Patent Publication Number: US-6991041-B2

Title: Compressed air foam pumping system

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to firefighting equipment, and more specifically, to compressed air foam systems used to mix a stream of water with foam chemical and compressed air to produce a water/foam/air mixture for firefighting purposes. Even more specifically, the present invention relates to systems for controlling the introduction of air into the water and foam chemical mixture ratiometrically. 
   The addition of foaming agents to firefighting water streams is known and can be particularly useful for fighting fires, for example, fires in industrial factories, chemical plants, petrochemical plants and petroleum refineries. The use of compressed air firefighting foam requires that air and a foam concentrate be mixed and added at constant proportions to the water stream. When the foam extinguisher solution is delivered, the foam effectively extinguishes the flames of chemical and petroleum fires as well as Class A materials which would otherwise not be effectively extinguished by the application of water alone. 
   Foam supply systems are known in the art by the term CAFS (Compressed Air Foam System) and WEPS (Water Expansion Pumping System). A typical system includes a foam injector system, a water pumping system, and an air system including an air compressor for supplying air under pressure. For example, when employing mixture ratios of 1 CFM of air to 1 GPM of water, these systems can produce very desirable results in fire fighting by the use of “Class A” or “Class B” foams to help achieve fire suppression and to deal with increased fire loads and related hazards. 
   Control of the foam concentrate addition to the water stream in the appropriate proportion is significant. If an excessive amount of foam concentrate is added, a lower fire-extinguishing quality can result due to an increased foam viscosity which limits the flowability of the foam and the ability of the foam to be spread on the fire. Further, the addition of excessive amounts of foam concentrate to the water stream increases the cost of the use of the foam and the frequency at which the foam concentrate supply must be replenished at the scene. With Class A foam, surface tension reduction is optimum at a specific injection ratio; too much or too little foam chemical will lead to increased surface tension which limits water absorption into Class A or woody, cellulose type fuels. Thus, it is important to fire fighting efficiencies to maintain proper control of the foam injection rate. 
   The amount of air added to the water and foam chemical mixture must also be properly regulated and controlled in the appropriate proportion. Controlling the amount of air introduced into the water and foam chemical mixture is necessary to achieve the desired consistency of foam. Firefighting foam that is either too watery due to insufficient air or too dry due to excessive air is less effective at fighting fires. Dry foam made by adding extra air to the foam solution has value in exposure protection and sealing the vapors on liquid spills; however, it is not effective for direct fire attack because there is not enough water content in the foam to cool the fuels. 
   As the nozzle operated by the firefighter at the end of the hose line is closed, extra air or water will tend to flow into the hose line depending on which one has a higher pressure. This may contribute to an unbalanced foam mixture. Existing firefighting foam systems have had difficulties in maintaining the pressures of the water and air equal to each other. The condition in which an excessive amount of air is introduced with the nozzle closed to create the foam is commonly referred to as air packing or just packing of the hose. Some firefighting foam systems recognized this and proportion the air introduced into the water using a venturi device. However, existing air proportioned systems generally increase the size, weight and cost of the firefighting foam system. Other firefighting foam systems use an operator to control the introduction of air by constantly making manual adjustments to maintain a desired foam mixture. Changes in hose elevation, length, nozzle opening and nozzle type can require the operator to compensate with manual adjustments. 
   In addition to controlling the introduction of air into the water and foam chemical stream to achieve a desired foam consistency, it is also desirable to reduce the air flow or completely shut off the air flow under certain conditions. For example, if foam chemical is not being added to the water then air should stop being introduced into the water stream. Air and water do not mix under pressure. If air is added to the water without the foam chemical the unmixed air and water will cause violent surging of the firefighting hoses, commonly called slug flow. The violent surging action can be sufficiently forceful to knockdown or injure the firefighter who is operating the fire hose. 
   When using the prior art systems without automatic controls, it is difficult under fire fighting conditions to maintain the water pressure and the air pressure at desired levels. At a fire fighting scene, unless an operator is present at all times to observe the flow conditions and is skilled at operating the equipment to make the necessary adjustments thereof, it is possible for the system to run out of water, to run out of foam, to lose prime in the water pump, to mix air with water by itself without the foam concentrate, to put air into the system by itself, and to even overpressurize the air. The occurrence of any of the above events, in addition to the occurrence of other possible problems, can be hazardous to the firefighter. 
