Abstract:
A sprinkler system and a method for mitigating scaling, microbiological influenced corrosion and oxidative corrosion are disclosed. The system includes a piping network in fluid communication with a source of pressurized water and an air pump. The network is vented to the ambient. The air pump moves initially dry ambient air through the system, either by maintaining a negative or a positive air pressure within the network. The dry air absorbs residual water within the network and exhausts it to the ambient. Rate of air flow through the system is controlled by restrictor elements such as orifices, throttle valves or venturies within the piping network.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority to U.S. Provisional Application No. 60/843,816, filed Sep. 12, 2006. 
     
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a fire suppression sprinkler system having a piping network that is dried to mitigate the adverse effects of scaling, oxidative corrosion and microbiologically influenced corrosion. 
       BACKGROUND OF THE INVENTION 
       [0003]    Microbiological influenced corrosion (MIC) can lead to significant problems in piping networks of fire suppression systems. Water borne microbiological entities, such as bacteria, molds and fungi, brought into a piping network of a sprinkler system with untreated water, feed on nutrients within the piping system and establish colonies in the stagnant water within the system. This occurs even in so-called “dry” sprinkler systems where significant amounts of residual water may be present in the piping network after a test or activation of the system. 
         [0004]    Over time, the biological activities of these living entities cause significant problems within the piping network. Both copper and steel pipes may suffer pitting corrosion leading to pin-hole leaks. Iron oxidizing bacteria form tubercles, which are corrosion deposits on the inside walls of the pipes that can grow to occlude the pipes. Tubercles may also break free from the pipe wall and lodge in sprinkler heads, thereby blocking the flow of water from the head either partially or entirely. Even stainless steel is not immune to the adverse effects of MIC, as certain sulfate-reducing bacteria are known to be responsible for rapid pitting and through-wall penetration of stainless steel pipes. 
         [0005]    In addition to MIC, other forms of corrosion are also of concern. For example, the presence of water and oxygen within the piping network can lead to oxidative corrosion of ferrous materials. Such corrosion can cause leaks as well as foul the network and sprinkler heads with rust particles. The presence of water in the piping network having a high mineral content can cause scaling as the various dissolved minerals, such as calcium and zinc, react with the water and the pipes to form mineral deposits on the inside walls which can inhibit flow or break free and clog sprinkler heads, preventing proper discharge in the event of a fire. 
         [0006]    There is clearly a need for a piping network for sprinkler systems wherein scaling, oxidative corrosion and MIC is mitigated so as to be insignificant. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention concerns a dry type fire suppression sprinkler system wherein MIC, other forms of corrosion, and scaling is mitigated. The system comprises a plurality of sprinkler heads, a source of pressurized water and a piping network connecting the sprinkler heads to the water source. Because it is a dry type system, the piping network is normally substantially devoid of water, i.e., when not responding to a fire. A supply valve is positioned in the piping network between the source of pressurized water and the sprinkler heads and controls the flow of water thereto. The supply valve is openable in the event of a fire to allow water to flow to the heads. An air vent is positioned in the piping network downstream of at least a portion of the sprinkler heads which provides fluid communication between the piping network and ambient air. An air pump is in fluid communication with the piping network between the valve and the sprinkler heads. The air pump moves ambient air through at least a portion of the piping network through the air vent. 
         [0008]    In one embodiment, the air pump comprises a vacuum pump adapted to draw ambient air into the piping network through the air vent and exhaust the ambient air back to the atmosphere. The embodiment further comprises a flow restrictor positioned within the piping network between the air vent and the vacuum pump for controlling the rate of air flow through the piping network. The flow restrictor may comprise an orifice, a throttle valve, a venture or other device which restricts fluid flow. The flow restrictor may comprise the air vent. 
         [0009]    The sprinkler system may further comprise a dryer positioned within the piping network between the air vent and the vacuum pump. The dryer removes moisture from air drawn through the air vent by the vacuum pump. The dryer may comprise a device such as a desiccant dryer, a refrigeration dryer, a membrane filter a compressed air dryer, or other drying apparatus. 
         [0010]    In another embodiment, the system comprises a source of pressurized water and a piping network comprising at least one branch, but preferably a plurality of branches. Because the system is a dry type system, the piping network is normally substantially devoid of water, i.e., when not responding to a fire. The branch is in fluid communication with the source of pressurized water. A supply valve is positioned in the piping network between the source of pressurized water and the branch and controls flow of water thereto. The supply valve is openable in the event of a fire to allow water to flow to the branch. A plurality of sprinkler heads are mounted on the branch. An air vent is positioned at an end of the branch and provides fluid communication between the branch and the ambient air. A vacuum pump is in fluid communication with the piping network between the valve and the branch. The vacuum pump draws ambient air through the one branch through the air vent. 
