Patent Application
20100314137
The present invention is directed, in general, to firefighting equipment and, more specifically, to fire fighting foam proportioning devices and systems having improved low flow performance.
The addition of a foam concentrate to a water stream is often used to fight flammable liquid fires in industrial factories, chemical plants, petrochemical plants and petroleum refineries. The foam concentrate must be added at a constant proportion to the water stream. When the foam/water solution is delivered, it generates foam which extinguishes the flames more effectively than by the application of water alone.
For different applications, foam concentrates are designed to be accurately mixed with water in specific proportions, such as 1%, 3% or 6% foam-to-water ratios. Proportioning equipment, foam concentrate, and discharge equipment must be matched to produce the proper concentration at system design operating pressures. If the system adds too much foam concentrate, the resulting foam viscosity is greater than desired, thereby limiting the ability of the foam to be spread on the fire and diminishing the fire-extinguishing quality. Furthermore, the addition of excessive amounts of 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.
There are two currently available types of foam proportioning systems. One type involves the drawing of the foam-forming concentrate into the water stream by an in-line or by-pass foam eductor. Two problems are associated with such eductor devices. First, the foam-to-water ratio is at times not accurate. Second, eductor devices create a substantial pressure drop across the eductor, which limits the flow through the system. The second type of system is commonly referred to as a balanced pressure proportioning system. Balanced pressure proportioning systems supply foam concentrate to the water stream under pressure and, as a result, the pressure drop across the eductor is reduced.
One type of balanced pressure proportioning system utilizes a foam concentrate bladder tank and a foam proportioner, or ratio controller, to mix foam concentrate with a primary water stream. A balanced pressure bladder tank includes a pressure vessel having an internal flexible bladder for holding a supply of foam concentrate. Water is supplied to the region intermediate to the pressure vessel and the flexible bladder from a main water supply. The bladder tank has a perforated discharge tube within the flexible bladder that is coupled through the inner bladder to a discharge outlet on the pressure vessel. The discharge tube includes small holes whereby foam concentrate is pushed through the holes and out through the discharge outlet as water pressure is applied to the outside of the flexible bladder. The foam concentrate is then forced through a concentrate pipe toward the ratio controller.
The ratio controller includes a foam concentrate inlet having a foam concentrate metering orifice and a water inlet orifice. As water flows through the ratio controller, a low pressure region is created which causes foam concentrate to pass into the water stream as required to balance the flow and pressure based on the metering orifice; the metering orifice is sized for the flow of the firefighting system and the foam concentrate mixing ratio. As water demand increases in the system, the foam concentrate flow also increases in order to maintain the proper mixing ratio.
Conventional balanced pressure bladder tank systems known in the art are often used with open deluge systems having multiple small discharge devices or a single large device. Such systems have a fixed flow rate in gallons per minute and the ratio controller is sized to fall in the mid to maximum flow rate for the system; the flow rate is a function of the number of discharge devices that simultaneously open. The discharge devices (i.e., nozzles or sprinklers) are evenly positioned over a protected area for even distribution of foam/water solution. Each discharge device includes a thermal trigger that keeps the device closed until the proximate temperature increases to the design limit.
In accordance with current National Fire Protection Association (NFPA) minimum standards, foam concentrate must be proportioned at the rated percentage in a system when only four discharge devices are in operation; i.e., a system must properly proportion foam concentrate at low flow rates. Where the proper foam mixture of 1%, 3% or 6% must be met at a four sprinkler flow rate to the system, this is typically 60-120 gallons per minute (GPM). In a typical system, when the foam/water solution is flowing at the minimum approved flow rate for the ratio controller, the foam percentage often can be lean; i.e., less than the recommended percentage. To overcome this problem, some prior art systems utilize multiple ratio controllers of smaller size or a complex variable-pressure type ratio controller having multiple moving components and very high pressure loss. The use of multiple or complex mechanical ratio controllers, however, increases system costs and the potential for mechanical failures. Accordingly, there is a need in the art for improved fire fighting foam proportioning devices and systems; such devices and systems should be of simple design and sufficient to meet NFPA operational requirements for low flow rates.
