Abstract:
A fire fighting foam dispensing system includes a water inlet adapted to receive a flow of water, a first variable speed pump adapted to inject foam concentrate into the flow of water, a second variable speed pump adapted to inject foam concentrate into the flow of water, a foam outlet adapted to discharge fire fighting foam, a measuring apparatus adapted to measure flow rate in at least one of the water inlet and the foam outlet, and a system controller adapted to detect the flow rate from the measuring apparatus, and activate the second variable speed pump only upon the measured flow rate exceeding a predetermined flow rate value.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    This patent application relates generally to a fire fighting system that utilizes foam to suppress fires. More particularly, this patent application relates to a foam dispensing system that precisely mixes a foam concentrate with water to make fire fighting foam. This patent application also relates to methods of precisely mixing the foam concentrate with the water. 
         [0003]    2. Related Art 
         [0004]    In order to accurately assess the fire suppressing qualities of fire fighting foam, a known quantity of the foam must be applied to a test fire. Typically, this involves applying a precise mixture of water and foam concentrate to the test fire. Some known foam dispensing systems use devices such as venturis, bladders, and diaphragms to control the mixture of foam concentrate and water. However, these known foam dispensing systems often fail to provide adequate precision in the foam concentrate/water mixture, for example, when variations in pressure and/or flow rate occur. Other known foam dispensing systems use a variable speed pump to inject foam concentrate into the water. However, when the variable speed pump reaches the low end or the high end of its speed range (e.g., in response to changes in flow rate), the pump&#39;s accuracy decreases, thereby decreasing the precision of the foam concentrate/water mixture. The inaccuracies in the foam concentrate/water ratio of existing dispensing systems often render it difficult to precisely determine the quantity of foam being applied to the fire. This may not provide a significant problem when fighting real life fires, because any inaccuracy in the ratio of foam concentrate to water can be compensated for by applying more foam to the fire than is necessary to extinguish it (although this can result in wasted foam concentrate). 
         [0005]    When the foam is being used in a testing environment, however, it is more important for the foam to comprise a precise mixture of foam concentrate and water. Known foam dispensing systems have often proved insufficient for use in testing environments, due to their inability to provide adequate precision in the foam concentrate/water ratio. Therefore, there remains a need in the art for foam dispensing systems and related methods that overcome the shortcomings of the prior art. 
       SUMMARY 
       [0006]    The system and, method disclosed in this patent application provide a precise ratio of foam concentrate to water over a wide range of flow values by injecting the foam concentrate into the water using two or more variable speed pumps in an array. By staging the operation of the variable speed pumps (e.g., bringing more pumps online as the demand for foam concentrate increases), each pump can be operated within a speed band where the pump provides a high level of accuracy. This in turn translates into a high level of accuracy with respect to the foam concentrate/water ratio over a wide range of system flows. 
         [0007]    According to an exemplary embodiment, a fire fighting foam dispensing system comprises a water inlet adapted to receive a flow of water, a first variable speed pump adapted to inject foam concentrate into the flow of water, a second variable speed pump adapted to inject foam concentrate into the flow of water, a foam outlet adapted to discharge fire fighting foam, a measuring apparatus adapted to measure flow rate in at least one of the water inlet and the foam outlet, and a system controller adapted to detect the flow rate from the measuring apparatus, and activate the second variable speed pump only upon the measured flow rate exceeding a predetermined flow rate value, wherein the predetermined upper threshold speed is less than the pump&#39;s maximum possible speed. 
         [0008]    According to another exemplary embodiment, a fire fighting foam dispensing system comprises a water inlet adapted to receive a flow of water, a pump array adapted to inject foam concentrate into the flow of water to create fire fighting foam, the pump array comprising at least a first variable speed pump and a second variable speed pump, a foam outlet adapted to discharge the fire fighting foam, a measuring apparatus adapted to measure flow rate in at least one of the water inlet and the foam outlet, and a controller adapted to operate each variable speed pump in the pump array at a speed that is substantially equal to or less than a predetermined upper threshold speed. 
         [0009]    According to another exemplary embodiment, a method of producing fire fighting foam comprises activating a first variable speed pump to inject a foam concentrate into a supply of water at a predetermined ratio to form fire fighting foam, measuring flow rate of at least one of the supply of water and the fire fighting foam, and after the measured flow rate exceeds a predetermined flow rate value, activating a second variable speed pump to inject foam concentrate into the supply of water at a predetermined ratio to form fire fighting foam. 
