Patent Publication Number: US-2005126476-A1

Title: Improved particulate material application system

Description:
RELATED APPLICATIONS  
      This application claims the benefit of pending U.S. provisional patent application Ser. nos.: 60/524,459 filed on Nov. 24, 2003, for PINCH PUMP WITH VACUUM TUBE; 60/481,602 filed on Nov. 5, 2003, for VIBRATORY SIEVE SCREEN WITH INTEGRAL MOTION GENERATOR; 60/523,012 filed on Nov. 18, 2003 for POWDER SPRAY APPLICATOR; and 60/554,655 filed on Mar. 19, 2004 for POWDER COATING MATERIAL SPRAY GUN; as well as pending International patent application serial no. PCT/US04/26887 filed on Aug. 18, 2004 for SPRAY APPLICATOR FOR PARTICULATE MATERIAL, the entire disclosures all of which are fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION  
      The invention relates generally to material application systems, for example but not limited to powder coating material application systems. More particularly, the invention relates to an applicator that reduces cleaning time, color change time and improves ease of use.  
     BACKGROUND OF THE INVENTION  
      Material application systems are used to apply one or more materials in one or more layers to an object. General examples are powder coating systems, as well as other particulate material application systems such as may be used in the food processing and chemical industries. These are but a few examples of a wide and numerous variety of systems used to apply particulate materials to an object and to which the present invention can find realization.  
      The application of dry particulate material is especially challenging on a number of different levels. An example, but by no means a limitation on the use and application of the present invention, is the application of powder coating material to objects using a powder spray gun. Because sprayed powder tends to expand into a cloud or diffused spray pattern, known powder application systems use a spray booth for containment. Powder particles that do not adhere to the target object are generally referred to as powder overspray, and these particles tend to fall randomly within the booth and will alight on almost any exposed surface within the spray booth. Therefore, cleaning time and color change times are strongly related to the amount of surface area that is exposed to powder overspray.  
      In addition to exterior surface areas exposed to powder overspray, color change times and cleaning are strongly related to the amount of interior surface area exposed to the flow of powder during an application process. Examples of such interior surface areas include all surface areas that form the powder flow path, from a supply of the powder all the way through the powder spray gun. The powder flow path typically includes a pump that is used to transfer powder from a powder supply to one or more spray guns. Hoses are commonly used to connect the supply, pumps and guns.  
      Interior surface areas of the powder flow path are typically cleaned by blowing a purge gas such as pressurized air through portions of the powder flow path. Wear items that have surfaces exposed to material impact, for example a spray nozzle in a typical powder spray gun, can be difficult to clean due to impact fusion of the powder on the wear surfaces.  
      Most powder spray application systems use a powder containment booth or spray booth in which the objects are sprayed. Powder overspray is collected by a powder recovery system, which typically operates on the basis of drawing a large volume of air from the spray booth, usually through openings in the walls or floor. This large air volume acts as containment air to prevent powder overspray from falling outside the spray booth. This containment air has entrained powder overspray which is separated from the containment air by a suitable device such as primary filters or cyclones. Since the primary filters or cyclones do not typically extract 100 percent of the entrained powder overspray, after filters are used to filter out residual powder from the air before venting to atmosphere.  
      Known supply systems for powder coating materials generally involve a container such as a box or hopper that holds a fresh supply of new or ‘virgin’ powder. This powder is usually fluidized within the hopper, meaning that air is pumped into the powder to produce an almost liquid-like bed of powder. Fluidized powder is typically a rich mixture of material to air. Often, recovered powder overspray is returned to the supply via a sieve arrangement. A venturi pump is used to draw powder through a suction line or tube from the supply into a feed hose and then to push the powder under positive pressure through the hose to a spray gun. Such systems are difficult to clean for a color change operation because the venturi pumps cannot be reverse purged, the suction tubes and associated support frames retain powder and changing the hoppers can be time consuming. The sieve is also challenging and time consuming to clean as it often is in a separate housing structure as part of the powder recovery system or is otherwise not easily accessible. Most of these components need to be cleaned by use of a high pressure air wand which an operator manually uses to blow powder residue back up into a cyclone or other powder recovery unit. Every minute that operators have to spend cleaning and purging the system for color change represents downtime for the system and inefficiency.  
      There are two generally known types of dry particulate material transfer processes, referred to herein as dilute phase and dense phase. Dilute phase systems utilize a substantial quantity of air to push material through one or more hoses from a supply to a spray applicator. A common pump design used in powder coating systems is the venturi pump which introduces a large volume of air at higher velocity into the powder flow. In order to achieve adequate powder flow rates (in pounds per minute or pounds per hour for example), the components that make up the flow path must be large enough to accommodate the flow with such a high air to material ratio (in other words lean flow) otherwise significant back pressure and other deleterious effects can occur.  
      Dense phase systems on the other hand are characterized by a high material to air ratio (in other words rich flow). A dense phase pump is described in pending U.S. patent application Ser. No. 10/501,693 filed on Jul. 16, 2004 for PROCESS AND EQUIPMENT FOR THE CONVEYANCE OF POWDERED MATERIAL, the entire disclosure of which is fully incorporated herein by reference, and which is owned by the assignee of the present invention. This pump is characterized in general by a pump chamber that is partially defined by a gas permeable member. Material, such as powder coating material as an example, is drawn into the chamber at one end by gravity and/or negative pressure and is pushed out of the chamber through an opposite end by positive air pressure. This pump design is very effective for transferring material, in part due to the novel arrangement of a gas permeable member forming part of the pump chamber. The overall pump, however, in some cases may be less than optimal for purging, cleaning, color change, maintenance and material flow rate control.  
      Many known material application systems utilize electrostatic charging of the particulate material to improve transfer efficiency. One form of electrostatic charging commonly used with powder coating material is corona charging that involves producing an ionized electric field through which the powder passes. The electrostatic field is produced by a high voltage source connected to a charging electrode that is installed in the electrostatic spray gun. Typically these electrodes are disposed directly within the powder path.  
     SUMMARY OF THE INVENTION  
      The invention provides apparatus and methods for improving the cleanability and reducing color change time for a material application system. Cleanability refers, among other things, to reducing the quantity of powder overspray that needs to be removed from exterior surfaces of the applicator. Cleanability also can refer to reducing the quantity of powder that needs to be purged or otherwise removed from interior surfaces that define the powder path through the spray applicator. Cleanability can also refer to the ease with which the powder flow path can be purged or otherwise cleaned. Improving cleanability results in faster color change times by reducing contamination risk and shortening the amount of time needed to remove a first color powder from the applicator prior to introducing a second color powder.  
      In accordance with one aspect of the invention, cleanability is improved by reducing the effective exterior surface areas of the spray applicator that are exposed to powder overspray. In accordance with another aspect of the invention, the exterior surfaces are contoured or profiled so as to allow the surface areas to more effectively shed powder overspray. In one embodiment, a spray applicator has a housing that is formed to have a narrow rounded upper portion with steeply sloped sides, as compared to a lower portion of the housing.  
      In accordance with another aspect of the invention, interior surface areas are reduced so as to reduce the amount of surface area exposed to the flow of material. In accordance with another aspect of the invention, wear surfaces and interior surface areas are reduced by providing a spray applicator that eliminates use of a nozzle device. In one embodiment, the material being applied by the applicator exits the applicator body directly from a feed tube that extends through a housing of the applicator.  
      In further accordance with this aspect of the invention, interior surface areas are reduced by designing the spray applicator to operate with high density low volume powder feed. In this context, high density means that the powder fed to the spray applicator has a substantially reduced amount of entrainment or flow air in the powder as compared to conventional powder flow systems. Low volume simply refers to the use of less volume of flow air needed to feed the powder due to its higher density as compared to conventional powder spray guns. By removing a substantial amount of the air in the powder flow, the associated conduits, such as a powder feed hose and a powder feed tube, can be substantially reduced in diameter, thereby substantially reducing the interior surface area. This also results in an significant reduction in the overall size of the spray applicator, thus further reducing the amount of exterior surface area exposed to powder overspray. For manually operated spray applicators, the invention provides an easily replaceable or removable powder path. In any case, a powder flow path is realized that optionally comprises only a single part.  
      In accordance with another aspect of the invention, a pump and applicator arrangement is contemplated that has a single internal diameter in the powder flow path from the pump outlet to the applicator outlet.  
      In accordance with another aspect of the invention, a spray applicator is contemplated that operates with high density low volume powder feed. In one embodiment, a spray applicator is provided that includes an air cap positioned at an outlet end of the spray applicator. The air cap permits an air stream to be directed at a high density powder flow that exits a powder feed tube. This arrangement not only eliminates the use of a nozzle, but also adds diffusing or atomizing air into the high density powder stream that exits the feed tube. In an alternative embodiment, an optional exterior electrode is provided in association with the air cap to provide an electrostatic spray applicator. The electrode is disposed exterior the spray applicator housing and powder flow path. In other alternative embodiments, the electrode is retained in an electrode holder that is molded about the electrode, and optionally the electrode holder is keyed to the air cap so that the electrode is always optimally positioned with respect to the outlet end of the powder feed tube.  
      In accordance with another aspect of the invention, use of the air cap allows for spray pattern control by adjusting the flow of air that impinges on the powder stream. In one embodiment, a switch is provided by which an operator can adjust the spray pattern by simple actuation of the switch while observing the change in pattern shape as more or less air is added to the flow. Software logic is provided to allow for easy adjustment of the spray pattern.  
      In accordance with another aspect of the invention, spray pattern adjustment is implemented with adjustment of the material flow rate. In one embodiment, when the spray pattern is adjusted by changing the air directed at the powder stream, the material flow rate is adjusted accordingly. The control of pattern shape and flow rates are additional parameters that may be individually or together included in the material application recipes for various objects being processed.  
      These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a simplified schematic diagram of a powder coating material application system utilizing the present invention;  
       FIG. 1A  illustrates an embodiment of a powder coating material application system of  FIG. 1  with the parts of the system as illustrated in the other drawings of the present application;  
       FIG. 2A  is a spray applicator in accordance with the invention and illustrated in longitudinal cross-section;  
       FIG. 2B  is an enlarged view of the forward circled portion of  FIG. 2A  and  FIG. 2C  is an enlarged view of the rearward circled portion of  FIG. 2A ;  
       FIGS. 3A and 3B  illustrate the spray applicator of  FIG. 2A  in exploded perspective;  
       FIG. 4  is an air cap illustrated in front perspective;  
       FIG. 5  is a longitudinal section of the air cap of  FIG. 4 ;  
       FIG. 6  is a longitudinal section of the air cap of  FIG. 4  to illustrate an electrode retained therewith;  
      FIGS.  7 A-C illustrate an electrode and holder assembly;  
       FIG. 8A  illustrates a manual spray applicator in elevation in accordance with the invention;  
       FIG. 8B  illustrates the applicator of  FIG. 8A  in longitudinal cross-section;  
       FIG. 8C  is a perspective illustration of a powder tube used in the applicator of  FIGS. 8A and 8B ; and  
       FIG. 9  is a logic flow diagram for a pattern adjust algorithm in accordance with the invention;  
       FIGS. 10A-10C  are assembled and exploded isometric views of a pump in accordance with the invention;  
       FIGS. 10D-10G  are elevation and cross-sectional views of the assembled pump of  FIG. 10A ;  
       FIGS. 11A and 11B  are an isometric and upper plan view of a pump manifold;  
       FIGS. 12A and 12B  illustrate a first Y-block;  
       FIGS. 13A and 13B  are perspective and cross-sectional views of a valve body;  
       FIGS. 14A and 14B  illustrate in perspective another Y-block arrangement;  
       FIG. 15  is an exploded perspective of a supply manifold;  
       FIG. 16  is an exemplary embodiment of a pneumatic flow arrangement for the pump of  FIG. 10A ;  
       FIGS. 17A and 17B  are an isometric and exploded isometric of a transfer pump in accordance with the invention;  
       FIG. 18  is an exemplary embodiment of a pneumatic flow arrangement for a transfer pump;  
       FIG. 19  is an alternative embodiment of a pneumatic circuit for the transfer pump;  
       FIG. 20  is a representation of material flow rate curves for a pump operating in accordance with the invention; and  
       FIG. 21  is a graph depicting powder flow rates versus pinch valve open duration for two different pump cycle rates;  
       FIG. 22  is an isometric illustration of a material supply in accordance with the invention;  
       FIG. 23  is an exploded isometric of a fluidizing arrangement and support frame;  
       FIG. 24  is the assembly of  FIG. 23  in longitudinal cross-section along the section line  4 - 4  in  FIG. 3 ;  
       FIG. 25  is the assembly of  FIG. 23  in longitudinal cross-section along the section line  25 - 25  in  FIG. 23 ;  
       FIG. 26  illustrates a gasket arrangement for the fluidizing arrangement of  FIG. 23 , in cross-sectional perspective, enlarged for clarity;  
       FIG. 27  is a perspective illustration of the material supply in an operational position;  
       FIG. 27A  shows a lance arrangement for drawing powder from a box;  
       FIGS. 28A-28D  illustrate a siphon ring in accordance with the invention, wherein  FIG. 28A  is a perspective from an top view,  FIG. 28B  is a section taken along the line  28 B- 28 B in  FIG. 28C ,  FIG. 28C  is a bottom view and  FIG. 28D  is an enlarged view of the circled region of  FIG. 28B ;  
       FIG. 29  is a cross-sectional illustration of the interface between the siphon ring of  FIGS. 28A-28D  and the fluidizing unit of  FIGS. 24-26 , taken along the line  29 - 29  in  FIG. 22 ;  
       FIG. 30  is a perspective of a supply in accordance with the invention installed in a material application system with portions of the system omitted for clarity;  
       FIG. 31  is another perspective of a supply in accordance with the invention installed in a material application system;  
       FIG. 32  illustrates a sieve arrangement in accordance with the invention in an operational position;  
       FIG. 33  illustrates the sieve arrangement of  FIG. 32  in a cleaning or color change position;  
       FIG. 34  illustrates the sieve arrangement of  FIGS. 32 and 33  in cross-section; and  
       FIG. 35  illustrates an alternative embodiment for the sieve arrangement. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND EXEMPLARY EMBODIMENTS THEREOF  
      The invention contemplates a variety of new aspects for a particulate material application system. In general, the invention is directed to three major system functions, namely the supply of material, the applicator used to apply material to an object and a transfer device or pump for transferring powder from the supply to an applicator or from a recovery system to the supply. The three main system functions operationally interface with each other as well as other functions of a typical material application system, including an overspray containment function typically in the form of a spray booth and an overspray recovery function typically in the form of a filter based or cyclone based material recovery devices.  
      From a system perspective, the invention is directed among other things to improving the cleanability of the system so as to significantly reduce the total time needed for a color change operation. In addition, the invention is directed to various aspects that make the system or subsystems easier to use with less manpower and time involved. In exemplary embodiments of the invention the material is handled in dense phase, but not all aspects of the invention need to be implemented only with dense phase systems. For example but not by way of limitation, many aspects of the invention related to the supply, such as for example the sieving arrangement, can be applied in dilute phase systems.  
