Abstract:
Method for generating foam for use in fire fighting having two plates housed in a chamber which respectively introduce pressurized air and a water/surfactant solution between the two plates where foam is generated and emitted from an aperture on the side of the chamber. The pressurized water/soap solution enters the chamber through an orifice in one plate. Pressurized air enters the chamber through a number of channels bored through the other plate, such channels appearing in an annular grove which circumscribes the water inlet. The plates are provided with surfaces which are brought together to form a restricted area therebetween. The restricted area balances the pressure between the incoming water and the incoming air by achieving an equilibrium at some particular radius out from the center of the two plates. This equilibrium radius moves in and out from the center as necessary to keep the two pressures balanced. The method also includes a pressure regulating system that automatically cuts off the flow of pressurized water and air when the foam dispensing nozzle is turned off.

Description:
The present application is a continuation of application Ser. No. 09/014,873, filed Jan. 28, 1998, now U.S. Pat. No. 6,086,052, which was in turn a continuation-in-part of application Ser. No. 08/759,888, filed Dec. 3, 1996, now U.S. Pat. No. 5,837,168, which are considered to be part of the disclosure of the present application and are thereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to devices for generating foam for use in fire fighting and specifically to a foam generator which provides for automatic balancing of pressure differentials between incoming pressurized water and pressurized air. 
     Foam generators utilizing pressurized water and pressurized air in combination with a surfactant are useful in fire fighting. There are certain well known means of mixing air, water, and a surfactant to generate foam, including mixing chambers, venturis, and nozzles. 
     U.S. Pat. No. 4,981,178 issued to Bundy on Jan. 1, 1991 discloses an apparatus for generating fire-fighting foam using a mixing chamber. 
     U.S. Pat. No. 4,505,431 issued to Huffman on March 19, 1985 for “Apparatus for Discharging Three Commingled Fluids” and U.S. Pat. No. 4,474,680 issued to Kroll on October 2, 1984 for “Foam Generating Apparatus and Method” disclose venturi-type foam generators. 
     It has been very difficult in the past to produce a simple device for generating foam from the mixing of pressurized air and pressurized water. (The foam also requires the presence of a soap or surfactant which is introduced into the water prior to the foam generator.) Pressure balancing between incoming pressurized air and incoming pressurized water requires elaborate measures to control both the air volume and pressure and the water volume and pressure. It has generally been necessary to use very complicated devices to balance the volumes and pressures or to require the operator to manually adjust the volumes and pressures on a continuous basis during operation to maintain a balance. Thus a skilled operator is typically required to operate such systems. 
     If a balanced pressure is not maintained, the quality of the foam being generated can be affected. Various types of foam may be desirable for particular applications. In some situations a dry foam is desirable; in other situations, a wetter foam is desirable. Too much water or too much air can result in a foam that is not efficient for the intended purpose. For example, in some situations, the most desirable type of foam contains sufficient moisture to aid in smothering a fire while it is sufficiently dry to cling to surfaces. If a balanced pressure and volume of water and air is not maintained, the result can be a foam that is either too wet or too dry or that has other deficiencies with respect to the desired quality. The volume of water in relation to the volume of air determines the consistency of the generated foam, so the control of both pressure and volume is necessary to assure the desired foam quality. 
     The prior art emphasizes the importance of maintaining balanced pressures between the water and air supplies. Bundy, at column 3, beginning at line 12, discusses the problem of achieving the proper combination of air pressure and volume with water pressure and volume to achieve the desired quality of foam. Bundy also discusses the desirability of maintaining equal pressure in the air and water supplies. 
     The prior art has addressed the problem of balancing the air and water supply pressure in a foam generator by various expedients as mentioned above. Even with the fairly complex and expensive means employed, the operation of a foam generating apparatus for fire fighting requires the services of an experienced operator and even then much experimentation is necessary. For example, even the simple act of changing a hose attached to the apparatus often requires difficult and time consuming rebalancing of the system. 
     It has been suggested that a high degree of turbulence may contribute to the quality of foam produced in that a finer foam structure is obtained. Foam comprised of large bubbles is less useful for typical fire-fighting applications. It may therefore be desirable to both balance the pressures of the incoming water and air and do so in a way that maximizes turbulence. 