         [0010]    Further objectives and advantages, as well as the structure and function of preferred embodiments, will become apparent from a consideration of the description, drawings, and examples. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The foregoing and other features and advantages of the invention will be apparent from the following drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. 
           [0012]      FIG. 1  is a schematic representation of an exemplary fire fighting foam dispensing system according to the present invention; and 
           [0013]      FIG. 2  is an enlarged, schematic representation of an exemplary pump subsystem of the foam dispensing system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , an exemplary fire fighting foam dispensing system  10  is shown schematically. The system  10  is configured to mix fire fighting foam concentrate with water to produce fire fighting foam. The system  10  can also be configured to supply the fire fighting foam to downstream equipment, such as fire hoses, sprinkler systems, testing systems, or other known apparatuses. 
         [0015]    The foam concentrate can be stored in a foam tank  12 . Although a single foam tank  12  is shown in  FIG. 1 , the system  10  can alternatively include a plurality of foam tanks, as described in more detail hereafter. The tank(s)  12  can be mounted on a scale, such as a load cell platform, to facilitate calculating the amount of foam concentrate used based on changes in weight. The foam concentrate can comprise Class A foam, Class B foam, Class A/B foam, alcohol resistant-aqueous film forming foam (AR-AFFF), alcohol tolerant concentrate-aqueous film forming foam (ATC-AFFF), high expansion foam, or any other foam concentrate known in the art. The system  10  combines the foam concentrate in the tank  12  with water supplied via a water inlet  14 . The water inlet  14  can receive water from various different water supplies, such as a fire hydrant, a building water supply, or other supplies known in the art. Once the water and foam concentrate are combined, the resulting foam is distributed via a foam outlet  16 , by which the foam can be supplied to various foam dispensing apparatuses known in the art. 
         [0016]    The system  10  includes a pump array depicted generally as  18 , which comprises two or more variable speed pumps adapted to inject the foam concentrate into the water, for example, at a point somewhere between the water inlet  14  and the foam outlet  16 . In the exemplary embodiment shown, the system comprises an inlet manifold  22  in communication with the water inlet  14 , and an outlet manifold  24  in communication with the foam outlet  16 . The inlet manifold  22  and outlet manifold  24  can be connected to one another by, for example, a plurality of intermediate conduits  21   a - 21   j . According to the exemplary embodiment shown, the inlet manifold  22  and outlet manifold  24  are connected to one another only by the intermediate conduits  21   a - 21   j , however, other configurations are possible. As shown in  FIG. 1 , conduits  21   a - 21   j  can be arranged in parallel to one other, however other configurations are possible. The pump array  18  can inject the foam concentrate into the water between the inlet manifold  22  and the outlet manifold  24 , for example, by injecting the foam concentrate into one or more of the conduits  21   a - 21   j . However, other arrangements and locations are possible for injecting the foam concentrate into the water. 
         [0017]    In the exemplary embodiment shown, the pump array  18  comprises ten variable speed pumps  20   a - 20   j , each of which injects foam concentrate into a respective conduit  21   a - 21   j . However, other arrangements are possible. For example, the array  18  can alternatively comprise more or less than ten pumps, and/or the pumps can introduce the foam concentrate into the water at locations other than the conduits. According to an exemplary embodiment, the variable speed pumps  20   a - 20   j  are 24 volt DC electric pumps with and auto-on feature manufactured by FoamPro under model number S206-2002, however a variety of variable speed pumps known in the art can alternatively be used. 
         [0018]    Still referring to  FIG. 1 , the system  10  can further include a system controller  26  in communication with, among other things, the pumps  20   a - 20   j . The system  10  can also include a power supply  28  adapted to provide power to, among other things, the pumps  20   a - 20   j . A flow meter  30  can be provided to measure the total fluid flow through the system. The flow meter  30  can measure the flow proximate the outlet manifold  24  or foam outlet  16 , as shown in  FIG. 1 . Alternatively or additionally, the flow meter  30  can measure the flow proximate the water inlet  14  or the inlet manifold  22 . According to an exemplary embodiment, the flow meter  30  is an ultrasonic unit manufactured by General Electric Panametrics, Model No. PT 878, although a variety of flow meters known in the art, including paddle-wheel flow meters, can alternatively be used. The flow meter  30  can transmit the flow data to the system controller  26 . 