   Some CAFS that adequately control the air/foam and water/foam ratios are disclosed in U.S. Pat. Nos. 5,255,747 of Teske et al. and 5,411,100 of Laskaris et al., which are incorporated by reference herein. The system of U.S. Pat. No. 5,411,100, in particular, discloses an automatically controlled CAFS which automatically controls compressed air flow. 
   However, what is needed but not provided by the prior art is an improved compressed air foam system which automatically controls the air flow into the mixture. Further, what is needed but not provided by the prior art is an improved compressed air foam system which automatically controls the ratio of air to foam into the mixture to optimize the resultant mixed output. Even further, what is needed but not provided by the prior art is a compressed air foam system which automatically controls the water flow to achieve higher air concentrations than otherwise possible. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention comprises a compressed air foam system for use in extinguishing fire. The compressed air foam system includes a mixer, a solution discharge device, a fire pump, a conduit, a water flow sensor, a foam proportioning apparatus, an air conduit, an air flow sensor, an air flow control valve and a system controller. The mixer has an inlet and an outlet. The solution discharge device is configured to receive mixed aerated foam solution from the outlet of the mixer and to output the mixed aerated foam solution from the system. The fire pump has a suction port and a discharge port. The fire pump is configured to pump water under pressure from the discharge port. The suction port is in fluid communication with a water source. The conduit provides a fluid path between the discharge port of the fire pump and the inlet of the mixer. The water flow sensor is configured to sense a water flow rate of the water flowing through the conduit. The foam proportioning apparatus is configured to inject foam chemical into the water flowing through the system. The air conduit is configured to inject compressed air at an air injection point into the water flowing through one of the conduit and the mixer. The air conduit is in fluid communication with a source of compressed air. The air flow sensor is configured to sense an air flow rate of the air flowing through the air conduit. The air flow control valve is configured to control the flow of the compressed air through the air conduit. The system controller has a user adjustable ratio input. The system controller is configured to receive the sensed water flow rate from the water flow sensor, to receive the sensed air flow rate from the air flow sensor, to output a first control signal to the air flow control valve for regulating the flow of compressed air and to output a second control signal to the foam proportioning apparatus for regulating the flow of foam relative to the sensed water flow rate. The system controller automatically adjusts the first and second control signals to maintain a ratio of air flow to foam flow based upon the user adjustable ratio input. 
   The present invention also comprises a control system for a compressed air foam system. The compressed air foam system has at least a pumped water line, a compressed air line coupled to an air source and to the water line, and a foam concentrate line coupled to a foam source and to the water line. The control system includes a water flow sensor, a water pressure sensor, an air flow sensor, an air flow control valve, a foam proportioning apparatus, and a system controller. The water flow sensor is configured to sense a flow rate of the water flowing through the water line. The water pressure sensor is configured to sense a water pressure of the water flowing through the water line. The air flow sensor is configured to sense a flow rate of the air flowing through the air line. The air flow control valve is configured to variably throttle the air flowing through the air line and into the water flowing through the system. The foam proportioning apparatus is configured to meter the foam chemical flowing through the foam concentrate line and into the water flowing through the system. The system controller has a user adjustable ratio input. The system controller is configured to receive the sensed water flow rate from the water flow sensor, to receive the sensed air flow rate from the air flow sensor, to output a first control signal to the air flow control valve for regulating the flow of air and to output a second control signal to the foam proportioning apparatus for regulating the flow of foam relative to the water flow rate. The system controller automatically adjusts the first and second control signals to maintain a user adjustable ratio of air flow to foam flow. 
   The present invention also comprises a compressed air foam system for use in extinguishing fire including a mixer, a solution discharge device, a fire pump, a conduit, a foam proportioning apparatus, an air conduit and a variable water restriction device. The mixer has an inlet and an outlet. The solution discharge device is configured to receive mixed aerated foam solution from the outlet of the mixer and output the mixed aerated foam solution from the system. The fire pump has a suction port and a discharge port. The fire pump is configured to pump water under pressure from the discharge port. The suction port is in fluid communication with a water source. The conduit provides a fluid path between the discharge port of the fire pump and the inlet of the mixer. The foam proportioning apparatus is configured to inject foam chemical into the water flowing through the conduit. The air conduit is configured to inject air into the water flowing through one of the conduit and the mixer. The air conduit is in fluid communication with a source of compressed air. The variable water restriction device is disposed in the conduit. The variable water restriction device is configured to selectively reduce water flow and pressure when a user desires to create an aerated mixed foam solution having higher air concentrations once the flow rate of the air being injected has reached a maximum attainable value. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
     In the drawings: 
       FIG. 1  is a schematic view of a compressed air foam system in accordance with a first preferred embodiment of the invention; 
       FIG. 2  is a schematic view of an air pressure regulator and electric control valve used in the system shown in  FIG. 1 ; 
       FIG. 3A  is a front elevational view of a foam flow controller for use with the system of  FIG. 1 ; 
       FIG. 3B  is a front elevational view of an air flow controller for use with the system of  FIG. 1 ; 
       FIG. 4  is a sectional view of an inlet throttling valve for an air compressor for use with the system of  FIG. 1 ; and 
       FIG. 5  is a schematic view of a compressed air foam system in accordance with a second preferred embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower”, and “upper” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer direction toward and away from, respectively, the geometric center of the compressed air foam system and designated parts thereof. The terminology includes the words above specifically mentioned, derivatives thereof and words of similar import. Additionally, the word “a”, as used in the claims and in the corresponding portions of the specification, means “at least one.” 
