Electronically Controlled Direct Injection Foam Delivery System and Method of Regulating Flow of Foam into Water Stream Based on Conductivity Measure

Abstract

Fire fighting equipment uses an electronically controlled direct injection foam delivery system. A water pump pumps water through a pipe. A foam pump pumps foam into a mixing chamber within the pipe to produce a water-foam mixture. A microprocessor-based control unit controls the water pump and foam pump. A conductivity sensor is coupled in-line with the pipe for monitoring conductivity of the mixture and providing a feedback signal to the control unit to regulate the foam pump. A speed sensor monitors the foam usage. The conductivity sensor uses stainless steel plates positioned in the flow stream of the pipe for measuring conductivity of the mixture. A second conductivity sensor monitors conductivity of the water and provides a feedback signal to the control unit. An interface circuit generates a voltage having dual polarity and a fifty percent duty cycle for the conductivity sensors.

Description

FIELD OF THE INVENTION

The present invention relates in general to fluid mixing and delivery systems and, more particularly, to a system and method of mixing foam concentrate into a water stream while maintaining proportionately constant final mixture of the water and foam based on conductivity measure during fire fighting activities.

BACKGROUND OF THE INVENTION

Fire fighting equipment and processes are an essential part of public safety and protection of property. Fire fighting departments are organized under city, county, and private companies and brigades. The fire fighting departments use a variety of equipment, and provide training to fire fighters in proper use of such equipment in fighting fires, fire prevention, and personal and public safety.

Fire fighting equipment is often classified by the type of flammable material which it is most effective against. Class A fires and related equipment involve solid combustibles, building materials, structures, rubbish, vehicles, industrial, marine, wildlands, and the like. Class B fires relate to flammable liquids, Class C fires are electrical fires, and Class D fires involve combustible metals. Water alone is often not the most efficient and effective fire-extinguishing medium. Water addresses only the heat portion of the heat-fuel-oxygen fire interaction. In most situations, Class A foam mixed with water is more effective in extinguishing the flames. Class A foam contains a surface active agent, which reduces the surface tension of the water, allowing it to better penetrate into the fuel surface. The foam bubbles cling to the fuel surface, isolating the fuel from the heat and oxygen. The water droplets in Class A foam are smaller than in a conventional water fog spray pattern, which provides for a more rapid conversion to steam when applied to a fire, resulting in better heat absorption.

The water and foam combination must have the proper mixture or percent concentration of foam in the water stream. The water has a flow rate as determined by the pressure and diameter of pipe. The water further has a certain conductivity based on the mineral, foreign matter, or particulate content, also known as hardness, of the water source. The foam is pumped from a tank or reservoir and injected into the water stream. The flow rate of the foam must proportionately match the flow rate of the water stream and take into account the conductivity of the water source in order to produce an effective foam concentration in the water stream as projected onto the fire.

Conventional electronic direct injection foam proportioning equipment is based on a volumetric approach using the water flow rate as measured by a turbine-flow meter for the foam delivery system. The foam concentrate flow rate is adjusted either manually or automatically to the desired percentage of the water flow. The foam is introduced into the water stream according to the water flow rate.

However, there exist a number of variables in the various electronic direct injection foam delivery systems that can lead to an inaccurate ratio of foam concentration in the water stream as projected onto the fire. Volumetric flow-based electronic foam proportioners do not automatically adjust for varying water hardness, which affects the quality of the finished foam mixture. The volumetric foam proportioners also do not automatically or accurately adjust for the variation in the detergent strength of the commercially available foam concentrates, which also affects the quality of the finished foam. Some utilize a motor-mounted velocity feedback sensor, which may not accurately represent the actual foam concentrate flow. The velocity of the water flow rate and the foam concentration in the water stream are in fact independent variables, which relate only when the system is working perfectly. The foam pump could even run dry or pump the wrong liquid and the proportioner will continue to function as though it were operating correctly.

In some situations, e.g., when responding to a large fire, there may not be a fire hydrant in proximity to the blaze or, due to inadequate water pressure, it may be necessary to tap into supplemental water sources to provide the necessary flow to extinguish the fire. Water may be supplied from an alternate source such as a fire tanker or drafted from a nearby body of water. The water stored in the truck's tanks or drafted from a body of water may not have the same conductivity characteristics as the water available from the hydrant water system. Moreover, the conductivity of water is known to vary from location to location. Variation in water conductivity will likely lead to incorrect foam concentration or foam effectiveness in the water stream as projected onto the fire.

A need exists for a foam delivery system which accounts for variation in water and foam concentrate conductivity, and overcomes potential miscalibrations in proportioning equipment.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a unit of fire fighting equipment having a direct injection foam delivery system comprising a water pump for pumping water through a pipe. A foam pump is coupled to the pipe for mixing foam with the water and producing a mixture. A control unit controls the foam pump. A first conductivity sensor is coupled in-line with the pipe for monitoring conductivity of the mixture and providing a mixture conductivity signal to the control unit. A second conductivity sensor is coupled in-line with the pipe for monitoring conductivity of the water and providing a water conductivity signal to the control unit. The control unit uses a difference between the mixture conductivity signal and the water conductivity signal to regulate the foam pump.

