Abstract:
A corrosion prevention treatment of wet Fire Protection System (FPS) includes purging the pipes of O2 with an inert gas such as N2, followed by filling the pipes with deoxygenated water generated “on the fly” as the water enters a building, using one or more Gas Transfer Membrane (GTM) devices and N2 gas. The GTM device eliminates the need for a water reuse tank and its associated pipes, valves, recirculation regimen, and the like. Water is pumped directly from the building water supply to a GTM device, where it is deoxygenated to very low O2 levels—such as below 300 ppb (parts per billion). The deoxygenated water then flows directly into the O2-purged pipes of the FPS. When the FPS is drained for testing or repair, the deoxygenated water may be discharged, and replaced, upon return to service of the FPS, with water freshly deoxygenated from the building supply as the FPS piping is filled.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a Continuation-in-Part of U.S. patent application Ser. No. 13/589,542, titled “Deoxygenated Water Fill for Fire Protection System”, filed Aug. 20, 2012. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to wet fire protection systems, and in particular to a system and method of dynamically deoxygenating supply water as the pipes are filled. 
       BACKGROUND 
       [0003]    Fire sprinkler systems are a well-known type of active fire suppression system. Sprinklers are installed in all types of buildings, commercial and residential, and are generally required by fire and building codes for buildings open to the public. Typical sprinkler systems comprise a network of pipes, usually located at ceiling level, that are connected to a reliable water source. Automatically actuated valves called sprinkler heads are disposed along the pipes at regular intervals. Each sprinkler head is operative to open automatically in the event of a fire. For example, one design of sprinkler head includes a fusible element, or a frangible glass bulb, that is heat-sensitive and designed to fail at a predetermined temperature. Failure of the fusible element or glass bulb opens the valve, allowing water to flow through the head, where it is directed by a deflector into a predetermined spray pattern. Sprinkler systems may suppress a fire, or inhibit its growth, thereby saving lives and limiting inventory loss and structural damage. Sprinkler specifications are published by the National Fire Protection Association (e.g., NFPA 13, 13D, 13R). 
         [0004]    The sprinkler system (more generally, Fire Protection System, or FPS) is fed from a pump room or riser room. In a large building the FPS consist of several “zones,” each being fed from a riser in the pump room. The riser contains a main isolation valve and other monitoring equipment (e.g., flow switches, alarm sensors, and the like). The riser is typically a 6 or 8 inch diameter pipe coupled through a booster pump (called the fire pump) to the main water supply to the building. The riser then progressively branches off into smaller “cross mains” and branch lines, also known as “zones”. At the furthest point from the riser, typically at the end of each zone, there is an “inspector&#39;s test port,” which is used for flow testing. Numerous other valves, such as for filling and/or purging the pipes, testing internal pressure, measuring gas or water properties, and the like, may be included in the FPS pipes. 
         [0005]    FPS may be of the “wet” or “dry” types. In a “wet” system the sprinkler pipes in each room are full of water under a predetermined “internal set point” pressure. If the water pressure decreases below the set point, valves are opened and/or a pump is activated, and water flows into the sprinkler pipes in an attempt to maintain the pressure. The set point pressure drops when water escapes the system, such as due to the opening of a sprinkler head in a fire. 
         [0006]    To prevent damage to equipment or merchandise by water leaking from the FPS in conditions other than a fire, and in environment conditions in which water in the pipes may freeze, “dry” system are used. A dry FPS uses compressed air in the piping as a “supervisory gas.” The air is maintained at a supervisory pressure, e.g., typically ranging between 13-40 PSI. When a sprinkler head opens, the air pressure drops to atmospheric (e.g., 0 PSI), and a valve opens in response to the lower pressure. The valve locks in the open position and water rushes into the system. One type of dry FPS, known as a pre-action, provides increased protection against water damage by increasing the probability that the system is only activated by an actual fire. A pre-action FPS requires one (e.g., Single Interlock) or more (e.g., Double Interlock) action signals before water is injected into the system—for example, both a drop in supervisory air pressure and a signal from a heat or smoke detector. 