   Referring to the drawings in detail, wherein like reference numerals indicate like elements throughout, there is shown in  FIGS. 1–4  a compressed air foam system  6  in accordance with a first preferred embodiment of the present invention including a mixer  40 , a solution discharge device  18 , a fire pump  10 , a conduit  24 , a water flow sensor or water flowmeter  26 , a foam proportioning apparatus  14 , an air conduit  42 , an air flow sensor or air flowmeter  51 , an air flow control valve  60 , an air injector  16  and a system controller  20 . The mixer  40  has an inlet  41  and an outlet  43 . The solution discharge device  18  is configured to receive mixed aerated foam solution from the outlet  43  of the mixer  40  and to output the mixed aerated foam solution from the system  6 . The fire pump has a suction port  9  and a discharge port  11 . The fire pump  10  is configured to pump water under pressure from the discharge port  11 . The suction port  9  is in fluid communication with a water source  8 . The conduit  24  provides a fluid path between the discharge port  11  of the fire pump  10  and the inlet  41  of the mixer  40 . The water flow sensor  26  is configured to sense a water flow rate of the water flowing through the conduit  24 . The foam proportioning apparatus  14  is configured to inject foam chemical into the water flowing through the system  6 . The air conduit  42  is configured to inject compressed air at an air injection point, in this case at the air injector  16 , into the water flowing through one of the conduit  24  and the mixer  40 . The air conduit  42  is in fluid communication with a source of compressed air as will be described in greater detail below. The air flow sensor  51  is configured to sense an air flow rate of the air flowing through the air conduit  42 . The air flow control valve  60  is configured to control the flow of the compressed air through the air conduit  42 . The system controller  20  has a user adjustable ratio input which is entered via a keypad  132  ( FIG. 3B ). The system controller  20  is configured to receive the sensed water flow rate from the water flow sensor  26 , to receive the sensed air flow rate from the air flow sensor  51 , to output a first control signal to the air flow control valve  60  for regulating the flow of compressed air and to output a second control signal to the foam proportioning apparatus  14  for regulating the flow of foam relative to the sensed water flow rate. The system controller  20  automatically adjusts the first and second control signals to maintain a ratio of air flow to foam flow based upon the user adjustable ratio input. 
   The fire pump  10  is a suitable water pump which delivers water under pressure from the discharge  11 . The fire pump  10  is preferably a single-stage centrifugal pump which has impellers mounted on a rotating drive shaft and may be, for example, a QMAX 150 midship pump manufactured by Hale Fire Pump Company. 
   The mixer  40  is an improved type of motionless mixer which is described in U.S. Pat. No. 5,427,181 of Laskaris et al., which is incorporated by reference herein. Briefly, the mixer  40  comprises a plurality of flanges which are provided with fingers to create turbulence without losing much pressure as the mixture of foam solution and air flows from the air injector  16  to the upstream end  17  of the solution discharge device  18 . Mixers of this type are known in the art as motionless or static mixers and function to enhance mixing by adding turbulence to the flow while keeping the pressure loss to a minimum. Of course other types of mixers  40 , such as pumps, strainers, propellers and the like may be utilized without departing from the present invention. Additionally, if the system  6  has a significant length of discharge hose  17   a  (on the order of 150 feet of 1½ inch hose), the discharge hose  17   a  can function as the mixer  40 . Essentially what is needed for the mixer  40  is enough turbulence and frictional “scrubbing” to make a sufficient foam and water mix. But, the mixer  40  is not critical to the present invention, and therefore, shall not be described in greater detail herein. 
