Patent Publication Number: US-8534296-B2

Title: Smoking apparatus with filter and cooling

Description:
TECHNICAL FIELD 
     The present invention is an appliance used by smokers of tobacco to burn the tobacco and deliver the smoke to the user. Furthermore, the described appliance causes the smoke to pass through a liquid which cools and washes the smoke. 
     BACKGROUND ART 
     Devices commonly known as hookahs have been used for several centuries in the Mideast and oriental countries for the smoking of organic materials such as tobacco. Early hookahs were multi-stemmed pipes often made of glass. A variety of, generally dried, organic material, such as tobacco, herbal fruits and flower heads were placed in a combustion chamber or bowl and ignited. As a user would draw a vacuum on a stem of the pipe, the smoke would be drawn out of the combustion chamber, into the lungs of the user. Multiple stems allowed for multiple users to gather around the hookah to share its burning content in a social setting. 
     As users of hookahs grew less willing to accept the harsh high-temperature smoke produced by various substances that would irritate their lungs, a simple water bath was added to the basic pipe so that the smoke was bubbled through the water bath to remove ash and to cool and filter the smoke before it was drawn into the lungs of a user. A pipe from this subclass of hookahs became known as a “bong”, a name derived from a That word that was introduced into U.S. slang by Vietnam veterans during the 1960&#39;s. 
     The classic bong, or water pipe, has a single, vertical, elongate open pipe about 38 mm (1½ inch) in diameter sealed at the bottom, a bowl for burning the organic substance, a single tube used for mounting the bowl and leading at an angle into the elongate pipe near its bottom. Water is placed into the elongate pipe to a level just above the junction of the open pipe and the bowl tube so that when the smoker draws on the pipe, smoke is bubbled through the water to cool and clean it. The smoke is further cooled by expansion into the wide elongate pipe. Thus the elongate pipe operates as a combined water and inhalation chamber. To clear smoke from the chamber of most common water pipes the entire bowl must be removed. Somewhat more sophisticated pipes have a small diameter hole known as a “shotgun” located in the elongate pipe just above the water level to facilitate inhaling the smoke from the chamber. This hole, if present, is kept closed by the smoker&#39;s finger during the initial stages of a smoking session. When the elongate pipe is filled with smoke, the hole is opened and the smoke is driven into the lungs with a ram effect. 
     Until relatively recently, artisans in the design of pipes have generally prided themselves on the simplicity of their designs, setting their articles apart from those of others by the use of decals and hand-painted adornments. The present design takes a much different approach, setting it apart from previous designs by applying significant technological advancements to the cooling and filtering functions. Only a few others are known to have applied any mechanical sophistication to advance the basic design of a water pipe. 
     U.S. Pat. No. 3,881,499 issued to McFadden, et al. in 1975 discloses a bong wherein there is a water chamber located above an ash trap rather than below it. An extensive set of cooling tubes are routed from the ash trap to different levels in the water chamber so that one or more of the tubes are operative depending upon the strength of the draw. 
     An object of U.S. Pat. No. 4,253,475 issued in 1981 to Schreiber, et al. is to provide a bong wherein the water used for cooling and cleaning the smoke is caused to flush up the inhalation chamber in order to push the smoke into the lungs of the smoker, thereby easing the drawing of smoke. This design also takes into consideration that the components of the bong are easily removed in order to facilitate cleaning. 
     The invention described by Grihalva in his U.S. Pat. No. 3,805,806 included a gravity-actuated one-way ball check valve assembly. This created a smoke trap to inhibit the escape of smoke from the smoke collection chamber. 
     DISCLOSURE OF THE INVENTION 
     The present invention holds appeal for those people who enjoy smoking tobacco but would prefer to do so in as healthy a manner as possible. To this end the described apparatus provides a means of filtering and cooling the smoke before it is released to enter the lungs of the smoker. The filtering system has been designed to optimize the cleaning of particulate matter from the smoke while striving to minimize the effort required by the smoker to achieve a suitable draw. Consideration is also given to ease the cleaning of the apparatus. 
     As a user draws on the mouthpiece of the presently described pipe, smoke is drawn through a set of micro-perforated filters. These diffusion screens trap larger particles, such as ash, but allow passage for vapors. The diffusers are covered with water which then traps components of the smoke that are not gaseous, such as tars. In order to keep water from entering the diffusion cones, a flapper is used as a check valve to prevent backwash. Other mechanisms may assist or functionally replace the flapper valve in its operation. 
     After the smoke has been cleaned by the diffusion screens and water bath, it fills the main tube of the pipe which serves as an inhalation chamber. At the middle of the inhalation chamber a static turbine generates a swirling motion that forms a jacket of cool incoming air around the smoke, cooling it as it is forced out of the chamber into the mouth of the user. 