         [0011]    The system may also comprise an orifice positioned within the branch for controlling the rate of air flow therethrough. The orifice may comprises the air vent. Alternately, a throttle valve is positioned within the branch, the throttle valve being adjustable for controlling the rate of air flow through the one branch. The throttle valve may comprise the air vent. 
         [0012]    The system may also include a dryer positioned within the branch between the air vent and the sprinkler heads. The dryer removes moisture from air drawn through the air vent by the vacuum pump. The dryer may comprise, for example a desiccant dryer, a refrigeration dryer, a membrane filter, a compressed air dryer or other gas drying apparatus. 
         [0013]    In another embodiment of a dry type sprinkler system according to the invention the air pump comprises a compressor adapted to force ambient air into the piping network. The ambient air is exhausted back to the atmosphere through the air vent. The system may also comprise a flow restrictor positioned within the piping network between the air vent and the compressor for controlling the rate of air flow through the piping network. The flow restrictor may be an orifice, a throttle valve or a venturi. 
         [0014]    The system may also include a dryer positioned within an air flow of the compressor. The dryer removes moisture from air forced into the piping network. Preferably the dryer is positioned within the piping network between the compressor and the air vent. The dryer may comprises a desiccant dryer, a refrigeration dryer, a membrane filter or a compressed air dryer. 
         [0015]    The invention also encompasses a method of drying a piping network. The method comprises: 
         [0016]    (a) providing an air vent in the piping network; 
         [0017]    (b) moving air from the ambient, through the piping network; and 
         [0018]    (c) exhausting the air back to the ambient. 
         [0019]    In one aspect of the method, moving air through the piping network comprises drawing the air into the piping network through the air vent. In another aspect of the invention, moving air through the piping network comprises compressing the air into the piping network and exhausting the air back to the ambient comprises venting the air to the atmosphere through the air vent. The method may also include controlling the rate at which air moves through the piping network by restricting the flow. The method may also include drying the air before it is moved through the piping network. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1 and 2  are schematic diagrams of exemplary embodiments of dry type fire suppression sprinkler systems according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0021]      FIG. 1  shows a schematic diagram of a dry type fire suppression sprinkler system  10  according to the invention. System  10  comprises a piping network  12  formed of a plurality of branches  14  on which are mounted a plurality of sprinkler heads  16 . Because it is a dry type system, the piping network, including the branches, is normally substantially devoid of water when not responding to a fire. The branches  14  with their sprinkler heads  16  extend throughout a building, such as a residence, an apartment, an office complex, a warehouse or other structure to be protected. Sprinkler heads  16  may have one of various types of triggering mechanisms which open the heads in response to a fire condition to allow the discharge of water. The well known glass bulb containing a heat sensitive liquid is one example of a triggering mechanism. Other examples include collapsing mechanisms held together by a eutectic solder. 
         [0022]    The piping network  12  connects the sprinkler heads  16  to a source of pressurized water  18 , which could be, for example, a municipal water main, or a reservoir. Water flow from the source to the sprinkler heads  16  is controlled by a supply valve  20  positioned in the network  12  between the water source  18  and the various branches  14 ,  14   a - 14   f  of the piping network on which the heads  16  are mounted. As noted, the system shown is a dry type system wherein the piping network downstream of supply valve  20  is not charged with water in its ready state. However, there may still be residual stagnant water in the piping network, for example, water remaining due to incomplete draining after a test of the system or a previous actuation. 
         [0023]    Supply valve  20  is actuated by a control system  22 , for example, a programmable logic controller or a microprocessor with resident software. The control system may also include a pressure sensitive actuator (with or without an accelerator mechanism) that is in communication with the piping network, one or more heat sensitive actuators, radiation sensitive actuators, smoke sensitive actuators or other actuators that are capable of detecting a fire condition and providing a signal to the control system causing it to open the main valve and allow water to flow to the sprinkler heads. 
         [0024]    An air pump  24  is in fluid communication with the piping network  12  between the supply valve  20  and the sprinkler heads  16 . In the embodiment shown in  FIG. 1 , the air pump  24  is a vacuum pump which draws ambient air through the piping network while the system  10  is in a “ready” state (i.e., ready for actuation in the event of a fire) as described below. Preferably, the pump  24  is a rocking piston type vacuum pump which operates over a short duty cycle to ensure long pump life. Pump  24  is protected by a cut-off valve  26  which is open when the system is in the ready state. When the system is actuated and the supply valve  20  is opened, the cut-off valve  26  is closed, for example, by the control system  22 , to prevent water from being drawn into the pump. 