In another embodiment, the present invention is a mixing system comprising a pump for directing a chemical agent into a pipe for mixing with a liquid and producing a mixture. A control unit controls the pump. A first conductivity sensor is coupled to the pipe for monitoring conductivity of the mixture and providing a mixture conductivity signal to the control unit. A second conductivity sensor is coupled in-line with the pipe for monitoring conductivity of the liquid and providing a liquid conductivity signal to the control unit. The control unit regulates the pump in response to the mixture conductivity signal and the liquid conductivity signal.

In another embodiment, the present invention is a system for mixing first and second fluids comprising a conduit for transporting the first under pressure. The second fluid is injected into the conduit for producing a mixture of the first and second fluids. A control unit controls a flow rate of the second fluid. A first conductivity sensor monitors conductivity of the mixture and providing a mixture conductivity signal to the control unit. A second conductivity sensor is coupled in-line with the conduit for monitoring conductivity of the first fluid and providing a first fluid conductivity signal to the control unit. The control unit controls the flow rate of the second fluid in response to the mixture conductivity signal and the first fluid conductivity signal.

In another embodiment, the present invention is a method of regulating percent concentration of first and second fluids comprising the steps of transporting a first fluid through a conduit under pressure, mixing a second fluid with the first fluid to produce a mixture, sensing conductivity of the first fluid, sensing conductivity of the mixture, and regulating flow of the second fluid in response to the sensed conductivity of the first fluid and mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates fire fighting equipment with electronically controlled direct injection foam delivery system;

FIG. 2 is a block diagram of the electronically controlled direct injection foam delivery system;

FIG. 3 illustrates further detail of the mixture conductivity sensor;

FIG. 4 illustrates further detail of the conductivity sensor interface circuit;

FIG. 5 illustrates foam delivery subsystem using high volume motor and low volume motor;

FIG. 6 illustrates foam delivery subsystem using high volume pump and low volume pump;

FIG. 7 illustrates foam delivery subsystem accessing different foams from different tanks;

FIG. 8 is a block diagram of an alternate embodiment of the electronically controlled direct injection foam delivery system; and

FIG. 9 illustrates a process of controlling the foam delivery system.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in one or more embodiments in the following description with reference to the Figures, in which like numerals represent the same or similar elements. While the invention is described in terms of the best mode for achieving the invention's objectives, it will be appreciated by those skilled in the art that it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and their equivalents as supported by the following disclosure and drawings.

Referring to FIG. 1, a fire truck 8 is shown as a unit of fire fighting equipment with electronically controlled direct injection foam delivery system 10 mounted within the fire truck. Fire truck 8 contains a number of compartments and support frames for housing the foam delivery system. Electronically controlled direct injection foam delivery system 10 may also be mounted on fireboats, airplanes, helicopters, and portable fire fighting equipment.

Foam delivery system 10 is direct injection, electronically controlled and uses differential conductivity sensing to regulate foam concentration in the water stream for fire fighting applications. Fire fighting departments, companies, and brigades operating in urban and rural settings use the equipment shown in FIG. 1 to fight fires and maintain personal and public safety. Conductivity-based electronically controlled direct injection foam delivery system 10 provides substantial advantages over prior foam delivery systems.

A block diagram of electronically controlled direct injection foam delivery system 10 is shown in FIG. 2. A manual valve or pressure regulator sets the water flow rate from water source 12 into pipe 24. Water source 12 may be a fire hydrant, tanker truck, or fixed body of water. The water is pumped by water pump 14 with motor 16 acting as the prime mover to operate water pump 14. Motor 16 can be electric, diesel, or gasoline combustion engine. Motor 16 has a separate operator control panel.

Control unit 20 contains a microprocessor or other logic circuits for processing operator commands, receiving sensor information, executing software programs, and generating control signals. Control unit 20 contains non-volatile and electronic memory storage for the software programs to execute within the microprocessor and control foam delivery system 10. Control unit 20 further includes driver circuits to control devices such as motor 36.

The system operator, e.g., fire truck engineer, can set controls manually with hand-operated valves and levers, or enters commands by way of operator control panel and display 22. The system operator enters the foam proportioning ratio in terms of percentage of foam concentrate in the water through operator control panel 22. Control unit 20 receives the water pump flow rate command and generates a 0-10 volt control signal to motor 16, which in turn spins water pump 14 to draw water from water source 12. Water pump 14 pumps water into pipe, manifold, hose, or conduit 24 at the specified flow rate. Water pump 14 may also pump out clear water discharge, i.e., no foam content, by way of manifold 26.