     At the completion of a smoking session, or during an extended session, the apparatus is easily cleaned by removal of a drain plug. After draining the contaminated water bath, the pipe may be set aside for later or it may easily refilled with a small amount of water for continued use. 
     Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The particular features and advantages of the invention briefly described above as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of the smoking apparatus; 
         FIG. 2  is a close-up of the turbine subassembly; 
         FIG. 3  is a close-up of the base assembly with diffusion subassembly; 
         FIG. 4  shows a cutaway view of the base assembly; 
         FIG. 5  is a close-up section view from  FIG. 4  showing detail around the flapper valve; 
         FIGS. 6A-6D  depict an exploded view of the components of the entire apparatus beginning with  FIG. 6A  at the bottom and working upward to the top which is shown in  FIG. 6D ; 
         FIG. 7  is a schematic representation of a pipe within the present description showing airflow through the pipe in response to suction being applied by the user while the recirculation inlet hole is closed; 
         FIG. 8  is a schematic representation showing the airflow with an open air circulation inlet hole; 
         FIGS. 9-11  are a sequence of partial cutaway isometric views showing the airflow in response to action by a user; 
         FIG. 9  shows the flow of air through the pipe as a user applies suction to the mouthpiece while holding the recirculation inlet hole closed; 
         FIG. 10  shows the flow of smoke through the pipe shortly after the user has opened the recirculation inlet hole while continuing to apply suction to the mouthpiece; 
         FIG. 11  shows the flow of smoke through the pipe after the system has stabilized following the opening of the recirculation inlet hole as the user continues to apply suction to the mouthpiece; 
         FIG. 12  is a section view taken along line  12 - 12  of  FIG. 8  depicting the airflow as seen from the top of the pipe; 
         FIG. 13  is a perspective view showing a purge valve; 
         FIG. 14  is a schematic representation of apparatus incorporating a purge valve; 
         FIG. 15  represents in a cutaway view an alternate embodiment of the base chamber with a flat diffusion screen; 
         FIG. 16  shows a cutaway view of an alternate embodiment of the base chamber using an electromagnetically-assisted flapper valve; 
         FIG. 17  shows a perspective view of an apparatus using a water column as a valve; 
         FIG. 18  is a schematic of an apparatus to show the action of a water column; and 
         FIG. 19  shows a section view of nozzles within a diffusion cone. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention is a filtering and cooling system used within an apparatus for the smoking of tobacco. The construction of this smoking appliance  100 , as shown in  FIG. 1 , is based on a hollow cylindrical body tube  110  having an inner diameter of approximately 50 mm (2 inches) and an overall length of about 60 cm (24 inches). This body tube  110 , generally made of glass, is rigidly mounted to a canister-like base chamber  120 . Also connected into the base  120  is a tobacco combustion bowl  180  supported on a pipe stem. 
     The base  120  serves as a chamber for collecting the smoke from the combustion bowl  180  and channeling it through a filter system into the main body of the pipe  100 . By virtue of its canister-like form factor in the preferred embodiment, the significant ratio of surface area to volume of the base  120  shown here dissipates a significant amount of the heat of combustion. This cools the smoke and increases its density. By reducing the temperature of the smoke, the likelihood of clogging subsequent filter stages is decreased. Smoke that has not been cooled will contain much higher concentrations of tar condensates which will precipitate more violently when they later encounter a cool water bath. 
     About one quarter of the way up the length of the body tube  110  is a drain subassembly  160  which includes a drain hole fitted with a cap or plug. Housed in the base chamber  120  so as to protrude into the base end  118  of the body tube  110  is a diffusion subassembly  200  which is the core of the presently described apparatus. In the upper half of the cylindrical body tube is a turbine subassembly  300  adjacent to a recirculation inlet  114 . 
     A close-up detailing the components of the turbine subassembly  300  is shown in  FIG. 2 . This functions as a small carburetor for the mixing of air with smoke. Its operation will be described in more detail later with reference to the overall flow of air and smoke. Briefly, spiral-shaped blades surround the perimeter of a static turbine  320  which is seated on a lower carburetor ring  322 . An inner tube  310  is fitted with an upper carburetor nozzle  304 , and the combination is set atop the static turbine  320 . In operation, a low pressure will be applied to the throat of the upper carburetor nozzle  304  which is tapered so as to create a Venturi constriction that causes the flow of air to accelerate as it passes through the inner tube  310 . 