      By “dense phase” is meant that the air present in the particulate flow is about the same as the amount of air used to fluidize the material at the supply such as a feed hopper. As used herein, “dense phase” and “high density” are used to convey the same idea of a low air volume mode of material flow in a pneumatic conveying system where not all of the material particles are carried in suspension. In such a dense phase system, the material is forced along a flow passage by significantly less air volume, with the material flowing more in the nature of plugs that push each other along the passage, somewhat analogous to pushing the plugs as a piston through the passage. With smaller cross-sectional passages this movement can be effected under lower pressures.  
      In contrast, conventional flow systems tend to use a dilute phase which is a mode of material flow in a pneumatic conveying system where all the particles are carried in suspension. Conventional flow systems introduce a significant quantity of air into the flow stream in order to pump the material from a supply and push it through under positive pressure to the spray application devices. For example, most conventional powder coating spray systems utilize venturi pumps to draw fluidized powder from a supply into the pump. A venturi pump by design adds a significant amount of air to the powder stream. Typically, flow air and atomizing air are added to the powder to push the powder under positive pressure through a feed hose and an applicator device. Thus, in a conventional powder coating spray system, the powder is entrained in a high velocity high volume of air, thus necessitating large diameter powder passageways in order to attain usable powder flow rates.  
      Dense phase flow is oftentimes used in connection with the transfer of material to a closed vessel under high pressure. The present invention, in being directed to material application rather than simply transport or transfer of material, contemplates flow at substantially lower pressure and flow rates as compared to dense phase transfer under high pressure to a closed vessel.  
      As compared to conventional dilute phase systems having air volume flow rates of about 3 to about 6 cfm (such as with a venturi pump arrangement, for example), the present invention may operate at about 0.8 to about 1.6 cfm, for example. Thus, in the present invention, powder delivery rates may be on the order of about 150 to about 300 grams per minute.  
      Dense phase versus dilute phase flow can also be thought of as rich versus lean concentration of material in the air stream, such that the ratio of material to air is much higher in a dense phase system. In other words, in a dense phase system the same amount of material per unit time is transiting a cross-section (of a tube for example) of lesser area as compared to a dilute phase flow. For example, in some embodiments of the present invention, the cross-sectional area of a powder feed tube is about one-fourth the area of a feed tube for a conventional venturi type system. For comparable flow of material per unit time then, the material is about four times denser in the air stream as compared to conventional dilute phase systems.  
      The present invention is directed to a material application system that includes a spray applicator and various improvements therein, some of which are specific to a low pressure dense phase applicator, but others of which will find application in many types of material flow systems, whether dense phase, low pressure dense phase, or other. Accordingly, the present invention is not specifically concerned with the manner in which a dense phase material flow is created and fed to the applicator. In general, dense phase delivery is performed by a pump that operates to pull material into a chamber under negative pressure and discharge the material under positive pressure with a low air volume as noted above. There are a number of known dense phase pump and transfer systems, including but not limited to the following disclosures: EP Application No. 03/014,661.7; PCT Publication 03/024,613 A1; and PCT Publication 03/024,612 A1; the entire disclosures of which are fully incorporated herein by reference.  
      The invention also contemplates a number of new aspects for a dense phase pump for particulate material. The pump may be used in combination with any number or type of spray applicator devices or spray guns and material supply.  
      The invention also contemplates a number of new aspects and concepts for a supply that can be used with a particulate material application system. The supply may be used in combination with any number of spray applicator devices or spray guns, spray booths and pumps. The supply is particularly useful with dense phase transport, but may be used with dilute phase transport as well.  
      With reference to  FIG. 1 , in an exemplary embodiment, the present invention is illustrated being used with a material application system, such as, for example, a typical powder coating spray system  10 . Such an arrangement commonly includes a powder spray booth  12  in which an object or part P is to be sprayed with a powder coating material. The application of powder to the part P is generally referred to herein as a powder spray, coating or application operation or process, however, there may be any number of control functions, steps and parameters that are controlled and executed before, during and after powder is actually applied to the part.  
      As is known, the part P is suspended from an overhead conveyor  14  using hangers  16  or any other conveniently suitable arrangements. The booth  12  includes one or more openings  18  through which one or more spray applicators  20  may be used to apply coating material to the part P as it travels through the booth  12 . The applicators  20  may be of any number depending on the particular design of the overall system  10 . Each applicator can be a manually operated device as in device  20   a , or a system controlled device, referred to herein as an automatic applicator  20   b , wherein the term “automatic” simply refers to the fact that an automatic applicator is mounted on a support and is triggered on and off by a control system, rather than being manually supported and manually triggered.  
      It is common in the powder coating material application industry to refer to the powder applicators as powder spray guns, and with respect to the exemplary embodiments herein we will use the terms applicator and gun interchangeably. However, it is intended that the invention is applicable to material application devices other than powder spray guns, and hence the more general term applicator is used to convey the idea that the invention can be used in many material application systems in addition to powder coating material application systems. Some aspects of the invention are applicable to electrostatic spray guns as well as non-electrostatic spray guns. The invention is also not limited by functionality associated with the word “spray”. Although the invention is especially suited to powder spray application, the pump concepts and methods disclosed herein may find use with other material application techniques beyond just spraying, whether such techniques are referred to as dispensing, discharge, application or other terminology that might be used to describe a particular type of material application device.  
      The spray guns  20  receive powder from a feed center or supply  22  through an associated powder feed or supply hose  24 . The terms “feed center” and “supply” are used interchangeably herein to refer to any source of particulate material in accordance with the present invention. To the extent that the supply  22  mimics a feed hopper in the sense of being a container for powder, the supply  22  can be thought of and referred to as a hopper, but, the invention contemplates various design aspects of the supply  22  that are a significant advance over conventional hoppers used to supply powder to a powder spray application system.  
      The automatic guns  20   b  typically are mounted on a support  26 . The support  26  may be a simple stationary structure, or may be a movable structure, such as an oscillator that can move the guns up and down during a spraying operation, or a gun mover or reciprocator that can move the guns in and out of the spray booth, or a combination thereof.  
      The spray booth  12  is designed to contain powder overspray within the booth, usually by a large flow of containment air into the booth. This air flow into the booth is usually effected by a powder overspray reclamation or recovery system  28 . The recovery system  28  pulls air with entrained powder overspray from the booth, such as for example through a duct  30 . In some systems the powder overspray is returned to the feed center  22  as represented by the return line  32 . In other systems the powder overspray is either dumped or otherwise reclaimed in a separate receptacle.  
      In the exemplary embodiment herein, powder is transferred from the recovery system  28  back to the feed center  22  by a first transfer pump  400 . A respective gun pump  402  is used to supply powder from the feed center  22  to one or more associated spray applicator or gun  20 . For example, a first pump  402   a  is used to provide dense phase powder flow to the manual gun  20   a  and a second pump  402   b  is used to provide dense phase powder flow to the automatic gun  20   b . The design of the gun pumps and transfer pumps may be any conveniently available or suitable design. Dense phase pumps, such as for example the pump described in the patent application noted hereinabove, or dilute phase pumps may be used.  
      Each gun pump  402  operates from pressurized gas such as ordinary air supplied to the gun by a pneumatic supply manifold  404 . Although each manifold and pump assembly is schematically illustrated in  FIG. 1  as being directly joined, it is contemplated that in practice the manifolds  404  will be disposed in a cabinet or other enclosure and directly mounted to the pumps  402  through an opening in a wall of the cabinet. In this manner, the manifolds  404 , which may include electrical power such as solenoid valves, are isolated from the spraying environment.  
      The manifold  404  supplies pressurized air to its associated pump  402  for purposes that will be explained hereinafter. In addition, each manifold  404  includes a pressurized pattern air supply  405  that is provided to the spray guns  20  via air hoses or lines  406 . Main air  408  is provided to the manifold  404  from any convenient source within the manufacturing facility of the end user of the system  10 .  
      In this embodiment, a second transfer pump  410  is used to transfer powder from a supply  412  of virgin powder (that is to say, unused) to the feed center  22 . Those skilled in the art will understand that the number of required transfer pumps  410  and gun pumps  402  will be determined by the requirements of the overall system  10  as well as the spraying operations to be performed using the system  10 .  
      Other than the supply  22 , the guns  20  and the pumps  400 ,  402 , the selected design and operation of the material application system  10 , including the spray booth  12 , the gun mover  26 , the conveyor  14 , and the recovery system  28 , form no required part of the present invention and may be selected based on the requirements of a particular coating application. A control system  34  likewise may be a conventional control system architecture such as a programmable processor based system or other suitable control circuit. The control system  34  executes a wide variety of control functions and algorithms, typically through the use of programmable logic and program routines, which are generally indicated in  FIG. 1  as including but not necessarily limited to feed center control  36  (for example supply controls and pump operation controls), gun operation control  38 , gun position control  40  (such as for example control functions for the reciprocator/gun mover  26  when used), powder recovery system control  42  (for example, control functions for cyclone separators, after filter blowers and so on), conveyor control  44  and material application parameter controls  46  (such as for example, powder flow rates, applied film thickness, electrostatic or non-electrostatic application and so on). Conventional control system theory, design and programming may be utilized.  
      The control functions for gun operation  38  include but are not limited to gun trigger on and off times, electrostatic parameters such as voltage and current settings and monitoring, and powder and air flow rates to the guns. These functions and parameters make up what is commonly known as part recipes, meaning that each part may have its own set of parameters and control functions for each color or type of powder applied. These control functions and parameters may be conventional as is well known. However, in addition, the present invention does contemplate new control functions for the spray applicators and pumps of the present invention, specifically related to spray pattern adjusting and powder atomization air, as will be set forth herein below. This additional gun control function is made available by the present invention in the use of an air assist feature along with the feature of no longer using a nozzle device, used for dense phase powder flow, as contrasted to conventional systems wherein nozzles are commonly used and dense phase powder flow is not used. Still further, the present invention contemplates an optional feature of the pump control, wherein material flow rate is adjusted in response to changes in the spray pattern. These new control features may be incorporated into the overall part recipes.  
      While the described embodiments herein are presented in the context of a dense phase transport system for use in a powder coating material application system, those skilled in the art will readily appreciate that the present invention may be used in many different dry particulate material application systems, including but not limited in any manner to: talc on tires, super-absorbents such as for diapers, food related material such as flour, sugar, salt and so on, desiccants, release agents, and pharmaceuticals. These examples are intended to illustrate but not limit the broad application of the invention for dense phase application of particulate material to objects. The specific design and operation of the material application system selected provides no limitation on the present invention unless and except as otherwise expressly noted herein.  
      While various aspects of the invention are described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects may be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sun-combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices, software, hardware, control logic and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated.  
      Even from the general schematic illustration of  FIG. 1  it can be appreciated that such complex systems can be very difficult and time consuming to clean and to provide for color change. Typical powder coating material is very fine and tends to be applied in a fine cloud or spray pattern directed at the objects being sprayed. Even with the use of electrostatic technology, a significant amount of powder overspray is inevitable. Cross contamination during color change is a significant issue in many industries, therefore it is important that the material application system be able to be thoroughly cleaned between color changes. Color changes however necessitate taking the material application system offline and thus is a cost driver. The present invention is directed to providing a supply that is easier and faster to clean, and thus easier and faster to clean for a color change process. Additional features and aspects of the invention are advantageous separate and apart from the concern for cleanability and color change.  
       FIG. 1A  illustrates an embodiment of a material application system of  FIG. 1 , with details of the parts of the system being as set forth in the remaining drawings herein along with the accompanying detailed description associated with each figure.  
      With reference to  FIGS. 2A and 2B , an exemplary embodiment of an automatic spray applicator  20   b  in accordance with the invention is illustrated. The same embodiment is illustrated in exploded perspective in  FIGS. 3A and 3B .  
      The spray applicator  20   b  includes a main housing  100  that encloses most of the applicator components. The housing  100  has a powder inlet end  102  and an outlet end  104 . A powder tube  106  extends substantially through the housing  100 . The powder tube  106  forms a straight and uninterrupted powder path from an inlet end  106   a  thereof to an outlet end  106   b  thereof. The powder tube is preferably a single piece of tubing to minimize joints that can trap powder. This makes the applicator  20   b  easy to clean and purge internally. The only joint in the powder path within the gun housing  100  is where a powder hose (not shown) is connected to the inlet end  102  of the gun as will be described herein below.  
      In accordance with one aspect of the invention, the gun  20  design is particularly advantageous for cleaning and color change by virtue of being fully operable with a straight through powder tube  106  that extends from the inlet all the way through to the outlet. The tube has a reduced diameter as a result of the dense phase powder flow from the pumps  402  and therefore presents less internal surface area to clean. Moreover, the powder hose that is connected between the gun powder inlet and the pump outlet can be the same diameter as the powder tube diameter. Thus there is a continuous, uniform geometry in the form of a single diameter powder flow path from the pump to the gun outlet. This feature eliminates potential entrapment areas and minimizes resistance to flow. Moreover, the powder flow path is much easier and effective to purge for color change. In accordance with other aspects of the invention as will be set forth hereinbelow, the pumps  402  can be purged in two directions, including forward through the powder hose and through the powder tube. This purging works hand in hand and is facilitated by the uniform geometry of the powder flow path between the pump and gun.  
      The housing  100  in this embodiment is a three section housing including a front section  100   a , an elongated middle section  100   b  and a back section  100   c . The front section  100   a  includes a boss  108  at its back end that fits inside the forward end of the middle section  100   b  with preferably a snug friction fit. The back section  100   c  includes a boss  110  at its forward end that fits inside the rearward end of the middle section  100   b  with preferably a snug friction fit. The powder tube  106  includes a forward threaded portion  112  that threadably mates with an internally threaded portion of the front section  100   a . The powder tube  106  also includes a rearward threaded portion  114  ( FIG. 2C ) that threadably mates with a lock nut  116 . The lock nut  116  partially extends into a counterbore  118  of a heat sink  120 . The lock nut  116  abuts the counterbore during assembly of the gun. Once the powder tube  106  has been threadably joined to the front section  100   a  of the housing  100  and tightened down, the lock nut  116  is then tightened, which causes the powder tube  106  to be pulled backward in tension. This action pulls the three housing sections  100   a, b  and c axially together in compression such that the powder tube  106  acts like a tie rod to hold the housing sections tightly together. The lock nut  116  includes a seal  122 , such as for example an o-ring, that provides a friction fit between the lock nut  116  and the heat sink  120 .  
      A powder tube lock knob  124  is threadably joined to the lock nut  116 . A forward end of a powder feed hose  125  is inserted through a bore  126  of the lock knob and bottoms against an inner shoulder  128  formed in the powder tube  106 . A lock ring  130  is captured between a forward end of the lock knob  124  and the back edge of the powder tube  106 . The lock ring allows easy insertion of a powder feed tube  125  into the inlet end of the gun  20   b . The lock ring  130  however grips the outer wall of the feed tube and prevents the feed tube from backing out. The lock ring  130  tightly engages the feed tube  125  when the lock knob  124  is tightened down against the lock nut  116 . The powder tube  125  can be easily removed for color change by simply loosening the lock knob  124 . A seal  132  is provided to prevent loss of powder. The seal  132  also provides a friction fit so that when the powder tube  125  is removed from the gun, the lock knob  124  does not slide down the length of the powder tube.  
