying the vacuum pump capacity; vacuum pump speed modulation is not within the state of the art. 
         [0065]    Controlling cubic feet per minute of air flow is an indirect way of controlling plastic resin pellet speed as the plastic resin pellets flow through a conduit of a given diameter. Typically, a 2 inch diameter conduit requires about 60 cubic feet per minute of air flow to convey typical plastic resin pellets. A 2-½ inch diameter conduit typically requires about 100 cubic feet per minute of air flow to convey typical plastic resin pellets. To achieve these desired air flow volume flow rates, a designer must carefully match the horsepower of a vacuum pump, which has a given cubic feet of air per minute rating, to a selected size conduit, taking into consideration the average distance the plastic resin pellets must be conveyed through the conduit from a storage silo to a receiver or loader (because resin conveyance systems are not designed for modulation of vacuum pump speed for the reason noted above—vacuum pump speed modulation is not within the state of the art). If this results in selection of a 5 horsepower blower/vacuum pump, then a given facility may require several such blowers/vacuum pumps, with each blower/vacuum pump supplying only a selected number of receivers. 
         [0066]    A single plastic resin molding or extruding facility might theoretically require a 20 horsepower blower and the corresponding cubic feet per minute capability for conveyance provided by the single blower to meet the total conveying requirements for plastic resin pellets throughout the facility. However, a single twenty horsepower blower would result in far too high a conveying speed for the plastic resin pellets through any reasonable size conduit. As a result, the conveying system for the plastic resin pellets in a large facility is necessarily divided and powered by three or four smaller blowers, resulting in three or four different, separate systems for conveyance of plastic resin pellets. Sometimes several blowers are connected to a single set of receivers, with one or more of the extra blowers turning “on” only when required to furnish the required extra cubic feet per minute of air flow. This is controlled by a central station monitoring all receivers and all blowers, with the central station being programmed to maintain all of the hoppers associated with the process machines in a full condition, wherever those hoppers are located throughout the facility. 
         [0067]    Even with careful planning and design, results achieved by such pneumatic plastic resin pellet conveying systems are not consistent. Air flow speed and cubic feet per minute capacity of blowers often vary and are outside of selected design and specification values. 
       INCORPORATION BY REFERENCE 
       [0068]    This patent application incorporates by reference the disclosures of pending U.S. patent application Ser. No. 14/185,016 20, published 20 Aug. 2015 as United States patent publication 2015/0232287 A1; pending U.S. patent application Ser. No. 14/574,561, published 20 Aug. 2015 as United States patent publication 2015/0231801 A1; pending U.S. patent application Ser. No. 14/574,561, published 20 Aug. 2015 as United States patent publication 2015/0231801 A1; pending U.S. patent application Ser. No. 14/593,010, published 20 Aug. 2015 as United States patent publication 2015/0232289 A1; and pending U.S. patent application Ser. No. 14/602,784, published 20 Aug. 2015 as United States patent publication 2015/0232290 A1. 
         [0069]    The disclosure of U.S. Pat. No. 8,753,432 is also incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0070]    The inventive technology offers controls and devices that can maximize performance for the variety of conditions that actually exist in a plant. 
         [0071]    In one of its aspects, this invention provides apparatus for pneumatically conveying granular plastic resin material where the apparatus includes a resin supply, a vacuum pump having a suction intake, and a plurality of receivers for temporarily storing resin material until needed by an associated process machine. A conduit conveys granular resin material from the resin supply to the receivers in response to vacuum drawn through the conduit by the vacuum pump. One or more sensors associated with one or more of the receivers sense vacuum level at the receiver. A sensor at the vacuum pump suction intake senses vacuum level thereat. The method further embraces adjusting vacuum pump speed based on vacuum levels sensed optimally and optionally at the receivers and at the vacuum pump. Desirably, at least one sensor is associated with each receiver so that vacuum pump speed can be adjusted based on vacuum level sensed at all of the receivers, and desirably at the vacuum pump as well, thereby providing optimum conditions for a pneumatic transport of the granular plastic resin material from the supply to the receivers. 
         [0072]    In still another one of its aspects, this invention provides a method for pneumatically conveying plastic resin material from a resin supply using a resin pump having a suction intake where the method includes providing a plurality of receivers for temporarily storing resin material until needed by an associated process machine. The method further proceeds with providing a conduit for conveying granular resin material from the resin supply to the receivers in response to vacuum drawn through the conduit by a vacuum pump. The method yet further proceeds by periodically sensing vacuum level at each receiver, storing the sensed vacuum levels, actuating the vacuum pump and adjusting vacuum pump speed based on the stored vacuum levels. 