     The exterior of the base chamber  120  is shown in the close-up view of  FIG. 3 , while a cutaway view of the interior construction of the base chamber  120  appears in  FIG. 4 . A detailed close-up of the workings of the flapper valve  240 , which resides within the base chamber  120  near the center of diffusion subassembly  200  (of  FIG. 4 ) is offered in  FIG. 5 . The operation of these components will be described in more detail later with reference to the overall flow of air and smoke.  FIGS. 6A-6D  are exploded partial views showing the components of the preferred embodiment of the apparatus being presently described. These figures will be useful in understanding the overall operation of the disclosed pipe  100 . 
     For an understanding of the diffusion subassembly  200 , it will be useful to refer to  FIG. 4  in conjunction with  FIG. 6B . The diffusion subassembly  200  comprises one or more air diffusion cones  210  positioned in a series combination with a flapper valve  240 . As seen in  FIG. 1  the diffusion subassembly  200  is located at the base of the body tube  110  where it will be at least partially covered by water. 
     Having described the primary components, continue to refer to  FIG. 4  with support from the exploded view of  FIG. 6B  for a description of the disclosed smoking appliance  100  during operation by a user. Prior to a smoking session, the user adds a small amount of water to the smoking appliance  100 . Only enough water is used to fill the outer glass body tube  110  in the region extending vertically from the bottom of the cones  210  to their tops as can be seen in the schematic of  FIG. 7 . The diffusion cones  210  must have a sufficient wall thickness to withstand the pressure of the water, or other submersing liquid, so that the air inside the diffusion device  210  does not compress to such an extent that would allow the liquid to permeate to the interior of the diffusers  210 . 
     The number of cones in the diffusion subassembly  200  and their characteristics, including their size, and the number and size of the holes in each cone, are established by flow requirements. The diffusion cones  210  act to disperse through a water medium the gas that is to be washed, which in this case is smoke. There are currently no known products, either industrial or consumer, that are based upon a cone-shaped diffusion device having a similar diameter and distribution of holes. 
     Not only does the conical shape of the diffusers  210  provide a large surface area over which to distribute holes, the shape is also important here as it serves to gradually and automatically adjust filtration rates to variations in draw pressure. This self-adjustment feature assists to produce consistent filtering results. 
     As the cones distribute the filtered gas to different levels, variations in exit velocities occur which tends to keep the filtered bubbles from joining together after being expelled from the nozzles. As rejoining of the bubbles is delayed the gas being dispersed experiences improved filtration due to the extended period of time over which the bubbles maintain their original volume. This effect is also responsible for the “foaming” behavior of the water pipe during operation. As the water foams, assuming a consistent inner diameter of the main chamber, the water column will approximately quadruple in height as air is drawn through the pipe, causing a significant increase in gas-water exposure time. 
     The cones  210  used in the presently described apparatus are specifically designed to adjust their flow-rate in response to variations of applied pressure, and more particularly to perform well at very low pressures, below 0.01 psi. In contrast to this, a typical fritter disc as might be used in a similar application will impede airflow to the extent of a pressure drop of 2-15 psi. This performance at low-pressure is accomplished by sizing the diffusion holes  218  to have a much larger diameter than those in a typical fritter disc. By virtue of the conical design of the diffusers  210 , the number of holes  218  in these diffusers  210  increases as the cross-sectional diameter of the diffusers  210  increases. 
     When the diffusion cones  210  are submersed, the pressure of the surrounding water is counteracted by the reverse flow restriction of the series flapper valve  240 . The flapper valve  240  in turn keeps water from entering the inside of the cones and seeping down into the base chamber  120 . In addition to preventing the user from overfilling the water pipe  100 , this combination of diffusion cones  210  and flapper valve  240  plays two important roles. 
     Firstly, by keeping the water from entering the cones  210 , there is no need for the user to generate the large initial pressure gradient that would be necessary to draw water through the small diffusion holes  218 . In consideration of the viscosity of water in comparison to that of air, much more force would be required to pull water through the holes than to draw air. To avoid this, water is initially kept from flowing to the interior of the diffusion cones  210 . 
     Secondly, for use in tobacco applications, it is important to recognize that the tar by-products of tobacco smoke only exhibit major condensation at the boundaries where smoke and water meet. By keeping the water on the outside of the cones  210 , the majority of the tar will condense on the outside instead of inside where it would clog the holes  218 . This behavior significantly reduces the amount of cleaning required to keep the device operating properly. 