      It will thus be apparent from  FIGS. 2A and 2C  that the powder path through the spray applicator  20   b  is defined by the powder tube  116 . The only joint is the location  134  where the powder feed hose  125  abuts the powder tube  116  shoulder  128 . Other than that one joint, powder can flow along an uninterrupted path through the spray gun to the outlet end  104 . Thus the gun is easy to purge for color change and has no significant entrapment areas in the powder path. For use with a dense phase particulate material, the powder tube diameter is substantially reduced as compared to a conventional powder spray gun powder tube. For example, in one embodiment of the invention, the inner diameter of the powder tube may be about six millimeters whereas in a conventional dilute phase system it may be on the order of 11 to 12 millimeters.  
      The powder tube  106  extends through the housing  100  and the front end  106   b  is received in a central bore  136  of an air cap  138  that is retained on the front section  100   a  by a threaded retaining nut  140 . With the powder tube  106  extending all the way through the gun, there is no nozzle device as used in typical prior art powder spray guns. Rather, powder will exit the gun from the front end  106   b  of the powder tube. The powder tube end  106   b  may be but need not be aligned generally flush with the forward end of the central bore  136  of the air cap  138 .  
      At this point it is noted that the spray applicator  20   b  will typically be a rather long device, with most of the length of the applicator defined by the middle section  100   b . The overall gun length may be several feet, for example, five feet.  
      The air cap  138  is best illustrated in  FIGS. 4 and 5 . The air cap  138  is provided in accordance with one aspect of the invention to add air, primarily as atomizing or diffusion air, to the powder flow that exits the powder tube end  106   b . The invention contemplates adding air to the powder flow for dense phase particulate systems. In the absence of air being added, the powder flow in a dense phase system is nearly fluid like with the powder flowing much like water in a tube.  
      The air cap  138  includes a central passage  136  that receives the front end of the powder tube  106 . The passage  136  is sized so as to loosely receive the powder tube end. This helps to center the powder stream for proper presentation of the powder stream to the air jets  150 . This also allows air to pass around the outside of the tube end to prevent powder from migrating back inside the gun housing. The central passage  136  is defined by a male threaded inner tubular portion  142 . The male threads  144  receive a conductive diffuser ring as will be described herein shortly. An outer wall  146  of the air cap is also male threaded as at  148  and mates with the threaded retainer nut  140 . The retainer nut  140  is thus threadably joined to the air cap  138  and a threaded end of the front housing section  100   a  ( FIG. 2B ) to securely hold the air cap on the housing.  
      As best illustrated in  FIG. 5 , the air cap includes two air jet prongs  148   a  and  148   b . Each prong  148  includes one or more air jets  150 . The air jets  150  open into an atomizing or diffusing region  152  that is just forward of the powder tube end  106   b . The number of air jets and the angle that their direct air at the powder flow is a matter of design choice to optimize atomization of the powder and to shape the spray pattern as desired. Typically, the more air that is directed at the powder flow will tend to atomize the flow more and enlarge the spray pattern.  
      The air jets  150  open to an annular air passage  154 . The annular air passage  154  further communicates with an annular cavity  156 . The annular cavity  156  receives a female threaded air diffuser ring  158  ( FIG. 6 ). The ring  158  is threaded into the air cap  138  with the internal threads  144 . As best illustrated in  FIG. 3A , the ring  158  includes a plurality if air holes  161  that provide an even air flow within the air cap  138 . The ring  158  is also made of a electrically conductive material. For example, the ring  158  may be formed from carbon filled Teflon™. The ring  158  is made conductive because in addition to providing a diffused flow of air through the air cap  138 , the ring  158  also electrically connects an electrode assembly  160  to a high voltage multiplier  162 .  
      With reference to FIGS.  7 A-C and  FIG. 6 , in accordance with another aspect of the invention an external electrode is provided just downstream from where the powder exits the powder feed tube end  106   b . By placing the electrode on the outside of the gun housing  100 , it does not interfere with the powder flow or with the cleanability of the powder tube. This is particularly useful with dense phase material flow.  
      In one embodiment, an electrode assembly  160  is provided that includes an electrode conductor  164  and an electrode holder  166 . Preferably although not necessarily the holder  166  is molded over the conductor  164 . A short portion  164   a  of the conductor extends out of the holder  166  and a longer portion  164   b  extends from the opposite end of the holder  166 . The holder  166  is formed with an alignment key  168  in the form of a U-shaped boss that is received in a conforming recess  170  formed in the air cap  138  (see  FIGS. 4 and 6 ). In this manner, the electrode holder  166  can only be installed with one orientation, so that the electrode tip  164   a  is optimally positioned downstream from the powder tube end  106   b . The holder has an extended portion  166   b  that is inserted into a bore  172  in the air cap  138 . A forward portion  166   a  of the holder  166  positions the electrode tip and is formed at about a right angle to the extended portion  166   b.    
      As best illustrated in  FIGS. 4 and 6 , the inner portion  164   b  of the electrode is bent down and is captured between the conductive ring  158  and a shoulder  174  in the air cap. In this way, a solid electrical connection is made between the electrode conductor  164  and the conductive ring  158 .  
      With reference to  FIGS. 2A and 2B , a contact pin  180  is positioned in the front section  100   a  for intimate contact with a back side of the conductive ring  158 . The contact pin  180  is also in contact with a resistor cable  182  which extends back through a forward portion of the middle housing section  100   b . The resistor cable  182  may be any conventional resistive assembly that uses resistive carbon fiber and that provides current limiting protection for the electrostatic gun. This protection is enhanced by placing the resistance closer to the electrode. The resistor cable  182  may be supported in the housing with a guide member  184  and is supported at a back end thereof with a bias spring  186 . The spring  186  maintains good electrical contact between the pin  180  and the electrical cable  188 . The back end of the spring  186  makes electrical contact with a contact of an electrical cable  188 . The electrical cable may be in accordance, for example, with U.S. Pat. Nos. 4,576,827 and 4,739,935 issued to the assignee of the present invention, the entire disclosures of which are fully incorporated herein by reference.  
      The electrical cable  188  extends back through the extended housing mid-section  100   b . The electrical cable  188  at its back end makes electrical contact with an output contact  190  of the multiplier  162 . A nut  192  may be used to secure the electrical cable  188  to the multiplier output  190 .  
      Thus, in accordance with another aspect of the invention, the high voltage multiplier  162  is positioned in a rearward section of the gun housing, preferably near where the gun is mounted. In this manner the major weight of the gun is supported at the back end to significantly reduce the vibration and movement of the forward portion of the gun. If the multiplier were positioned closer to the front of the gun, as in conventional powder guns, the cantilever mounting could cause large bending moments. Thus, the invention contemplates an arrangement of a multiplier in line with an electrical cable coupled to a resistance and the electrode, with the multiplier in a rearward portion of the gun and the resistance positioned near the front of the gun.  
      The multiplier  162  is mounted to a bracket member  194  by a bolt  196 . The bracket is thermally conductive, such as made of aluminum that is also mounted to the heat sink  120  by a pair of screws  198 . In this manner the multiplier can be cooled by the heat sink  120 . A conventional electrical input connector  121  is used to provide the input drive voltage, typically a low DC voltage, to the multiplier input as is known.  
      An air tube  200  is pushed onto a nipple  202  formed in the front housing section  100   a . The nipple  202  forms an air passage to a main air passage  204  that opens to the annular cavity  156  just behind the conductive ring  158 . Air that flows down the air tube  200  thus passes through the holes  161  in the ring  158  and then out the air jets  150  in the air cap  138  as described herein above.  
      The air tube  200  extends back through the gun housing  100  to a male connector  206 . The male connector  206  mates with a first bore  208  that is formed in the front face  210  of the heat sink  120  (see  FIG. 2C ). The first bore  208  opens to a second bore  212  that is formed in the back face  214  of the heat sink  120 . It will be noted from  FIG. 2C  that the centerline axis of the first bore  208  is offset from the centerline axis of the second bore  212  even though they are in fluid communication. This causes air turbulence and better cooling of the heat sink  120 . A second fitting  216  is connected to the second bore  212  and serves as a connection for a main air hose (not shown). By this arrangement, air is thus provided to the air cap at the front of the gun, and the multiplier is cooled by the heat sink that is exposed to the same flow of air that goes to the air cap.  
      The exploded views of  FIGS. 3A and 3B  are provided to better illustrate the assembly described herein above.  
      In accordance with another aspect of the invention, as best illustrated in  FIGS. 3A and 3B , the housing  100  sections are preferably formed with a tapered upper portion  220  formed by two rather steep walls  222  that join at a small radius apex  224 . Preferably the apex is the top of the gun housing when the gun is being used for spraying material, so that the profile of the gun housing  100  reduces the amount of powder overspray that can alight on the gun and the steep sides can help shed powder.  
      With reference to  FIGS. 8A and 8B , the present invention also contemplates a manual spray applicator  250  that is particularly but not exclusively suited for dense phase material application. Many features of the manual version are the same as the automatic spray applicator described herein above.  
      The manual gun  250  includes a housing  252  that in this embodiment is a two piece housing including a rear or multiplier section  254  and a front or powder tube section  256  in the form of a barrel. These sections can be releasably secured together by any convenient mechanism such as a set screw for example. There is an air cap  258  that is retained on the outlet end of the front housing  256  by a retainer nut  260 . The air cap holds an electrode assembly  262  and also a conductive diffuser ring  263  (shown in  FIG. 8B ). The air cap includes air jets  259 . The air cap  258 , retainer nut  260 , electrode assembly  262  (including an electrode conductor and over-molded electrode holder) and conductive diffuser ring  263  may be the same design and operation as the corresponding parts in the automatic gun version described herein above.  
      The manual gun  250  further includes an air inlet, such as a fitting  264  that is connectable to an air line (not shown). An electrical connector  266  is provided for connection with an external low voltage power supply to operate the internal high voltage multiplier  268  (shown in dotted line in  FIG. 8 ). The multiplier  268  is disposed in the rear housing section  254  above the grip handle  270  to reduce operator fatigue. The powder tube housing may be provided in any length as needed, or alternatively can be connectable to an extension housing if so desired for additional length of the spray applicator  250 .  
      Operation of the manual gun  250  is similar to the automatic version except that the manual gun is manually triggered by an operator. Thus the manual gun includes a control trigger device  271 . When this trigger  271  is depressed it causes electrical power to be delivered to the multiplier when electrostatic operation is to be used. Actuation of the control trigger  271  also allows air to flow to the air cap  258  via passages that extend through the handle  270  and the housing  252 . Air may also be used to cool the multiplier via a heat sink as in the automatic version. The control trigger  271  actuation also causes powder to flow through the gun from a powder feed hose  273  and out the front end of the gun.  
      Air enters the applicator  250  via the air fitting  264  and into a passage  272  in the handle  270 . This air can be used to help cool the multiplier  268 . The passage  272  is in fluid communication with an air passage  274  in the front housing section  256 . The passage  274  extends through the front housing section and opens to a recess  276  in the air cap  258  that receives the diffuser ring  263 .  
      The electrode  262  makes electrical contact with the diffuser ring  263  in a manner as described herein above. There is also a contact pin  278  that contacts the ring  263 . The contact pin  278  is part of an electrical circuit that includes a spring electrode  280  and a resistor assembly  282  and a conductive electrode spacer  282   a  that is electrically coupled to an output of the multiplier  268 . The electrode spacer  282   a  may for example be made of a conductive Teflon™ material. This electrical circuit may be similar as described herein above in the embodiment of the automatic gun.  
      The powder feed hose  273  is inserted into a tubular extension  284  of the front housing section  256 . A female threaded tube lock knob  286  and a lock ring  288  may be used to retain the feed hose  273  in the tubular extension  284 . The lock ring and lock knob may be designed to function in a manner similar to the corresponding parts in the automatic gun described herein before.  
      The forward end  273   a  of the feed hose  273  inserts into a hose passageway  290  formed in a powder tube  292 . The passageway  290  opens to a powder passage  294  that preferably lies along the central longitudinal axis of the applicator  250 . The distal end  294   a  of the passageway  294  is formed by a tubular portion  296  of the powder tube  292  (see also  FIG. 8C ). The powder tube  292  is slip fit or otherwise slideably installed into the front housing section  256  with the passageway  290  aligning with the tubular extension  284  so that the powder feed hose  273  can easily be inserted into the powder tube  292 . Note that the distal end  294   a  is received in the air cap  258  in a manner similar to the feed tube  106  and the air cap  138  in the automatic gun embodiment described herein above. The powder tube  292  thus forms a small diameter passageway for powder flow to the front of the gun, so that the manual gun  250  is well suited, for example, for dense phase powder flow.  
      The powder tube  292  thus provides an easily removable unit that forms the entire powder flow path for the spray gun  250 . This makes the manual gun easy to clean for color change.  
      In accordance with another aspect of the invention, an adjusting member or control device in the form of a second trigger device  298  is provided. This trigger  298  may be actuated alone or in combination with the control trigger  271 . The second trigger  298  is a pattern adjust trigger by which an operator can adjust the flow of air to the air cap  258 . By increasing the air flow, the spray pattern is made larger and vice-versa. As shown in  FIG. 1 , the control system  34  receives a signal from the pattern adjust trigger  298  (such as, for example, a change in impedance when the contacts close) and in response thereto issues a gun air control signal  299  The air control signal  299  can be used to control an air valve (not shown) disposed either inside the gun  250  or preferably in a pneumatic control section of the overall powder application system  10  to increase or decrease air flow to the air cap jets  259  as required.  
      With reference to  FIG. 9 , an exemplary flow diagram is provided for a pattern adjust logic routine or algorithm. At step  300  the logic determines if the gun pattern adjust trigger  298  is activated (a de-bounce subroutine may optionally be included to prevent air adjustment unless the trigger has been activated for a minimum time period.) If it is not, the program waits until a valid trigger signal is received. When the trigger  298  is activated, at step  302  the air flow is incrementally increased. The amount of the incremental increase is a matter of design choice, wherein the operator can be provided with fine adjustment, course adjustment or both. At step  304  the program determines whether maximum air flow is being provided to the spray applicator  250 . If it is not, then at step  306  the program checks if the trigger  298  is still on. If it is, the logic loops back to  302  to increment the air flow again. In this manner, the operator can hold the trigger  298  down and watch the pattern change with the increasing air flow, and stop by releasing the trigger  298 .  
      At step  306  if the trigger  298  is not still on then the program holds that air flow rate at  308  and loops back to wait for the next trigger actuation at step  300 .  