         [0019]    Each variable speed pump  20   a - 20   j  within the array  18  can form part of a pump subsystem.  FIG. 2  depicts an exemplary pump subsystem  40   a  including variable speed pump  20   a  (note that  FIG. 2  and the related description can apply equally to the other pump subsystems in the array  18 ). As shown in  FIG. 2 , the variable speed pump  20   a  can receive foam concentrate from a foam tank  12   a . In the schematic representation of  FIG. 1 , a single foam tank  12  is shown supplying foam concentrate to all of the pumps  20   a - 20   j  in the array, however, an individual foam tank  12   a  can alternatively be provided for each pump, as shown in  FIG. 2 . Pump  20   a  withdraws foam concentrate from the tank  12   a , pressurizes the foam concentrate, and then injects it into the conduit  21   a , for example, through a foam injection port  42   a . Conduit  21   a  can include a check valve  44   a , located upstream from the foam injection port  42   a , that substantially prevents water, foam concentrate, and/or foam from flowing backwards through the system (i.e., upstream) towards the inlet manifold  22 . 
         [0020]    Still referring to  FIG. 2 , a valve  46   a  can be provided in the conduit  21   a  to selectively allow or disallow water flow through the conduit  21   a  between the inlet manifold  22  and the outlet manifold  24 . The valve  46   a  can be controlled remotely, for example, by the system controller  26  (shown in  FIG. 1 ), as will be described in more detail below. The valve  46   a  can comprise, for example, a pneumatic ball valve, although other known types of valves can be used as alternatives, such as a pneumatically or electrically actuated butterfly valve, an electrically actuated solenoid valve, or an electric/hydraulic actuated globe valve. 
         [0021]    A flow meter  48   a , such as a paddle wheel flow meter, can be located in conduit  21   a  to measure the total fluid flow through conduit  21   a . Flow meter  48   a  can comprise a turbine flow meter, or a magnetic flow meter, although other types of flow meters known in the art can alternatively be used. Subsystem  40   a  can further include a pump controller  50   a  that can turn variable speed pump  20   a  on or of, and can also control the speed of pump  20   a . The pump controller  50   a  can comprise, for example, a Programmable Logic Controller (PLC), an Advanced Digital Feature Controller (ADFC), such as manufactured by FoamPro, or other type of controller known in the art. Pump  20   a  can provide data regarding its rotation rate (i.e., speed) back to its respective pump controller  50   a . The pump controller  50   a  can be in communication with the flow meter  48   a , such that the fluid flow rate through conduit  21   a  is transmitted from flow meter  48   a  to pump controller  50   a.    
         [0022]    The system controller  26  can open or close each of the conduits  21   a - 21   j , for example, using the respective valve  46   a - 46   j  associated with the conduit. For example, as the total flow through the system increases beyond certain predetermined flow levels, the system controller  26  can open one or more additional valves  46   a - 46   j , thereby bringing online additional conduits  21   a - 21   j  and the associated pump subsystems. Alternatively, as the total flow through the system decreases below certain predetermined flow levels, the system controller  26  can close one or more of the open valves  46   a - 46   j , thereby shutting down the respective conduit  21   a - 21   j  and associated pump subsystem. As will be described in more detail hereinafter, this system of opening and closing the conduits in response to changes in demand on the pump subsystem(s) can provide a high level of accuracy in the foam concentrate to water ratio over a wide range of system flow rates. 
         [0023]    Each pump subsystem, when activated, can operate to supply a precise mixture of foam concentrate/water to the outlet manifold  24 . The desired ratio of foam concentrate to water (selected by the operator) can be input into the pump controller  50   a . For example, the desired ratio can be input by the operator directly at the pump controller  50   a . Alternatively or additionally, the desired ratio can be set at the system controller  26 , and then communicated from the system controller  26  to each of the pump controllers  50   a.    
