CROSS REFERENCES TO RELATED APPLICATIONS 
     The instant application is a continuation-in-part of Applicant&#39;s patent application Ser. No. 11/165,953, filed Jun. 24, 2005, now abandoned, which is a continuation-in-part of Applicant&#39;s patent application Ser. No. 11/137,890, filed May 26, 2005, now U.S. Pat. No. 7,329,343, which is a continuation-in-part of Applicant&#39;s patent application Ser. No. 10/701,310, filed Nov. 4, 2003, now U.S. Pat. No. 7,186,334, issued Mar. 6, 2007, which is a continuation-in-part of Applicant&#39;s patent application Ser. No. 10/636,071, filed Aug. 7, 2003, now U.S. Pat. No. 6,881,331, issued Apr. 19, 2005, which is a continuation of Applicant&#39;s now abandoned patent application Ser. No. 09/794,601, filed Feb. 27, 2001, which is a continuation-in-part of Applicant&#39;s patent application Ser. No. 09/393,437, filed Sep. 10, 1999, now U.S. Pat. No. 6,192,911, issued Feb. 27, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to systems that use a venturi device, and more particularly to a system wherein an input portion, a center portion, and an output portion of a venturi are constructed as separate components so that the venturi may be customized by interchanging the different portions. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Commonly known ozone water purification systems comprise the elements of an ozone gas generating apparatus, a water carrying tube including an ozone contact segment, and in some instances a bubble separating column or chamber. The ozone generating apparatus may comprise a cylindrical chamber through which atmospheric air containing diatomic oxygen is pumped or drawn. Radiation from a lamp capable of emitting intense ultraviolet light having a wavelength of approximately 185 nanometers and 254 nanometers excites the diatomic oxygen within the chamber. As a result of such molecular excitation, a fraction of the diatomic oxygen within the chamber is split, producing free atoms of oxygen. The extremely high chemical reactivity of free oxygen atoms within the chamber causes them to rapidly react with the remaining intact oxygen, forming ozone gas (O 3 ). 
     Another commonly known method of producing ozone gas within a chamber is to introduce closely spaced electrodes therein and to apply a sufficiently high electrical potential between the electrodes to produce electric discharge arcing. Diatomic oxygen molecules in close proximity with such electrical arcing similarly degrade into free oxygen atoms, which quickly react with diatomic oxygen to form ozone gas. 
     In commonly known configurations of ozone water purification systems utilizing ozone, ozone-rich air emitted from the ozone generator apparatus is introduced into a stream of water in need of purification, such water typically moving through a tube. Where air is forced through the ozone-generating apparatus by, for example, an air compressor, the output of the ozone generator may be introduced into the water-carrying tube by a simple air line interlinking ozone-rich air from the ozone generator to an aperture extending through the wall of the water-carrying tube. In other applications, the air line may terminate that a venturi installed in the water line so that water flowing through the venturi provides motive force to draw the ozone-rich air into the flow of water. 
     Ozone carrying air either injected into the contaminated water stream or drawn into the stream by a venturi initially exists in the form of air bubbles. In order for the ozone gas to have a purifying effect upon the water, such gas must be dissolved into the water. Such dissolving of the gas into the water necessarily occurs at the spherical surface tension boundaries between the gas and the water. A high solubility differential between common air components and ozone gas causes the ozone within such air bubbles to dissolve more quickly than other gases. An exception to this occurs where an ozone residual exists in water in close proximity to the bubbles. Here, rate of infusion of ozone into the water may be reduced due to the strong negative charge of the ozone molecules. In any case, ozone carrying bubbles must remain immersed in water a sufficient length of time to achieve sufficient diffusion of ozone into the water. In addition, it is well known that where the bubbles are kept small, i.e. prevented from merging into larger bubbles, rate of ozone diffusing into the water is increased. Initially, bubbles from a venturi orifice are small, but soon merge with other bubbles while travelling in the flow of water, which basically becomes laminar just after the venturi. 