      If at step  304  the system determines that the maximum air flow is being provided, then at step  310  the logic checks if the trigger  298  is still activated. If it is not the program branches to step  308  and holds the air flow rate (and hence the selected pattern). If at step  310  the trigger is still on, then the program resets the air flow back to the minimum air flow rate at  312  and loops back to step  300 . Alternatively, at step  312  instead of resetting to the minimum flow rate and waiting for another trigger, the program could branch to step  302  and start incrementing again. This alternative method would allow the operator to keep the trigger depressed and observe the spray pattern as the air flow was adjusted through the maximum air flow rate and them incremented again from the minimum air flow rate. As still another alternative, rather than having the operator hold the pattern adjust trigger  298  actuated, the system can be programmed to look for a first actuation and then to stop the adjustment in response to a second actuation of the trigger.  
      As another alternative to the “ramp” feature that is described previously for the pattern shaping air, the control function may be programmed to incorporate a “hi/lo” feature. This “hi/lo” feature would use discrete actuation of the trigger  298  to switch between a “high” and a “low” pattern shaping air flow setting. During normal spraying, say the operator is using the high setting, which he controls from the manual gun controller, to give a large fan pattern. He then comes to an area where he needs a narrow fan pattern to better coat the part. He can actuate trigger  298  once, and the controller will change the flow of pattern shaping air to a lower setting, which the operator has previously set to a certain value through the manual gun controller. A second actuation of trigger  298  will revert the pattern shaping air flow back to the “high” setting.  
      It should be noted that varying the spray pattern by adjusting the air flow can also be implemented in the automatic spray applicator described herein above because the adjustment is essentially a software logic control function. In the automatic gun version the control system could be provided with a switch for the operator to activate to increment the air flow rate to the gun.  
      In accordance with another aspect of the invention, the adjustability of the spray pattern can be implemented with an optional adjustment of the material flow rate from the pump  402 . As will be described hereinbelow, a pump in accordance with the invention can operate with controllable material flow rates, even at rather low flow rates. This control is based in part on various timing functions within the pump. As used in combination with the spray gun, the control system  39  may be programmed so that in response to a change in the spray pattern, the material flow rate is also adjusted. For example, if the operator changes the spray pattern from a large pattern to a smaller pattern, it may be desirable to lower the material flow rate. Vice-versa, if the operator increases the spray pattern size it may be desirable to increase the material flow rate. These complementary adjustments can be incorporated into the part recipes within the control logic of the control system  39 . As another alternative, the control system  39  may be programmed to adjust the material flow rate as a percentage of a change in the pattern size. Adjustment of the flow rate can save on powder since less powder can be used for special touch ups or other spray operations in which a smaller pattern is used. Those skilled in the art will readily appreciate that there are many such related adjustments that can be made in accordance with the invention. The invention provides such flexibility, in part, by providing a pump that has a scalable flow rate (to be described herein below) and a spray gun that has a scalable or at least an adjustable air flow to the air cap.  
      In yet another alternative embodiment, a setup mode can be programmed into the control system  39 . During the setup mode, an operator can activate the pattern adjust trigger, and either in the ramping mode or step mode the operator can observe the spray patter as applied to an object. The operator can then assess the optimal spray pattern for the object. The air setting and flow rate settings at this optimal spray pattern can then be recorded for future reference when the same part is sprayed again. This information could also be entered into the part recipe database so that the control system  39  can automatically select the pattern and material flow rates the next time that the system is used to spray that part with a similar coating material.  
      With reference to  FIGS. 10A, 10B  and  10 C there is illustrated an exemplary embodiment of a dense phase pump  402  in accordance with the present invention. Although the pump  402  can be used as a transfer pump as well, it is particularly designed as a gun pump for supplying material to the spray applicators  20 . The gun pumps  402  and transfer pumps  400  and  410  share many common design features which will be readily apparent from the detailed descriptions herein.  
      The pump  402  is preferably although need not be modular in design. The modular construction of the pump  402  is realized with a pump manifold body  414  and a valve body  416 . The manifold body  414  houses a pair of pump chambers along with a number of air passages as will be further explained herein. The valve body  416  houses a plurality of valve elements as will also be explained herein. The valves respond to air pressure signals that are communicated into the valve body  416  from the manifold body  414 . Although the exemplary embodiments herein illustrate the use of pneumatic pinch valves, those skilled in the are will readily appreciate that various aspects and advantages of the present invention can be realized with the use of other control valve designs other than pneumatic pinch valves.  
      The upper portion  402   a  of the pump is adapted for purge air arrangements  418   a  and  418   b , and the lower portion  402   b  of the pump is adapted for a powder inlet hose connector  420  and a powder outlet hose connector  422 . A powder feed hose  24  ( FIG. 1 ) is connected to the inlet connector  420  to supply a flow of powder from a supply such as the feed hopper  22 . A powder supply hose  406  ( FIG. 1 ) is used to connect the outlet  422  to a spray applicator whether it be a manual or automatic spray gun positioned up at the spray booth  12 . The powder supplied to the pump  402  may, but not necessarily must, be fluidized.  
      Powder flow into an out of the pump  402  thus occurs on a single end  402   b  of the pump. This allows a purge function  418  to be provided at the opposite end  402   a  of the pump thus providing an easier purging operation as will be further explained herein.  
      If there were only one pump chamber (which is a useable embodiment of the invention) then the valve body  416  could be directly connected to the manifold because there would only be the need for two powder paths through the pump. However, in order to produce a steady, consistent and adjustable flow of powder from the pump, two or more pump chambers are provided. When two pump chambers are used, they are preferably operated out of phase so that as one chamber is receiving powder from the inlet the other is supplying powder to the outlet. In this way, powder flows substantially continuously from the pump. With a single chamber this would not be the case because there is a gap in the powder flow from each individual pump chamber due to the need to first fill the pump chamber with powder. When more than two chambers are used, their timing can be adjusted as needed. In any case it is preferred though not required that all pump chambers communicate with a single inlet and a single outlet.  
      In accordance with one aspect of the present invention, material flow into and out of each of the pump chambers is accomplished at a single end of the chamber. This provides an arrangement by which a straight through purge function can be used at an opposite end of the pump chamber. Since each pump chamber communicates with the same pump inlet and outlet in the exemplary embodiment, additional modular units are used to provide branched powder flow paths in the form of Y blocks.  
      A first Y-block  424  is interconnected between the manifold body  414  and the valve body  416 . A second Y-block  426  forms the inlet/outlet end of the pump and is connected to the side of the valve body  416  that is opposite the first Y-block  424 . A first set of bolts  428  are used to join the manifold body  414 , first Y-block  424  and the valve body  416  together. A second set of bolts  430  are used to join the second Y-block  426  to the valve body  416 . Thus the pump in  FIG. 10A  when fully assembled is very compact and sturdy, yet the lower Y-block  426  can easily and separately be removed for replacement of flow path wear parts without complete disassembly of the pump. The first Y-block  424  provides a two branch powder flow path away from each powder chamber. One branch from each chamber communicates with the pump inlet  420  through the valve body  416  and the other branch from each chamber communicates with the pump outlet  422  through the valve body  416 . The second Y-block  426  is used to combine the common powder flow paths from the valve body  416  to the inlet  420  and outlet  422  of the pump. In this manner, each pump chamber communicates with the pump inlet through a control valve and with the pump outlet through another control valve. Thus, in the exemplary embodiment, there are four control valves in the valve body that control flow of powder into and out of the pump chambers.  
      The manifold body  414  is shown in detail in  FIGS. 10B, 10E ,  10 G,  11 A and  11 B. The manifold  414  includes a body  432  having first and second bores therethrough  434 ,  436  respectively. Each of the bores receives a generally cylindrical gas permeable filter member  438  and  440  respectively. The gas permeable filter members  438 ,  440  include lower reduced outside diameter ends  438   a  and  440   a  which insert into a counterbore inside the first Y-block  424  ( FIG. 12B ) which helps to maintain the members  438 ,  440  aligned and stable. The upper ends of the filter members abut the bottom ends of purge air fittings  504  with appropriate seals as required. The filter members  438 ,  440  each define an interior volume ( 438   c ,  440   c ) that serves as a powder pump chamber so that there are two pump powder chambers provided in this embodiment. A portion of the bores  434 ,  436  are adapted to receive the purge air arrangements  418   a  and  418   b  as will be described hereinafter.  
      The filter members  438 ,  440  may be identical and allow a gas, such as ordinary air, to pass through the cylindrical wall of the member but not powder. The filter members  438 ,  440  may be made of porous polyethylene, for example. This material is commonly used for fluidizing plates in powder feed hoppers. An exemplary material has about a forty micron opening size and about a 40-50 percent porosity. Such material is commercially available from Genpore or Poron. Other porous materials may be used as needed. The filter members  438 ,  440  each have a diameter that is less than the diameter of its associated bore  434 ,  436  so that a small annular space is provided between the wall of the bore and the wall of the filter member (see  FIGS. 10E, 10G ). This annular space serves as a pneumatic pressure chamber. When a pressure chamber has negative pressure applied to it, powder is drawn up into the powder pump chamber and when positive pressure is applied to the pressure chamber the powder in the powder pump chamber is forced out.  
      The manifold body  432  includes a series of six inlet orifices  442 . These orifices  442  are used to input pneumatic energy or signals into the pump. Four of the orifices  442   a, c, d  and  f  are in fluid communication via respective air passages  444   a, c, d  and  f  with a respective pressure chamber  446  in the valve block  416  and thus are used to provide valve actuation air as will be explained hereinafter. Note that the air passages  444  extend horizontally from the manifold surface  448  into the manifold body and then extend vertically downward to the bottom surface of the manifold body where they communicate with respective vertical air passages through the upper Y-block  424  and the valve body  416  wherein they join to respective horizontal air passages in the valve body  416  to open into each respective valve pressure chamber. Air filters (not shown) may be included in these air passages to prevent powder from flowing up into the pump manifold  414  and the supply manifold  404  in the event that a valve element or other seal should become compromised. The remaining two orifices,  442   b  and  442   e  are respectively in fluid communication with the bores  434 ,  436  via air passages  444   b  and  444   e . These orifices  442   b  and  442   e  are thus used to provide positive and negative pressure to the pump pressure chambers in the manifold body.  
      The orifices  442  are preferably, although need not be, formed in a single planar surface  448  of the manifold body. The air supply manifold  404  includes a corresponding set of orifices that align with the pump orifices  442  and are in fluid communication therewith when the supply manifold  404  is mounted on the pump manifold  414 . In this manner the supply manifold  404  can supply all required pump air for the valves and pump chambers through a simple planar interface. A seal gasket  450  is compressed between the faces of the pump manifold  414  and the supply manifold  404  to provide fluid tight seals between the orifices. Because of the volume, pressure and velocity desired for purge air, preferably separate purge air connections are used between the supply manifold and the pump manifold. Although the planar interface between the two manifolds is preferred it is not required, and individual connections for each pneumatic input to the pump from the supply manifold  404  could be used as required. The planar interface allows for the supply manifold  404 , which in some embodiments includes electrical solenoids, to be placed inside a cabinet with the pump on the outside of the cabinet (mounted to the supply manifold through an opening in a cabinet wall) so as to help isolate electrical energy from the overall system  10 . It is noted in passing that the pump  402  need not be mounted in any particular orientation during use.  
      With reference to  FIGS. 12A and 12B , the first Y-block  424  includes first and second ports  452 ,  454  that align with their respective pump chamber  434 ,  436 . Each of the ports  452 ,  454  communicates with two branches  452   a ,  452   b  and  454   a ,  454   b  respectively ( FIG. 12B  only shows the branches for the port  452 ). Thus, the port  452  communicates with branches  452   a  and  452   b . Therefore, there are a total of four branches in the first Y-block  424  wherein two of the branches communicate with one pressure chamber and the other two communicate with the other pressure chamber. The branches  452   a, b  and  454   a, b  form part of the powder path through the pump for the two pump chambers. Flow of powder through each of the four branches is controlled by a separate pinch valve in the valve body  416  as will be described herein. Note that the Y-block  424  also includes four through air passages  456   a, c, d, f  which are in fluid communication with the air passages  444   a, c, d  and  f  respectively in the manifold body  414 . A gasket  459  may be used to provide fluid tight connection between the manifold body  414  and the first Y-block  424 .  
      The ports  452  and  454  include counterbores  458 ,  460  which receive seals  462 ,  464  ( FIG. 10C ) such as conventional o-rings. These seals provide a fluid tight seal between the lower ends of the filter members  438 ,  440  and the Y-block ports  452 ,  454 . They also allow for slight tolerance variations so that the filter members are tightly held in place.  
      With additional reference to  FIGS. 13A and 13B , the valve body  416  includes four through bores  446   a ,  446   b ,  446   c  and  446   d  that function as pressure chambers for a corresponding number of pinch valves. The upper surface  466  of the valve body includes two recessed regions  468  and  470  each of which includes two ports, each port being formed by one end of a respective bore  446 . In this embodiment, the first recessed portion  468  includes orifices  472  and  474  which are formed by their respective bores  446   b  and  446   a  respectively. Likewise, the second recessed portion  470  includes orifices  476  and  478  which are formed by their respective bores  446   d  and  446   c  respectively. Corresponding orifices are formed on the opposite side face  479  of the valve body  416 .  
      Each of the pressure chambers  446   a - d  retains either an inlet pinch valve element  480  or an outlet pinch valve  481 . Each pinch valve element  480 ,  481  is a fairly soft flexible member made of a suitable material, such as for example, natural rubber, latex or silicone. Each valve element  480 ,  481  includes a central generally cylindrical body  482  and two flanged ends  484  of a wider diameter than the central body  482 . The flanged ends function as seals and are compressed about the bores  446   a - d  when the valve body  416  is sandwiched between the first Y-block  424  and the second Y-block  426 . In this manner, each pinch valve defines a flow path for powder through the valve body  416  to a respective one of the branches  452 ,  454  in the first Y-block  424 . Therefore, one pair of pinch valves (a suction valve and a delivery valve) communicates with one of the pump chambers  440  in the manifold body while the other pair of pinch valves communicates with the other pump chamber  438 . There are two pinch valves per chamber because one pinch valve controls the flow of powder into the pump chamber (suction) and the other pinch valve controls the flow of powder out of the pump chamber (delivery). The outer diameter of each pinch valve central body portion  482  is less than the bore diameter of its respect pressure chamber  446 . This leaves an annular space surrounding each pinch valve that functions as the pressure chamber for that valve.  
      The valve body  416  includes air passages  486   a - d  that communicate respectively with the four pressure chamber bores  446   a - d . as illustrated in  FIG. 13B . These air passages  486   a - d  include vertical extensions (as viewed in  FIG. 13B )  488   a - d . These four air passage extensions  488   a, b, c, d  respectively are in fluid communication with the vertical portions of the four air passages  444   d, f, a, c  in the manifold  414  and the vertical passages  456   d , f, a, c in the upper Y-block  424 . Seals  490  are provided for air tight connections.  