     The entire diffusion subassembly  200  is shown in the cutaway view of  FIG. 4 . For explanation of the individual components, refer to the exploded view in  FIG. 6B . A cone divider  220  provides a support structure for a multiplicity of cones  210  while allowing an open path for flow of air through the center of each of the cones  210 . Each cone  210  is mounted on a cone-to-core connector  214  having a hollow shaft. An O-ring  212  is used to provide a resilient mount between each diffusion cone  210  and its respective cone-to-core connector  214  that will withstand exposure to differential thermal expansions and mechanical shock. It is to be noted here that all O-rings in the preferred embodiment are made from white US FDA-approved Buna-N Nitrile and, unless otherwise specified, all have a durometer of 70 in the preferred embodiment. 
     The shafts of the cone-to-core connectors  214  are pressed to fit, or glued, into the cone divider  220  which establishes appropriate spacing for the multiplicity of cones  210 . Another function of the cone divider  220  is to provide a structure for joining of the flapper valve  240  and its associated components to the cone-to-core connectors  214 . A groove at the circumference of the cone divider  220  is fitted with O-ring  216  which will assist to seal the entire diffusion subassembly  200  within the cylindrical body tube  110 . There is some advantage for O-ring  216  to have a durometer of 55, rather than 70 which is otherwise typical. 
     In the preferred embodiment the diffusion cones  210 , cone-to-core connectors  214 , and flapper valve retainer  230  are made of a suitable plastic polymer, such as polyoxymethylene or POM Acetal. The same material is used for the flapper valve frame  250  with its inner stepped sleeve which serves as a lower flapper retainer. The cone divider  220  is an alloy of aluminum, with type  6061  having properties that are particularly well-suited for the present application. 
     The flapper valve  240  must be pliable in order to minimize the pressure required for its proper operation while providing reliable one-way pressure regulation within the presently described system. In the preferred embodiment it is made of a thin elastomeric material. The flapper valve  240  is placed over the flapper valve support  244  and this combination is then set around a hollow pedestal  248  at the center of a flapper valve frame  250 . The flapper valve frame  250  provides a valve seat against which the flapper valve  240  will seal when the fluid flow attempts to reverse. The primary function of the flapper valve support  244  is to provide support to prevent damage from excessive back pressure by keeping the flapper valve  240  from buckling and falling into the air cavity below it. Due to the material (316 Stainless Steel, US FDA Grade) from which it is constructed, the flapper valve support  244  also serves a secondary function as a filter screen. 
     A flapper retainer  230  is slipped onto the pedestal  248  to hold the flapper valve  240  in place, and to keep it from rising out of its seat in the presence of excessive forward flow which would occur in response to heavy suction. The cone divider  220  is placed atop the flapper subassembly separated by O-ring  222 . O-ring  252  is then set into a relief at the underside of the flapper valve frame  250  and this combination is stacked atop the Tighten Frame  256 . Capscrew  260 , inserted into the underside of Tighten Frame  256 , goes through the flapper valve frame  250  and threads into the underside of cone divider  220 . As capscrew  260  is tightened to seat against the underside of the Tighten Frame  256  the entire diffusion subassembly  200  including cone divider  220  and flapper valve components are drawn snugly together. 
     The assembly of the core of the Smoking Appliance  100  detailed in the present description continues with the Base Chamber  120  whose components are shown in  FIG. 6A  with details of the fittings in  FIG. 4 . The first stage filter disc  140  is inserted into the underside of the Base Chamber  120  to remove particles that are physically too large to pass through subsequent filter stages. Bottom cap  144  is fitted with O-ring  142  about its perimeter and placed into the Base Chamber  120 . A larger capscrew  148  is fitted with O-ring  146  and inserted through the bottom cap  120  and filter  140 . A recess in the upper side of the Base Chamber  120  receives Tighten Ring  124 . Another O-ring  126  is placed over the Tighten Ring  124  and the entire pre-assembled diffusion subassembly  200  is set above that. The base end  118  of outer body tube  110  is slipped over the diffusion subassembly  200  into the recess in the Chamber  120 . As capscrew  148  is tightened into the underside of Tighten Frame  256 , O-ring  126  is compressed to seal against the inner wall of the outer body tube  110  to hold it in place. 
     A Hollow Stem  184  is fitted with two O-rings  186  and  188  and inserted into Base Chamber  120 . Fitting of a nickel-plated brass Combustion Bowl  180  into the open end of Hollow Stem  184  completes the assembly of the base components. The coating of the Combustion Bowl  180  serves as a thermal barrier and distributes the heat of the burning load while also preventing oxidation of the brass which would affect the flavor of the smoke. Those skilled in these arts will recognize other material coatings that may be useful in this application. 