         [0007]    Building codes specify a minimum angle, measured from the horizontal, at which wet FPS pipe is to be hung. The purpose of this angle is to ensure that water flows to the end of the pipe, so that the internal volume of the pipe is full of water along its entire length, minimizing the delay in water discharge when a sprinkler head opens. Also, codes specify that air vents can be installed at the far end of each pipe from the street valve, to purge air from the pipe interior as the system is “charged” (i.e., when water is initially introduced). However, in practice, there are usually one or more “high” or elevated points in the FPS wet pipe system where air is trapped. This air includes oxygen (O2), which reacts with the water and pipe steel to cause corrosion, which may be of either galvanic or organic origin. Sometimes, microbes can grow in the water and accelerate the corrosion by means of the byproducts produced during their metabolic cycle. This is called Microbiologically Influenced Corrosion (MIC). Over time, MIC or galvanic corrosion can cause extensive damage to a wet FPS, eventually resulting in leaks. Both the damage caused by leaking water, and the need to replace corroded FPS pipes, provide significant incentive to minimize or eliminate wet FPS corrosion due to O2 within the pipes. 
         [0008]    One approach to solving this problem is to purge atmospheric air from the FPS pipes using an inert gas, such as nitrogen (N2), prior to charging the system. Nitrogen is an inert gas, and pure N2 contains no oxygen. However, commercially common means of generating N2, such as by membrane-filtering atmospheric air, generate N2 in the range of 95%-98% purity and Pressure Swing Adsorption systems generate N2 in the range of 95%-99.999% purity; accordingly, this N2 may contain some concentration of O2. Additionally, nitrogen has a dew point of −40° F., meaning it can absorb water vapor (as well as other gases dissolved in the water) at any higher temperature. 
         [0009]    Water usually contains dissolved oxygen—that is, O2 molecules, apart from the oxygen bound up in the H2O molecules forming the water itself. As one example, a test of local city water at 60 degrees F. in Charlotte, N.C. revealed an O2 content of 9.617 ppm (parts per million). Due to the partial pressure of gases, O2 from such water will outgas into the pockets containing N2, providing enough O2 for the onset of detrimental corrosion. Accordingly, simply purging wet FPS pipes with N2 prior to charging the system is not a long-term solution to corrosion. 
         [0010]    Deoxygenating water—the process of reducing the number of free oxygen molecules dissolved in water—prior to charging a wet FPS system is known. Water may be deoxygenated by exposure to low-O2-concentration gas and/or vacuum conditions to draw O2 and other residual free gasses out of the water, causing the dissolved O2 to “outgas” into the lower-concentration gas or vacuum. It is known to use N2 gas to deoxygenate water for wet FPS systems. For example, U.S. Patent Application Publication No. 2011/0226495 discloses a wet FPS system having a water reuse tank and in-line static mixer. The reuse tank is filled with sufficient fresh water to fill the FPS pipe volume. This water is circulated from the tank through the in-line static mixer, with N2 gas being injected in the circulation line from an N2 generator. The water is circulated through the in-line static mixer until a desired level of deoxygenation is achieved. As this reference discloses, such a system is effective to deoxygenate water to approximately 0.1 ppm (parts per million) of O2. When the FPS is drained for testing or maintenance, the deoxygenated water is retained in the water reuse tank, for reuse when the FPS is again made operational. Reusing the water avoids the need to spend the considerable time required to deoxygenate fresh water by circulation through the in-line static mixer. 
         [0011]    The system disclosed in US 2011/0226495 presents numerous deficiencies. A water reuse tank of sufficient volume to hold all of the water in the wet FPS is required. Such a tank is large and heavy, requiring ample space and possibly structural reinforcement to deploy it in many buildings. The oxygenation process is lengthy, requiring continuous recirculation of water in the reuse tank through the in-line static mixer, in the presence of N2 gas, to achieve a sufficient level of deoxygenation. Additionally, separate piping systems for circulating water and gas to/from the reuse tank, each with multiple valves that must be coordinated and controlled, result in significant complexity and cost, increase maintenance requirements, and introduce potential failure points. Furthermore, such a system may ultimately limit the amount of deoxygenation that can be achieved, leaving some residual amount of O2 gas dissolved in the water, which may eventually outgas into the FPS piping. 
         [0012]    The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section. 