      In this manner, each of the pressure chambers  446  in the valve body  416  is in fluid communication with a respective one of the air orifices  442  in the manifold body  414 , all through internal passages through the manifold body, the first Y-block and the valve body. When positive air pressure is received from the supply manifold  404  ( FIG. 1 ) into the pump manifold  414 , the corresponding valve  480 ,  481  is closed by the force of the air pressure acting against the outer flexible surface of the flexible valve body. The valves open due to their own resilience and elasticity when external air pressure in the pressure chamber is removed. This true pneumatic actuation avoids any mechanical actuation or other control member being used to open and close the pinch valves which is a significant improvement over the conventional designs. Each of the four pinch valves  480 ,  481  is preferably separately controlled for the gun pump  402 .  
      In accordance with another aspect of the invention, the valve body  416  is preferably made of a sufficiently transparent material so that an operator can visually observe the opening and closing of the pinch valves therein. A suitable material is acrylic but other transparent materials may be used. The ability to view the pinch valves also gives a good visual indication of a pinch valve failure since powder will be visible.  
      With additional reference to  FIGS. 14A and 14B , the remaining part of the pump is the inlet end  402   b  formed by a second Y-block end body  492 . The end body  492  includes first and second recesses  494 ,  496  each of which is adapted to receive a Y-block  498   a  and  498   b . One of the Y-blocks is used for powder inlet and the other is used for powder outlet. Each Y-block  498  is a wear component due to exposure of its internal surfaces to powder flow. Since the body  492  is simply bolted to the valve body  416 , it is a simple matter to replace the wear parts by removing the body  492 , thus avoiding having to disassemble the rest of the pump.  
      Each Y-block  498  includes a lower port  500  that is adapted to receive a fitting or other suitable hose connector  420 ,  422  ( FIG. 10A ) with one fitting connected to a hose  24  that runs to a powder supply and another hose  406  to a spray applicator such as a spray gun  20  ( FIG. 1 ). Each Y-block includes two powder path branches  502   a ,  502   b ,  502   c  and  502   d  that extend away from the port  500 . Each powder path in the second Y-blocks  498  are in fluid communication with a respective one of the pinch valves  480 ,  481  in the pinch valve body  416 . Thus, powder that enters the pump at the inlet  420  branches through a first of the two lower Y-blocks  498  into two of the pinch valves and from there to the pump chambers. Likewise powder from the two pump chambers recombine from the other two pinch valves into a single outlet  422  by way of the other lower Y-block  498 .  
      The powder flow paths are as follows. Powder enters through a common inlet  420  and branches via paths  502   a  or  502   b  in the lower Y-block  498   b  to the two inlet or suction pinch valves  480 . Each of the inlet pinch valves  480  is connected to a respective one of the powder pump chambers  434 ,  436  via a respective one branch  452 ,  454  of a respective path through the first or upper Y-block  424 . Each of the other branches  452 ,  454  of the upper Y-block  424  receive powder from a respective pump chamber, with the powder flowing through the first Y-block  424  to the two outlet or delivery pinch valves  481 . Each of the outlet pinch valves  481  is also connected to a respect one of the branches  502  in the lower Y-block  498   a  wherein the powder from both pump chambers is recombined to the single outlet  422 .  
      The pneumatic flow paths are as follows. When any of the pinch valves is to be closed, the supply manifold  404  issues a pressure increase at the respective orifice  442  in the manifold body  414 . The increased air pressure flows through the respective air passage  442 ,  444  in the manifold body  414 , down through the respective air passage  456  in the first Y-block  424  and into the respective air passage  486  in the valve body  416  to the appropriate pressure chamber  446 .  
      It should be noted that a pump in accordance with the present invention provides for a scalable flow rate based on percent fill of the powder pump chambers, meaning that the flow rate of powder from the pump can be accurately controlled by controlling the open time of the pinch valves that feed powder to the pump chambers. This allows the pump cycle (i.e. the time duration for filling and emptying the pump chambers) to be short enough so that a smooth flow of powder is achieved independent of the flow rate, with the flow rate being separately controlled by operation of the pinch valves. Thus, flow rate can be adjusted entirely by control of the pinch valves without necessarily having to make any physical changes to the pump.  
      The purge function is greatly simplified in accordance with another aspect of the invention. Because the invention provides a way for powder to enter and exit the pump chambers from a single end, the opposite end of the pump chamber can be used for purge air. With reference to  FIGS. 10A, 10C ,  10 E and  10 G, a purge air fitting  504  is inserted into the upper end of its respective pump chamber  438 ,  440 . The fittings  504  receive respective check valves  506  that are arranged to only permit flow into the pump chambers  438 ,  440 . The check valves  506  receive respective purge air hose fittings  508  to which a purge air hose can be connected. Purge air is supplied to the pump from the supply manifold  404  as will be described hereinbelow. The purge air thus can flow straight through the powder pump chambers and through the rest of the powder path inside the pump to very effectively purge the pump for a color change operation. No special connections or changes need to be made by the operator to effect this purging operation, thereby reducing cleaning time. Once the system  10  is installed, the purging function is always connected and available, thereby significantly reducing color change time because the purging function can be executed by the control system  39  without the operator having to make or break any powder or pneumatic connections with the pump.  
      Note from  FIGS. 1 and 10 A that with all four pinch valves  480 ,  481  in an open condition purge air will flow straight through the pump chambers, through the powder paths in the first Y-block  424 , the pinch valves themselves  480 ,  481 , the second Y-block  498  and out both the inlet  420  and the outlet  422 . Purge air thus can be supplied throughout the pump and then on to the spray applicator to purge that device as well as to purge the feed hoses back to the powder supply  22 . Thus in accordance with the invention, a dense phase pump concept is provided that allows forward and reverse purging.  
      With reference to  FIG. 15 , the supply manifold  404  illustrated is in essence a series of solenoid valves and air sources that control the flow of air to the pump  402 . The particular arrangement illustrated in  FIG. 15  is exemplary and not intended to be limiting. The supply of air to operate the pump  402  can be done without a manifold arrangement and in a wide variety of ways. The embodiment of  FIG. 15  is provided as it is particularly useful for the planar interface arrangement with the pump, however, other manifold designs can also be used.  
      The supply manifold  404  includes a supply manifold body  510  that has a first planar face  512  that is mounted against the surface  448  of the pump manifold body  414  ( FIG. 11A ) as previously described herein. Thus the face  512  includes six orifices  514  that align with their respective orifices  442  in the pump manifold  414 . The supply manifold body  510  is machined to have the appropriate number and location of air passages therein so that the proper air signals are delivered to the orifices  514  at the correct times. As such, the manifold further includes a series of valves that are used to control the flow of air to the orifices  514  as well as to control the purge air flow. Negative pressure is generated in the manifold  404  by use of a conventional venturi pump  518 . System or shop air is provided to the manifold  404  via appropriate fittings  520 . The details of the physical manifold arrangement are not necessary to understand and practice the present invention since the manifold simply operates to provide air passages for air sources to operate the pump and can be implemented in a wide variety of ways. Rather, the details of note are described in the context of a schematic diagram of the pneumatic flow. It is noted at this time, however, that in accordance with another aspect of the invention, a separate control valve is provided for each of the pinch valves in the valve body  414  for purposes that will be described hereinafter.  
      With reference to  FIG. 16 , a pneumatic diagram is provided for a first embodiment of the invention. Main air  408  enters the supply manifold  404  and goes to a first regulator  532  to provide pump pressure source  534  to the pump chambers  438 ,  440 , as well as pattern shaping air source  405  to the spray applicator  20  via air hose  406 . Main air also is used as purge air source  536  under control of a purge air solenoid valve  538 . Main air also goes to a second regulator  540  to produce venturi air pressure source  542  used to operate the venturi pump (to produce the negative pressure to the pump chambers  438 ,  440 ) and also to produce pinch air source  544  to operate the pinch valves  480 ,  481 .  
      In accordance with another aspect of the invention, the use of the solenoid control valve  538  or other suitable control device for the purge air provides multiple purge capability. The first aspect is that two or more different purge air pressures and flows can be selected, thus allowing a soft and hard purge function. Other control arrangements besides a solenoid valve can be used to provide two or more purge air flow characteristics. The control system  39  selects soft or hard purge, or a manual input could be used for this selection. For a soft purge function, a lower purge air flow is supplied through the supply manifold  404  into the pump pressure chambers  434 ,  436  which is the annular space between the porous members  438 ,  440  and their respective bores  434 ,  436 . The control system  39  further selects one set of pinch valves (suction or delivery) to open while the other set is closed. The purge air bleeds through the porous filters  438 ,  440  and out the open valves to either purge the system forward to the spray gun  20  or reverse (backward) to the supply  22 . The control system  39  then reverses which pinch valves are open and closed. Soft purge may also be done in both directions at the same time by opening all four pinch valves. Similarly, higher purge air pressure and flow may be used for a hard purge function forward, reverse or at the same time. The purge function carried out by bleeding air through the porous members  438 ,  440  also helps to remove powder that has been trapped by the porous members, thus extending the useful life of the porous members before they need to be replaced.  
      Hard or system purge can also be effected using the two purge arrangements  418   a  and  418   b . High pressure flow air can be input through the purge air fittings  508  (the purge air can be provided from the supply manifold  404 ) and this air flows straight through the powder pump chambers defined in part by the porous members  438 ,  440  and out the pump. Again, the pinch valves  480 ,  481  can be selectively operated as desired to purge forward or reverse or at the same time.  
      It should be noted that the ability to optionally purge in only the forward or reverse direction provides a better purging capability because if purging can only be done in both directions at the same time, the purge air will flow through the path of least resistance whereby some of the powder path regions may not get adequately purged. Fir example, when trying the purge a spray applicator and a supply hopper, if the applicator is completely open to air flow, the purge air will tend to flow out the applicator and might not adequately purge the hopper or supply.  
      The invention thus provides a pump design by which the entire powder path from the supply to and through the spray guns can be purged separately or at the same time with virtually no operator action required. The optional soft purge may be useful to gently blow out residue powder from the flow path before hitting the powder path with hard purge air, thereby preventing impact fusion or other deleterious effects from a hard purge being performed first.  
      The positive air pressure  542  for the venturi enters a control solenoid valve  546  and from there goes to the venturi pump  518 . The output  518   a  of the venturi pump is a negative pressure or partial vacuum that is connected to an inlet of two pump solenoid valves  548 ,  550 . The pump valves  548  and  550  are used to control whether positive or negative pressure is applied to the pump chambers  438 ,  440 . Additional inputs of the valves  548 ,  550  receive positive pressure air from a first servo valve  552  that receives pump pressure air  534 . The outlets of the pump valves  548 ,  550  are connected to a respective one of the pump chambers through the air passage scheme described hereinabove. Note that the purge air  536  is schematically indicated as passing through the porous tubes  438 ,  440 .  
      Thus, the pump valves  550  and  552  are used to control operation of the pump  402  by alternately applying positive and negative pressure to the pump chambers, typically 180° out of phase so that as one chamber is being pressurized the other is under negative pressure and vice-versa. In this manner, one chamber is filling with powder while the other chamber is emptying. It should be noted that the pump chambers may or may not completely “fill” with powder. As will be explained herein, very low powder flow rates can be accurately controlled using the present invention by use of the independent control valves for the pinch valves. That is, the pinch valves can be independently controlled apart from the cycle rate of the pump chambers to feed more or less powder into the chambers during each pumping cycle.  
      Pinch valve air  544  is input to four pinch valve control solenoids  554 ,  556 ,  558  and  560 . Four valves are used so that there is preferably independent timing control of the operation of each of the four pinch valves  480 ,  481 . In  FIG. 16 , “delivery pinch valve” refers to those two pinch valves  481  through which powder exits the pump chambers and “suction pinch valve” refers to those two pinch valves  480  through which powder is fed to the pump chambers. Though the same reference numeral is used, each suction pinch valve and each delivery pinch valve is separately controlled.  
      A first delivery solenoid valve  554  controls air pressure to a first delivery pinch valve  481 ; a second delivery solenoid valve  558  controls air pressure to a second delivery pinch valve  481 ; a first suction solenoid valve  556  controls air pressure to a first suction pinch valve  480  and a second suction solenoid valve  560  controls air pressure to a second suction pinch valve  480 .  
      The pneumatic diagram of  FIG. 16  thus illustrates the functional air flow that the manifold  404  produces in response to various control signals from the control system  39  ( FIG. 1 ).  
      With reference to  FIGS. 17A and 17B , and in accordance with another aspect of the invention, a transfer pump  400  is also contemplated. Many aspects of the transfer pump are the same or similar to the spray applicator pump  402  and therefore need not be repeated in detail.  
      Although a gun pump  402  may be used as a transfer pump as well, a transfer pump is primarily used for moving larger amounts of powder between receptacles as quickly as needed. Moreover, although a transfer pump as described herein will not have the same four way independent pinch valve operation, a transfer valve may be operated with the same control process as the gun pump. For example, some applications require large amounts of material to be applied over large surfaces yet maintaining control of the finish. A transfer pump could be used as a pump for the applicators by also incorporating the four independent pinch valve control process described herein.  
      In the system of  FIG. 1 a  transfer pump  400  is used to move powder from the recovery system  28  (such as a cyclone) back to the feed center  22 . A transfer pump  410  is also used to transfer virgin powder from a supply, such as a box, to the feed center  22 . In such examples as well as others, the flow characteristics are not as important in a transfer pump because the powder flow is not being sent to a spray applicator. In accordance then with an aspect of the invention, the gun pump is modified to accommodate the performance expectations for a transfer pump.  
      In the transfer pump  400 , to increase the powder flow rate larger pump chambers are needed. In the embodiment of  FIGS. 17A and 17B , the pump manifold is now replaced with two extended tubular housings  564  and  566  which enclose lengthened porous tubes  568  and  570 . The longer tubes  568 ,  570  can accommodate a greater amount of powder during each pump cycle. The porous tubes  568 ,  570  have a slightly smaller diameter than the housings  564 ,  566  so that an annular space is provided therebetween that serves as a pressure chamber for both positive and negative pressure. Air hose fittings  572  and  574  are provided to connect air hoses that are also connected to a source of positive and negative pressure at a transfer pump air supply system to be described hereinafter. Since a pump manifold is not being used, the pneumatic energy is individually plumbed into the pump  400 .  
      The air hose fittings  572  and  574  are in fluid communication with the pressure chambers within the respective housings  564  and  566 . In this manner, powder is drawn into and pushed out of the powder chambers  568 ,  570  by negative and positive pressure as in the gun pump design. Also similarly, purge port arrangements  576  and  578  are provided and function the same way as in the gun pump design, including check valves  580 ,  582 .  
      A valve body  584  is provided that houses four pinch valves  585  which control the flow of powder into and out of the pump chambers  568  and  570  as in the gun pump design. As in the gun pump, the pinch valves are disposed in respective pressure chambers in the valve body  584  such that positive air pressure is used to close a valve and the valves open under their own resilience when the positive pressure is removed. A different pinch valve actuation scheme however is used as will be described shortly. An upper Y-block  586  and a lower Y-block  588  are also provided to provide branched powder flow paths as in the gun pump design. The lower Y-block  588  thus is also in communication with a powder inlet fitting  590  and a powder outlet fitting  592 . Thus, powder in from the single inlet flows to both pump chambers  568 ,  570  through respective pinch valves and the upper Y-block  586 , and powder out of the pump chambers  568 ,  570  flows through respective pinch valves to the single outlet  592 . The branched powder flow paths are realized in a manner similar to the gun pump embodiment and need not be repeated herein. The transfer pump may also incorporate replaceable wear parts or inserts in the lower Y-block  588  as in the gun pump.  