     In some commonly configured ozone water purification systems, the water-carrying tube serves dual functions, both transporting water containing dissolved ozone to its desired destination, and providing an elongated contact distance where air bubbles containing ozone may remain in contact with the water for a sufficient length of time to allow dispersion of the ozone into the water. In order for ozone dispersion to occur within the water-carrying tube, the tube must have a sufficient length, i.e., an ozone contact length. The contact length of the tube may typically be between approximately 1-4 feet or so, and possibly up to 8 feet in length. However, the length may vary depending upon variables such as rate of flow within the tube, size of the tube, turbulence and water temperature. Sharp turns within the tube or turbulence-inducing baffles or screens installed within the bore of the water carrying tube may serve the function of breaking larger ozone-carrying bubbles into smaller bubbles, increasing the overall surface area of the bubbles, and increasing the rate the ozone dissolves into the water. In addition, and as stated, where an ozone residual exists in the water proximate the bubbles, such as where the flow becomes laminar, transfer of ozone from the bubbles is inhibited. 
     While venturi injectors or mixers such as those used in dissolving ozone into water provide a small bubble size, and as stated, the flow of water just downstream the injector, within 12-15 inches or so, becomes laminar. As such, the bubbles, being entrained in a laminar flow just downstream the injector, become so closely packed together that they merge into larger bubbles. Further, the fluid moving with the bubbles in the laminar flow becomes permeated with ozone, inhibiting further transfer of ozone from the bubbles. 
     Where water having dissolved ozone gas therein is poured into a body of water such as, for example, a swimming pool, the ozone beneficially reacts with various contaminants. For example, ozone rapidly reacts with metal ions within the water, forming precipitants which may be removed through filtration. Ozone dissolved in water also degenerates or causes lysis of cell walls of bacteria, viruses, protozoan organisms, algae and other microbiota. However, while ozone kills bacteria and viruses almost instantly, protozoa such as those that serve as hosts for bacteria that cause Legionnaires disease require longer exposure to higher concentrations of ozone in order to be killed. Ozone within water also beneficially oxidizes and neutralizes sulfides, nitrates, chloramines, cyanides, detergents, and pesticides. In all such cases, the efficacy of ozone in reacting with such contaminants is enhanced by reducing the physical distance between contaminant organisms or molecules and the molecules of ozone within the water. In a large volume of water, such as a drinking water storage tank, spa, or swimming pool, the concentration of dissolved ozone becomes undesirably low, slowing the rate at which the ozone reacts with contaminants. To prevent such dilution of ozone concentration, it is desirable to first introduce the ozone-carrying water into a reaction chamber having a smaller interior volume which maintains higher concentrations of ozone. 
     In addition to the foregoing, one problem with indoor pools, spas, hot tubs, jetted bathing facilities and other similar immersion facilities that utilize ozone for sanitization purposes is one of outgassing of the ozone into the area surrounding the facility. Here, strict rules have been enacted that require that outgassing of ozone from such a facility not exceed 0.1 ppm. Thus, it becomes necessary to ensure that little or no ozone is allowed to escape from the water. Further yet, where ozone is generated from air, only a fraction of the approximately 20% oxygen content of the air is converted to ozone. As a result, a relatively large quantity of atmospheric gasses are introduced into the water flow. In some systems, this is undesirable as the gasses produce cavitation of pumps, and where the flow is fast, can erode pipes and other parts of the water-carrying system. As a result, it is necessary in some systems to remove these atmospheric gasses in order to prevent deleterious effects on the system. 
     In all systems where ozone is used in conjunction with other sanitizers, such as bromine or chlorine, premixing of the sanitizer with ozone or air containing ozone is beneficial. Here, when ozone is premixed with halogens, such as sodium bromide, the bromine is released. With chloramines that are usually present, free chlorine is released. Where bicarbonate of soda is present, hydroxyl radicals are created, which acts as a sanitizer and increases the oxidation potential of the water. Ozone also increases the ground state of halogen sanitizers so that they are more reactive, increasing their sanitizing effects and potential to reduce contaminants. 