         [0073]    Desirably the sensed vacuum levels are sensed serially at the receivers. The method may further embrace adjusting the pump speed based on multiple collections of serially sensed vacuum levels. The method may yet further embrace periodically sensing vacuum level at the vacuum pump, which vacuum level may be sensed serially. The method then further embraces adjusting the pump speed based on multiple collections of serially sensed vacuum levels including vacuum level at the vacuum pump. 
         [0074]    In another one of its aspects, this invention provides a method for conveying granular plastic resin material from a supply thereof to at least one receiver, for temporary storage of the granular plastic resin material in the receiver until the material is needed by a process machine associated with the receiver, where the method includes positioning a first conduit with an open end in the supply of granular plastic resin material. The method proceeds by drawing vacuum through the first conduit, thereby conveying granular plastic resin material out of the supply and along the conduit. The method then provides a receiver connected to the conduit for receipt of granular resin material from the conduit. Next, a second conduit is provided, connecting the receiver to a source of the drawn vacuum, which draws vacuum through the first conduit via the receiver. Next, the invention proceeds by providing at least one vacuum sensor in the first conduit and regulates vacuum drawing according to sensed vacuum level at the vacuum sensor. 
         [0075]    In this aspect of the invention, the method may further provide a second vacuum sensor in the second conduit and regulate vacuum draw according to vacuum levels sensed at the two vacuum sensors. 
         [0076]    In this aspect of the invention, the method may yet further involve providing a vacuum sensor at the receiver and regulating vacuum draw according to vacuum levels sensed at the three vacuum sensors, one sensor at the receiver, one sensor in the second conduit, and one sensor in the first conduit. 
         [0077]    In this one of its aspects, the invention further provides a method for conveying granular plastic resin material from a supply thereof to at least one receiver as noted in the three preceding paragraphs, where the method further includes regulating vacuum draw according to an algorithm executed by a computing device based on input signals received from the vacuum sensors. 
         [0078]    In still yet another one of its aspects, this invention provides a method for conveying granular plastic resin material from a supply thereof to at least one receiver for temporary storage of granular plastic resin material in the receiver until the material is needed by a process machine associated with the receiver. In this aspect of the invention, the method commences with positioning a first conduit with an open end in the resin supply. The method proceeds by drawing vacuum through the first conduit, thereby conveying granular plastic resin material out of the supply and along the conduit. The method yet further proceeds by providing a receiver connected with the conduit for receipt of granular resin material from the conduit. A second conduit is provided connecting the receiver to the vacuum source providing the drawn vacuum via the receiver to the first conduit. At least one vacuum sensor is provided on the first conduit. Vacuum levels are then recorded as provided by the sensor. Recorded vacuum levels are correlated with observed conveyance of granular resin material from the supply to the receiver, with the recording being done in a computing device, preferably a microprocessor, to create an executable algorithm for optimized conveyance of the granular resin material. The algorithm is executed in the computing device to regulate the vacuum draw. 
         [0079]    In this aspect of the invention, the computing device is desirably a microprocessor. The method yet further includes the steps of recording physical parameter data including at least one of ambient temperature, atmospheric pressure, relative humidity, and available line voltage, and using data reflecting at least one of those physical parameters in creating the executable algorithm. 
         [0080]    The foregoing outlines rather broadly features of the invention in order that the detailed description of the invention that follows may be best understood. Additional features and advantages of the invention, as described hereinafter, may form the subject of certain of the claims of the application. It will be appreciated by those skilled in the art that the concepts and specific embodiments disclosed herein may be readily utilized as a basis for modifying or designing apparatus or other methods for carrying out the goals and results attained by this invention. It should also be realized by those skilled in the art that such equivalent implementations do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0081]      FIG. 1  is a schematic representation of a resin delivery system in accordance with aspects of the invention. 
           [0082]      FIG. 2  is a schematic representation of an alternate embodiment of a resin delivery system in accordance with aspects of this invention. 
       
    
    
       [0083]    In reference to the drawings, where reference numbers are identical to those used in the description to designate like or similar elements throughout the various views, illustrative implementations of the invention are described. The figures are schematic and therefore not to scale. In some instances the drawings have been exaggerated and/or simplified for illustrative purposes. One of skill in the art will appreciate the many possible applications and variations of the invention that are possible based on the following description of this invention. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0084]    In this application, unless otherwise apparent from the context, it is to be understood that the use of the term “vacuum” means “air at slightly below atmospheric pressure.” The vacuum (meaning air slightly below atmospheric pressure) provides a suction effect that is used to draw granular plastic resin material out of a supply and to convey that granular plastic resin material through various conduits to receivers where the granular resin material can be temporarily stored before being molded or extruded. Hence, in this application it is useful for the reader mentally to equate the term “vacuum” with the term “suction”. 