The water stream has a flow rate determined by the pressure introduced by water pump 14 and the diameter of pipe or hose 24. The water also has certain electrochemical properties, known as conductivity, which is a measure of the mineral, foreign matter, particulate content, or hardness of the water source. The water conductivity changes based on the location, region, and source of the water. The water hardness may vary from de-ionized water, i.e., substantially no particulates, to very harsh water such as seawater. Conductivity sensor 30 is placed in-line in pipe 24 to measure the conductivity of water in pipe 24. Conductivity sensor 30 is a precision mohms conductivity sensor. Conductivity sensor 30 measures the conductivity value of the water prior to introduction of any foam concentrate. The conductivity measure is sent to control unit 20 by way of interface circuit 31 for providing a baseline or reference point of water conductivity. The baseline water conductivity reference point is regularly updated, say six times per second, in control unit 20 by conductivity sensor 30. Check valve 32 is also placed in-line in pipe 24 to prevent any reverse flow back toward the water source.

Control unit 20 also sends a 0-10 volt control signal to motor 36. Motor 36 is the prime mover to operate foam pump 38. Motor 36 is typically an electric motor, but may be implemented as a diesel or gasoline combustion engine, water-driven motor, or hydraulically driven motor. Foam pump 38 draws foam concentrate or other fire retardant or chemical agent from foam tank 40. Foam pump 38 pumps the foam concentrate into pipe 42 at the specified flow rate. Check valve 44 may be placed in-line in pipe 42 to prevent any reverse flow from pipe 42 back into foam tank 40.

Mixing chamber 46 directly injects the foam concentrate from pipe 42 into the main water stream in pipe 24. Mixing chamber 46 may be a pipe union, “T”, or “Y” connecting pipe 42 into the main stream pipe 24. Alternatively, mixing chamber 46 may provide a circular or turbulent mixing operation to thoroughly blend and mix the foam concentrate into the water stream.

Flow meter 48 is placed in-line in pipe 49. Flow meter 48 has an impeller or paddle wheel driven velocity flow sensor which monitors the flow rate of the water-foam mixture in pipe 49 following mixing chamber 46. The flow meter reading is sent to control unit 20 to provide a real-time measure of the water-foam flow rate. Flow meter 48 may be placed anywhere along pipes 24 or 49, e.g. between conductivity sensor 30 and check valve 32.

The water-foam mixture in pipe 49, following mixing chamber 46, contains a certain percentage or concentration based on the volume of foam from pump 38 and the volume of water from pump 14. The water-foam mixture also has conductivity as determined by the conductivity of foam in the water stream and the conductivity of the water. The conductivity attributed to the foam is proportional to the concentration of foam in the water.

The mixture must maintain the proper ratio of foam and water to be effective as a fire fighting agent. By knowing the conductivity of the water-foam mixture, and conductivity of the water, the percent concentration of the foam in the water can be determined. If the conductivity of the water is subtracted from the conductivity of the water-foam mixture, the difference is that portion of the conductivity attributed to the foam itself. The concentration of the foam in the water can then be derived from the conductivity of the foam. In other words, the differential conductivity of the water and water-foam mixture is an indicator of the percent concentration of the foam in the water stream necessary to maintain the effectiveness of the water-foam mixture as a fire fighting agent.

The conductivity of the water is measured by conductivity sensor 30. To measure the conductivity of the water-foam mixture, conductivity sensor 50 is placed in-line with pipe 49. Similar to conductivity sensor 30, conductivity sensor 50 sends signals to and receives signals from control unit 20 by way of interface circuit 54.

Further detail of conductivity sensors 30 and 50 is shown in FIG. 3. Conductivity sensors 30 and 50 are precision mohms conductivity sensors positioned in-line with pipe 24 and 49, before and after mixing chamber 46, in order to read and report the conductivity of water alone and the combined water and foam mixture. Conductive plate or wires 60 and 62 are placed in the flow stream of the pipe. Plates 60 and 62 are made with stainless steel or other non-corrosive metal, and have identical and equal mass. Plate 60 is coupled to ground with conductor 64, and plate 62 is coupled to conductor 66.

An embodiment of the interface circuits 31 and 54 is shown in FIG. 4. Control unit 20 provides a digital square wave signal operating at known frequency, say 1 kHz, and precise 50% duty cycle. When the digital signal is logic zero, p-channel field effect transistor 70 conducts and charges capacitor 72 through resistor 78 with the voltage on power supply conductor 74. Capacitor 72 is selected as a 10 microfarad, 10% variance, ceramic capacitor. The power supply conductor 74 operates at V_DD=5 volts DC (VDC). When the digital signal is logic one, n-channel field effect transistor 76 conducts and discharges capacitor 72 through resistor 78 with the voltage on power supply conductor 64, which operates at ground potential. When the plate of capacitor 72 at the junction between transistors 70 and 76 is pulled to ground, the voltage on the other plate of capacitor 72, i.e., on conductor 66, reverses polarity to −5 VDC. Hence, the voltage on conductor 66 as developed across resistor 80 alternates from +5 VDC to −5 VDC with the frequency and duty cycle of the digital signal.

