Patent Application
20090095492
1. Technical Field
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.
2. Related Art
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'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).
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.
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.
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's maximum possible speed.
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.
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.
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.
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.
Referring to
The foam concentrate can be stored in a foam tank 12. Although a single foam tank 12 is shown in
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 21a-21j. According to the exemplary embodiment shown, the inlet manifold 22 and outlet manifold 24 are connected to one another only by the intermediate conduits 21a-21j, however, other configurations are possible. As shown in
In the exemplary embodiment shown, the pump array 18 comprises ten variable speed pumps 20a-20j, each of which injects foam concentrate into a respective conduit 21a-21j. 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 20a-20j 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.
Still referring to
Each variable speed pump 20a-20j within the array 18 can form part of a pump subsystem.
Still referring to
A flow meter 48a, such as a paddle wheel flow meter, can be located in conduit 21a to measure the total fluid flow through conduit 21a. Flow meter 48a 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 40a can further include a pump controller 50a that can turn variable speed pump 20a on or of, and can also control the speed of pump 20a. The pump controller 50a 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 20a can provide data regarding its rotation rate (i.e., speed) back to its respective pump controller 50a. The pump controller 50a can be in communication with the flow meter 48a, such that the fluid flow rate through conduit 21a is transmitted from flow meter 48a to pump controller 50a.
The system controller 26 can open or close each of the conduits 21a-21j, for example, using the respective valve 46a-46j 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 46a-46j, thereby bringing online additional conduits 21a-21j 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 46a-46j, thereby shutting down the respective conduit 21a-21j 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.
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 50a. For example, the desired ratio can be input by the operator directly at the pump controller 50a. 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 50a.
Still referring to
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's minimum speed (i.e., off) and the pump's maximum speed. The specific speed range, sometimes referred to herein as the pump'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 20a-20j 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'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's speed (i.e., its RPM), or alternatively, can refer to some indirect measurement that is reflective of the pump's speed, for example, the fluid flow output rate of the pump.
Referring to
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 21a-21j (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.
Exemplary Operation
The operation of an exemplary embodiment of the system 10 shown in
A fire fighting foam dispensing system was constructed in accordance with
The system 10 was activated with the first valve 46a in the open position, allowing fluid flow between the inlet manifold 22 and the outlet manifold 24 through the first conduit 21a. The remaining valves 46b-j and associated conduits 21-j were in the closed position upon startup. A test fire was started, which caused the sprinklers to open.
Upon initial opening of the sprinklers, water began flowing through the first conduit 21a, and the first variable speed pump 20a injected the foam concentrate into the conduit 21a in the selected 1% ratio under the control of pump controller 50a. 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 21a), the system controller 26 opened the valve 46b in second conduit 21b. The resulting fluid flow through second conduit 21b in turn caused the second variable speed pump 20b to inject the foam concentrate into the second conduit 21b in the selected 1% ratio, under the control of second pump controller 50b. With fluid flowing through the first conduit 21a and the second conduit 21b, 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 46c in third conduit 21c. The resulting fluid flow through the third conduit 21c caused the third variable speed pump 20c to inject foam concentrate into the third conduit 21c in the selected 1% ratio, under the control of third pump controller 50c. 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 21a-21j were open and all ten variable speed pumps 20a-20j 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 46c, reducing the system to two conduits 21a and 21b, 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 20a-20f 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%.
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.