         [0024]    Still referring to  FIG. 2 , when operating, each subsystem can operate as follows. The flow meter  21   a  measures the total flow rate through the conduit  21   a , and communicates that flow rate to the pump controller  50   a . Based on the measured flow rate and the set water/concentrate ratio, the pump controller  50   a  determines the amount of foam concentrate that needs to be injected into the conduit  21   a  in order to maintain the set ratio. The pump controller  50   a  then instructs the variable speed pump  20   a  to pump the necessary amount of foam concentrate into the conduit  21   a  (e.g., via hose  52   a ). For example, the pump controller  50   a  adjusts the operating speed of the variable speed pump  20   a . The pump controller  50   a  continuously monitors the flow rate in the conduit  21   a , based on the data from the flow meter  21   a , and adjusts the speed of the variable speed pump  20   a  to maintain the desired water/concentrate ratio. Therefore, each subsystem can monitor the total flow rate through its conduit, e.g., conduit  21   a , and inject the appropriate amount of foam concentrate into that conduit to maintain the set ratio of water/concentrate through that conduit. 
         [0025]    Typically, variable speed pumps provide their highest level of accuracy (e.g., with respect to speed or flow rate) when operating within a specific speed range that is somewhere between the pump&#39;s minimum speed (i.e., off) and the pump&#39;s maximum speed. The specific speed range, sometimes referred to herein as the pump&#39;s “optimum speed band,” can be defined on the lower end by a lower threshold speed that is somewhere above zero revolutions per minute (RPMs). On the upper end the optimum speed band can be defined by an upper threshold speed somewhere below the maximum operating speed of the pump. The accuracy of the pump typically drops significantly when the pump speed falls outside of the optimum speed band. In order for the foam dispensing system  10  described herein to operate at a high level of precision, the system  10  can be adapted to operate each of the variable speed pumps  20   a - 20   j  in the array  18  within its optimum speed band. One of ordinary skill in the art will understand that the “optimum speed band” can vary depending on the type and specifications of the specific pumps being used in the system, and therefore, the upper threshold speed and lower threshold speed will vary depending on the specific pumps used in the system. The optimum speed band for a given pump can be determined hypothetically, for example, based on the specifications for a given pump, or empirically, for example, by testing a pump&#39;s accuracy over its entire operating speed range. As used herein, the term “optimum speed band” of the pumps can refer to the absolute value, of the pump&#39;s speed (i.e., its RPM), or alternatively, can refer to some indirect measurement that is reflective of the pump&#39;s speed, for example, the fluid flow output rate of the pump. 
         [0026]    Referring to  FIG. 1 , the system controller  26  can monitor the total flow through system  10 , for example, via the flow meter  30  located in the outlet manifold  24 . Based on the total system flow, or other factors described hereinafter, the system controller  26  can determine how many pumps in the array  18  are needed in order for each pump to operate within its optimum speed band. The system controller  26  can then turn on the necessary amount of pumps in the array  18 , for example, by opening the valve  46  in the respective conduit  21 , thereby allowing fluid to flow through the conduit  21  from the inlet manifold  22  to the outlet manifold  24 . Once the valve  46  in a respective conduit, for example, conduit  21   a , is opened, the pump controller  50   a  and flow meter  21   a  associated with that conduit  21   a  work in unison to maintain the desired ratio of concentrate to water in that conduit, as discussed previously. In the event that the total system flow (as measured, e.g., by flow meter  30 ) increases or decreases to the extent that additional or fewer pumps are needed in order for each of the operating pumps to stay within their optimum speed band, the system controller  26  can bring additional pumps online by opening the valve  46  associated with a respective conduit  21 , or alternatively, can shut pumps off by closing a valve  46  associated with a respective conduit  21 . As discussed above, once a particular valve  46  is open and fluid is flowing through the respective conduit  21 , the respective pump controller  50 , flow meter  21 , and variable speed pump  20  of the subsystem operate in unison to maintain the desired concentrate/water ratio in that conduit  21 . According to an alternative embodiment, the system controller  26  (in addition to, or instead of the pump controller) can operate to maintain the desired concentrate/water ratio in each conduit  21 . 