     Prior foam generating systems lack a means to automatically cut off the flow of water and air into the system&#39;s hose when the hose nozzle is turned off. This may create an unsafe condition if system air and water pressures are not precisely balanced. If the system water pressure exceeds the system air pressure, closing the nozzle may cause a “slug” of water to build inside the hose. When the operator again opens the nozzle and expects a relatively low-density foam to emerge, the slug of water that squirts forth may cause the operator to lose control of the hose. Conversely, if the system air pressure exceeds the system water pressure, a pocket of air may build in the hose when the nozzle is closed. Subsequent opening of the nozzle may send forth a burst of oxygen onto a flame thereby aiding the spread of a fire rather than extinguishing it. Either a slug of water or burst of air may thus result in serious injury to the hose operator or bystanders. Given the difficulty in prior art foam generating systems of maintaining a precise balance between system air and water pressure, it has been difficult to prevent these unsafe conditions. 
     The problems and limitations of the prior art are overcome by the present invention as summarized below. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus for generating foam for use in fire fighting. The invention utilizes a unique mixing chamber designed to automatically balance the dynamic pressure of incoming air and water streams and thereby produce high-quality foam even if the incoming static air and water pressure vary significantly. This allows the foam generator to work in a wide variety of situations and environments, even with makeshift compressor and pump equipment, without the necessity of complicated calibration steps. Such versatility is highly desirable for firefighting, especially in rural areas where specialized equipment may be unavailable. 
     In the present invention, pressurized water (including a surfactant) and pressurized air are introduced in such a way as to automatically achieve the desired balance between water and air pressures, and also produce a highly turbulent environment which conduces to the formation of a high quality foam. The apparatus includes an automatic regulator that stops the flow of air and water when the nozzle is turned off, thereby preventing the safety hazard created if the hose were to fill with unmixed water or air. This automatic regulator also prevents the backpressure in the hose from exceeding either the incoming air or water pressure. 
     The water and air pressures in a foam generator derive from three components: a static or head pressure, which is the input pressure from the water pump and air compressor of the system; a dynamic pressure within the mixing chamber, which is determined by the flow rate of water and air input into the chamber; and a residual pressure or backpressure from the hose. Prior art foam generators have attempted to balance the static water and air pressure. In conventional systems, this balance is necessary since if either pressure exceeds the other, it will prevent the formation of high-quality foam. Thus conventional foam generators are only effective for firefighting purposes if the input air and water are at precisely the same pressure. 
     The present invention, by contrast, focuses on dynamic pressure as a means to both balance the water and air pressure within the mixing chamber and to achieve a highly turbulent environment conducive to excellent foam quality. In the present invention, water is introduced into a restricted area in the mixing chamber with an ever-widening area for expansion as it travels farther toward the air source. The water pressure falls as the water travels through the widening area approaching the air inlets, such that a point is eventually reached where the water pressure falls to equal the air pressure it encounters. If either the static air or water pressure is changed, the equalization point may move further or closer to the air or water inlets, but will still lie somewhere between the two inlets so that mixing will occur. Thus equalization of dynamic pressures takes place automatically due to the design of the mixing chamber. As long as the static pressures are maintained within a certain range, the system will automatically readjust and still deliver excellent-quality foam since an equalization pressure will still be reached. The energy lost as the water and air lose energy is converted into turbulence that serves to thoroughly mix the water and air and thereby produce high-quality foam. 
     In order to achieve this rapid conversion of the dynamic pressures of the incoming water and air into turbulent energy, the incoming water and air streams should be directed onto a surface which stops or splatters the streams, or against another stream. In addition to balancing the water and air pressures, the “splattering” effect also produces the highly desirable turbulent environment and separates the incoming water into fine droplets to speed mixing with the incoming air. 
     In the preferred embodiment of the invention, the heart of the foam generator is two plates housed in a chamber where pressurized air and water are introduced into the restricted area between the two plates. The pressurized water is introduced through an opening in one plate. The pressurized air is introduced into the restricted area through a number of channels bored through the other plate. The air channels may appear in an annular grove, placed on the surface of the plate, that circumscribes the water inlet. While introducing the pressurized air into an annular groove is not necessary to the practice of the present invention, it does serve to improve mixing of the water and air by producing still more turbulence upon exit of the water and air from between the two plates. 