     In accordance with the foregoing, it is an object of the present invention to provide an ozone-based water purification system which incorporates in series an ozone generating apparatus and a mixer for mixing ozone-containing gas and a sanitizer prior to insertion of the mixed compounds into the water. 
     It is another object of the invention to provide such an ozone-based water purification system wherein turbulence and mixing of the flow of water and bubbles is induced well downstream of the venturi. This keeps bubble size small, and does not allow a buildup of ozone in water proximate the bubbles, allowing more ozone to dissipate into the water. In addition, this mixing and turbulence enhances killing of bacteria and viral organisms. 
     It is yet another object of the invention to provide a system wherein after the water is sanitized by exposure to at least ozone, any residual ozone remaining in the water is eliminated. 
     It is still another object of the invention to remove any atmospheric gasses from the flow of water after sterilization. 
     Other objects and benefits of the present invention will become known to those skilled in the art upon review of the detailed description which follows, and upon review of the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of the instant invention. 
         FIG. 1   a  is a diagrammatic alternate view of the enclosure or housing shown in  FIG. 1 . 
         FIG. 2  is a sectional, partially exploded view taken along lines  2 - 2  of  FIGS. 3  and  4 . 
         FIG. 3  is an elevational view of an internal portion of an inlet venturi portion showing construction details thereof. 
         FIG. 4  is an elevational view of an internal portion of an outlet venturi portion showing construction details thereof. 
         FIG. 5  is an enlarged elevational view of a plug or stop for a check valve of, the instant invention. 
         FIG. 6  is an enlarged side view of the plug or stop as shown in  FIG. 5 . 
         FIG. 7  is a cut-away view of another venturi of the present invention. 
         FIG. 8  is an exploded view showing parts of the venturi of  FIG. 7 . 
         FIG. 9  is an enlarged, cut-away view of the venturi of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and in particular to  FIG. 1 , the instant inventive assembly for purifying water is referred to generally by reference arrow  10 . The major components and compartments of assembly  10  may be, but not necessarily, be constructed integrally with or housed within a rigid casing  12 , with access thereto provided by making one side removable. Such a casing  12  may be rectangular or square, as seen from a side, and relatively narrow in width so as to be conveniently mountable within a spa or hot tub enclosure. In this application, a casing about 18 inches high has proved to function well. For other applications, the configuration as shown and described conveniently compartmentalizes the assembly  10  for use in conjunction with pool plumbing systems, spa plumbing systems, drinking water systems and other similar applications. Conveniently, the compartments may be formed by a linear extrusion process where the extrusion is cut to length and capped on each side. In this instance, the internal structures for directing water flow are inserted from ends of the compartments, and may be mounted to the end caps. 
     Referring further to  FIG. 1 , assembly  10  is shown having a number of compartments  14 ,  16 ,  18 ,  20 ,  22  and  24 , each of these compartment communicating with adjacent compartments via openings at tops and bottoms thereof so that the flow of water, as indicated by arrows, traverses the full length of each compartment. As shown in  FIG. 1   a , those compartments wherein water is flowing upward may be larger in cross section or diameter, and compartments wherein water flows downward may be smaller in cross section or diameter. Here, where the flow is upward, the flow is slower, allowing ozone in the bubbles a longer time to dissipate in the water. In those compartments where the flow is downward against the natural buoyancy of the bubbles, the compartments are smaller with a corresponding increased flow of water that entrains the bubbles in a faster, more turbulent flow. Initially, compartment  14  serves as a contact chamber wherein bubbles containing ozone are first exposed to the water. Where compartment  14  is larger ( FIG. 1   a ), the contact time is more prolonged. In addition, particular structures located in the compartments where the flow is downward or at entrances/exits thereof ensure that water flow is turbulent. 