      Again, since a pump manifold is not being used in the transfer pump, separate air inlets  594  and  596  are provided for operation of the pinch valves which are disposed in pressure chambers as in the gun pump design. Only two air inlets are needed even though there are four pinch valves for reasons set forth below. An end cap  598  may be used to hold the housings in alignment and provide a structure for the air fittings and purge fittings.  
      Because quantity of flow is of greater interest in the transfer pump than quality of the powder flow, individual control of all four pinch valves is not needed although it could alternatively be done. As such, pairs of the pinch valves can be actuated at the same time, coincident with the pump cycle rate. In other words, when the one pump chamber is filling with powder, the other is discharging powder, and respective pairs of the pinch valves are thus open and closed. The pinch valves can be actuated synchronously with actuation of positive and negative pressure to the pump chambers. Moreover, single air inlets to the pinch valve pressure chambers can be used by internally connecting respective pairs of the pressure chambers for the pinch valve pairs that operate together. Thus, two pinch valves are used as delivery valves for powder leaving the pump, and two pinch valves are used as suction valves for powder being drawing into the pump. However, because the pump chambers alternate delivery and suction, during each half cycle there is one suction pinch valve open and one delivery pinch valve open, each connected to different ones of the pump chambers. Therefore, internally the valve body  584  the pressure chamber of one of the suction pinch valves and the pressure chamber for one of the delivery pinch valves are connected together, and the pressure chambers of the other two pinch valves are also connected together. This is done for pinch valve pairs in which each pinch valve is connected to a different pump chamber. The interconnection can be accomplished by simply providing cross-passages within the valve body between the pair of pressure chambers.  
      With reference to  FIG. 18 , the pneumatic diagram for the transfer pump  400  is somewhat more simplified than for a pump that is used with a spray applicator. Main air  408  is input to a venturi pump  600  that is used to produce negative pressure for the transfer pump chambers. Main air also is input to a regulator  602  with delivery air being supplied to respective inputs to first and second chamber solenoid valves  604 ,  606 . The chamber valves also receive as an input the negative pressure from the venturi pump  600 . The solenoid valves  604 ,  606  have respective outputs  608 ,  610  that are in fluid communication with the respective pressure chambers of the transfer pump.  
      The solenoid valves in this embodiment are air actuated rather than electrically actuated. Thus, air signals  612  and  614  from a pneumatic timer or shuttle valve  616  are used to alternate the valves  604 ,  606  between positive and negative pressure outputs to the pressure chambers of the pump. An example of a suitable pneumatic timer or shuttle valve is model S9 568/68-1/4-SO available from Hoerbiger-Origa. As in the gun pump, the pump chambers alternate such that as one is filling the other is discharging. The shuttle timer signal  612  is also used to actuate a 4-way valve  618 . Main air is reduced to a lower pressure by a regulator  620  to produce pinch air  622  for the transfer pump pinch valves. The pinch air  622  is delivered to the 4-way valve  618 . The pinch air is coupled to the pinch valves  624  for the one pump chamber and  626  for the other pump chamber such that associated pairs are open and closed together during the same cycle times as the pump chambers. For example, when the delivery pinch valve  624   a  is open to the one pump chamber, the delivery pinch valve  626   a  for the other pump chamber is closed, while the suction pinch valve  624   b  is closed and the suction pinch valve  626   b  is open. The valves reverse during the second half of each pump cycle so that the pump chambers alternate as with the gun pump. Since the pinch valves operate on the same timing cycle as the pump chambers, a continuous flow of powder is achieved.  
       FIG. 19  illustrates an alternative embodiment of the transfer pump pneumatic circuit. In this embodiment, the basic operation of the pump is the same, however, now a single valve  628  is used to alternate positive and negative pressure to the pump chambers. In this case, a pneumatic frequency generator  630  is used. A suitable device is model 81 506 490 available from Crouzet. The generator  630  produces a varying air signal that actuates the chamber 4-way valve  628  and the pinch air 4-way valve  618 . As such, the alternating cycles of the pump chambers and the associated pinch valves is accomplished.  
       FIG. 20  illustrates a flow control aspect of the present invention that is made possible by the independent control of the pinch valves  480 ,  481 . This illustration is for explanation purposes and does not represent actual measured data, but a typical pump in accordance with the present invention will show a similar performance. The graph plots total flow rate in pounds per hour out of the pump versus pump cycle time. A typical pump cycle time of 400 milliseconds means that each pump chamber is filling or discharging during a 400 msec time window as a result of the application of negative and positive pressure to the pressure chambers that surround the porous members. Thus, each chamber fills and discharges during a total time of 800 msec. Graph A shows a typical response if the pinch valves are operated at the same time intervals as the pump chamber. This produces the maximum powder flow for a given cycle time. Thus, as the cycle time increases the amount of powder flow decreases because the pump is operating slower. Flow rate thus increases as the cycle time decreases because the actual time it takes to fill the pump chambers is much less than the pump cycle time. Thus there is a direct relationship between how fast or slow the pump is running (pump cycle time based on the time duration for applying negative and positive pressure to the pump pressure chambers) and the powder flow rate.  
      Graph B is significant because it illustrates that the powder flow rate, especially low flow rates, can be controlled and selected by changing the pinch valve cycle time relative to the pump cycle time. For example, by shortening the time that the suction pinch valves stay open, less powder will enter the pump chamber, no matter how long the pump chamber is in suction mode. In  FIG. 20 , for example, graph A shows that at pump cycle time of 400 msec, a flow rate of about 39 pounds per hour is achieved, as at point X. If the pinch valves however are closed in less than 400 msec time, the flow rated drops to point Y or about 111 pounds per hour, even though the pump cycle time remains at 400 msec. What this assures is a smooth consistent powder flow even at low flow rates. Smoother powder flow is effected by higher pump cycle rates, but as noted above this would also produce higher powder flow rates. So to achieve low powder flow rates but with smooth powder flow, the present invention allows control of the powder flow rate even for faster pump cycle rates, because of the ability to individually control operation of the suction pinch valves, and optionally the delivery pinch valves as well. An operator can easily change flow rate by simply entering in a desired rate. The control system  39  is programmed so that the desired flow rate is effected by an appropriate adjustment of the pinch valve open times. It is contemplated that the flow rate control is accurate enough that in effect this is an open loop flow rate control scheme, as opposed to a closed loop system that uses a sensor to measure actual flow rates. Empirical data can be collected for given overall system designs to measure flow rates at different pump cycle and pinch valve cycle times. This empirical data is then stored as recipes for material flow rates, meaning that if a particular flow rate is requested the control system will know what pinch valve cycle times will achieve that rate. Control of the flow rate, especially at low flow rates, is more accurate and produces a better, more uniform flow by adjusting the pinch valve open or suction times rather than slowing down the pump cycle times as would have to be done with prior systems. Thus the invention provides a scalable pump by which the flow rate of material from the pump can be, if desired, controlled without changing the pump cycle rate.  
       FIG. 21  further illustrates the pump control concept of the present invention. Graph A shows flow rate versus pinch valve open duration at a pump cycle rate of 500 msec, and Graph B shows the data for a pump cycle rate of 800 msec. Both graphs are for dual chamber pumps as described herein. First it will be noted that for both graphs, flow rate increases with increasing pinch valve open times. Graph B shows however that the flow rate reaches a maximum above a determinable pinch valve open duration. This is because only so much powder can fill the pump chambers regardless of how long the pinch valves are open. Graph A would show a similar plateau if plotted out for the same pinch valve duration times. Both graphs also illustrate that there is a determinable minimum pinch valve open duration in order to get any powder flow from the pump. This is because the pinch valves must be open long enough for powder to actually be sucked into and pushed out of the pump chambers. Note that in general the faster pump rate of Graph A provides a higher flow rate for a given pinch valve duration.  
      The data and values and graphs provided herein are intended to be exemplary and non-limiting as they are highly dependent on the actual pump design. The control system  39  is easily programmed to provide variable flow rates by simply having the control system  39  adjust the valve open times for the pinch valves and the suction/pressure times for the pump chambers. These functions are handled by the material flow rate control  672  process.  
      In an alternative embodiment, the material flow rate from the pump can be controlled by adjusting the time duration that suction is applied to the pump pressure chamber to suck powder into the powder pump chamber. While the overall pump cycle may be kept constant, for example 800 msec, the amount of time that suction is actually applied during the 400 msec fill time can be adjusted so as to control the amount of powder that is drawn into the powder pump chamber. The longer the vacuum is applied, the more powder is pulled into the chamber. This allows control and adjustment of the material flow rate separate from using control of the suction and delivery pinch valves.  
      Use of the separate pinch valve controls however can augment the material flow rate control of this alternative embodiment. For example, as noted the suction time can be adjusted so as to control the amount of powder sucked into the powder chamber each cycle. By also controlling operation of the pinch valves, the timing of when this suction occurs can also be controlled. Suction will only occur while negative pressure is applied to the pressure chamber, but also only while the suction pinch valve is open. Therefore, at the time that the suction time is finished, the suction pinch valve can be closed and the negative pressure to the pressure chamber can be turned off. This has several benefits. One benefit is that by removing the suction force from the pressure chamber, less pressurized air consumption is needed for the venturi pump that creates the negative pressure. Another benefit is that the suction period can be completely isolated from the delivery period (the delivery period being that time period during which positive pressure is applied to the pressure chamber) so that there is no overlap between suction and delivery. This prevents backflow from occurring between the transition time from suction to delivery of powder in the powder pump chamber. Thus, by using independent pinch valve control with the use of controlling the suction time, the timing of when suction occurs can be controlled to be, for example, in the middle of the suction portion of the pump cycle to prevent overlap into the delivery cycle when positive pressure is applied. As in the embodiment herein of using the pinch valves to control material flow rate, this alternative embodiment can utilize empirical data or other appropriate analysis to determine the appropriate suction duration times and optional pinch valve operation times to control for the desired flow rates.  
      Thus, the invention contemplates a scalable material flow rate pump output by which is meant that the operator can select the output flow rate of the pump without having to make any changes to the system other than to input the desired flow rate. This can be done through any convenient interface device such as a keyboard or other suitable mechanism, or the flow rates can be programmed into the control system  39  as part of the recipes for applying material to an object. Such recipes commonly include such things as flow rates, voltages, air flow control, pattern shaping, trigger times and so on.  
      In accordance with further aspects of the invention, a supply for material to a material application system is contemplated that dramatically improves cleanability and ease of use over conventional hopper and other container type designs, thereby also producing a dramatic improvement in color change time. These improvements derive from several unique combinations, sub-combinations and implementation of various functions that heretofore has been carried out separately in a material application system. These functions include, but are not necessarily limited to, a material container or hopper, a material recovery system, a fluidizing arrangement, a sieving arrangement and a suction interface between the container and one or more pumps. In prior systems, the implementation of these various functions led to various structural features and limitations that made cleaning and color change a rather time consuming and labor intensive undertaking. By implementing a drastic departure from conventional implementation approaches, the present invention provides a supply that is easier and faster to use and to clean, and can be used with dense phase and dilute phase transport processes.  
      Thus, in accordance with one aspect of the invention, a material supply is provided that is not a conventional container, such as a fluidizing box or hopper, but rather takes a form that facilitates cleaning the supply by an interface with a rather high volume air flow. The exemplary embodiments of the supply are realized in the form of a duct that can be connected and disconnected from a source of negative pressure, especially negative pressure associated with a high volume of air flow. One opening to the duct is available to the negative pressure source, and optionally another opening to the duct is releasably closed by a fluidizing arrangement. A suction interface is also optionally provided with the supply. Thus, the negative pressure air flow cleans not only the duct but also the fluidizing arrangement and the suction interface. The invention especially contemplates interfacing the supply to an air flow system that establishes containment air flow for the spray booth that originates from a material overspray recovery system such as a cyclone and/or filter recovery system. In the exemplary embodiment herein the supply duct is connectable to a filtered flow of air, in this case an after filter unit. In accordance with further aspects of the invention, the supply can optionally accommodate powder feed from a virgin supply, such as a conventional box, and from a recovery system, or both at the same time. Still further, the supply can optionally accommodate a removable sieving arrangement, also with an optional and integrated vibration function.  
      With reference to  FIG. 22  then, a supply  22  in accordance with the present invention is illustrated without being fully interconnected to other functions of the material application system  10 . The supply  22  (as used herein with respect to the invention, the words “supply  22 ” and “hopper  22 ” are used interchangeably) includes a main body or duct  700  that defines an interior volume  702  for holding powder coating material that will be applied to objects transported through the spray booth  12  ( FIG. 1 ). In the exemplary embodiment the body  700  is generally cylindrical in form, although a cylinder is not required. A cylindrical form is preferred as it is easier to clean. But other profiles and shapes, including but not limited to frusto-conical receptacles, may be used as required.  
      An access door  704  is provided in the main body  700 . The access door  704  is hinged and provides access to the interior region  702  of the body  700 . This access door can be used by an operator to add powder manually to the system and can also be used for cleaning the interior surfaces of the supply  22 . The door  704  also provides access to a sieve mounted within the body  700  as will be described in detail hereinafter. In  FIG. 22  the door  704  conforms to the cylindrical shape of the main body  700 , but any shaped door can be used. In other drawings herein, for example, a rectangular door can be provided or other shape as required.  
      In this example, the body  700  is formed by a cylindrical portion of sheet metal in the form of a duct. An upper end  700   a  of the duct is open and is connectable to duct work associated with a powder recovery system, as will be further described herein. A lower portion  700   b  of the duct has a siphon ring  706  mounted thereto. The siphon ring  706  sealingly engages a fluidizing unit  708  and functions as a suction interface between the supply  22  and the pumps  400 ,  402  and  410 . The fluidizing unit  708  is mounted on a support frame  710  that has two legs  712 . The support frame  710  is mounted to a platen  714  that is secured to a lifting mechanism  716 . The lifting mechanism  716  operates to raise and lower the platen  714  and hence the fluidizing unit  708  into and out of sealing contact with the bottom of the siphon ring  706 . The design of the lifting mechanism  716  in this example is a scissors-like mechanism, but any suitable arrangement can be used to effect a vertical lifting and lower function of the frame  710  and fluidizing unit  708 .  
      The supply  22  may be disposed within a supporting structure  718  that includes a ceiling  720  that secures the upper end  700   a  to provide a mounting frame for attachment to additional ductwork as will be described hereinafter. A rear wall  722  serves to partially enclose the structure  718 , and a large bay  724  is provided on one side of the structure. The bay  724  can be used to enclose various support components of the spray application system, including in this example electronics and pneumatic controls associated with the gun and transfer pumps  20 . An equalization duct opening  726  is provided in the rear wall  722 . When the supply  22  is connected into the overall system, as illustrated in additional drawings herein, a containment air flow is produced through the opening  726  that can be used during a color change operation to prevent powder from escaping the interior of the structure  718 . Containment air also flows up into the duct  700  as well as the cyclone during a cleaning operation.  