         [0027]    One of ordinary skill in the art will appreciate based on this disclosure that the system  10  is not limited to activating or deactivating the pumps in the array  18  based on the total flow rate of the system. That is, other variables may alternatively or additionally be used to determine appropriate tripping points for activating or deactivating pumps within the array  18 . For example, the flow rate within each of the conduits  21   a - 21   j  (or other locations) can be measured and analyzed to determine whether pumps within the array need to be activated or deactivated. Alternatively or additionally, the speed or flow rate of each active pump within the array can be monitored to determine if any of the active pumps are outside of its optimum speed band, at which point pumps can be activated or deactivated as needed. One of ordinary skill in the art will appreciate based on this disclosure that other criteria for activating and deactivating pumps within the array  18  are also possible for the system  10 . 
         [0028]    Exemplary Operation 
         [0029]    The operation of an exemplary embodiment of the system  10  shown in  FIGS. 1 and 2  will now be described in connection with the following example. 
         [0030]    A fire fighting foam dispensing system was constructed in accordance with  FIGS. 1 and 2 . Two elevated 300 gallon totes were piped together to serve as the foam tank  12 , which supplied the variable speed pumps  20   a - 20   j  via a gravity feed. The water inlet  14  was connected to a private water supply. The foam outlet  16  was connected to a network of overhead sprinklers in a fire testing and evaluation laboratory. The pump controllers  50   a - 50   j  were each set to inject a 1% ratio of foam concentrate into the water supply (i.e., 1 part foam concentrate per 100 parts water). The system controller  26  was set at a trigger point of 400 gallons per minute (GPM) for activating/deactivating pumps within the array  18 . The trigger point of 400 GPM was determined based on the optimum speed band of the variable speed pumps  20   a - 20   j  used, which were the HYDRO Power Line Plus Model 2345B-P-8, and may be different for other types, sizes, etc., of pumps. 
         [0031]    The system  10  was activated with the first valve  46   a  in the open position, allowing fluid flow between the inlet manifold  22  and the outlet manifold  24  through the first conduit  21   a . The remaining valves  46   b - j  and associated conduits  21 - j  were in the closed position upon startup. A test fire was started, which caused the sprinklers to open. 
         [0032]    Upon initial opening of the sprinklers, water began flowing through the first conduit  21   a , and the first variable speed pump  20   a  injected the foam concentrate into the conduit  21   a  in the selected 1% ratio under the control of pump controller  50   a . Once the flow meter  30  detected a total system flow of 400 GPM (also corresponding to a flow of 400 GPM through the first conduit  21   a ), the system controller  26  opened the valve  46   b  in second conduit  21   b . The resulting fluid flow through second conduit  21   b  in turn caused the second variable speed pump  20   b  to inject the foam concentrate into the second conduit  21   b  in the selected 1% ratio, under the control of second pump controller  50   b . With fluid flowing through the first conduit  21   a  and the second conduit  21   b , the flow rate through each conduit was reduced by half (e.g., to 200 GPM each). As the total system flow continued to increase (e.g., as more sprinklers in the sprinkler network opened), and reached 800 GPM, the system controller opened the valve  46   c  in third conduit  21   c . The resulting fluid flow through the third conduit  21   c  caused the third variable speed pump  20   c  to inject foam concentrate into the third conduit  21   c  in the selected 1% ratio, under the control of third pump controller  50   c . This operational trend continued as the total system flow increased, with additional valves  46  and associated conduits  21  being opened as total flow increased in intervals of 400 GPM, until all ten conduits  21   a - 21   j  were open and all ten variable speed pumps  20   a - 20   j  were operating. In the event of a significant decrease in the total system flow, for example, from 1,000 GPM to 600 GPM, the system controller  26  would close one of the valves, for example, valve  46   c , reducing the system to two conduits  21   a  and  21   b , both flowing at about 300 GPM. By deactivating conduits and pump subsystems in response to decreases in total system flow, the system  10  can ensure that the pumps in the array not only operate below their upper threshold speed, but also operate above their lower threshold speed. The exemplary system with ten variable speed pumps  20   a - 20   f  provided a precise 1% foam concentration across a broad range of flows up to 4,000 GPM. The total capacity of the system  10  can be increased or decreased, for example, by adding or removing variable speed pumps from the array  18 . While the exemplary system used in the example was operated at a 1% foam concentration, it can alternatively be operated at other foam concentrations, for example, anywhere from 0.1% to 5.0%. 
         [0033]    The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.