     In the preferred embodiment, the two plates are provided with flat surfaces, and when in operation, are in close proximity to each other. The narrow restricted area between the plates provides part of the mechanism that helps to equalize the pressure between the incoming water and the incoming air. Preferably the two plates are placed in such proximity that the turbulence effect created by the plate walls is significantly enhanced. 
     The water/surfactant solution and the air will intermingle in this restricted area in a highly turbulent fashion, and upon exiting the restricted area will produce a foam. The consistency of the foam can be adjusted by the operator by adjusting the incoming water pressure or volume, the incoming air pressure or volume, or by moving the plates relative to one another. 
     In some embodiments the air inlets may be set at an angle, such that the air inlets are turned somewhat toward the water inlet. It is believed that forcing the pressurized air between the plates at this angle, which preferably is about a 45°, creates even greater turbulence when the air and water meet, thus improving the quality of the resulting foam. 
     It is therefore an object of the present invention to provide for a self-balancing, foam-generating mechanism using pressurized water and pressurized air. 
     A further object of the present invention is to provide for a foam-generating mechanism using pressurized water and pressurized air which is simple and economical to construct and easy to operate. 
     An additional object of the present invention is to provide for a foam-generating mechanism using pressurized water and pressurized air which produces varying qualities and quantities of foam and accepts varying lengths and types of hoses without requiring complicated and delicate rebalancing of air and water pressures. 
     A further object of the present invention is to provide for a foam-generating mechanism using pressurized water and pressurized air that may be used with a wide assortment of different compressors and water pump mechanisms and may be operated by less skilled persons. 
     A still further object of the present invention is to provide for highly turbulent mixing of the pressurized water and air to produce an exceptionally high-quality foam. 
     Yet another object of the present invention is to provide a foam-generating mechanism with a regulator that automatically cuts off the flow of pressurized air and water into the system when the nozzle is closed, thus preventing the dangerous situation of a slug of water or burst of air emerging from the hose when the nozzle is reopened. 
     Further objects and advantages of the present invention will be apparent from a consideration of the following detailed description of the preferred embodiments in conjunction with the appended drawings as briefly described following. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exterior perspective view of a chamber containing the foam generating plates and having incoming lines for pressurized water and air and an exit for foam generated in the chamber. 
     FIG. 2 is a sectional elevation view of the chamber of FIG. 1 showing the pressurized water plate and the pressurized air plate located to the top and bottom respectively of the chamber with the foam generating area therebetween. 
     FIG. 3 is a sectional plan view of the chamber showing the pressurized air plate and the annular groove thereon. 
     FIG. 4 is a schematic diagram showing the components of a complete foam generating system employing the present invention. 
     FIG. 5 is a perspective view of a second embodiment of the present invention for use in high pressure situations in which the plates are carried on respective plugs which are held to the chamber by bolts. 
     FIG. 6 is a sectional view of the embodiment of FIG.  5 . 
     FIG. 7 is a sectional plan view of a third embodiment of the present invention with an adjustable distance between the plates and a foam exit tube that is perpendicular to the air and water inlets. 
     FIG. 8 is a sectional plan view of a fourth embodiment of the present invention having a fixed distance between the plates and a water inlet and foam outlet that are in line with one another. 
     FIG. 9 is a schematic diagram showing a preferred embodiment of the regulator and automatic cut-off system of the present invention. 
     FIG. 10 is a schematic diagram of a detail section from FIG. 9 showing the operation of the pressure regulator cylinder and automatic cut-off microswitch. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention may be described with reference to FIGS. 1 and 2. A chamber  10  is provided which accepts an incoming pressurized water line  20  and pressurized air line  30 . Foam generated in the chamber  10  exits through the outlet  40 . 
     The heart of the present invention is found in the provision for two plates  50 ,  60  where the incoming water and air are introduced to each other. The shape of the chamber  10  in which the foam is generated is not critical to the invention, although the chamber  10  should allow space around the plates  50 ,  60  for the generated foam to exit. Furthermore, it is desirable to avoid shaping the chamber  10  such that a spiraling action is induced in the foam. Such action can separate foam into its primary constituents by centrifugal force. 