While the voltage on conductor 66 swings from +5 volts DC to −5 volts DC, the steady state differential voltage on plates 60 and 62 remains a constant 5 volts. The 50% duty cycle of the differential voltage reduces electroplating effects on plates 60 and 62. Without the precise 50% duty cycle, the minerals, impurities, and particulate content of the water-foam mixture could adhere to plates 60 and 62, causing errors in the conductivity reading and maintenance problems.

The conductivity measure is provided through resistor 82 as the CONDUCTIVITY signal, which is sent to an analog to digital converter within control unit 20 in FIG. 2 to sample the voltage on conductor 66. The voltage is measured at the high point, i.e., when conductor 66 is +5 volts DC, and again measured at the low point, i.e., when conductor 66 is −5 volts DC. The high point above ground is the same proportion as the low point below ground. The high measurement is subtracted from the low measurement to give a difference or offset resistance value, which is proportional to the conductivity of the fluid being measured. The offset resistance value is representative of and proportional to the titration of the fluid being measured.

The resistance measurement between plates 60 and 62 is determined by the electrochemical conduction properties of the water or water-foam mixture. As stated above, the water conductivity can change depending on the hardness of the water source. The water-foam mixture conductivity can change with the concentration of foam in the water. The greater the concentration of impurities and particulate content, the lesser the resistance and conductivity measurement. The lesser the concentration of impurities and particulate content, the greater the resistance and conductivity measurement.

Returning to FIG. 2, the conductivity signals from sensors 30 and 50 are sent to control unit 20. The concentration of impurities and particulate content in the water-foam mixture is a function of the percent concentration of foam in the water stream and the base conductivity of the water. Control unit 30 subtracts the base conductivity of water from the conductivity of the water-foam mixture to determine the difference between the two measurements, i.e., the differential conductivity measurement. The differential conductivity measurement represents the conductivity attributed to the foam, which is proportional to the concentration of foam in the water. The greater the differential conductivity measurement, the greater the percent concentration of foam in the water stream. The lesser the differential conductivity measurement, the lesser the percent concentration of foam in the water stream.

Control unit 20 uses the differential conductivity measurement to control motor 36 to increase or decrease the flow rate of foam pump 38 to maintain the conductivity of the water-foam mixture in pipe 49 at a desired value or within a proper range. As the conductivity of the water-foam mixture increases or decreases from its set value, the differential conductivity measure changes accordingly and foam pump 38 adjusts the foam flow rate to maintain the desired percent concentration of foam in the water steam. If the differential conductivity increases, then the foam flow rate decreases. If the differential conductivity decreases, then the foam flow rate increases. Thus, conductivity sensors 30 and 50 provide feedback information based on conductivity measure which is representative of the actual foam concentration in the water to regulate the flow rate of foam pump 38. The proper conductivity ranges of the water and water-foam mixture translate to the correct percent concentration of foam in the water stream. The water-foam mixture having the correct percent concentration of foam is projected from manifold 52 to effectively fight fires.

In one embodiment, the foam fire retardant in foam tank 40 is a class A foam available under various trade names. Class A foam is useful for fires involving solid combustibles, building materials, structures, rubbish, vehicles, industrial, marine, wildlands, and the like. Other classes of foam can be stored in foam tank 40 and used with system 10. For example, class B foam is used for flammable liquid fires, class C foam is more effective against electrical fires, and class D foam is best suited for combustible metals. Tank 40 may contain other fire retardants and chemical agents.

Fires require heat, oxygen, and fuel, known as the fire triangle, to continue burning. Water alone reduces the heat portion of the fire interaction. A water-foam mixture offers the advantage of attacking all three legs of the fire triangle. The foam coats the fuel and isolates the heat and oxygen. The foam also reduces water droplet size to more effectively reduce heat. For many types of fires, the use of water-foam mixture extinguishes fires more quickly, requires less water, reduces property damage, and preserves arson-related evidence.

Turning to FIG. 5, an alternate embodiment of foam pump 38 is shown including low volume motor 96 and high volume motor 98 driving a common foam pump 100. The dynamics of foam pump 38 being driven by a single high volume motor 36 are such that it becomes difficult to maintain accurate titration in the water-foam mixture at low water flow rates and low percent foam concentrations, due to the inability to sufficiently and accurately slow down the high flow pump motor. To solve the low water flow rate and low percent foam concentration problem, control unit 20 selects either low volume motor 96 or high volume motor 98 to drive foam pump 100 based on the titration set point and water flow rate. The water flow rate is determined by flow meter 48. Low volume motor 96 is used when the titration has a low set point, e.g., on the order of 0.3% foam at 10 GPM water flow rate. Control unit 20 controls low volume motor 96 to set the flow rate of foam pump 100. High volume motor 98 is used at higher titration set points and water flow rates. Control unit 20 controls high volume motor 98 to set the flow rate of foam pump 100.