       SUMMARY 
       [0013]    The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure is not intended to identify key/critical elements of embodiments of the invention or delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
         [0014]    According to one or more embodiments described and claimed herein, a corrosion prevention treatment of wet FPS including purging the pipes of O2 with an inert gas such as N2, followed by filling the pipes with deoxygenated water generated “on the fly” as the water enters a building, using one or more Gas Transfer Membrane (GTM) devices and N2 gas. The GTM device eliminates the need for a water reuse tank and its associated pipes, valves, recirculation regimen, and the like. Water is pumped directly from the building water supply to a GTM device, where it is deoxygenated to very low O2 levels—such as below 300 ppb (parts per billion). The deoxygenated water then flows directly into the O2-purged pipes of the FPS. When the FPS is drained for testing or repair, the deoxygenated water may be discharged, and replaced, upon return to service of the FPS, with water freshly deoxygenated from the building supply as the FPS piping is filled. 
         [0015]    One embodiment relates to a method of suppressing corrosion in a wet fire protection system including at least one pipe. Each pipe includes a plurality of automatically activated valves operative to open and discharge water in the event of a fire. The system further includes at least gas fill and purge valves located at spaced-apart distances in one or more pipes. Atmospheric oxygen is purged from the pipes by injecting a first inert gas into at least one gas fill valve, and discharging oxygen displaced by the first inert gas via at least one gas purge valve. A Gas Transfer Membrane (GTM) deoxygenating device is interposed between a building water supply and the wet fire protection system pipes and the first inert gas is supplied to the GTM device. After purging oxygen from the pipes, water is directed from the building water supply through the GTM device, where it is deoxygenated to an oxygen concentration of 500 ppb (parts per billion) or less. The deoxygenated water is directed from the GTM device into the wet fire protection system pipes. 
         [0016]    Another embodiment relates to a corrosion-inhibiting wet fire protection system (FPS) in a building having a water supply. The FPS includes at least one pipe. Each pipe includes a plurality of automatically activated valves operative to open and discharge water in the event of a fire. The FPS also includes at least one gas fill valve and one gas purge valve in one or more pipes. The gas fill and purge valves are located at spaced-apart distances. The FPS further includes a Gas Transfer Membrane (GTM) deoxygenating device. The GTM device is connected in fluid flow relationship with the pipes via a fluid fill valve. The GTM device is operative to deoxygenate building supply water to a concentration of 500 ppb (parts per billion) or less in a single pass. The FPS additionally includes a nitrogen gas source connected to the at least one fill valve and to the GTM device. The FPS also includes a controller operative to control the gas fill valve, gas purge valve, nitrogen gas source, and GTM device. The controller controls these elements to displace atmospheric oxygen in the pipes with nitrogen gas by injecting nitrogen gas into at least one fill valve and discharging oxygen displaced by the nitrogen gas via at least one purge valve. After purging oxygen from the pipes, the controller directs water from the building water supply through the GTM device, where it is deoxygenated to an oxygen concentration of 500 ppb (parts per billion) or less. At the same time the N2 sweep gas to the GTM can saturate the fill water with Nitrogen to allow for outgassing of N2 into the gas pockets allowing for higher level of corrosion protection. The deoxygenated water is then directed from the GTM device into the wet FPS pipes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a functional block diagram of a corrosion-inhibiting wet Fire Protection System. 
           [0018]      FIG. 2  is a partial sectional diagram of a Gas Transfer Membrane (GTM) deoxygenating device. 
           [0019]      FIG. 3  is a sectional diagram of a microporous, hollow fiber used in the GTM device of  FIG. 3 . 
           [0020]      FIG. 4  is a flow diagram of a method of suppressing corrosion in a wet Fire Protection System. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  depicts, in functional schematic form, a corrosion-inhibiting wet Fire Protection System (FPS)  10 , according to a representative embodiment of the present invention, which inhibits Microbiologically Influenced Corrosion (MIC) and/or galvanic corrosion and thus prevents or minimizes corrosion-induced leaks to the system. Once configured and charged, the corrosion-inhibiting wet FPS  10  operates similarly to a conventional wet FPS; the corrosion-inhibiting wet FPS  10  differs in its initialization and charging. In particular, air in the corrosion-inhibiting wet FPS  10  piping is purged of atmospheric oxygen (O2) prior to charging by displacing it with an inert gas. The system  10  is then charged with water from the building supply that is dynamically deoxygenated and saturated with inert gas as the FPS  10  piping is filled. This combination virtually eliminates O2 from the interior volume of the corrosion-inhibiting wet FPS  10  piping, thus inhibiting or eliminating corrosion over extended durations by suppressing oxidation. In a presently preferred embodiment, the inert gas is nitrogen (N 2 ), due to the ease and low cost of extracting high-purity nitrogen from ambient air. However, any non-reactive gas, such as helium, neon, argon, or the like, may be utilized within the scope of the present invention. 