   The solution discharge device  18  can take various forms, such as a deck gun or one or more fire hoses with nozzles at the end thereof. In  FIG. 1 , the solution discharge device  18  is shown as a single fire hose  17   a  having a nozzle  19  as is commonly known in the art. Of course the particular discharge device  18  is not critical to the present invention and may be any type of discharge device. 
   Preferably, the source of compressed air  47  includes an air tank  48  and an air compressor  12  having an intake  12   a  and a discharge  12   b . The air compressor  12  draws in air from the intake  12   a  and discharges compressed air out of the compressor discharge  12   b  to the air conduit  42 . Preferably, the air flow control valve  60  is coupled to the intake  12   a  of the air compressor  12 . The air compressor  12  is preferably a rotary type of compressor of a conventional construction and comprises a rotating drive shaft (not shown). By way of example, the compressor  12  is constructed to operate at up to 400 cubic feet per minute (CFM). The design of the compressor  12  must allow for throttling the inlet air flow as a way to control the air discharge flow and pressure. 
   A transmission or power take-off  22  of the type disclosed in U.S. Pat. No. 5,145,014 of Eberhardt, the contents of which is incorporated by reference herein, is provided to cause rotation of the drive shafts of both the fire pump  10  and compressor  12  from the transmission on the fire truck. The power take-off  22  includes a split shaft gearbox (not shown) arranged to cause rotation of the drive shafts of the fire pump  10  and compressor  12  whereby said shafts are caused to rotate at a set proportional speed. Of course any power take-off device may be utilized without departing from the present invention including a dedicated electrical or internal combustion engine and the like. 
   The conduit  24  extends between the discharge  11  of the fire pump  10  and the inlet  15  of air injector  16  and includes therebetween, in the direction of flow, a check valve  25  and a foam injector  27 . The check valve  25  is constructed and arranged to permit flow in the direction from discharge  11  to the inlet  15  of the air injector  16  and block reverse flow (i.e., flow in the opposite direction). The foam injector  27  is connected as part of the flow proportioning apparatus  14  as will be described hereafter. The water flowmeter  26  is also disposed along this portion of the conduit  24 . By way of example, the flowmeter  26  may be a Hale FoamMaster Paddlewheel flowmeter as manufactured by Class  1 , Ocala, Fla. The water flowmeter  26  includes a transmitter  26 ′ which transmits an electrical signal corresponding to the rate of water flow therethrough. Of course other types of flowmeters may be utilized such as venturi tubes, orifice plates, vortex meters, propeller meters and the like without departing from the spirit of the present invention. 
   The foam proportioning apparatus  14  may be of any suitable type well known in the art, such as that used in the FoamMaster series electronic injection automatic foam proportioning system manufactured by Hale Products Inc. In this type or system, the proportioning apparatus  14  includes a foam concentrate pump  14   b  and an electric variable speed motor  14   c  for driving the pump, as is shown in  FIG. 1 . The proportioning apparatus  14  is controlled based on the water flow through the water flowmeter  26  as will be described in greater detail hereinafter. 
   As best shown in  FIG. 1 , the air injector  16  comprises a tee connection having an inlet  15 , which is connected to the downstream end of the conduit  24  as shown in  FIG. 1 , and an outlet  32  which is connected to direct the flow from the air injector  16  into a mixer  40 . The mixer  40  is connected at its downstream end to the upstream end  17  of the fire hose  17   a  of the solution discharge device  18  as is shown in  FIG. 1 . The air injector  16  also comprises an inlet portion providing an air inlet for receiving air flow delivered from air compressor  12  as will be described hereafter. The air injector tee or simply the injector  16 , may be constructed of any commercially available fittings as the control unit  20  compensates for pressure drop and flow characteristics in the range of operation. 
   The air conduit  42  for delivering air to the air inlet portion of air injector  16  includes a check valve  44  connected therein and configured to permit flow into the air injector  16  and to prevent flow in the opposite direction. The preferred method of construction for the check valve  44  is two independent check valves arranged at least several pipe diameters apart to prevent water back flow into the sensor. This is commonly known in the industry as a double detector check valve arrangement. The air conduit  42  also has a shut-off valve  50  connected therein for controlling flow therethrough, and an air flowmeter  51  connected therein for measuring flow therethrough. The shut-off valve  50  is actuable between open and closed positions. Optionally, the shut-off valve  50  is an integral part of the air flowmeter  51  and is just a solenoid configured to keep an inner piston of the air flowmeter  51  in a closed position, and the shut-off valve  50  and air flowmeter  51  are indicated as a combined device  201  on  FIG. 1 . The air flowmeter  51  may be of any suitable type such as the Hale SCFM Air Flowmeter manufactured by Hale Fire Pump Company. The air flowmeter  51  has a air flowmeter transmitter  51 ′ which transmits an electric signal corresponding to the rate of air flow therethrough, the signal being sent to system controller  20  via electrical line  51   a.    