         [0085]    Referring to the drawings in general and to  FIG. 1  in particular, apparatus for conveying granular plastic resin material from the supply to receivers that retain and dispense the resin material when needed by a process machine is illustrated in  FIG. 1 . The apparatus, which is designated generally  88  in  FIG. 1 , preferably includes a vacuum pump designated generally  92  and shown schematically in  FIG. 1 . Vacuum pump  92  preferably includes a vacuum pump suction head  93  also shown schematically in  FIG. 1 . Connected to the vacuum pump suction head  93  may be an optional airflow limiter  30  shown only in schematic form in  FIG. 1 . Optional airflow limiter  30  receives vacuum drawn by vacuum pump  92  through vacuum drawing conduit  100 . 
         [0086]    The optional air flow limiter  30  is preferably one of the types of air flow limiters disclosed in U.S. patent application Ser. No. 14/185,016 published 20 Aug. 2015 as United States patent publication 2015/0232287 A1; pending U.S. patent application Ser. No. 14/574,561, published 20 Aug. 2015 as United States patent publication 2015/0231801 A1; pending U.S. patent application Ser. No. 14/574,561, published 20 Aug. 2015 as United States patent publication 2015/0231801 A1; and pending U.S. patent application Ser. No. 14/593,010, published 20 Aug. 2015 as United States patent publication 2015/0232289 A1. All of the flow limiters, which are the preferable type of flow limiters for use in the instant invention, as described in the preceding sentence, must be vertical or essentially vertical in order to function properly. In the drawings, all of flow limiters  30  have been illustrated in a vertical orientation. However, it is to be understood that other kinds and styles of flow limiters may be used in the course of practice of the invention. 
         [0087]    Vacuum drawing conduit  100  is connected to a plurality of receivers  16 , each of which receives, retains and dispenses, as needed, granular plastic resin material to a process machine, such as a gravimetric blender, or an extruder, or a molding press as located preferably below a receiver  16 . The process machines are not illustrated in  FIG. 1  to enhance the clarity of the drawing. 
         [0088]    Further illustrated in  FIG. 1  is a hopper  18  for storage of granular plastic resin material therein and a resin conveying conduit  98 , which serves to draw resin from hopper  18  and to deliver the resin through resin conveying conduit  98  to the respective receivers  16  as vacuum is drawn by the vacuum pump  92 , with vacuum propagating through optional air flow limiter  30 , vacuum drawing conduit  100 , the various receivers  16 , and resin conveying conduit  98 , to hopper  18 . Receivers  16  are preferably of the type disclosed and claimed in U.S. Pat. No. 8,753,432. 
         [0089]    Still referring to  FIG. 1 , a plurality of vacuum sensors are illustrated. Vacuum sensors  130  are provided associated with each receiver and located upstream of each receiver to sense the vacuum in resin conveying conduit  98  as that resin conveying conduit conveys resin into a receiver  16 . Vacuum sensors  132  are positioned downstream of each receiver to sense vacuum at a position proximate to each receiver in vacuum drawing conduit  100 . A vacuum sensor  134  is provided to sense the vacuum being drawn by vacuum pump  92  at a position proximate to vacuum pump suction head  93 . 
         [0090]    While the resin conveying system  88  illustrated in  FIG. 1  has been depicted with vacuum sensors  130  upstream of each receiver, vacuum sensors  132  downstream of each receiver, and a vacuum sensor  134  at vacuum pump  92 , in some implementations of the invention, only vacuum sensors upstream of receiver  16 , or vacuum sensors downstream of receiver  16  may be used. Moreover, it is within the scope of the invention to provide a vacuum sensor within one or more of the receivers  16  as indicated by vacuum sensors  136  illustrated in  FIG. 1 . It is further within the scope of the invention to provide only a few vacuum sensors  130  or  132  or  136 , located at strategic positions upstream of a receiver, downstream of a selected receiver, or within a selected receiver. Optionally but desirably a vacuum sensor  138  may also be provided at resin supply  18  to sense the level of vacuum being drawn by vacuum pump  92  through resin conveying conduit  98  proximate resin supply  18 . 
         [0091]    However many vacuum sensors are used, all of these vacuum sensors provide data, preferably wirelessly, to a controller illustrated only schematically in the drawings, which is desirably in the form of a microprocessor  200 . Microprocessor  200  collects data from one or more of the sensors  130 , 132 ,  134 ,  136 ,  138  preferably sequentially through the sensors in that only a single receiver  16  is usually active at a given time, so desirably the vacuum data relevant to a given receiver  16  is collected only when that receiver  16  is active. (Other data collection schemes, such as serial or random, and algorithmic protocols based on various physical and other parameters such as relative humidity, ambient temperature, atmospheric pressure, available line voltage for the vacuum pump, and the like, are also within the scope of this invention.) This sensed vacuum data and the other physical parameter data are preferably stored and used based preferably on an experientially developed algorithm (developed using such data) which is executed by microprocessor  200  to optimally modulate operation of vacuum pump  92 . This data may desirably be correlated with time of day, the type of resin being conveyed, the temperature within the facility, and other physical parameters so as to provide a mathematical algorithm that may be used to optimize the speed of vacuum pump  92 . 