         [0022]    The corrosion-resistant wet FPS  10  includes all of the functions and features of a conventional wet FPS. Indeed, most of the elements depicted in  FIG. 1  to the right of the dashed vertical line are present in a conventional wet FPS. These include a riser  12  connected to a reliable source of water, such as local city water as it enters the building. A pump or valve  14  isolates the riser  12  from one or more FPS zones  16 . Although depicted schematically as a single pipe, an FPS zone  16  may comprise a small network of pipes, such as required to cover a floor of a building, a particular portion of a floor, or the like. Disposed at regular intervals along each zone  16  pipe is a plurality of sprinkler heads  18 . As discussed above, a sprinkler head  18  is a normally-closed valve that is automatically actuated in the event of a fire, to release water from the FPS  10  for fire suppression. 
         [0023]    At the end of or at various locations within each zone  16  at least one purge valve  20  may be opened to vent atmospheric air from the interior of the zone  16  pipes. In one embodiment, the purge valve  20  is actuated under the control of a controller  22 , via a wired or wireless connection. In other embodiments, the purge valve is  20  may be manually actuated. In one embodiment, an O2 sensor  24  may additionally be disposed at the end of each FPS zone  16 . The O2 sensor  24  is operative to detect and quantify the concentration of O2 in air or other gas being vented by the purge valve  20 . In one embodiment, the O2 sensor  24  is operative to communicate a sensed O2 concentration to the controller  22 , via a wired or wireless connection. In other embodiments, the O2 sensor  24  includes a gauge or other display that is read manually. 
         [0024]    The controller  22  may additionally receive input from one or more sensors (not depicted). For example, a pressure sensor disposed in the zone  16  piping may detect a drop in water pressure, indicating that a sprinkler head  18  has opened, triggering the controller  22  to activated or open the pump or valve  14 . Additionally, the controller  22  may receive inputs from smoke detectors, heat sensors, and the like. The controller  22  may additionally generate outputs, such as an alarm indication if a fire is detected, routine status and operating parameter outputs, and the like. In particular, the controller  22  may communicate with, or may indeed form a part of, a building-wide automated maintenance system, that includes and controls fire detection and suppression, access and security functions, HVAC, lighting, and the like. 
         [0025]    According to embodiments of the present invention, the corrosion-inhibiting wet FPS  10  of the present invention is initialized and charged in a way that virtually eliminates O2 from the interior volume of FPS  10  pipes, and maintains that O2-free environment. 
         [0026]    Prior to charging the corrosion-inhibiting wet FPS  10 , atmospheric air is purged from the zone  16  piping by displacing it with an inert gas, such as nitrogen (N2). To facilitate this, a N2 generator  28  may be provided and selectively coupled to the FPS  10  pipes via a normally-closed fill valve  26 . In a permanent installation, the N2 generator and fill valve  26  may be controlled by the controller  22 , via a wired or wireless connection. A suitable N2 generator  28  is the MICBlast™ or the N2-Blast™ FPS Nitrogen Generator, available from South-Tek Systems of Wilmington, N.C. In one embodiment, the N2 generator  28  preferably generates N2 of 95% or greater purity. In one embodiment, the N2 generator  28  preferably generates N2 of 98% or greater purity. In one embodiment, the N2 generator  28  preferably generates N2 of 99.9% or greater purity. 
         [0027]    Reserve nitrogen may be generated and stored in a tank  30 . In one embodiment, for example in a small building with only one or a few zones  16 , a N2 generator  28  may not be required, and sufficient N2 may be supplied by a portable tank  30  provided on-site only for the initialization and charging of the FPS  10 . In this case, the N2 generator  28  is located off-site. 