      At this point it is noted that the supply  22  has two basic operational modes. The first is referred to herein as the supply mode or hopper mode. In this mode, the supply  22  is arranged such that the duct  700  is substantially disconnected from the material recovery system and is in sealed contact with the fluidizing arrangement  708  (via the siphon ring  706 .) The supply  22  thus has a configuration in the supply mode much like a container that holds fluidized powder that is sucked out of the container by operation of the pumps. In the supply mode, the lower opening  726  is in fluid communication with the surrounding atmosphere so that the supply  22  operates generally at ambient pressure. In the exemplary embodiments herein the supply  22 , when being used in the supply mode, is isolated from negative pressure by virtue of the upper damper being closed, the lower damper being open to balance pressure across the duct  700 , and the presence of the transfer pump  400  between the cyclone output and the supply  22  (the pump  400  thus functioning among other things as an isolation device between the supply  22  and the negative pressure of the cyclone.  
      The other operational mode of the supply  22  is a cleaning mode or color change mode. In this mode, the supply  22  is arranged such that the duct  700  is in fluid communication with the material recovery system (e.g. the after filter unit) and the siphon ring  706  (which is mounted to the duct  700 ) is separated from the fluidizing unit  708 . This allows air to enter the duct to remove by suction powder that is in the duct and on the siphon ring and fluidizing bed, as well as to facilitate cleaning the suction ports by reverse purging the pumps.  
      The frame  710  includes an open space between the legs  712 . This space is provided so that an operator can position a box of virgin powder coating material (see  FIG. 27 ) onto the platen  714  and under the fluidizing unit  708 . This arrangement provides for an easy to reach location for a box of virgin powder coating material, but there is no requirement that the virgin powder supply be positioned immediately with the supply  22 , because the transfer pump  410  is used to transfer powder from the box or container to an upper portion of the supply  22  as is later described hereinafter in more detail. But, having the powder box or container near the supply enables the air flow through the opening  726  produced by the powder recovery system to contain powder from the box from flowing outside of the structure  718 . This location also allows powder to be dumped from the supply  22  during a color change operation. A separate or different box could also be used as required.  
      An optional box vibration unit  725  may be mounted on the platen  714 . The vibration unit  725  typically includes a support frame  725   a  and a vibration inducing device  725   b  as is well known.  
      With reference to  FIGS. 23, 24 ,  25  and  26 , the legs  712  of the support frame  710  are attached to a bottom plate  728  of the fluidizing unit  708 . The fluidizing unit  708  includes a plenum  730  which includes the lower plate  728  and an upwardly extending ring  732  that is provided with an inwardly extending lip  734 . The lip  734  provides an annular surface to which a fluidizing member  736  is attached, such as for example, by bolt arrangements  738 . The fluidizing member  736  is made of air permeable material that does not allow the powder material to pass through. The fluidizing member  736  thus may be made of the same material as conventional fluidizing plates, such as for example, partially sintered thermoplastic such as polypropylene available from Porex Technologies. The fluidizing member  736  preferably although not necessarily is a somewhat dish shaped plate having an inwardly and downwardly directed slope towards the center region  736   a  thereof. This slight taper or slope assists powder to fall towards the central region  736   a  and maintain a fluidized condition during a cleaning or color change operation.  
      The fluidizing member  736  includes a peripheral recess portion  740  that receives along its inner edge an annular gasket  742 . The gasket  742  is held in place by an adhesive. A retainer ring  744  that secures the fluidizing member  736  to the plenum  730  as by the bolts  738 . Preferably the gasket  742  includes a generally flat upper surface  742   a  that is flush or nearly flush with the upper surfaces of the fluidizing plate  736  and the retainer ring  744 . This upper surface of the gasket  742  engages with a seal surface of the siphon ring as will be further described hereinafter. Another annular gasket  746  provides a fluid tight seal between the plenum  730  and the fluidizing member  736 . The plenum  730  is thus a air tight box into which pressurized air is introduced through an appropriate fitting (not shown). This pressurized air is forced up through the permeable fluidizing member  736  and fluidizes powder that is present in the interior volume of the siphon ring  706  and lower regions of the cylinder  700 .  
      With the fluidizing unit  730  (which includes the plenum, the fluidizing member and the upper exposed siphon ring gasket) integrally mounted on the support frame  710 , the fluidizing unit can be raised and lowered into and out of sealed contact with a lower seal surface of the siphon ring  706 , by operation of the vertically moveable platen  714 .  
      A central drain hole  748  is provided in the fluidizing bed member  736 . During a color change or cleaning operation fluidized powder will flow down through this hole  748  to a dump valve assembly  750 . The dump valve assembly  750  may be any convenient design, and may be manually operated or under control of an actuator member. In this exemplary embodiment, the dump valve assembly  750  includes a drain  752  that extends from the fluidizing member drain hole  748  through the bottom plate  728  of the plenum  730 . A face gasket or other suitable seal device  754  is used to seal the plenum and trap around the drain hole  748 . The drain  752  prevents powder from getting into the plenum  730  interior. A gasketed valve cap  756  is used to selectively open and close the drain  752 . The cap  756  is hinged so that it can open in response to actuation of a lever  758 . This actuation lever  758  may be operated by a control actuator  760  such as a linear piston type actuator, or other suitable mechanism. An access door  762  is provided so that an operator can have manual access to the actuator  760 . When the valve cap  756  is pivoted away from the drain  752 , fluidized powder will drain into the box or other container B positioned between the support legs  712  of the frame  710 . This allows most of the powder that falls onto the fluidizing plate  736  to be dumped to the box just prior to initiating a color change or cleaning process. The dumped powder can be dropped into a virgin powder supply box B (also labeled  410  in the drawings) or any other suitable container below the drain  752  for disposal or removal as needed.  
      One or more sealed air inlets  764  are provided in the drain  752 . These inlets are used as purge ports to initially clear unfluidized powder from the drain  752  by injecting pressurized air into the trap to remove residue powder from the trap during a color change or cleaning process.  
       FIG. 27  illustrates the supply  22  in an exemplary operational position. A boot  766  covers the lifting mechanism  716  to prevent stray powder from getting into the mechanism and acts as a safety guard. The platen  714  may include the vibration device so as to prevent powder inside the box B from compacting. The transfer pump  410  (see  FIG. 1  also) is used to transfer powder from the box B into a new powder inlet  770  provided in an upper region  700   a  of the duct  700  via a powder hose  774 . The pump  768  draws powder from the box B through another powder hose  776  that may be, for example, connected to a lance that is inserted into the box.  FIG. 27A  shows the lance  900  in more detail. The hose  776  would be connected by a coupling member  902  to the lance  900  by O-rings (not shown) or other suitable connectors. Hose  776  and lance  900  would have the same internal diameter. The lance would be inserted into the powder contained within box  412  through the top layer  904  of the powder. Box  412  would be supported by a vibrator  906  to facilitate drawing the powder from the box through the lance  900  and hose  776  into transfer pump  410 . During color change, the lance would be inserted through a collar  908  of the lower duct portion  700   b . The collar  908  would be capped during our normal operation and only uncapped during the color change process when the lance is inserted into the collar. During the color change process, the powder coating material on the outside of the lance  900  will be drawn off by the air flow through the duct. Alternatively, powder can be blow off the outside of the lance by an air wand similar to the way the sieve is cleaned as described herein. When the lance is inserted into collar  908  during the color change operation, any powder remaining within the interior of the hose  776  and lance  900  will be purged into the duct.  
      Although not visible in  FIG. 27 , a sieve is provided, at the mounting flange  772 , between the upper region  700   a  and a central region  700   b  of the duct body  700 . New powder is pumped above the sieve so as to mix with reclaimed powder as will be described hereinafter. The door  704  however can be used for manually adding virgin powder to the supply  22 , which is added below the sieve.  
      The lifting mechanism  716  is used to securely push the fluidizing unit  708  up against the bottom of the siphon ring, in the position illustrated in  FIG. 29 . The lifting mechanism  716  maintains the fluidizing unit against the siphon ring when the supply is in the supply mode configuration. Clamps  778  or other suitable devices may be used to tightly hold the siphon ring  706  against the fluidizing unit  708  in the case of a loss of lift pressure.  
       FIG. 27  further shows a series of pumps  402  which are used to transfer powder from within the siphon ring  706  to associated spray application devices such as spray guns  20  ( FIG. 1 ). The pumps  402  may be conventional in design, and preferably although not necessarily are dense phase pumps. Typically there will be one pump per spray application device. As shown in  FIG. 1 , each pump has an associated powder hose  24  that connects the pump to an outlet in the siphon ring  706  in the supply  22 .  
      Reclaimed powder can also be introduced into the supply  22 . This powder is recovered powder overspray from the spray booth  12  ( FIG. 1 ). In the exemplary embodiment, air entrained powder is drawn into a cyclonic separator  780  that functions as part of the powder overspray recovery system  28  (the cyclone is partially shown in  FIG. 27 ). Separated powder falls through the cyclone  780  into a pan or bin  830  (see also  FIG. 30 ) where it is transferred by the transfer pump  400  through a first hose  32  to a second or reclaimed powder inlet  782  in the upper region  700   a  of the supply duct  700  via another hose  784 .  
      In the operational position of  FIG. 27 , powder is introduced into the duct  700  through any one or combination of the access door  704  (manual addition), the new powder inlet  770  (virgin powder via transfer pump  410 ) or the second inlet  782  (reclaimed powder via transfer pump  400 ). When the powder enters the upper region  700   a  of the supply duct  700 , it is sieved before falling to the fluidizing unit  708 . The gun pumps  402  draw the powder from the siphon ring  706  and pump it to the spray application devices  20 . Conventional level sensors  786  may be provided in the vicinity of the siphon ring  706 , for example, to detect when powder needs to be added. The control system  39  ( FIG. 1 ) as part of the feed center control function  36  monitors the level sensors  786  and operates the transfer pumps  400 ,  410  to add powder as needed to the supply duct  700 .  
      With reference to  FIGS. 28A-28D  and  FIG. 29 , in accordance with another aspect of the invention, the suction interface and function may also be incorporated into the new supply  22  concept. In the exemplary embodiment, the siphon ring  706  is used to provide a device by which the gun pumps  402  can draw fluidized powder out of the supply  22 . Gun pumps, whether dense phase or dilute phase, draw powder from a supply by application of a negative pressure to a hose or tube that connects the pump inlet to the powder source. The siphon ring  706  in the exemplary embodiment thus provides a suction interface between the pumps and the fluidized powder swirling within the duct  700  so that the fluidized powder can be drawn out for spraying. The siphon ring  706  can also be reverse purged to help clean the overall supply, as will be further described hereinafter.  
      The siphon ring  706  includes an upper generally planar mounting surface  800  formed by a radially inwardly extending flange  802  that extends from a cylindrical outer side wall  804 . The flange  802  includes a series of mounting holes  806  that allow the siphon ring  706  to be bolted or otherwise mounted on a flange extension  700   c  of the lower duct portion  700   b  (see  FIGS. 22 and 29 ). The siphon ring  706  also is formed with an internal profile or geometry defined by the curved surface  808  about its internal periphery. In the exemplary embodiment the surface  808  is defined by an involute such that there is a constantly changing radius to the surface relative to a reference point. However, an involute profile is not required, and other curved or non-curved surface profiles may be used.  
      A lowermost portion  808   a  of the siphon ring sealingly contacts the gasket  742  of the fluidizing unit  708  when the fluidizing unit is raised to the position illustrated in  FIG. 29 . This position is the configuration of the supply  22  when operated in the supply mode.  
      In accordance with one aspect of the invention, the fluidizing function is enhanced to improve fluidizing and mixing of the powder coating material. The invention contemplates the use of the fluidizing bed member  736  having a diameter that is greater than the diameter of the duct  700 . Air flows from the plenum  730  upward through the porous fluidizing bed. The fluidizing bed produces a diffused flow of air across its entire surface, which ventilates through powder through a decreasing volume presented by the transition between the fluidizing bed and the duct  700 . This transition causes a higher air flow velocity, like an updraft, at the outer portion of the fluidizing bed. This outer portion is generally defined by the perimeter portion of the fluidizing bed that is radially greater than the outside diameter of the duct  700 . The high air flow velocity updraft in this perimeter region produces a suction effect generally across the surface of the fluidizing bed that draws powder radially outward from a central region to the perimeter region. The powder is drawn upward along the outside portion of the siphon ring and the inside wall of the duct  700   b , and by gravity and head pressure within the duct  700  the powder then flows across towards the center region and then back downwardly in the central region of the duct and siphon ring. Thus, a circulating, somewhat like a convective flow pattern, is produced within the lower region of the duct  700  and the siphon ring, as represented by the arrows  810  in  FIG. 29 . This circulatory flow pattern significantly improves the fluidization and mixing of the powder.  
      The circulating flow can be realized with generally any transition profile between the fluidizing bed and the duct  700 . However, in accordance with another aspect of the invention, by providing the involute or other smooth transition profile to the interior perimeter of the siphon ring, there are no entrapment areas within the fluidizing zone, wherein the fluidizing zone can generally be understood as the volume within the lower portion of the duct  700   b  and within the volume of the siphon ring wherein air is used to fluidize the powder. The smoothly curved profile of the siphon ring, such as by using an involute for example, presents a single continuous surface having any number of recessed or flush suction ports formed therein (for coupling to pumps) with no entrapment areas within the fluidizing zone. The lack of entrapment areas is further effected by locating the suction ports  814  ( FIGS. 28B and 28D ) near the bottom of the siphon ring, just above the upper surface of the fluidizing bed.  
      When the fluidizing bed is lowered, such as during a color change operation, an operator can easily blow off or wipe off the siphon ring and duct without any irregular surfaces to clean. Much of the residual powder is sucked up from these surfaces by air flow up through the duct  700  and the equalization duct  832  (the equalization duct  832  acts as an exhaust duct for residue powder when the supply  22  is operating in the cleaning mode). In this mode, with the fluidizing bed lowered, air flow also follows up along the siphon ring inner surface and flows in a laminar manner up the sides of the duct  700  to help clean out the duct  700 .  
      Thus, other curved or non-curved profiles for the siphon ring interior surface  808  may be used, particularly if the interior profile of the duct is not cylindrical. Preferably the surface  808  blends with a smooth transition as at  812  to the interior surface of the duct  700   b.    
      By providing the fluidizing bed member  726  with an enlarged diameter relative to the duct  700 , the head of powder in the duct  700  does not change drastically even if a substantial amount of powder is added to the supply  22 , thereby minimizing any adverse impact on flow rate and uniformity of the powder to the applicators.  