     The pressurized water plate  50  is simply a circular disc  51  with a bore  52  through the center for the introduction of pressurized water to a restricted area  70  between the plates  50 ,  60 . The bore  52  may be reduced by an orifice for better control of the pressure and for adjustment of the volume of the incoming water. As will be discussed hereinafter, the pressurized water contains an admixture of surfactant which is introduced to the pressurized water prior to the chamber  10  by various means well known in the art. 
     As shown in FIGS. 2 and 3, the pressurized air plate  60  is likewise a circular disc  61  having a restricted area-facing surface  62  on which an annular groove  63  is disposed on the surface  62  and may be located at various radial distances from the periphery of the surface  62 . In some embodiments, it may be desirable to place surface roughening features such as ripples or grooves between the annular groove  63  and the periphery of the surface  62  in order to enhance turbulence and mixing. The annular groove  63  is fed pressurized air from a plurality of radial passages  64  communicating with an inlet bore  65 . The inlet bore  65  in turn communicates with the incoming pressurized air line  30 . Alternatively, the radial passages  64  may be replace by a plenum receiving pressurized air and communicating with the annular groove  63  by simple openings. When a plenum is employed it may be desirable to have the pressurized air enter the plenum at right angles to the openings communicating with the annular groove  63  in order to ensure an even pressure among the openings and therefore at all points on the annular groove  63 . 
     FIG. 4 is an overall schematic of a complete system incorporating the present invention showing an air compressor  80  connected by air line  81  leading to the air inlet  30  of the chamber  10 , and a water pump  82  connected to water reservoir  84  and to water line  83  leading to the water inlet  20  of the chamber  10 . Not shown are valves in the air line  81  and the water line  83  for setting the volume and pressure of the incoming water and air. Also shown in the schematic is a soap reservoir  85  and dispenser  86  into the water inlet line  83 . 
     FIGS. 5 and 6 show a second preferred embodiment of the present invention. There are three primary pieces to the preferred embodiment of the foam generator of the present invention. The assembled foam generator is shown in perspective in FIG.  5 . First, there is a housing  90 , which is preferably constructed of stainless steel. The housing is a T-shaped hollow chamber having an water inlet section  91  and air inlet section  92  across the top of the “T” and a foam outlet section  93  at the base of the “T”. The foam outlet section  93  at the base of the T-shaped chamber is reduced to a pipe which is the nozzle opening  94  or connection point for a hose. While the prior art normally uses the hose as part of the foam generating apparatus, the present invention requires only a minimal length of hose. Foam is generated in the housing  90  and available in close proximity to the nozzle opening  94 . 
     Fitting into the housing  90  are two plugs  95 ,  96 , preferably of plastic, which fit in respective open ends  97 ,  98  of the water inlet section  91  and air inlet. section  92 , respectively, at the top of the T of the housing  90 . These two plugs  95 ,  96  incorporate the plates  100 ,  101 , which introduce pressurized water and air into the restricted area  104  between the two plates  100 ,  101 . 
     A section of the embodiment of FIG. 5 showing the two plates  100 ,  101  is given in FIG.  6 . Each plug  100 ,  101  is provided with a flange  102 ,  103 , respectively, which fits against the respective open ends  97 ,  98 , and serve to fix the plugs into position so as to form a restricted area  104  of the requisite width. Each plug  95 ,  96  is reduced to a middle section  105 ,  106  sized to fit tightly in either open end  97 ,  98 . Each plug is further reduced to an inner section  107 ,  108 . When the two plugs  95 ,  96  are assembled into the housing  90 , the restricted area  102  between the two plugs  95 ,  96  is set at the desired distance. 
     Plate  100  introduces pressurized water into the restricted area  102  through a bore  112  which is connected to the inlet water supply by an integral water inlet connection  113 . Likewise, plate  101  introduces pressurized air into the restricted area  102  through an annular groove  114  fed by radial passages  115  from an inlet bore  116  provided with an integral air inlet connection  117 . The generation of foam is otherwise identical to that described above for the embodiment of FIGS. 1-4. 