The conductivity measurements are sent to control unit 20 where the conductivity value of the final discharge mixture is compared with the operated-entered conductivity set point according to the conductivity table. For low titration levels and low water flow rates, if the measured conductivity is less than the conductivity set point, then control unit 20 causes low volume motor 96 to increase the flow rate of the foam from pump 100. Again, for low titration levels and low water flow rates, if the measured conductivity is greater than the conductivity set point, then control unit 20 causes low volume motor 96 to decrease the flow rate of the foam from pump 100. For higher titration levels and higher water flow rates, if the measured conductivity is less than the conductivity set point, then control unit 20 causes high volume motor 98 to increase the flow rate of the foam from pump 100. Again, for higher titration levels and higher water flow rates, if the measured conductivity is greater than the conductivity set point, then control unit 20 causes high volume motor 98 to decrease the flow rate of the foam from pump 100.

By measuring the actual conductivity of the water and water-foam mixture and comparing the measured conductivity to the conductivity set point, for the given water conductivity, control unit 20 can maintain the correct percent concentration in foam in the water stream for discharge from manifold 52. Control unit 20 automatically selects between the low volume pump motor 96 and the high volume motor 98. The low volume motor 96 driving foam pump 100 is better suited for the low titration levels and low water flow rates. The high volume motor 98 driving foam pump 100 is better suited for the higher titration levels and higher water flow rates.

In FIG. 6, control circuit 20 controls the pump motor 96 to drive low volume foam pump 102 and high volume foam pump 104. Control unit 20 selects either low volume foam pump 102 or high volume foam pump 104 based on the titration set point and water flow rate. Again, the water flow rate is determined by flow meter 48. Low volume pump 102 is used when the titration has a low set point, e.g., on the order of 0.3% foam at 10 GPM water flow rate. High volume foam pump 104 is used at higher titration set points and water flow rates.

In FIG. 7, foam tank 110 contains a first type of foam, e.g., class A foam, and foam tank 112 contains a second type of foam, e.g., class B foam. Selector valve 114 selects between foam tank 110 and foam tank 112. Control unit 20 controls selector valve 114 in response to system operator input via operator control panel and display 22. Control unit 20 further controls motor 36 to spin foam pump 38 and pump the selected foam through pipe 42. The dual foam tank system can be used with the dual volume pump system discussed in FIG. 5 or 6.

In an alternate embodiment, a block diagram of electronically controlled direct injection foam delivery system 120 is shown in FIG. 8. A manual valve or pressure regulator sets the water flow rate from water source 122 into pipe 134. Water source 122 may be a fire hydrant, tanker truck, or fixed body of water. Alternately, water from water source 122 can be pumped by water pump 124. In this case, motor 126 is the prime mover to operate water pump 124. Motor 126 can be electric, diesel, or gasoline combustion engine. Motor 126 has a separate operator control panel or receives control signals from control unit 130. Control unit 130 contains a microprocessor or other logic circuits for processing operator commands, receiving sensor information, executing software programs, generating control signals, and displaying system status LEDs. Control unit 130 sends system status information to display 132. Control unit 130 contains non-volatile and electronic memory storage capacity for software programs to execute within the microprocessor and control foam delivery system 120. Control unit 130 further includes driver circuits to control devices such as motor 126 and motor 146.

The system operator, e.g., fire truck engineer, can set controls manually with hand-operated valves and levers, or enters commands by way of operator control panel and display 132. The system operator enters the foam proportioning ratio in terms of percentage of foam concentrate in the water through operator control panel 132. The foam proportioning ratio can also be automatically set by the software program executing in control unit 130. Control unit 130 receives the water pump flow rate command and generates a 0-10 volt control signal to motor 126, which in turn spins water pump 124 to draw water from water source 122. Water pump 124 pumps water into pipe, manifold, hose, or conduit 134 at the specified flow rate. Water pump 124 may also pump out clear water discharge, i.e., no foam content, by way of manifold 136.

The water stream has a flow rate determined by the pressure introduced by water pump 124 and the diameter of pipe or hose 134. Conductivity sensor 140 is placed in-line in pipe 134 to measure the conductivity of water in pipe 134. Conductivity sensor 140 is a precision mohms conductivity sensor. Conductivity sensor 140 measures the conductivity value of the water prior to introduction of any foam concentrate. The conductivity measure is sent to control unit 130 through interface circuit 141 for providing a baseline or reference point of water conductivity. The baseline water conductivity reference point is regularly updated in control unit 130 by conductivity sensor 140. Check valve 142 is also placed in-line in pipe 134 to prevent any reverse flow back toward the water source.