         [0028]    In either case, prior to charging the corrosion-inhibiting wet FPS  10  by introducing water into the zone  16  piping, atmospheric air (which includes approximately 20.8% O2 by volume) is purged from the zone  16  piping. To accomplish this, both the purge valve  20  and fill valve  26  are opened, and either the N2 generator is actuated or the N2 tank  30  is opened. The gas purged from the zone  16  piping is monitored by the O2 sensor  24 . When the gas escaping from the purge valve  20  is sufficiently oxygen-free (e.g., when the N2 has displaced all atmospheric air in the pipes), the purge valve  20  and fill valve  26  are closed. In some embodiments, the air purging operation may include additional steps, such as over-pressurizing the zone  16  piping with N2 to well over atmospheric pressure, incrementally bleeding gas from the purge valve  20  and periodically injecting N2 gas at the fill valve  26 , until the desired concentration of N2 is achieved. 
         [0029]    After O2 has been purged from the zone  16  piping, and the corrosion-inhibiting wet FPS  10  is charged with deoxygenated water. Typically, water contains approximately 10 to 14 ppm (parts per million) O2 near freezing, decreasing to about 6 to 10 ppm O2 at 45° C. Water is considered to be hypoxic when it contains less than 0.2 ppm O2. Water completely devoid of O2 is called anoxic. As used herein, the term “deoxygenated water” includes both hypoxic and anoxic water. In particular, as used herein, the term “deoxygenated water” for corrosion inhibiting purposes means water with an O2 concentration of 500 ppb (parts per billion) or less. The O2 concentration of water will vary with temperature. In one embodiment, the oxygenated water preferably has an O2 concentration of 300 ppb or less. In one embodiment, the oxygenated water preferably has an O2 concentration of 150 ppb or less. 
         [0030]    A recent development in the industry is the Gas Transfer Membrane (GTM) method of deoxygenation. With the main pump or valve  14  closed and the zone  16  piping flooded with N2 gas, a GTM device  32  receives supply water from the street supply via valve  34  (under the control of controller  22 ), and N2 gas from the N2 generator  28  or tank  30 . The GTM device  32  removes dissolved O2 molecules from the water, as described in greater detail herein and the water through the GTM may become saturated with N2 gas. Deoxygenated water from the GTM device  32  is injected into the riser  12  via valve  36  (under the control of controller  22 ), downstream of the main pump or valve  14 , to fill the FPS pipes. The controller  22  may open one or more purge valves  20  to discharge N2 gas displaced by the deoxygenated water. The GTM device  32  may supply deoxygenated water at flow rates of up to 1000 gal/hr. In installations where a higher flow rate is required to fill the FPS zone  16  piping in a reasonable time, multiple GTM devices  32  may be configured in parallel, with concomitant additional piping and flow control valves. The GTM device  32  eliminates the need for a water recirculation tank, and by eliminating the recirculation necessary in known deoxygenation processes, dramatically reduces the time and cost required to deoxygenate water when filling a wet FPS system  10 . A suitable GTM device  32  is available from the Membrana company of Charlotte, N.C. 
         [0031]    Ideally, the deoxygenated water should fully fill the interior volume of all zone  16  pipes. In practice, there will be at least some voids in which N2 gas remains. However, because the charging water has been deoxygenated, there is essentially no dissolved oxygen to offgas into the N2-filled spaces, and hence no free oxygen is available for the oxidation processes that cause corrosion, or to support microorganisms involved in MIC. Furthermore, absent some significant leak in the system, there is no mechanism for O2 to enter the pipes; hence, embodiments of the present invention provide a long-term corrosion-inhibiting solution. 
         [0032]      FIG. 2  depicts the structure and operation of the Gas Transfer Membrane deoxygenating device  32 . The GTM device  32  includes a street water inlet  40  and deoxygenated water outlet  42 , as well as an N2 sweep gas inlet  44  and gas discharge  46 . The GTM device  32  uses a membrane array  48  knit from microporous, hydrophobic, hollow fibers to remove dissolved O2 from supply water. The fibers may be approximately 300 um in diameter, with approximately 0.03 um diameter pores formed in the fiber walls. The device  32  additionally dissolves N2 molecules into the water, which further assists corrosion resistance in the FPS  10  piping. 