     With respect to these structures, at an entrance  26  of compartment  16  is mounted a static mixer assembly  28 , as shown and described in Applicant&#39;s pending patent application Ser. No. 09/752,982, filed Dec. 31, 2000, now U.S. Pat. No. 6,623,635 which is incorporated herein by reference in its entirety. Assembly  28  serves to generate turbulence in the flow of water for reasons earlier described. Within compartment  16 , there are mounted a plurality of baffles  30  mounted at one edge  32  to the inner walls of the compartment, and have an opposite edge  34  angled or bent downward with respect to edge  30 . With this construction, and as shown by arrows, the downward water flow through compartment  16  is to forced to take a circuitous path around baffles  30 . Baffles  30  also generate turbulence in the water. Where an extension is used to form the compartments, baffles  30  may be mounted to a strip or rod. Alternately, a free-standing structure, such as a plurality of spheres having openings cut therein, may be placed in compartments wherein turbulence and extended contact distance is desired. 
     At the bottom of compartment  16  is a combination water exit/entrance  36  where the water exits compartment  16  and flows into compartment  18 . Just as the flow of water enters compartment  18  it encounters a water-directing assembly  38  enforces the water to flow upward with a circular, spiraling motion. As stated, compartment  18  may be larger in cross section or diameter, allowing a prolonged contact distance as earlier described for compartment  14 . 
     At an upper end of compartment  18 , a combined water outlet/inlet  40  passes the water from compartment  18  to compartment  20 . As the water flows into compartment  20 , from outlet/inlet  40 , it encounters a static mixer assembly  42  as described for static mixer assembly  28 . Once in compartment  20 , a smaller compartment, the flow of water is again forced to follow a circuitous path around baffles  44  constructed as described for baffles  30 , and which are mounted to sides of the compartment (or to an end cap) and extended inward to direct the flow of water in a turbulent manner. 
     At a bottom of compartment  20 , a water exit/inlet  46  is provided to pass the flow of water from compartment  20  to compartment  22 . Here, as the water flows into compartment  22 , it encounters a second water-directing assembly  48  that directs the upward flow of water along a circular, spiral path. Alternately, the flow of water may be introduced into compartment  22  at an angle so as to induce a spiral motion to the water flowing through compartment  22 . 
     Also positioned in compartment  22  is a watertight, sealed enclosure  50  within which an ultraviolet light-emitting lamp  52  is mounted or otherwise positioned. Lamp  52  is conventionally powered, as by a ballast connected to AC power and to the lamp. Watertight and airtight conductor connections through enclosure  50  would typically be employed. Enclosure  50  forms a portion of the ozone generator of the instant invention, as will be described hereinafter. Significantly, the walls of enclosure  50  are of a transparent, ultraviolet-transmitting material, such as, but not limited to, quartz, which passes the ultraviolet radiation to the water. In this compartment, water is forced to move in a spiral around enclosure  50  while being exposed to ultraviolet light. This beneficially exposes any pathogens that may have survived to that point to lethal levels of ultraviolet radiation, and disassociates any residual ozone in the water into diatomic oxygen and free oxygen. Of course, the free oxygen is highly reactive, and reacts with practically any compound in the water almost instantaneously. 
     At a top of chamber  22  is a water outlet/inlet  54  that passes the flow of water to the last compartment  24 . Structure herein is similar to that shown and described in Applicant&#39;s pending application Ser. No. 09/418,915, filed Oct. 15, 1999, now U.S. Pat. No. 6,342,154 and which is incorporated herein in its entirety by reference. Such structure removes entrapped air from the flow of water. Here, at a top of chamber  24  is a solenoid valve  54  that operates in conjunction with a water level sensor  56  and, in some instances, a valve  58  is positioned at an outlet  60  of assembly  10 . A small drain chamber  55  may be provided in the vent line after valve  54  in order to trap and drain small amounts of water expelled through valve  54 . Operation of valves  54 ,  58  and sensor  56  may generally be such that when sensor  56  detects a lowered water level indicative of a gas buildup within compartment  24 , a signal is sent to valve  54  to open this valve, thus venting the gas. In instances where the water system is pressurized, water pressure forcefully expels the gas through valve  54 . In some of these pressurized systems, where the water pressure is sufficiently high to expel gas through valve  54 , valve  58  may be omitted. In instances where the water pressure is somewhat lower, a small constriction may be provided that an exit  60  in order to cause the gas to be expelled through open valve  54 . In other of these pressurized systems where valve  58  is installed, valve  58  may be closed when valve  54  is opened. In this instance, pressure in the system increases to more forcefully expel gas through valve  54 . In any instance, after the water level rises (due to the gas is being expelled) to a preset point where the water level almost reaches valve  54 , sensor  56  closes valve  54 . In order to prevent gas buildup in compartments with low flow rates, such as compartment  14 , a small vent line may be installed from the top of the compartment to a top of compartment  24 . This line would be sized so as to readily vent gas, but not allow passage of a significant quantity of liquid to pass therethrough. 