     The flapper valve  240  restricts the flow of fluid, whether air or water, in one direction. Its use in the presently described apparatus is to keep water from flowing into the interior of the diffusion cones  210 . The flapper valve  240  works in conjunction with the diffusion cones  210  to maintain a constant opposing pressure that resists the water as gravity tends to push it downward toward the interior of the cones  210 . This pressure is counteracted by the restriction against the reverse flow that is provided by the flapper valve  240  arranged in series with the dispersion cones  210 . Because of this opposite and equal pressure, an air-water barrier is maintained at some depth into the diffusion holes  218 , with the penetration distance depending on the depth of component submersion. This is the primary reason for providing the walls of the cones  210  with some thickness, since a deeper submersion causes a deeper dispersion which results in greater penetration of the cone thereby requiring a thicker cone wall. 
     The thickness of the cone wall is critical for a variety of reasons. Thicker walls increase the surface area to which tars can adhere, requiring an increased shear force to expel the adhered tars. In contrast, a wall thickness that is small compared to the nozzle diameter causes the tar to be subjected to a bending and tearing force, which requires significantly less pressure to achieve satisfactory removal of the tar from within the holes. Thinner walls contribute significantly to reduce clogging. Even under extreme conditions, such as when very cold water is placed into the chamber causing tars of greater density to form earlier in the filtering process, accumulation of tar with in the holes of thin-walled cones may still be negligible. Thinner cone walls also allow water to penetrate to the interior of the cones which flushes the nozzles as air is drawn through them. 
     During a smoking session the water bath will remain on the outside of the cones. However, if the pipe is set aside for more than two hours or so without being drained, then some of the water may eventually leak into the base due to imperfections in the flapper valve. If this should occur, most or all of the water that leaked into the base will be drawn back up into the chamber when the pipe is again placed into service. This does not hinder the performance of the pipe at all, and may serve as an occasional flush of the cones to prevent clogs. An alternate embodiment may incorporate one or more small overflow reservoirs into the base to accommodate this drainage. 
     When a gas moves through a flapper valve, the slight disturbance in the flow allows the more dense components of the gas to fall out of the stream. As applied to the presently described system, this means that the liquidus type of tar will condense out of the smoke and be deposited on top of the upward facing surface of the flapper valve  240 . This offers the advantage of increasing the amount of tar removed from the smoke. 
     For an understanding of the operation of the presently described smoking appliance, it will be useful to refer now to the schematic representation in  FIG. 7  along with the partial cutaway view of  FIG. 9 . In preparation for a smoking session, a small amount of water is poured into the outer glass body tube  110  of the smoking appliance  100 . Just enough water is used to fill the region containing the diffusion cones  210 , from their flared lower edges to their tops as can be seen in the schematic of  FIG. 7 . At this point in an operation cycle, no other region will contain any water, all other interior spaces of the smoking appliance  100  will contain clean air. 
     An amount of smokable material is then placed into the combustion bowl  180  and ignited. The user places a finger over the hole at the recirculation inlet  114  to close it off and begins to apply suction at the mouthpiece  112  to draw air through the burning load. As the combustible load burns, the lower portion of the base  120  will fill with smoke. The first stage micro-perforated filter  140  will trap the larger ash particles before they are drawn into the primary diffusion subassembly  200 . In the preferred embodiment of the appliance presently being described, this filter is a photo-chemically perforated piece of 316-type stainless steel with holes having a diameter on the order of 0.43 mm (0.017-inch). 
     In a short time, the region that includes the base  120  and the core interior below the flapper valve  240  will fill with smoke. With a lower pressure above the flapper valve  240  due to the applied suction, the valve will open to allow the smoke to fill the entire volume up to and including the interior of the diffusion cones  210 . As discussed earlier, some amount of the liquidus tar will condense out of the smoke and be deposited on top of the upward facing surface of the flapper valve  240 , amounting to a second stage in cleaning of the smoke. 
     With continued application of vacuum pressure to the mouthpiece  112 , the smoke will be pulled through the diffusion cones  210 . A third stage of the smoke cleaning occurs as the tar by-products condense out of the smoke at the boundary where the smoke and water meet. With a properly designed combination of flapper valve  240  and diffusion cones  210  water is kept to the outside of the cones so that most of the tar will condense in the water above the holes  218  rather than in them so as not to form a clog. 
     After the smoke is drawn through the water, it gradually accumulates to fill the central portion of the chamber above the surface of the water as can be seen in the partial cutaway view of  FIG. 9 . As the user continues to apply suction to the mouthpiece  112  while covering the recirculation inlet hole  114  to keep it closed, the smoke works its way upward towards the turbine subassembly  300 . The chamber fills smoothly from bottom to top as the smoke displaces the clean air, stratifying in a denser-than-air manner. Once the smoke reaches the turbine subassembly  300  it is directed through the inner tube  310  ( FIG. 6C ) to the upper chamber where it is drawn out through the mouthpiece  112  into the mouth of the user. 