Control unit 130 also sends a 0-10 volt control signal to motor 146. Motor 146 is the prime mover to operate foam pump 148. Motor 146 is typically a DC electric motor, but may be implemented as a diesel or gasoline combustion engine, water-driven motor, or hydraulically driven motor. Foam pump 148 draws foam concentrate or other fire retardant or chemical agent from foam tank 150.

Control unit 130 generates the 0-10 volt control signal to motor 146, which in turn spins foam pump 148 to draw foam from tank 150. The system may use the high and low volume pumps as described in FIGS. 5 and 6, and the two foam tanks as described in FIG. 7. Foam pump 148 pumps the foam concentrate into pipe 152 at the specified flow rate. Check valve 154 may be placed in-line in pipe 152 to prevent any reverse flow from pipe 152 back into foam tank 150.

Speed sensor 155 is placed in-line with pipe 154 to provide a flow rate of the foam concentrate. Speed sensor 155 includes wheel with a plurality of teeth, say 30-40 teeth, that each generate an electrical pulse as the wheel rotates. One pulse per tooth movement in response to the flow of foam concentrate. Forty electrical pulses could indicate one revolution of the speed sensor wheel which translates to a specific volume of foam passing through the speed sensor. The pulses are sent to control unit 130, which adds a scaling factor to convert to any specified units of volume per unit time. For example, the foam flow rate may be gallons or liters per minute. Control unit 130 tracks instantaneous foam concentrate flow rate as well as cumulative foam concentrate usage. The flow rate tracked over a period of time provides total foam concentrated used in any given time period. Alternatively, the speed sensor can be integrated into foam pump 148 or motor 146.

Mixing chamber 156 directly injects the foam concentrate from pipe 152 into the main water stream in pipe 134. Mixing chamber 156 may be a pipe union, “T”, or “Y” connecting pipe 152 into the main stream pipe 134. Alternatively, mixing chamber 156 may provide a circular or turbulent mixing operation to thoroughly blend and mix the foam concentrate into the water stream.

Flow meter 158 is placed in-line in pipe 159. Flow meter 158 has an impeller or paddle wheel driven velocity flow sensor which monitors the flow rate of the water-foam mixture in pipe 159 following mixing chamber 156. Flow meter 158 generates one electrical pulse for each movement of the paddle in response to the water-foam mixture flow. The pulse count over time provides a pulse frequency, which is sent to control unit 130. The pulse frequency is a real-time measure of the water flow rate, e.g., gallons or liters per minute. Control unit 130 can track instantaneous flow rate or cumulate water-foam mixture volume over time. Flow meter 158 may be placed anywhere along pipe 134 or 159, e.g. between conductivity sensor 40 and check valve 142.

The water-foam mixture in pipe 159, following mixing chamber 156, contains a certain percentage or concentration based on the volume of foam from pump 148 and the volume of water from pump 124. The water-foam mixture also has conductivity as determined by the conductivity of foam in the water stream and the conductivity of the water. The conductivity attributed to the foam is proportional to the concentration of foam in the water.

The mixture must maintain the proper ratio of foam and water to be effective as a fire fighting agent. By knowing the conductivity of the water, and conductivity of the water-foam mixture, the percent concentration of the foam in the water can be determined. If the conductivity of the water is subtracted from the conductivity of the water-foam mixture, then the difference is that portion of the conductivity attributed to the foam itself. The concentration of the foam in the water can be derived from the conductivity of the foam. In other words, the differential conductivity of the water and water-foam mixture is an indicator of the percent concentration of the foam in the water stream necessary to maintain the effectiveness of the water-foam mixture as a fire fighting agent.

As described in FIGS. 3 and 4, conductivity sensor 140 is placed in-line with pipe 134 to measure the conductivity of the water supply. Likewise, conductivity sensor 160 is placed in-line with pipe 159 to measure the conductivity of the water-foam mixture. Conductivity sensors 140 and 160 send signals to and receives signals from control unit 130 by way of interface circuits 141 and 164, respectively.

Control unit 130 uses the difference between the water-foam mixture conductivity and the water conductivity to control motor 146 to increase or decrease the flow rate of foam pump 148 to maintain the conductivity of the water-foam mixture in pipe 159 within a proper range. As the differential conductivity increases or decreases from its set value, foam pump 148 adjusts the foam flow rate to maintain the desired percent concentration of foam in the water steam. If the differential conductivity increases, then the foam flow rate decreases. If the differential conductivity decreases, then the foam flow rate increases. Thus, conductivity sensors 140 and 160 provide the feedback information needed to determine the differential conductivity measure which is representative of the actual foam concentration in the water to regulate the flow rate of foam pump 148. The proper conductivity range of the water-foam mixture translates to the correct percent concentration of foam in the water stream. The water-foam mixture having the correct percent concentration of foam is projected from manifold 162 to effectively fight fires.

FIG. 9 illustrates the steps involved in using direct injection foam delivery system 120. The steps described herein can be implemented as software programs executing in the microprocessor and memory of control unit 130.