   The air compressor  12  is arranged to deliver air at a delivery pressure to the upstream end of air conduit  42 . To this end, the discharge  13  of compressor  12  is connected to the compressor tank  48  which provides a capacity or buffer of compressed air at the compressor discharge pressure. The upstream end of the air conduit  42  is connected to the compressor tank  48  to receive a supply of air at the compressor discharge pressure whereby the conduit  42  delivers air to the air to air injector  16  through the shut-off valve  50 , the air flowmeter  51  and the check valve  44 . 
   Air is supplied to compressor  12  through an inlet  12   a . The air flow control valve  60  is configured to vary the flow of air to the inlet  12   a  of compressor  12  to thereby control the compressor discharge pressure. Compressor tank  48  is provided with a conventional pressure relief valve  49  which prevents the system from being subjected to a high pressure which could cause damage to the components thereof. By way of example, the relief valve  49  is set to open the compressor tank  48  to the atmosphere. 
   In order to control the compressor discharge pressure, air flow control valve  60  is provided with a control valve member  62  which cooperates with a valve seat  64  to vary the amount of the air flow to the compressor inlet  12   a  in response to a pilot or control air pressure from the air regulating valve  33 . The control valve member  62  is constructed and arranged to be positioned relative to the valve seat  64  to control the amount of air entering the air compressor  12  through inlet  12   a  until the compressor discharge pressure provides an air flow through line  42 . The inlet throttling valve  60  is of a type well known in the art such as those manufactured by Aircon Inc., Erie, Pa., which is shown in detail in  FIG. 4 . 
   As shown in cross-section in  FIG. 4 , the air flow control valve  60  includes the control valve member  62  which is mounted for movement with a control piston  66  guided for movement in a cylinder  68  which defines a control chamber  61  at the one (lower) side of the control piston  66 . The pilot or control pressure is delivered to the control chamber  61  by way of a passage  63  formed in the body of valve  60 , the upstream end of the passage  63  being in flow communication with a flow line  20   a  communicating therewith and mounted in the side of the body of the valve  60 . The flow line  20   a  delivers the pilot or control air pressure to valve  60  so that it, in effect, controls or modulates the compressor discharge pressure by controlling the inlet air volume. The control valve member  62  cooperates with the valve seat  64  and moves between the solid line (or fully opened) position shown in  FIG. 4  and a closed position as shown in dotted lines in  FIG. 4 . The upstream side of the valve seat  64  is connected to atmosphere by an inlet tube  65  as is conventional in the art. A spring  69  biases the valve member  62  toward the full open position against the control air pressure. Accordingly, the air flow control valve  60  is a fail open type valve. 
   Referring now to FIGS.  1  and  3 A– 3 B, preferably, the system controller  20  includes an air flow controller  20   c  and a foam flow controller  20   d . The air flow controller  20   c  is configured to receive the sensed air flow rate from the air flow sensor  51  and to output the first control signal to the air flow control valve  60  for regulating the flow of air. The foam flow controller  20   d  is configured to receive the sensed water flow rate from the water flow sensor  26  and to output the second control signal to the foam proportioning apparatus  14  for regulating the flow of foam. Preferably, the foam flow controller  20   d  communicates to the air flow controller  20   c  in order to automatically adjust the first and second control signals and in order to maintain the user adjustable ratio of air flow to foam flow as a function of the sensed water flow rate. In one configuration, the foam flow controller  20   d  communicates to the air flow controller  20   c  by a hardwired network cable  20   b , such as an RS485-type cable, using a standard communication protocol. Of course other communications methods can be utilized without departing from the present invention including radio frequency (RF), infrared (IR), fiber optic, Ethernet and the like. 
   Preferably, the foam flow controller  20   d  and the air flow controller  20   c  each include a memory U 2  and a processor U 1 . The processor U 1  is preferably a programmable microprocessor manufactured by Intel, but the processor U 1  may be another device such as a microcontroller, an application specific integrated circuit (ASIC), a programmable logic array (PAL) and the like, without departing from the invention. 