     A device sized to deliver foam to a 1½ inch hose from a 100 psi water supply and 100 psi air supply would have inlets  91 ,  92  about 3 inches in diameter. The foam outlet section  93  at the base of the T-shaped chamber is reduced to a pipe approximately the diameter of the hose. In this sized embodiment, the outermost part of each flange  102 ,  103  is about 6 inches in diameter. Each plug  95 ,  96  is reduced to a 3 inch diameter middle section  105 ,  106  to fit tightly in either open end  97 ,  98 . Each plug is further reduced to an inner section  107 ,  108  of about 2 inches in diameter. In this embodiment, when the two plugs  95 ,  96  are assembled into the housing  90 , the restricted area  102  between the two plugs  95 ,  96  is preferably about {fraction (3/16)} inch. 
     As shown in FIGS. 5 and 6, the two plugs  95 ,  96  are held to the housing  90  by four bolts  110  through holes in the flanges  102 ,  103 . Although not critical, it is desirable that a space  111  be left around the plates  100 ,  101  and the restricted area  102  to allow the free exit of foam generated between the plates  100 ,  101 . 
     A third preferred embodiment of the present invention is shown in FIG.  7 . This embodiment uses a chamber of generally cylindrical shape, with a water inlet  120  directed into the center of one end of the chamber. Air inlet  122  passes through this same end of the chamber, allowing pressurized air to pass into the chamber and then through air orifices  132  in first plate  133 . Air orifices  132  are angled toward the center of the chamber and thus toward the direction that water will travel when it enters through water inlet  120  and strikes second plate  131 . Second plate  131  includes an adjustment feature  130 , which may be in the form of a threaded bolt that extends through the opposite end of the chamber. Adjustment feature  130  allows the operator to vary the width of the restricted area between first plate  133  and second plate  131  which will affect the type of foam that is produced. In this way the operator may create whichever type of foam is necessary for a given application, such as when a dryer foam is needed to adhere to vertical surfaces, or a wetter foam is needed for spraying foam long distances against a wind. The foam exits the chamber at foam outlet  124 . 
     A fourth preferred embodiment of the present invention is illustrated in FIG.  8 . Like the embodiment of FIG. 7, this embodiment uses a chamber of generally cylindrical shape, with a water inlet  134  directed into the center of one end of the chamber. Air inlet  136  allows pressurized air to pass into the chamber and then through air orifices  144  in first plate  145 . Air orifices  144  are angled as in the embodiment of FIG.  7 . In this embodiment, second plate  143  is fixed in position relative to first plate  145  by bolts. The foam exits the chamber through foam outlet  138 , which extends from the opposite end of the chamber through which water inlet  134  passes. 
     The system by which air and water pressure is regulated in the preferred embodiment of the foam generator apparatus is illustrated in FIGS. 9 and 10. Water is drawn from water reservoir  194  and pressurized by water pump  146 . A surfactant from soap reservoir  148  is added to the pressurized water by soap dispenser  150 . The mixture is pumped through water manifold  152 , then through water check valve  154  which prevents backflow of water or air through the system. Flow sensor  156  feeds flow information to flow indicator  192 , which may be used by the operator to adjust the system to reach a desired volume of water per unit time. The water then flows through water valve  158  (the function of which will be described below) and into mixing chamber  160 . 
     Turning now to the pressurized air side of the system, compressor  196  forces pressurized air through air manifold  162  and through air valve  164  (the function of which will be described below), then through flow control valve  166  and air flow meter  168 . Based on the reading on air flow meter  168 , the operator may adjust flow control valve  166  to reach a desired air flow volume per unit time. Air then flows through air check valve  170 , which prevents the backflow of air or water through the system, and into mixing chamber  160 . Foam created in mixing chamber  160  travels through hose  172  and out through nozzle  174 . 