      A series of radial through bores  814  are provided and generally, although not necessarily, are equally spaced about a portion of the siphon ring. Each bore  814  includes a counterbore  816  that serves as a powder suction port and is adapted to receive one end of a pump suction hose  24  and/or an appropriate hose connector (see  FIGS. 22 and 27 ). These ports are preferably located near the bottom of the ring  706  so that the material application system can operate with as low a material supply as possible to quicken color change.  
      With reference to  FIGS. 30 and 31 , the material application system  10  can include a number of components including the spray booth  12 , the automatic spray guns  20   b  mounted on a gun mover  820 , and a powder overspray recovery system  28 , which in the exemplary embodiments includes a twin cyclone separator  780 . The spray guns  20   b  extend into the spray booth through openings or gun slots  18 . The cyclones receive powder entrained air at a cyclone inlet  822  via a recovery duct  824  that is in fluid communication with the booth interior. In this example, overspray powder is drawn into the recovery duct  824  by a large air flow created by an after filter blower system (not shown). These blowers move large amounts of air through an exhaust duct  826  that is in fluid communication with an exhaust outlet  828  from the cyclones  780 . The after filters provide final filtering of the cyclone exhaust air. The air drawn through the cyclones pulls powder entrained air from the spray booth into the cyclone inlet where the cyclonic operation separates the powder from the air. The recovered powder falls down into the lower portion of the cyclone to a bin or other receptacle  830  where it is transferred by the transfer pump  400  over to the supply  22  through the powder recovery hose  784  as described herein above.  
      In accordance with another aspect of the invention, the supply  22  is optionally connectable to a source of negative pressure, preferably accompanied by high air flow. In the exemplary embodiment, this aspect of the invention is realized by providing a duct that interconnects the supply  22  with the duct work of the powder recovery system. This allows the high air flow from the recovery system, such as the after filter blowers, to help clean powder from the duct  700  (and the supply  22  in general) and associated components. This concept is dramatically different from prior powder supply arrangements in which there was no direct connection like that shown between the supply hopper or box and the recovery system.  
      In accordance with the invention, an equalization duct  832  is provided between the lower opening  726  near the supply  22  and a banjo housing  834 . The banjo  834  is simply a duct that provides a common plenum for the dual stack exhausts (not shown) from the twin cyclones. In a single cyclone system the equalization duct  832  can be simply connected into the duct work of the recovery system at any convenient location, typically downstream from the cyclone exhaust port. A first damper  836  is positioned between the equalization duct  832  and the banjo  834 . Another duct  838  connects the duct  700  of the supply  22  to the equalization duct  832 . In this manner, the negative pressure of the recovery system  28  can be used to produce a high flow of air through the supply  22 , including the duct  700  and the siphon ring during a cleaning and/or color change operations. This is also referred to herein as the supply  22  being used in the cleaning mode.  
      A second or lower damper  840  is provided in the equalization duct  832  above the opening  726 . This damper can be a simple two position damper, namely open and closed positions. The damper  840  is closed when the supply  22  is being cleaned or during color change, and is fully open when the supply  22  is being used in the hopper or supply mode. When closed, the damper  840  isolates the opening  726  from the suction force of the after-filter fan. The lower damper is re-opened during the final step of a color change procedure to clean out the partially enclosed supporting structure  718  so that residual powder can be exhausted through the opening  26  or up the cyclone.  
      The upper damper  836  is preferably a three position damper for reasons that will be explained hereinafter. In one position, the upper damper is fully closed so as to isolate the duct  700  from the negative pressure of the recovery system. This is the normal damper position during a powder application process for which the supply  22  is being used in the supply mode to supply powder to the pumps  402 . It is possible that the damper  836  might not completely isolate the supply  22  from the negative pressure of the recovery system  28 . Accordingly, the equalization duct  832  is used to provide a pressure balance across the duct  700  during use of the supply  22  in the supply mode. Thus, in the supply mode the supply  22 , and particularly the duct  700  and siphon ring operate generally at ambient atmospheric pressure, meaning the atmospheric pressure of the surrounding environment of the material application system  10 . This is accomplished by having the lower damper  840  fully open. The equalization duct  832  also provides additional make up air into the duct  700  for the pumps  402  because the fluidization air may not be enough for the pumps to adequately draw powder out of the siphon ring  706 . During the cleaning mode, the equalization duct acts as an exhaust duct between the supply  22  and the recovery systems, namely the after filter unit in this embodiment.  
      Although the upper damper may typically be fully closed during a material application process (i.e. the supply  22  operating in the supply mode), it is possible to partially open the upper damper  836  during a material application process. The lower damper is also open. Opening the upper damper partially provides just enough air flow up through the duct  700  so that the door  704  can be opened without powder flowing out of the duct  700 . With the door open during fluidization and suction of powder within the supply  22 , an operator can observe the fluidization as well as operation of the sieve located in the upper portion of the duct  700  (described hereinafter). The upper duct can be opened just enough so that the flow of air up the duct  700  contains powder within the duct without adversely impacting the fluidization and suction functions in the fluidization zone of the supply  22 .  
      When a color change or cleaning process is to be performed, the lower damper  840  is fully closed. The after filter blowers are on thereby drawing substantial air flow through the cyclone and through the duct work associated with the supply  22 , as well as the duct work associated with the spray booth. With the upper damper partially opened, the platen  714  is lowered about an inch to separate the fluidizing unit  708  from the siphon ring  706 . Then the upper damper is fully opened to allow for a substantial air flow to be drawn up into the siphon ring  705  and the duct  700  through the gap created between the fluidizing unit and the siphon ring. This air flow not only removes residue powder within the duct  700  but also cleans off the fluidizing plate and the interior surfaces of the siphon ring. At the same time, the siphon ring can be reverse purged by forcing air back through the bores  814  into the ring interior and up through the duct  700 . The reverse air flow can be effected by a purging operation associated with the pumps  402  for example or by any other suitable technique.  
      When the initial cleaning has been completed, the platen  714  is fully lowered so that all the siphon ring/gasket  804 / 742  contact points can be visually inspected and wiped down or blown off as needed. The upper damper  836  is still fully opened so that maximum air continues to flow through the duct  700  and out to the recovery system such as the after filter unit.  
      Accordingly, a significant advantage of this aspect of the present invention is that the supply  22  is connectable to the recovery system to greatly increase the speed of cleaning and color change yet with a simple arrangement requiring significantly reduced labor. Another advantage is that the supply  22  can be, if so desired, physically distant from the cyclone because there is no need to use the cyclone to capture residue powder cleaned from the system. This greatly increases the flexibility in design and layout of the material application system  10  because the supply  22  can be located at its own convenient location on the shop floor regardless of the location of the cyclone. The cyclones can also be positioned much lower to the shop floor since the box or supply need not be positioned there under.  
       FIGS. 31, 32  and  33  illustrate an embodiment of another aspect of the invention. In accordance with this aspect, a sieving arrangement is contemplated in which the sieve has an integral expandable seal and an integral vibration function. The integrated vibration function produces vibration in the sieve arrangement itself only and not the rest of the supply  22  such as the duct  700 .  
      In the exemplary embodiment, the sieve arrangement  842  is designed to be installed in the duct  700 , between the upper portion  700   a  into which virgin and reclaimed powder is added (as described hereinabove) and the lower portion  700   b  (see  FIG. 27 ). This location provides adequate volume for powder to be added and sieved prior to falling into the fluidizing zone of the duct  700 , wherein the fluidizing zone is generally defined as the volume above the fluidizing plate  736  and generally but not necessarily completely within the siphon ring  706 . The sieving function not only provides a more consistent feed of material into the fluidizing zone but also helps to uniformly mix the reclaimed and virgin powder, particularly when the vibration function is added to the sieve.  
      The sieve arrangement  842  preferably can be manually positioned as illustrated in  FIGS. 32 and 33 , and can be reached by an operator through the access door  704 . The access door  704  may be provided with hooks or other suitable devices  844  for holding the sieve arrangement  842  during cleaning. Alternatively the sieve could be provided with a hanging device or one can be optionally installed by the operator each time the sieve is cleaned. During the cleaning mode, substantial air is being drawn into the duct  700  through the door opening  704   a , therefore, an operator can use an air wand to blow residue off the sieve and into the duct  700 . Note also that with the door  704  open the operator can use a mitt or air wand or other suitable cleaning device or combination thereof to finish cleaning the duct  700  interior during a cleaning or color change process.  
      The sieve arrangement  842  includes a hollow ring  846  that can be made of any suitable material, including metal, plastic, composite and so on. The ring  846  supports a sieve screen  848  so that the assembly can be installed inside the duct  700  by resting on compliant support pegs  850 . An inflatable/deflatable seal device  852  is provided about the periphery of the sieve screen  848  such as within a groove of a screen frame  848   a . An air hose  854  is in fluid communication with the seal  852  and is also connected to a source of air pressure (not shown) outside the duct  700  through an opening in the duct wall. The air lines for the sieve are contained within an umbilical  853 . The umbilical  853  can alternatively be used to also enclose an ultrasonic energy source for supplemental vibration energy for the sieve. A valve or other control device (not shown) can be provided to allow an operator to inflate or deflate the seal  852 . With the sieve in place up inside the duct  700  and resting on the pegs  850 , the operator adds air into the seal  852  to expand it. The seal engages the inside wall of the duct  700 . The screen seal  852  has the effect of not only installing the sieve in a fluid tight manner within the duct (so that all powder must pass through the sieve screen  848  and not around its perimeter) but it also is a compliant mount that centers the sieve screen within the duct. The seal  852  also dampens the sieve vibrations from being coupled into the duct  700 .  
      To remove the sieve arrangement for cleaning, the operator simply deflates the seal  852 , manually grasps the sieve  842  and hangs it on the door  704  outside of the duct  700  for cleaning. In this embodiment, the umbilical  853 ′ may include a quick disconnect arrangement (not shown) so that the entire sieve arrangement hangs from the door and can be easily cleaned off.  
      The hollow ring  846  has one or more elements inside, such as for example a ball bearing  856 . Pressurized air is also injected into the ring  846  through one or more tangential air jets so as to impart motion to the elements  856  which induces vibration into the ring  846  and sieve screen  848 . Air may be provided from a branch of the seal air line  854  or separately provided. The ring  846  thus functions as a race for the ball bearing  856 . The motion air is exhausted from the ring  846  through an exhaust line  858  and can be exhausted to atmosphere or other locations in the system  10  that uses a pressurized air source. The ball diameter is slightly less than the inside diameter of the tube  846  so that air pressure will force the ball to spin around the inside of the ring. Supplemental energy may also be provided for vibrating the sieve. For example, ultrasonic energy may also be used in addition to the motion induced vibration.  
       FIG. 35  illustrates an alternative embodiment of the sieve arrangement as used with a door that conforms to the cylindrical shape of the duct  700 . In this embodiment, a strut  860  is associated with the door  704 ′. In this embodiment, the sieve arrangement  842 ′ is designed to be hung on the strut  860  when the door is open. The strut swings out with the door and swings back out of the way when the door is closed.  
      The various features of the supply  10  and associated components provide a fast and simple supply design to clean and for color change. An exemplary color change process will now be described, it being understood that this process can be used for cleaning as well as for color change, and that the particular order of the steps is not necessarily required and that various steps may be optional depending on the overall performance requirements of the material application system.  
      Presuming that the system  10  has been operational during a powder application process, when the spray applicators and pumps are turned off there may be a significant amount of powder still in the duct  700  and the siphon ring  706 . The after filter blowers stay on and the fluidizing air to the fluidizing unit  708  remains on. The upper damper  836  is partially opened and the lower damper  840  is fully closed. The dump valve  756  is opened and much of the powder on the fluidizing plate falls down into the box B. The air being drawn into the duct  700  via the upper damper  836  and the ducts  832 ,  838  also removes powder from inside the duct  700  and the siphon ring and fluidizing unit. The gun pumps  402  and transfer pumps  400 ,  410  may optionally be reverse purged so that air blows through the radial ports in the siphon ring to clean the ports and help clean the siphon ring, as well as cleaning out the hoses that connect the gun pumps to the siphon ring and the transfer pumps to the duct  700 . Air is also fed into the drain  752  ( FIG. 25 ) to keep powder from remaining in the trap and also to clean the opening  748  in the fluidizing plate  736 . The dump valve  750  is closed and the box can be removed. The platen  714  is then lowered a small amount, for example about one inch, to break the fluid tight seal between the fluidizing unit and the siphon ring. Then the upper damper is fully opened and air is drawn into the duct  700  through this small gap and cleans powder from the siphon ring as well as the fluidizing plate. This air flow also back washes the sieve screen  848  (initial air flow when the upper damper is first partially opened also sucks up powder that had remained on top of the sieve screen).  
      After an appropriate amount of time, such as for example about 10 seconds or so, the plate  714  is completely lowered. Not all of the after filter air however is pulled through the supply  22 . Some of the after filter containment air still is pulled through the cyclone to prevent cyclone contamination into the supply duct  700  or into the partially enclosed supporting structure  718 .  
      The operator opens the access door and can use an air wand, a mitt or other cleaning devices or combinations thereof to finish cleaning any small amount of powder that still may be inside the duct  700 , the siphon ring and the fluidizing unit. This powder is easily drawn up into the duct  700  and out to the recovery system due to the large air flow. The operator also removes the sieve by deflating the seal and hangs the assembly on the door (or alternatively the strut) so that the air wand can be used to finish blowing off any residue powder on the sieve arrangement. Also, the sieve seal  852  can be cycled between inflated and deflated states, for example about every three seconds, to further dislodge powder from the seal. This also allows an operator to observe proper operation of the inflatable seal. The sieve then is repositioned up into the duct  700 . The operator can then clean down the cyclone as needed and as is well known. After final cleaning is done, the lower damper may be closed and the upper damper partially closed. The platen  714  is raised so that the fluidizing unit re-engages the siphon ring. A new box of material can then be positioned under the fluidizing unit and the system is then ready to go back online (the upper damper will then be fully closed before starting the next material application process.)  
      By having the supply  22  connectable into the recovery system, cleaning and color change is much faster and easier because the large air flow can be used as an integral part of the cleaning operation even when the supply  22  is positioned remote from the cyclone. One operator is able to clean the supply and cyclone and provide color change in a matter of minutes with little effort and almost no tools. This arrangement also improves the purging and cleaning of the pumps and associated equipment.  
      As a still further alternative embodiment, it will be appreciated by those skilled in the art that the supply  22  lower works, including a lower portion of the duct  700 , the siphon ring  706 , the fluidizing unit  708  and the supporting structure and moveable platen  714 , can be positioned directly under the cyclone outlet, particularly if a single cyclone is used. This configuration allows the supply  22  to be exhausted through the cyclone to the after filter, rather than using the additional duct work described in the exemplary embodiment herein above. In most cases, this configuration would utilize a vortice breaker between the cyclone and the supply  22  so as to minimize adverse affects, if any, of the cyclone operation on the fluidization and suction functions of the supply  22 . Operation of the supply  22  would be substantially the same as the exemplary embodiment herein.  
      The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of this specification and drawings. The invention is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.