     FIG. 3B  shows that the air flow controller  20   d  has a keypad  132  including an on/off pushbutton  133 , up and down arrow keys  134   a ,  134   b , a digital readout or display  135  and mode indicator lights  136   a – 136   d . The mode indicator lights  136   a – 136   d  are for indicating which variable is being displayed on the digital display  135  and which mode the air flow controller  20   d  is set to operate. The mode indicator lights  136   a – 136   d  include water flow pacing  136   a , adjustable percent ratio of air to foam flow and water flow  136   b , the air temperature  136   c  and the time  136   d . By pressing a mode or information button  137 , a user can scroll or scan through the four different display modes indicated by mode indicator lights  136   a – 136   d . When the percent of air flow to water flow is selected, the user can use the up and down arrow keys  134   a ,  134   b  to increase or decrease the desired setpoint for pacing the air to water between 0.0% and 100%. Likewise, when the adjustable percent ratio of air to foam flow and water flow is selected, the user can also use the up and down arrow keys  134   a ,  134   b  to increase or decrease the desired setpoint for pacing the adjustable percent ratio of air to foam flow and water flow between 0.0% and 100%. 
   The air flow controller  20   c  has two sensor inputs which receives input control signals through the electrical lines  51   a  and  26   b  which transmit electrical signals from air flowmeter transmitter  51 ′ and the water flowmeter transmitter  26 ′ of the air and water flowmeters  51  and  26 , respectively. It is contemplated that the water flow is provided from the foam flow controller  20   d  by way of the network connection  20   b  in lieu of providing an additional water flow sensor input in the air flow controller  20   c . The microprocessor U 1  of the air flow controller  20   c  has a user adjustable setpoint for air/water ratio, and an output, electrically connected to the air regulating valve  33  by way of the electrical line  33   a.    
   Flow line  20   a , which delivers the pilot or control air pressure to valve  60  in order to control or modulate the compressor discharge pressure, is part of an air regulating system  30  which is configured to regulate the air pressure in the flow line  20   a . The air regulating system  30  includes an air regulating valve  33  and a relief valve  90  both having their respective inlet connections  90   a  and  33   b  in fluid communication with the compressor tank  48  outlet via conduits  31  and  91  that combine into a tee fitting communicating to conduit  81 . The air regulating system  30  also includes a line  31  connected between flow line  81  and the inlet or supply port of the air regulating valve  33 , and a line  35  connected between the outlet port of the air regulating valve  33  and conduit  205  to communicate to the control chamber  61  of the inlet throttling valve  60  via flow line  20   a . The control chamber  61  is vented thru connection  20   e  and relief valve  207  to the atmosphere. 
   The air regulating system  30  is a flow-through system and inherently functions with a throttling action as air flows through the air regulating valve  33  communicating to connection  20   a  of the air flow control valve  60  through conduit  35  and  205  act to change the net air pressure delivered to air flow control valve  60 . The air regulating valve  33  may be a proportional flow control valve as used in the industry or preferably is an on/off solenoid-type valve controlled by pulse width modulation (PWM) or other suitable signal as required to change the net air pressure delivered to the air flow control valve  60 . One such valve is made by Parker Hannifin Corporation as is known in industry. Thus, the air controller  20   c  has control over the air flow control valve  60  and can modulate the discharge flow and air pressure from air compressor  12  by modulating the intake air flow through the air flow control valve  60 . 
   Referring to  FIG. 2 , the air regulating valve  33  is an electrically controlled valve of a well known type constructed to receive an electric control signal from the system controller  20  to vary the air pressure delivered to the pilot line  20   a . While various types of electrically controlled air control valves may be used as the air regulating valve  33 , one suitable valve is the Model SPC1R of Buzmatics Corporation of Indianapolis, Ind. This valve, which is shown schematically in  FIG. 2 , comprises solid state electronics, indicated generally at  130 , an intake valve  132 , an exhaust valve  134 , a relieving pressure exhaust port  136 , an air supply pressure port  131 , and a controlled pressure output “work port”  135 . In operation, when a set point command signal is applied to the input electrical line  33   a  from system controller  20 , the solid state electronics  130  compare the pressure present at the pressure output work port  135  to the pressure required by the command signal. If the command signal is higher than the pressure present, then the electronics sends a signal to the intake valve  132 , opening the intake valve  132  and increasing the pressure in the output work port  135 . If the command signal is lower than the pressure in the output work port  135 , then the electronics sends a signal to the exhaust valve  134  opening it and thereby decreasing the pressure in the output work port  135 . As stated above, valves of this type are well known in the art and operate as briefly described above to receive an electrical signal and deliver a controlled pressure output. 