     Pressure regulator  182  (shown in detail in FIG. 10) is used to cut off the flow of air and water automatically when nozzle  174  is closed, thereby preventing the buildup of either a slug of water or burst of air in hose  172 . When nozzle  174  is closed, backpressure builds in the hose and back through the chamber, which quickly exceeds the system static air pressure. This backpressure forces diaphragm  200  in pressure regulator  182  upward. The arm extending vertically from diaphragm  200  thus presses against contact arm  198  of microswitch  180 , causing contact arm  198  to bridge the two electrical contacts of microswitch  180  and close the electrical circuit formed thereby. Closing this circuit activates electric solenoid  186 , which in turn actuates shut-off control valve  188 , which simultaneously closes both water valve  158  and air valve  164 . This prevents the flow of either water or air to mixing chamber  160 , thus preventing the buildup of a slug of water or burst of air in hose  172  when nozzle  174  is closed. 
     Once nozzle  174  is opened again, the system backpressure will fall, thereby allowing diaphragm  200  to fall and opening the electrical circuit previously closed by contact arm  198  of microswitch  180 . Spring return  190  will then simultaneously open water valve  158  and air valve  164 . This will allow water and air to again enter chamber  160  and thus the system will begin generating foam again automatically. 
     Alternatively, the pressure regulator could use a controller (not shown) in communication with microswitch  180  that activates microswitch  180  when the system backpressure rises above a threshold value. Once microswitch  180  is activated, water valve  158  and air valve  164  will simultaneously close. When the system backpressure falls below the threshold value, the controller deactivates microswitch  180  thereby allowing spring return  190  to simultaneously open water valve  158  and air valve  164 . The controller can be preset to a certain threshold pressure value, or can include means (such as a dial or keypad) to enter the threshold pressure desired by the operator. 
     In operation of the preferred embodiments described herein, the incoming static water pressure is generally set to a level in excess of the incoming static air pressure. The difference is not critical. The pressure at the periphery of the plates is determined by the outlet back pressure due to the chamber size, the hose, nozzle, and any orifice or restriction in the outlet side of the system. The pressure at the center of the plates is determined by the inlet water pressure, and the pressure available at the annular grooves is determined by the inlet air pressure. The back pressure at the periphery of the plates is at some level higher than atmospheric, but lower than either the pressure at the water inlet or the air inlet. Air is of course compressible, while water is not. It is believed therefore that due to the lower air pressure and the compressibility of the air, a balanced pressure between the air and water is reached at some radial point between the air inlet at the annular groove and the water inlet at the central bore. This radial equilibrium point will shift radially between the air and water inlets depending on the incoming volume and pressure of water, thus automatically balancing the two. As the back pressure changes, the pressure at the balance point will change proportionally. The balancing of the dynamic water pressure and air pressure is therefore automatic without the need for intervention by the user. This mechanism is believed to explain the operation of the present invention but the invention is not limited thereto. Additional adjustment of the mechanism to enhance the quality and quantity of the foam is possible through adjustment of the size of the restricted area between the two plates. 
     Furthermore, it is desirable that the proximity of the plates be such as to induce a high degree of turbulence into the mixing. This is accomplished by putting the two plates in close proximity. Thus a large proportion of the mixing takes place between the plates and the hose is not as necessary to act as a turbulent mixing chamber. This frees the operator from any problems involved in rebalancing the system when hoses or lengths of hoses are changed. Furthermore, since the hose is not occupied by unrestricted air, the hose may be operated at peak capacity resulting in maximum flow and increased trajectory for the foam exiting from the nozzle of the hose. Better mixing before the hose also allows better foam quality with finer structure when such is desirable. In those embodiments of the present invention utilizing plates that are movable relative to one another so as to vary the size of the restricted area between them, the water pressure within the mixing chamber may also be regulated by movement of the plates. 
     The present invention also has the advantage that it allows more flexibility in the use of pumps and compressors. As an example, one large pump might supply several foam lines independently of each other. Oversize pumps and compressors may be utilized without alteration. The present invention allows the air pressure to fluctuate which enables the compressor to cycle without adverse effect on the foam. 
     Although the preferred embodiment has been described with respect to a version of the present invention in which two plates are used and each plate introduces only water or air to the restricted area between for mixing, an alternative embodiment may employ two plates in which one plate serves as the impingement surface and the other plate contains passages for introducing both pressurized air and a pressurized solution of water and surfactant. This arrangement utilizes the same principles for operation, but may have advantages allowing a compact design. 
     The present invention has been described with reference to certain preferred and alternative embodiments which are considered exemplary only and not limiting to the full scope of the invention as set forth in the appended claims.