To address the deficiencies of the prior art, disclosed are improved fire fighting foam proportioning devices and systems including an improved ratio controller and an improved bladder tank. The improved ratio controller is characterized by: a venturi body having a throat portion and a diffuser portion; a water inlet orifice coupled to the venturi body upstream to the throat portion for receiving a stream of water, wherein the water inlet orifice and the throat portion of the venturi body form an annular low pressure chamber having an inner circumferential passage for fluid communication of a foam concentrate from the annular low pressure chamber into the stream of water; a foam concentrate inlet to the annular low pressure chamber for receiving foam concentrate; and, a non-adjustable foam concentrate metering orifice disposed in the foam concentrate inlet proximate to the annular low pressure chamber, the metering orifice having a central circular passage having a length at least 50 per cent of the diameter of the passage in order to decrease the turbulence of foam concentrate and provide a smoother flow transition into the annular low pressure chamber. In an exemplary embodiment, the foam concentrate inlet of the ratio controller comprises a cylindrical portion terminating at an inwardly-extending lip forming an opening into the annular low pressure chamber, the foam concentrate metering orifice having an outer diameter less than the foam concentrate inlet and greater than the opening into the annular low pressure chamber. The foam concentrate metering orifice can have a central body extending through the opening into the annular low pressure chamber and an outwardly-extending lip that abuts the inwardly-extending lip of the foam concentrate inlet.
The improved bladder tank comprises: a pressure vessel; a flexible inner bladder for holding a supply of foam concentrate; and, a modified discharge tube disposed within the inner bladder, wherein the discharge tube comprises a plurality of holes disposed along its length and wherein the combined area of holes per foot of length is at least 50 per cent of the inner diameter of the perforated tube. In an exemplary embodiment, the discharge tube of the improved bladder tank has a diameter in the range of 2 to 4 inches and the holes have a diameter in the range of ⅝ to ¾ inches.
In certain system implementations, the bladder tank is coupled to the water supply pipe at an upstream point remote to the ratio controller, wherein one or more valves in the water supply pipe leading to the ratio controller are downstream from the point at which the bladder tank is coupled to the water supply pipe; this modification of conventional system design provides a lower pressure loss differential from the water supply to the bladder tank and the foam concentrate inlet of the ratio controller. In other system implementations, a balancing valve can be utilized intermediate to a foam discharge outlet of the bladder tank and the foam concentrate inlet of the ratio controller, wherein the balancing valve senses the pressure of the water supply proximate to the ratio controller and lowers the foam concentrate pressure to substantially equal the water supply pressure.
The foregoing has outlined, rather broadly, the principles of the present invention so that those skilled in the art may better understand the detailed description of the exemplary embodiments that follow. Those skilled in the art should appreciate that they can readily use the disclosed conception and exemplary embodiments as a basis for designing or modifying other structures and methods for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
For a more complete understanding of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying drawings, in which:
Referring to
According to the prior art, ratio controllers of the design type illustrated in
Turning now to
In an exemplary embodiment, the improved foam concentrate metering orifice 270 has a central body 272 that extends through the opening into the annular low pressure chamber 140, and an outwardly-extending lip 273 that abuts the inwardly-extending lip 162 of the foam concentrate inlet 160. This embodiment of the foam concentrate metering orifice 270 provides the capability to easily retrofit existing ratio controllers since it does not require a change to the position of the retaining ring 180; i.e., the thickness of the outwardly-extending lip 273 can have the same thickness as the prior art foam concentrate metering orifice 170, while the increase in the length of the passage through the orifice is accommodated by the extension of the central body 272 through the opening in the annular low pressure chamber 140. For newly-designed ratio controllers, the greater thickness of the foam concentrate metering orifice 270 can be alternatively accommodated with an appropriate relocation of the retaining slot 181 in the wall of the foam concentrate inlet 160. Because of the thicker profile of a foam concentrate metering orifice according to the principles of the invention, another alternative for newly-designed ratio controllers would be for the metering orifice to have external threads with an appropriately-threaded receiving portion within foam concentrate inlet 160. Those skilled in the art will appreciate that an improved foam concentrate metering orifice according to the principles of the invention could also be press-fit or otherwise secured within the foam concentrate inlet 160; it is intended that all such means of securing the improved foam concentrate metering orifice be within the scope of the claims.