In step 170, the direct injection foam delivery system 120 is initially calibrated. The relationship between conductivity of the water-foam mixture and the percent concentration of foam in the water stream is determined in a calibration process. A known manufacturer and quality of foam concentrate is used as a benchmark. The calibration process measures conductivity of the water-foam mixture over a range of foam concentrations. The foam concentrations, ranging from 0.1% to 1.0% in 0.1% increments, 3.0% and 6.0% concentrate in solution, are established in the water stream of pipe 134. At each known step of solution concentration, the conductivity is measured. The process is repeated for a range of water conductivity levels. A table of conductivity measures and corresponding foam concentrations for each level of water-only conductivity is created and stored in the memory of control unit 130.

In step 172, the foam delivery system 120 undergoes auto-start, which can be triggered by application of the power supply to the system or by sensing water pressure from water source 122. Alternatively, the foam delivery system can be manually started by the operator. The water pump flow rate is set automatically or through operator control panel and display 132. Likewise, the conductivity set point is selected automatically or through operator control panel and display 132 according to the data table stored in the memory of control unit 130. The water volume flow rate and conductivity set point or foam concentration level are displayed to provide information as to system settings. Any units of measure can be displayed for the convenience of the operator. The conductivity set point is representative of the intended conductivity of the final proportionate water-foam mixture and determines the percentage or concentration of foam in the water stream of pipe 159. A higher conductivity set point translates to a higher percent concentration of foam in the water stream; a lower conductivity set point corresponds to a lower percent concentration of foam in the water stream. The conductivity set point is an accurate measure of the total titration of the water-foam mixture and, by direct relationship, the actual concentration of foam in the water stream. The conductivity of the water-foam mixture in pipe 159 changes in proportion to the foam concentration.

The foam delivery system 120 starts with water flow only. The system runs for a few seconds to purge any foam from the pipes and get a conductivity measurement of water only on both sides of mixing chamber 156. The water-only measurement by conductivity sensors 140 and 160 allows the system to zero out any measurement offset in the sensors.

After the line purge and zero offset of the conductivity sensors, the control unit 130 sets the flow concentration according to the conductivity set point from the data table, as per step 174. Foam concentrate flows through pipe 134 into mixing chamber 156. The foam-water mixture flows out through manifold 162.

In step 176, the conductivity of the water is measured by conductivity sensor 140, the conductivity of the water-foam mixture is measured by conductivity sensor 160, and the readings are sent to control unit 130. The difference between the two conductivity readings is compared with the conductivity set point according to the conductivity table.

For a specific water conductivity, the conductivity table translates to the conductivity set point for the desired foam concentration in the water-foam mixture. In step 178, the flow rate of the foam is adjusted as necessary to maintain the desired foam concentration. If the differential conductivity measurement is less than the conductivity set point, then control unit 130 causes motor 146 to increase the flow rate of the foam from pump 148. If the differential conductivity measurement is greater than the conductivity set point, then control unit 130 causes motor 146 to decrease the flow rate of the foam from pump 148. The foam concentration in the final discharge mixture can also be controlled by adjusting the flow rate of water pump 124. By measuring the actual conductivity measurements and comparing the measured conductivity value to the conductivity set point, for the given water conductivity, control unit 130 can maintain the correct percent concentration in foam in the water stream for discharge from manifold 162. The feedback system compensates for errors, misalignment, and miscalibrations in system 120 and achieves a proper foam concentration to effectively and efficiently fight fires and at the same time reducing foam concentrate waste.

Control unit 130 produces an audible or visual alarm if it is unable to correct the conductivity of the water-foam mixture to match the conductivity set point by altering the foam pump flow rate. If the system switches to volumetric control of the foam concentration if it is unable to compensate by the conductivity measure. The operator can check the system for problems; perhaps the foam tank is empty or contains the wrong product. The foam delivery system 120 uses a foam tank float sensor to detect low foam concentrate.

While one or more embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims. More specifically, while the present discussion is directed to water and fire retardant foam, the direct injection delivery system 10 is also applicable to other fluids, liquids, and chemical agents where the relationship of the conductivity measurements of the two fluids is representative of the final combined mixture.

Claims

1. A unit of fire fighting equipment having a direct injection foam delivery system, comprising: a water pump for pumping water through a pipe; a foam pump coupled to the pipe for mixing foam with the water and producing a mixture; a control unit for controlling the foam pump; a first conductivity sensor coupled in-line with the pipe for monitoring conductivity of the mixture and providing a mixture conductivity signal to the control unit; and a second conductivity sensor coupled in-line with the pipe for monitoring conductivity of the water and providing a water conductivity signal to the control unit, wherein the control unit uses a difference between the mixture conductivity signal and the water conductivity signal to regulate the foam pump.

2. The unit of fire fighting equipment of claim 1, further including a mixing chamber coupled for receiving the water and the foam and producing the mixture.