     Since the Upper Carburetor Nozzle  304  is sealed against the inner surface of the outer body tube  110  by O-ring  302  ( FIG. 6C ), as long as the recirculation inlet hole  114  ( FIG. 7 ) remains closed there will be no pressure gradient in the region that extends downward from O-ring  302  to the lower rim (mouth) of the Carburetor Ring  322 . At this point in the smoking session, the small volume of air between the inner tube  310  and the outer body tube  110  that is bounded by the region between Carburetor Ring  322  and O-ring  302  is the only volume that remains clear, containing no smoke. 
     In the typical operation of a smoking session, when the smoke reaches the mouth of the user, the finger that is covering the recirculation inlet  114  will be removed. Referring to the schematic of  FIG. 8  in conjunction with the partial cutaway view of  FIG. 10 , it can be seen that as the user continues to apply suction to the mouthpiece with an open recirculation inlet  114 , the relatively lower pressure present inside the chamber will draw clean air inward through the recirculation inlet  114  and direct it downward through the spiral veins of the static turbine  320 . This downward flow will receive some small convective assist due to the fact that the incoming air is cooler than the smoke-laden air within the pipe  100 . Positioning of the recirculation inlet  114  for use in conjunction with the turbine subassembly  300  has a secondary benefit of allowing the user to introduce incoming air from an aesthetically pleasing location, without having to touch a hot combustion bowl. 
     As the cooler incoming air is made to swirl downward a spinning hollow jacket of air is created that moves along the inside wall of the outer body tube  110  toward the water. The swirling motion maximizes the surface area of the exposure boundary between smoke and incoming atmospheric air assisting to quickly cool the smoke without diluting it, while the outer jacket of cool air has some additional cooling effect on the smoke-laden air which it surrounds.  FIG. 11  shows the generation of the vortex which develops with a lower pressure at its center. The resultant centrifugal force expels heavier tar particulates from the swirling smoke toward the inner wall of the body tube  110  while keeping incoming air from diluting the smoke during the cooling process. 
     Furthermore, the spiraling downward air loses its vertical momentum as it encounters the water surface where it effectively ricochets back upward while maintaining its angular momentum as it is drawn to a smaller radius. This circular motion is depicted in  FIG. 12  which has been taken along the section line  12 - 12  of  FIG. 8 . The overall effect of this helical fluidic motion is that the formerly stratified smoke-laden air will be compressed toward the center of the outer body tube  110  and drawn upward through the smaller diameter of the inner tube  310  of the turbine assembly  300  with a pressure-assisted velocity boost. The effect upon the user is that moving of the finger to unblock the recirculation inlet  114  results in the user&#39;s lungs receiving a sudden influx of smoke as it is driven out of the pipe  100  with little to no resistance internal to the pipe  100 . 
     As pressures equalize within the pipe  100 , the incoming cooler clean air will push the smoke upwards from the water-smoke boundary until the entire device, with the exception of the lower interior core area within the base chamber  120  is again filled with the clean air. With the user supplying continued suction to the mouthpiece  112 , in a short while the system will stabilize to a condition similar to that which existed shortly after the smokable material was ignited. 
     The above operation may be modified in part by the addition to the system of a Purge Valve subassembly  270  ( FIG. 13 ). The Purge Valve subassembly  270  complements the performance of the flapper valve  240  by reducing the amount of time required for backwash of the diffusion subsystem each time the user relieves pressure after a draw at the mouthpiece  112 . The schematic of  FIG. 14  shows that a buoyant plastic ball  280  is enclosed within a valve body, or chamber,  274 . The ball achieves its buoyancy by virtue of being hollow. The interior of the chamber  274  is formed with a tapered seat at each end, a lower tapered seat  282  and an upper seat  284 . Although described as tapered seats ( 282  and  284 ), those skilled in such art will recognize advantages to seats that are shaped other than tapered, for example, the seats may be radiused. The lower end of the body  274  is connected through a purge valve inlet tube  272  to the pressurized side of the chamber containing the flapper valve  240 , while the upper end of the body  274  is open to the atmosphere outside of the tube  110  through a snorkel  276 , or exhaust tube. 
     Before starting a smoking session the diffusion chamber  205  will be filled with water to cover the diffusion cones  210  until equilibrium is reached. This occurs as the water bath seeps through the diffusion cones and down into the distribution chamber  225  where water pressure keeps flapper valve  240  in the closed position. Thus sealed, the distribution chamber  225  fills and water rises into the purge valve body  274  causing the buoyant plastic ball  280  to float until it reaches the upper seat  284  where it seals the opening to the snorkel  276 , preventing escape of water into the exhaust tube. 