     In other systems, such as gravity-operated flow systems, pressures in the assembly  10  are not as high. In this instance, valve  58  would be shut as valve  54  is opened by sensor  56 . In these systems, when this occurs, the entire system would experience a drop in pressure, and a corresponding increase in pressure when valve  54  is closed and valve  58  is opened. Such pressure fluctuations are beneficial due to ozone diffusing more rapidly into the water when the pressure is higher. As a result, more ozone diffuses into the water sooner to develop initial higher concentrations of dissolved ozone. 
     Still referring to  FIG. 1 , another feature of Applicant&#39;s invention may include premixing ozone gas with another sanitizing compound prior to insertion of the mixed compounds into the flow of water. Here, a venturi injector  62  similar to a venturi injector as shown and described in Applicant&#39;s pending application Ser. No. 09/393,437, now U.S. Pat. No. 6,192,911 and which is incorporated herein in its entirety by reference. This venturi  62  is conventionally provided with a water Inlet  63  and a water outlet  65  through which a motive flow of water (as indicated by arrows) is pumped by a water pump (not shown). Venturi  62  is also provided with an annular cavity  65  (diagrammatically illustrated in  FIG. 1 ) which in turn communicates with at least two sanitizer injection ports  64  and  66 . As shown, port  64  may be coupled to a canister  68  having a removable top  70  within which a solid, slowly dissolving form of sanitizer is placed at appropriate intervals. An inlet line  72  provides a flow of water from the motive flow to canister  68 , where the sanitizer is dissolved into the water, and an outlet line  74  provides the water containing the dissolved sanitizer to inlet port  64 . Inlet port  66  of the venturi is coupled to an outlet tube  76  of enclosure  50  through which air is circulated around ultraviolet tube  52 . To accomplish this, an inlet tube  78  is provided to enclosure  50 . An air filter  80  may be coupled in line  78  to filter particulates from air circulated through enclosure  50 . In some instances, an air pump  82  may be also placed in line  78  to pump air through enclosure  50 . In any case, ozone-containing air from enclosure  50  is provided to port  66  of venturi  62 , where the ozone-containing air is mixed with the sanitizer-containing water from canister  68  in annular chamber  65  of venturi  62 . Alternately, any liquid sanitizer dispenser may be used, such as a liquid dispenser of that dispenses a liquid containing a halogen or other sanitizer. 
     A multiport venturi  62  as contemplated by the present invention is more particularly described in  FIGS. 2-6 . Here, it is seen that venturi  62  is constructed in two portions or halves, an inlet portion  90  and an outlet portion  92 . Nut/bolt pairs (not shown) extend through 8 pairs of aligned openings  93 ,  93   a  in each of portions  90 ,  92 , and hold portions  90 ,  92  together while allowing disassembly thereof, as will be further explained. As shown, a flange  94  extends around a periphery of a body of inlet portion  90 , flange  94  defining a cavity  96  therearound. As shown in  FIGS. 2 and 3 , small cavities  98 ,  98   a  generally receive sanitizing compounds from their respective inlets  64 ,  66 , and channels  100 ,  100   a  carry the sanitizing compounds to an annular mixing cavity  102  where the sanitizing compounds are mixed. After being mixed, the sanitizing compounds are drawn by venturi action across a flat venturi interface  104 , as will be further explained, and into the motive flow of water flowing through opening  106 . 