         [0033]    The array  48  is wrapped around a center tube  50  inside of the GEM device  32  housing  56 . During FPS  10  fill operations, water flows over the outside of the hollow fibers while high-purity N2 gas flows through the inside of the fibers. The water enters a distribution tube  50 , and is directed outwardly through the array  48  by a baffle  52 . On the other side of the baffle  52 , the water is directed back inwardly through the array  48  and into a collection tube  54 . N2 gas entering the device  32  at the gas inlet  44  is directed down the interior of the fibers comprising the array  48 , in an opposite direction to that of the H2O flow. In other embodiments, this arrangement may be reversed, with water flowing through the fibers and N2 gas flowing around them. Because the membrane is hydrophobic, it acts as an inert support that allows direct contact between the N2 gas and liquid phase H2O without dispersion. Applying a higher pressure to the H2O stream relative to the N2 stream creates the driving force for dissolved O2 gas in the H2O to pass through the membrane pores into the interior of the hollow fibers. The O2 gas is carried away by the N2 gas flow, through the hollow fibers, to the gas discharge  46 . 
         [0034]      FIG. 3  depicts a sectional view of an individual microporous, hydrophobic, hollow fiber of the membrane array  48 . Water flows around the outside of the fiber (in an upward direction, as depicted in  FIG. 3 ). N2 gas flows through the fiber (downwardly, as depicted in  FIG. 3 ). The greater H2O pressure forces free O2 molecules to disperse from the H2O into the fiber, at the liquid/gas contact points at each micropore in the fiber. Due to the much greater concentration of N2 molecules than O2, this process additionally dissolves some N2 molecules into the deoxygenated water. This feature that aids in corrosion resistance, since at the interface between deoxygenated water and any residual N2 gas pockets in the FPS piping, the only dissolved gas to diffuse out of the deoxygenated water is N2 gas, which further suppresses bacteriological activity, and hence MIC corrosion. 
         [0035]    At flow rates up to 1000 gal/hr, the GTM device  32  can deoxygenate typical street water to levels at or below 300 ppb of O2. For higher flow rates, multiple GTM devices  32  may be configured in parallel. To achieve greater deoxygenation, without a reduction in flow rate, a larger size GTM device  32  may be used, or multiple GTM devices  32  may be configured in serial. By generating deoxygenated water “on the fly” from ordinary building supply water, embodiments of the present invention eliminate the need for a bulky, heavy water reuse tank, and vastly increase the speed of deoxygenating water over the recirculation methods known in the art. An additional value to this art is by decreasing the deoxygenated water fill time, the fire protection system if off line for less time during such fill operation versus prior deoxygenated water fill methods. 
         [0036]      FIG. 2  depicts a flow diagram of the steps of a method  100  of suppressing corrosion in a wet FPS  10 . The corrosion-inhibiting wet FPS  10  includes at least one pipe, and each pipe includes a plurality of automatically activated valves  18  operative to open and discharge water in the event of a fire. The corrosion-inhibiting wet FPS  10  further includes at least a fill valve  26  and a purge valve  20  located at spaced-apart distances in one or more pipes. The method begins by purging atmospheric oxygen from the pipes by injecting an inert gas into at least the fill valve  26 , and discharging oxygen displaced by the inert gas via at least the purge valve  20  (block  102 ). After purging O2 from the pipes, the method continues by filling the pipes with deoxygenated water having an O2 concentration of 500 ppm or less (block  104 ). In particular, this method steps may comprise opening the purge valve  20  to allow the inert gas to escape while pumping deoxygenated water into the zone  16  from a deoxygenated water tank  34 , and then closing the purge valve  20 . Finally, after filling the pipes with deoxygenated water, the method continues by connecting the zone  16  pipes to a source of water (e.g., via pump or valve  14 ) having sufficient pressure to expel water from at least one automatically activated valve  20  in the event of a fire. Although the non-deoxygenated water includes dissolved oxygen, all of the FPS  10  pipes downstream of the main pump or valve  14  are full of deoxygenated water, and little of the non-deoxygenated water will mix therewith. In particular, no non-deoxygenated water will migrate to the near-horizontal zone  16  pipes, in which corrosion is a concern. 
         [0037]    The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.