     As the user draws vacuum pressure at the mouthpiece  112 , the purge assembly  270  empties of water and gravity causes the ball  280  to drop into the lower tapered seat  282  where it becomes lodged at the bottom of the chamber  274 . Continued negative pressure causes the flapper valve to open to position  240 ′ allowing smoke to be drawn from the filter chamber  150  through the filters  140 . The smoke continues to fill the distribution chamber  225  and then passes through the diffusion cones  210  into the water bath in the diffusion chamber  205  where it is cleaned and cooled before passing upward through the tube  110  to the user&#39;s mouth. 
     As the user ceases to inhale, the pressure interior to the tube  110  equalizes toward the atmospheric pressure at the mouthpiece  112  causing the pressure gradient across the purge chamber  274  to invert. This change in pressure allows water to rush down through the diffusion cones  210 , then through the inlet tube  272  into the bottom of the purge valve chamber  274 . This reverse flow causes the ball  280  to be forced out of the lower tapered seat  282 . The ball  280  then is carried by motion of the incoming water and floats up toward the upper tapered seat  284  into which it is pressed, sealing against the seat  284  to disrupt the flow of water into the chamber  274 . 
     When the user again applies a vacuum to the mouthpiece  112 , water that has accumulated in the purge valve chamber  274  is drawn back out into the main tube  110  until the ball  280  again drops against the lower seat  282 . With the purge valve  280  thus effectively stoppered, the vacuum is diverted to draw smoke through the flapper valve  240 . This washing, or flushing, motion serves the overall smoking appliance  100  as a self-cleaning feature. 
     At the end of a smoking session, it is important that the pipe  100  be cleaned. Referring to  FIG. 6D , the cleaning operation is facilitated by the drain subassembly  160 . This subassembly includes a drain hole  162  in the side of the outer body tube  110  which has been fitted with a drain body  164  and O-ring  166 . During a smoking session a drain cap  168  is used to cover the drain body  164  to maintain an airtight seal. 
     Additional cleaning of filters and diffusers is facilitated by Clean-out plug  170  shown in  FIG. 17 . Removal of the plug allows the user to force water through the hole into the filter chamber  150  for backwashing of the filters  140 . At the same time water is forced into the distribution chamber  225  to flush the diffusion cones  210 . This process provides a quick and effective means of cleaning the smoking apparatus  100  without requiring any disassembly. 
     When it is time to empty the water pipe of its water bath at the end of a smoking session, the user will remove the drain cap  168  and gently tip the pipe  100  so as to direct the contaminated water through the drain hole  162  into an appropriate disposal basin. Since the used water bath is likely to contain solid matter, it is desirable that the water pipe  100  be drained in this manner so as to avoid contamination of the turbine subassembly  300 , though this is more a matter of maintaining an attractive appearance than it is an operational consideration. The position of the drain subassembly is such that the water pipe  100  may be filled in the basins of most lavatories. 
     Having described in some detail the features of the preferred embodiment, it will be recognized by those skilled in the associated arts that the function of each of the subassemblies may be accomplished by alternate constructions. As a first example, consider the diffusion subassembly  200 , the function of which is to disperse tobacco smoke through a water medium while avoiding clogging of the diffusers. This function requires that both of the sub-functions of the flapper valve  240  and the diffuser must be present. However, these may be accomplished in manners other than those described in reference to the preferred embodiment. 
     For a brief discussion of one alternate embodiment of the diffusion subassembly  200 , refer to  FIG. 15 . Here, the multiple diffusion cones  210  of the preferred embodiment have been replaced with a solid one-part flat diffusion matrix  208 . The diffusion holes  218  in this alternate embodiment point directly upward toward the surface of the water instead of outward as in the earlier described cone-style distributor. 
     A further alteration (not shown) takes a single diffusion cone and relocates the flapper valve within that cone, above any cone-to-core connector. Yet another alternate embodiment uses multiple instances of cones each containing its own flapper valve. In such an embodiment each cone is mounted on its own cone-to-core connector (similar to  214 ) and the multiplicity of cone-to-core connectors is then supported by a single cone divider (similar to  220 ). These alternate embodiments offer the advantage of being able to handle higher back pressure due to the decreased volume of air that is compressed beneath the cones. 