     The outlet portion  92  is provided on an external side with inlets  64  and  66  for supplying sanitizers to the venturi. This may be the same sanitizer applied to each of inlets  64 ,  66  or dissimilar sanitizers may be applied to inlets  64 ,  66  as described above. In the latter instance, the dissimilar sanitizers are at least partially mixed prior to being introduced into the water flowing through the venturi. Of course, inlets  64 ,  66  may be located on the inlet portion  90  with appropriate modification, as should be apparent to one skilled of the art. Inlets  64 ,  66  each communicate with respective cavities  108 , 108   a , these cavities provided with stepped regions  110 ,  110   a  where the cavities are reduced to a smaller diameter. Within the smaller diameter areas the cavity is tapered as shown toward inlet bores  64   a ,  66   a  and the respective openings through which sanitizing compound flows. Within the smaller-in-diameter and tapered portions of cavities 108 ,  108   a  disks  112 ,  112   a  of a thin, flexible material are placed, these disks serving as check valves to allow only a one-way flow of sanitizer through inlets  64 ,  66 . As these disks  112 ,  112   a  must move slightly within their cavities, the cavities are constructed slightly thicker and larger in diameter than the disks. For holding disks  112 ,  112   a  in place, plugs  114 ,  114   a  bar provided, as particularly shown in  FIGS. 5 and 6 . These plugs are sized to snugly fit as shown into the larger portions of cavities  108 ,  108   a  and loosely hold disks  112 , 112   a  in place. These plugs each are provided with a series of ridges  116  forming a plurality of grooves  118  in faces of the plug facing disks  112  (dashed lines in  FIG. 5 ). As such, when sanitizer is flowing through the inlets  64 ,  66 , the disks are moved away from the internal openings of the bores  64   a  and  66   a  and generally pressed against the grooves of plugs  114 ,  114   a . As the disks are smaller than the radial extent of the grooves  118 , sanitizer flows around the disks, into grooves  118  and through a central opening  120 , 120   a  in the plugs. Openings  120 ,  120   a  in the plugs communicate via slots  100 ,  100   a  with annular mixing chamber  102 , where the sanitizers are mixed and drawn into the venturi interface. 
     Additionally provided in outlet portion  92  is an annular cavity  122  surrounding opening  124  through which the motive flow of water flows from opening  106  of inlet portion  90 . Together, annular cavities  102  and  122  form the cavity  65  diagrammatically shown in  FIG. 1 . A venturi interface  104   a  is located proximate venturi interface  104  of inlet portion  90 , this dimension determined by thickness of a gasket  126  fitted between the inlet portion and outlet portion. Thus, the venturi may be adjusted for differing rates of flow by placing a gasket of appropriate thickness between the two portions. Here, where the flow rate is higher, a thicker gasket may be used, which in turn draws more sanitizing compounds into the venturi, and where the flow rate is lower, a thinner gasket may be used, which in turn draws less sanitizing compounds into the venturi. Of course, openings are cut in the gasket to allow flow of sanitizer therethrough and to allow motive flow of water through the gasket. Additionally, slots in the gasket may be cut along slots  100 ,  100   a  to allow the sanitizers to more fully be mixed in both annular chamber&#39;s  102  and  122 . 
     While a number of features are shown in assembly  10 , it is to be understood that a system with fewer features may be implemented, as should be apparent to one skilled of the art. For example, a viable system would include contact compartment  14 , a single turbulence compartment  16  and an ozone generations/reaction chamber  22 . Further, in some systems, the gas removal compartment  24  may be omitted. In other systems, a conventional venturi may be used to inject ozone, with other sanitizers being conventionally dissolved in the water. Further, fewer turbulence-inducing assemblies may be employed. In venturi  62 , multiple ports (more than two) may be constructed therein, and the venturi itself may be scaled in size, in addition to adjusting the venturi gap depending on the flow. 