   In operation, the air flow controller  20   c  receives the water flow signal from flowmeter  26  and multiplies the water flow signal by the user set air/water ratio. This total value is compared to the air flow signal received from the air flowmeter  51  and the output signal through line  33   a  is changed accordingly for more or reduced air flow. Thus, the system controller  20  is a “closed loop” type controller, and is preferably configured so that the update rates from the flowmeters  26  and  51  and out to the air regulating valve  33  can be adjusted to prevent hunting. For example, the update rate for the flowmeters  26  and  51  would typically be three times the update rate for the output to the air regulating valve  33 . The software for the microprocessor is then made to have three data points to check for a trend off nominal before changing the output. However, the system controller  20  may employ any type of feedback control algorithm without departing from the present invention such as proportional, integral, derivative, cycle time, time proportion and the like. 
   The air flow controller  20   c  can cause additional air to flow by increasing compressor  12  discharge air pressure as measured by air pressure sensor  202 . This is done by sending a signal from the air flow controller  20   c  through line  33   a  to the air regulating valve  33  so that the air regulating valve  33  closes, sending a lower control air pressure to the intake valve  60  via conduit  35 . The lower control air pressure allows valve  60  to open due to reduced pressure in control chamber  61  acting on piston  66 . Thus, more air flows into compressor  12  and the air flow into the air source  48  and the line  42  is increased and controlled by the system  6 , and subsequently, the air being injected into the water flow at the air injector  16 . Likewise the air flow controller  20   c  can reduce air flow via the aforementioned throttling of the intake valve  60 . 
   In operation, air pressure from the compressor tank  48  communicates through conduit  81  and  91  to relief valve  90 . In normal operation the pressure at  90   a  will be less than the setting of relief valve  90 . If a system problem allows the operation pressure to rise above the setting of the relief valve  90  then pressure will be transmitted through relief valve  90  and out connection  90   b  through conduit  92  and  205  providing an increase in pressure at connection  20   a  and into the air flow control valve  60 . This pressure acts on piston  66  closing intake valve member  62  and restricting intake air flow into the compressor  12 , which in turn limits the air discharge from compressor tank  48 , and keeps the system under control during a potential electrical failure. 
   As mentioned above, the compressed air foam system  6  further includes an air pressure sensor  202  coupled to the air flow controller  20   c  for sensing the pressure of the air in the air conduit  42 . The air shut-off valve  50  is disposed between the source of compressed air  47  and the air injection point  16 . The air flow controller  20   c  uses the sensed air pressure to control the pressure of the air when the air shut-off valve  50  is closed to thereby maintain a startup pressure. Generally, the air shut-off valve  50  closes when the water flow drops below a minimum value which may be preprogrammed or which is user adjustable. The control  20  can also operatively turn off all air flow by communicating with valve  50  so this valve closes and prevents any air flow. This is required when water flow is stopped by the nozzle  19  and extra air moving into the system is not desirable. 
     FIG. 3A  shows that the foam flow controller  20   d  has a keypad  122  including an on/off pushbutton  123 , up and down arrow keys  124   a ,  124   b , a digital readout or display  125  and mode indicator lights  126   a – 126   d . The mode indicator lights  126   a – 126   d  are for indicating which variable is being displayed on the digital display  125  and include water flow  126   a , adjustable percent of foam flow to water flow  126   b , the total water flow (quantity)  126   c  and the total foam flow  126   d . By pressing a mode or information button  127 , a user can scroll or scan through the four different display modes indicated by mode indicator lights  126   a – 126   d . When the percent of foam flow to water flow is selected, the user can use the up and down arrow keys  124   a ,  124   b  to increase or decrease the desired setpoint for pacing the foam to water between 0.0% and 100%. 
   Referring now to  FIG. 1 , the foam flow controller  20   d  has at least one sensor input which receives input control signals through the electrical line  26   a  which transmits electrical signals from the water flowmeter transmitter  26 ′ of the water flowmeter  26 . It is contemplated that the water flow is provided to the air flow controller  20   c  by way of the network connection  20   b  in lieu of providing an additional water flow sensor input in the air flow controller  20   c . The microprocessor U 1  of the foam flow controller  20   d  has a user adjustable setpoint entered through the keypad  122  ( FIG. 3A ) for foam/water ratio, and an output, electrically connected to the foam proportioning apparatus  14  by way of the electrical line  14   d . The foam flow controller  20   d  operates in a second mode which is based upon the ratio of air/foam flow as set in the air flow controller  20   c.    