Referring now to
According to known prior art designs, the holes are typically approximately ½ inch in diameter and the combined area of holes per foot of length is approximately 25 per cent of the internal diameter of the discharge tube. It has been found, however, that the pressure drop in the foam concentrate supply to the ratio controller is minimized, and the flow characteristics of foam concentrate out of the bladder tank are optimized, if the combined area of holes per foot of length is at least 50 per cent of the inner diameter of the discharge tube 320. In an exemplary embodiment, the discharge tube 320 of the improved bladder tank 300 has a diameter in the range of 2 to 4 inches and the holes have a diameter in the range of ⅝ to ¾ inches.
Now turning to
The firefighting system 400 includes a water supply pipe 410 for receiving a primary flow of water. The water supply pipe 410 is coupled to a water supply control valve 411 upstream from the water inlet of the ratio controller 200. In the illustrated system, an alarm check valve 412 is included intermediate to the water supply control valve 411 and the water inlet of ratio controller 200; the alarm check valve prevents the reverse flow of water from the firefighting system to the water supply.
The water supply must also be coupled to the bladder tank 300. In prior art systems, the water supply to provide motive pressure to the bladder tank 300 is typically taken from a location 420 immediately upstream of the ratio controller 200. In the exemplary system illustrated in
The foam concentrate inlet of ratio controller 200 is coupled to the foam discharge outlet 330 of bladder tank 300. In the exemplary system illustrated, the foam supply line from the foam discharge outlet 330 of bladder tank 300 includes a control valve 440; the valve is normally open but can be closed for system servicing.
Finally,
The firefighting system 500 includes a water supply pipe 410 for receiving a primary flow of water. The water supply pipe 410 is coupled to a water supply control valve 411 upstream from the water inlet of the ratio controller 200. In the illustrated system, a pressure control assembly 512 is included intermediate to the water supply control valve 411 and the water inlet of ratio controller 200; the pressure control assembly 512 is used to control the water pressure supplied to the ratio controller 200. The purpose of controlling the water pressure is due to variable water supply pressure that at initial operation of the system can be high and will require more foam concentrate; by controlling the pressure, the system discharge is controlled as required for proper operation.
The firefighting system 500, rather than utilizing a bladder tank for delivering foam concentrate to the ratio controller 200, further includes a foam concentrate reservoir 520 and a positive displacement foam concentrate pump 530 coupled to the foam concentrate reservoir for supplying foam concentrate at a higher pressure than the flow of water to the ratio controller 200. This allows the foam concentrate reservoir 520 to be at a greater distance from the point of application and also allows the use of multiple discharge systems with a single foam concentrate supply. As the system water pressures can vary due to demand, the ratio controller 200 can still proportion foam concentrate into the water supply at all points at the proper percentage. A balancing valve 540 is coupled intermediate to the positive displacement foam concentrate pump 530 and the foam concentrate inlet of the ratio controller 200; the balancing valve 540 senses the pressures of the water supply and the foam concentrate to the ratio controller 200 and opens to bypass foam concentrate back to the foam concentrate reservoir 520 until the pressure of the foam concentrate is substantially equal to the water supply pressure.
The principles disclosed herein provide significant improvements to the art of fire fighting foam proportioning devices and systems, particularly to the capability of the improved ratio controller and bladder tank to contribute to the operation of such systems at low flow rates. In prior art designs of this type system, the minimum flow rate where the proper foam percentage was obtainable was much higher than allowed for a four discharge device flow rate as required by the NFPA. Utilizing the design principles disclosed herein, however, a system can provide very low flow rates (e.g., less than 60 gpm).
Although the present invention has been described in detail, those skilled in the art will conceive of various changes, substitutions and alterations to the exemplary embodiments described herein without departing from the spirit and scope of the invention in its broadest form. The exemplary embodiments presented herein illustrate the principles of the invention and are not intended to be exhaustive or to limit the invention to the form disclosed; it is intended that the scope of the invention be limited only to the claims appended hereto, and their equivalents.