         [0092]    Alternatively to wireless communication of the vacuum sensors  130  through  138  with microprocessor  200 , wiring can, of course, be used. 
         [0093]      FIG. 2  shows an alternate embodiment of the resin conveying system of the invention where this alternate embodiment of the conveying system has been designated  88 A.  FIG. 2 , as in  FIG. 1 , depicts a vacuum pump  92  shown in schematic form having a vacuum pump suction head  93  also depicted in schematic form. In the alternate embodiment of the invention illustrated in  FIG. 2 , vacuum drawing conduit  100  leads directly into and communicates with vacuum pump suction head  93 . In the embodiment illustrated in  FIG. 2 , an optional air flow limiter  30  is shown as being provided for each receiver  16 , with the air flow limiter  30  for a respective receiver  16  being located in a portion of a connection conduit  102  that connects a respective receiver  16  to vacuum drawing conduit  100 . In  FIG. 2 , each air flow limiter  30  is depicted in a vertical orientation, just as is airflow limiter  30  depicted in a vertical orientation in  FIG. 1 . Each receiver  16  is connected by connection conduit  102  to vacuum drawing conduit  100  with optional air flow limiter  30  forming a portion of connection conduit  102 . The air flow limiters  30  illustrated in  FIG. 2  are desirably one of the type of air flow limiters disclosed above with reference to  FIG. 1 . 
         [0094]    In  FIG. 2 , as in  FIG. 1 , a first conduit  98  serves to convey granular plastic resin from hopper  18  to the respective receivers in response to vacuum drawn by vacuum pump  92  as that vacuum propagates from vacuum pump  92  through second conduit  100 , connection conduits  102 , receivers  16 , and resin conveying conduit  98  to hopper  18 . The resin conveying system shown in  FIG. 2  is similar to that shown in  FIG. 1  in that it includes a variety of vacuum sensors with vacuum sensors  130  being located upstream of associated receivers  16 ; vacuum sensors  132  being located downstream of respective receivers  16 ; a vacuum sensor  134  being provided at vacuum pump  92 ; a plurality of vacuum sensors  136  being provided within receivers  16 ; and a vacuum sensor  138  desirably being provided at the resin supply to measure the vacuum drawn within resin supply conduit  98  proximate resin supply  18 . As with the resin conveying system illustrated in  FIG. 1 , the vacuum sensors illustrated in  FIG. 2  are desirably connected to a microprocessor  200 , or other, more powerful computing device, wirelessly. Alternatively, the vacuum sensors can be connected by wires to microprocessor  200  or some other computing device, if necessary. The same approach to optimizing speed and modulation of the vacuum pump  92  as described above with respect to  FIG. 1  is applicable to the resin conveying system illustrated in  FIG. 2 . 
         [0095]    During operation of the resin conveying systems shown schematically in  FIGS. 1 and 2 , upon actuation of vacuum pump  92 , a vacuum is drawn at vacuum pump suction head  93 . This vacuum, as it propagates to hopper  18 , serves to draw resin out of hopper  18  and into respective receivers  16 . In the embodiment illustrated in  FIG. 2 , optional individual air flow limiters  30  limit the suction or vacuum drawn by vacuum pump  92  through a given associated receiver  16 . In the embodiment illustrated in  FIG. 1 , an optional single air flow limiter  30  limits vacuum drawn through all of receivers  16  forming a portion of the granular resin conveying system illustrated in  FIG. 1 . 
         [0096]    Although schematic implementations of present invention and at least some of its advantages have been described in detail hereinabove, it should be understood that various changes, substitutions and alterations may be made to the apparatus and methods disclosed herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of this patent application is not intended to be limited to the particular implementations of apparatus and methods described in the specification, nor to any methods that may be described or inferentially understood by those skilled in the art to be present as described in this specification. 
         [0097]    As one of skill in the art will readily appreciate from the disclosure of the invention as set forth hereinabove, apparatus, methods, and steps presently existing or later developed, which perform substantially the same function or achieve substantially the same result as the corresponding embodiments described and disclosed hereinabove, may be utilized according to the description of the invention and the claims appended hereto. Accordingly, the appended claims are intended to include within their scope such apparatus, methods, and processes that provide the same result or which are, as a matter of law, embraced by the doctrine of the equivalents respecting the claims of this application. 
         [0098]    As respecting the claims appended hereto, the term “comprising” means “including but not limited to”, whereas the term “consisting of” means “having only and no more”, and the term “consisting essentially of” means “having only and no more except for minor additions which would be known to one of skill in the art as possibly needed for operation of the invention.”