   In operation, in response to an electrical signal transmitted from the water flowmeter transmitter  26 ′ of the water flowmeter  26  by way of electrical line  26   a  to the foam controller  20   d , the amount of the foam concentrate delivered from a foam concentrate supply tank  14   a  to conduit  24  through the foam injector  27  is controlled to be at a specified injection rate as set by a user adjustable foam/water ratio setpoint. Alternately, the foam controller  20   d  is responsive to the user adjustable foam/air ratio setpoint set at the air flow controller  20   c.    
   In order to protect the pump  14   b  and motor  14   c  of the foam proportioner  14 , a foam concentrate supply tank low level float switch (not shown) is typically provided so that the foam proportioner  14  is interlocked when the foam concentrate tank  14   a  is empty (i.e., the drive motor  14   c  and the pump  14   b  will not run). 
   The compressed air foam system  6  further includes a water pressure sensor  102  coupled to the system controller  20  for measuring the pressure of the water in the conduit. The processor U 1  of either the air flow controller  20   c  or the foam flow controller  20   d  is configured in a first mode to read pressure values from the water pressure sensor  102  over a range of water flow rates and in a second mode to write the pressure values read in the first mode to a data table in the memory U 2 . The processor U 1  subsequently uses the data table to calibrate the system controller  20 . 
   Optionally, a temperature sensor  12   c  is coupled to the air source  47  and provides an input to the system controller  20  for measuring the temperature of the air. The temperature sensor  12   c  is installed in an oil system (not shown) in the compressor  12  and communicates with the air flow controller  20   c  to allow the display of oil temperature on the air flow controller  20   c . The air flow controller  20   c  can then bias the sensed air flow rate to compensate for temperature changes to maintain a standardized air flow rate. This also allows the compensated air flow readings to maintain standardized display of air flow in standard cubic feet per minute (SCFM). Of course, the temperature sensor  12   c  could also be coupled to the air compressor tank  48  or the air conduit  42  without departing from the present invention. 
   In an alternate embodiment, the compressed air foam system  6  for use in extinguishing fire further includes a variable water restriction device  200 . The variable water restriction device  200  is disposed in the conduit  24 . The variable water restriction device  200  is configured to selectively reduce water flow and pressure when a user desires to create an aerated mixed foam solution having higher air concentrations once the flow rate of the air being injected has reached a maximum attainable value because there is a practical saturation limit to the amount of air that may be induced into the water flow stream at the injector  16 . To allow very dry mixtures of compressed air foam discharge, often in excess of SCFM to 1 gpm, a variable restriction  200  is installed between foam injection  27  and air injection  16  components. The variable restriction device  200  may be a ball valve with an actuator that permits multiple positions or a modulating type valve. The system controller  20  can restrict the water flow when an increase in air pressure can no longer increase the air flow and more air is required (i.e., when the air compressor  12  reaches its maximum output). For example, in one such possible construction the variable restriction device  200  may be a ball valve with an electric actuator such as manufactured by KZCO of Greenwood, Nebr. The ball valve  200  will optionally have a hole drilled in the ball or a bypass installed around the main valve port to prevent the complete shut off of water flow. Of course other types of valves may also be successfully employed without departing from the broad inventive scope of the present invention. 
   In another alternate embodiment shown in  FIG. 5 , the compressed air foam system  6  for use in extinguishing fire further includes a branch conduit  124  for foam and water only (i.e., no air). Because some of the water flow will be diverted through the branch conduit  124  and some will continue to the air injector  16 , a second water flowmeter  126  is required in order to provide a proper water flow signal for pacing the air controller  20   c . The branch conduit may include an automatic shut-off valve  180  so that the side stream of foam and water only can be selectively disabled. The compressed air foam system  6  also includes an additional solution discharge device  118  including a hose  117   a  having a nozzle  119 , which is connected to the branch conduit  124 . The solution discharge device  118  can be any number of discharge devices as set forth above regarding the solution discharge device  18  without departing from the present invention. The alternate embodiment provides a compressed air foam system  6  capable of delivering both water/foam and air/water/foam mixes simultaneously and/or alternately. 
   From the foregoing, it can be seen that the present invention comprises an apparatus and a method for controlling a compressed air foam system by monitoring and controlling water pressure, air flow, air pressure and foam flow, concurrently. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.