3. The unit of fire fighting equipment of claim 2, further including a speed sensor coupled between the foam pump and the mixing chamber.

4. The unit of fire fighting equipment of claim 1, wherein the control unit includes a microprocessor coupled for receiving the mixture conductivity signal and generating control signals to regulate the foam pump.

5. The unit of fire fighting equipment of claim 1, wherein the first conductivity sensor includes first and second plates positioned in the flow stream of the pipe for measuring conductivity of the mixture.

6. The unit of fire fighting equipment of claim 1, further including: a first interface circuit coupled between the first conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle; and a second interface circuit coupled between the second conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle.

7. The unit of fire fighting equipment of claim 1, wherein the foam pump includes: a first foam pump providing a first range of flow rates in response to the control unit and having an output coupled to the pipe; and a second foam pump providing a second range of flow rates in response to the control unit and having an output coupled to the pipe, the second range of flow rates being greater than the first range of flow rates.

8. The unit of fire fighting equipment of claim 7, wherein the control unit enables the first foam pump or the second foam pump to provide the foam to the pipe.

9. The unit of fire fighting equipment of claim 1, further including: a first foam tank for providing a first foam to the pipe to mix with the water; and a second foam tank for providing a second foam to the pipe to mix with the water.

10. A mixing system, comprising: a pump for directing a chemical agent into a pipe for mixing with a liquid and producing a mixture; a control unit for controlling the pump; a first conductivity sensor coupled to the pipe for monitoring conductivity of the mixture and providing a mixture conductivity signal to the control unit; and a second conductivity sensor coupled in-line with the pipe for monitoring conductivity of the liquid and providing a liquid conductivity signal to the control unit, wherein the control unit regulates the pump in response to the mixture conductivity signal and the liquid conductivity signal.

11. The mixing system of claim 10, further including a mixing chamber coupled for receiving the liquid and the chemical agent and producing the mixture.

12. The mixing system of claim 11, further including a speed sensor coupled between the foam pump and the mixing chamber.

13. The mixing system of claim 10, wherein the control unit includes a microprocessor coupled for receiving the mixture conductivity signal and generating control signals to regulate the pump.

14. The mixing system of claim 10, wherein the first conductivity sensor includes first and second plates positioned in the flow stream of the pipe for measuring conductivity of the mixture.

15. The mixing system of claim 10, further including: a first interface circuit coupled between the first conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle; and a second interface circuit coupled between the second conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle.

16. The mixing system of claim 10, wherein the pump includes: a first pump providing a first range of flow rates in response to the control unit and having an output coupled to the pipe; and a second pump providing a second range of flow rates in response to the control unit and having an output coupled to the pipe, the second range of flow rates being greater than the first range of flow rates.

17. The mixing system of claim 16, wherein the control unit enables the first pump or the second pump to provide the chemical agent to the pipe.

18. The mixing system of claim 10, further including: a first tank for providing a first chemical agent to the pipe to mix with the liquid; and a second tank for providing a second chemical agent to the pipe to mix with the liquid.

19. A system for mixing first and second fluids, comprising: a conduit for transporting the first under pressure, wherein the second fluid is injected into the conduit for producing a mixture of the first and second fluids; a control unit for controlling a flow rate of the second fluid; a first conductivity sensor for monitoring conductivity of the mixture and providing a mixture conductivity signal to the control unit; and a second conductivity sensor coupled in-line with the conduit for monitoring conductivity of the first fluid and providing a first fluid conductivity signal to the control unit, wherein the control unit controls the flow rate of the second fluid in response to the mixture conductivity signal and the first fluid conductivity signal.

20. The system of claim 19, further including a mixing chamber coupled in the conduit for receiving the first and second fluids and producing the mixture.

21. The system of claim 20, further including a speed sensor coupled between the foam pump and the mixing chamber.

22. The system of claim 19, wherein the first conductivity sensor includes first and second plates positioned in the flow stream of the conduit for measuring conductivity of the mixture.

23. The system of claim 19, further including: a first interface circuit coupled between the first conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle; and a second interface circuit coupled between the second conductivity sensor and the control unit for generating a voltage having dual polarity and a fifty percent duty cycle.

24. A method of regulating percent concentration of first and second fluids, comprising: transporting a first fluid through a conduit under pressure; mixing a second fluid with the first fluid to produce a mixture; sensing conductivity of the first fluid; sensing conductivity of the mixture; and regulating flow of the second fluid in response to the sensed conductivity of the first fluid and mixture.

25. The method of claim 24, further including sensing volume of the second fluid.

26. The method of claim 24, wherein the step of mixing the first and second fluids includes injecting the first and second fluids into a mixing chamber to produce the mixture.

27. The method of claim 24, further including: enabling a first pump having a first range of flow rates for transporting the second fluid; and enabling a second pump having a second range of flow rates for transporting the second fluid, the second range of flow rates being greater than the first range of flow rates.