       FIG. 7  shows another Venturi that may be used in conjunction with any water or flow circulation apparatus or device. Here, a body or housing  200  is shown, which body or housing  200  may be integral to a fluid circulation device or a separate component. Housing  200  is provided with a bore  202  that receives a first portion  204  and a second portion  206 . Bore  202  may be circular or cylindrical, square or rectangular, or of any other convenient shape. Likewise, portions  204 ,  206  and  216  may be of a corresponding shape so as to snugly fit within bore  202 . Where necessary, seals such as o-rings or the like may be used where required. The portion  204  is constructed as a Venturi inlet  208  having a tapered portion  210 . Portion  206  is constructed having a venturi outlet  212 . A center portion  214  is constructed to fit between portions  204  and  206 , and is provided with a channel  216  that communicates via passageway  218  with a source of gas or fluid  220  to be drawn into the motive flow passing through the venturi. The pressurized motive flow provided to inlet  208 , as indicated by arrow  222 , may be a fluid or gas, with outlet  212  connected to an application using the venturi. As shown in  FIG. 8 , portions  204 ,  206  and  214  of venturi may be removed from bore  202  and replaced with corresponding portions having the same external shape so as to snugly fit within bore  202 , but having different conical portions  210  and the bore shown in outlet  212 . The center portion  214  may be constructed as a disk having a slot  217 , or as shown in  FIG. 9 , channels  222 . Also, a disk  217   a  may have a plurality of channels  222  in order to draw from multiple sources  220 . With this construction, the venturi may be customized for any particular application by interchanging portions  204 ,  206 , and  217 . As shown in  FIG. 9 , an outlet portion  206   a  may have a wider inlet, as indicated by arrow  224 , while the outlet of portion  204  may be smaller, as indicated by arrow  210   a . As shown in  FIG. 9 , the opening  226  in disk  217   a  may be of a beveled configuration so that on the opening  226  inlet side and outlet side the respective openings interface smoothly between portion  204   a ,  206   a  and  217   a . Alternately, the central opening in disk  217   a  may have straight sides as shown by dashed line  228 , as would be produced by simply drilling through the disk  217   a . Significantly, Applicant has discovered that such a disparity in size between the exit opening  210   a  and inlet opening  224  causes the venturi to draw a higher negative pressure than a conventional venturi. Also, and as noted, the respective venturi portions may be interchanged with other venturi portions having inlets  208 , conical portions  210 , discs  214  and outlets  212  of different shapes and sizes so as to conveniently change the operational characteristics of the venturi. This allows the venturi to be built into an application such as a water treatment system for a spa, hot tub or other bathing facility, or any other application. Examples of such applications may be treatment systems for water cooling towers and agricultural equipment that uses venturii to draw a concentrated liquid fertilizer into a motive flow for subsequent application to plants. Such a customization of a venturi may be necessary where water or other fluid pressure used as a motive flow may vary over time, or where equipment or apparatus is installed in many different locations where the motive flow may vary. In the aforementioned bathing receptacles, the fluid pressure from a circulation pump or bypass loop may vary a great deal between bathing facilities from different manufacturers. Thus, for any given pressure or flow rate, the portions  204 ,  206  and  217  may be selected to achieve a desired negative pressure or suction through slot  217  or channels  222 .
An adjustable Venturi is disclosed, and having a plurality of inlet ports providing substances to be mixed with a flow of fluid through the Venturi. In one embodiment, the Venturi is constructed having an inlet portion, an outlet portion, with an annular mixing chamber coupled to inlet ports so that substances provided through inlet ports are mixed in the mixing chamber, and such mixture introduced into the flow. A gasket sealably disposed between inlet portion and outlet portion is selectable in thickness, for adjusting width of a Venturi interface between the inlet portion and outlet portion. In another embodiment, the inlet portion and outlet portion are fitted in an elongated opening, and are replaceable to change operational characteristics of the Venturi. A replaceable disk having a central opening and substance-providing passageways is disposed between the inlet portion and outlet portion, and may be changed to change characteristics of the Venturi.