     Yet another alternate embodiment addresses the flapper valve. The implementation of  FIG. 16  increases the efficiency of the diffusion system by reducing the amount of pressure required of the user to draw air through the diffusers. This is accomplished by an electromagnetic assist mechanism. A fixed-position electromagnetic coil  238  is supported by an electromagnetic core  236 . A movable linear-motion sliding ceramic-coated magnet  234  is located on the opposite (lower) side of the flapper valve  240 . When activated, the electromagnetic coil  238  assists to move the flapper valve  240 . The electric current to operate the electromagnetic coil  238  may be produced by a power source and controlled by a sensor mounted in the vacuum area. The sensor detects the pressure gradient and the amount of current supplied to the coil is adjusted as a function of that differential. In this embodiment the pressure necessary to operate the flapper valve can be tuned as the lifting force of the magnet is used to cancel the downward force of the flapper which results in minimal overall pressure required to operate the entire device. For purposes of clarity the sectioned electromagnetic coil  238  of  FIG. 16  is not hatched. 
     Unlike the Purge Valve subassembly  270  which assisted in the operation of the flapper valve  240 , a Water Column subassembly  290  may be used as a substitute to replace the flapper valve  240  completely. As shown in the perspective view of  FIG. 17  and depicted schematically in  FIG. 18 , an inverted a U-shaped tube  290  is placed into the diffusion chamber  205  which surrounds the outside of the diffusion cones  210 . A higher end  292  of the water column tube  290  forms a watertight connection to the distribution chamber  225  at the underside of the diffusion cones  210  and the manifold that supports them. A lower end  294  of the water column tube  290  extends through the distribution chamber  225  and fits into channel  298  which connects to the filter chamber  150 . 
     Prior to use, the diffusion chamber  205  is filled with sufficient water to cover the diffusion cones  210 . The water seeps through the diffusion cones  210  into the distribution chamber  225  and enters the higher end  292  of the water column tube  290  until equilibrium is reached at which point the water level inside the water column matches the level of the water bath in the surrounding diffusion chamber  205  outside. If the diffusion chamber  205  is overfilled, the water level will reach the midsection  296  of the water column tube  290  and will drain down through the lower end  294  of the water column tube  290  into the filter chamber  150  from which it will need to be drained. 
     When the diffusion chamber  205  is properly filled to cover the diffusion cones  210  without overfilling, the pipe  100  is ready for the user to apply suction to the mouthpiece  112 . Negative pressure in the tube  110  draws the water bath slightly upward within the tube  110  which in turn draws smoke out of the filter chamber  150  and through the entire length of the water column tube  290  until the distribution chamber  225  is completely filled with smoke. As the user continues to draw, smoke is pulled through the diffusion cones  210 , is cleansed and cooled by the water bath upward through the tube  110  as with other embodiments. 
     When the user ceases to draw vacuum pressure, the water bath within the diffusion chamber  205  drops under the influence of gravity and seeps through the diffusers  210  until the distribution chamber  225  is completely filled with water which then rises into the upper end  292  of the water column  290  until it again reaches equilibrium at the same elevation of the water contained in the main chamber  110 . This cycle produces a mild flushing action following each draw by a user. Over an extended life of a smoking apparatus  100 , the use of a water column subassembly  290  offers an advantage in reliability over the flapper valve  240  due to its lack of moving parts. 
     As mentioned above in the discussion of the general assembly of the pipe in  FIGS. 4 and 6B , the thickness of the wall of the diffusion cones  210  is critical. When a water column  290  is used, thicker walls become desirable in order to withstand the extra pressure of water washing back and forth through the perforated surface. However, as discussed earlier, thicker walls increase the surface area to which tars can adhere, requiring an increased shear force to expel the adhered tars, whereas thinner walls tend to reduce clogging. This is especially true when the wall thickness is small compared to the nozzle diameter which subjects accumulated tar to bending and tearing forces, enabling removal of the tar from within the holes with less pressure. 
     One solution to this seeming paradox is shown in the close-up cutaway view of the diffuser cones  210  in  FIG. 19 . Here it can be seen that the outward facing counterbore of each hole throughout the multiplicity of holes has a diameter that is large relative to the diameter of the hole at the inner surface of the diffusion cone. The relatively thick wall of the diffusion cone  210  holds up well against higher pressures. At the same time the counterbored holes present a relatively thin wall at the inner surface of the diffusion cone  210  to enable the bending and tearing action that discourages the accumulation of tar within the holes and enables cleaning at lower pressures. 
     Although the presently disclosed apparatus has been described as a water pipe for the cleaning of tobacco smoke, it will be recognized by those skilled in the related arts that the described method has other applications in other industries. The method is especially useful for the washing of gases where the gas flow is not constant, or may even be intermittent, cycling on and off. The method is also applicable to the washing of gases that contain heavy condensates such as airborne tar particulates. Furthermore, the presently described method is useful for gases that may react with the liquid medium used in the bath where it is specifically preferred that the reaction take place outside of the diffusion device. 
     It will be obvious to those having skill in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present disclosure should, therefore, be determined only by the following claims.