         [0025]    Various branches  14  of the piping network may have an air vent  28 , preferably positioned downstream of the last sprinkler head  16  in the branch. The air vents allow ambient air  30  to be drawn into the piping network through the branches by the vacuum pump  24 . Preferably the air vents provide continuous fluid communication between the piping network and the ambient when the system is in the ready state. The air flow may be substantially continuous through the branches with the pump  24  operating intermittently to maintain a negative pressure between a predetermined minimum and maximum within the piping network. Negative pressure may be maintained within the system  10  through the use of a simple feed back loop which comprises a pressure sensor  32  which senses the gas pressure within the piping network  12  and returns a signal to the control system  22 , which cycles the vacuum pump  24  on and off as needed to maintain the desired pressure. Air  30 , drawn through the network, is exhausted to the atmosphere by the vacuum pump. 
         [0026]    Air flow through each branch  14  is controlled by a flow restrictor  34  depicted schematically in branch  14 . Various types of restrictors may be employed, such as an orifice  36  shown in branch  14   a , a throttle valve  38  in branch  14   b , as well as a venturi  40 , shown in branch  14   c . Other types of flow restrictors are also feasible. The restrictors may be all of the same type, or mixed types may be used in a single system. The flow characteristics of the flow restrictors may be varied to balance the air flow through the various branches. Thus, the sizes of the orifices  36  may be different in different branches depending upon their length and distance from the vacuum pump  24 , with longer branches and more distant branches having larger orifices than shorter, closer branches to compensate for the greater resistance to flow through the longer or more distant branch. Similarly, throttle valves may be adjusted individually as required to different opening sizes to balance the flow for a particular negative pressure. 
         [0027]    In branches  14   a - 14   c , the flow restrictors  36 ,  38  and  40  also comprise the air vents  28 . Alternately, as depicted in branches  14   d - 14   f , the flow restrictors  36 ,  38  and  40  are positioned within the piping network  12  in spaced relation away from the air vents  28 . Filters  42  may be used in conjunction with the air vents  28  to filter particulates from the air  30  to prevent clogging of the various flow restrictors. 
         [0028]    An air dryer  44  may be positioned between each air vent  28  and the last sprinkler head  16  in each branch of the piping network  12 . Desiccant dryers, which absorb water using granular material such as activated alumina or silica gel, are particularly advantageous because they are effective, inexpensive, compact and require little maintenance. Other drying devices, such as refrigeration dryers, membrane filters and compressed air dryers, are also feasible. Each dryer  44  is protected from water in the branch by a check valve  46  positioned in the branch between the dryer and the last sprinkler head. The check valves  46  are arranged to permit flow of air  30  from the air vent  28  to the vacuum pump  24 , but prevent water flow from the water source  18  to the dryers  44 . 
         [0029]    In operation, the fire suppression sprinkler system  10  may be activated, for example, in a test or in an actual fire event. The control system  22  opens supply valve  20 , supplying water to the network  12  and its various branches  14 . In a fire event, one or more sprinkler heads  16  in the vicinity of the fire will trigger, allowing water to be discharged to suppress the fire. The check valves  46  prevent water from entering the dryers  44  and exiting the system through air vents  28 . The control system also closes cut-off valve  26 , protecting vacuum pump  24 . 
         [0030]    Upon completion of the fire or test event, the supply valve  20  is closed and a drain valve  48  is opened to drain the piping network  12  so that it is substantially devoid of water as appropriate for a dry type system in the absence of a fire. Any sprinkler heads  16  that opened during the fire are replaced, and the cut-off valve  26  is then opened. The system  10  is again reset in the ready state, capable of detecting a fire and operating to suppress it. It is expected, however, that despite draining the system, residual water will remain in the piping network  12 , for example, in any or all of the branches  14 . The water may remain stagnant within the pipes for long periods of time between system actuations, providing ample opportunity for microbiological influenced corrosion, oxidative corrosion and scaling to damage the pipes and cause leaks or blockages. To mitigate this damage, the vacuum pump  28  is run intermittently to maintain a negative pressure within the piping network. This causes air  30  to be drawn into the branches through air vents  28 . The flow rate is determined largely by the flow restrictors  34 , such as the orifices  36 , the throttling valves  38  and the venturis  40  in each branch in conjunction with the negative system pressure. The flow rate is established to ensure an adequate, substantially continuous air flow throughout the system capable of removing the residual water while operating within reasonable parameters for the duty cycle of the vacuum pump. For large systems multiple vacuum pumps  24  may be employed. 
         [0031]    Moisture is removed from the ambient air  30  drawn into the piping network through air vents  28  as it passes through the dryers  44 . The incoming air is dried to a predetermined dew point and then continues on through the piping network  12 , whereupon it is exhausted to the atmosphere by the vacuum pump  24 . As it travels through the various branches of the network, the dry air absorbs the residual water that would otherwise stagnate within the pipes. The continuous flow of initially dry air gradually removes the water from the piping network, starving the microbiological entities of the water they need to survive, and effectively curtailing microbiologically influenced corrosion damage. Other forms of corrosion, such as oxidative corrosion as well as scaling effects, are also significantly inhibited by removal of the water. In dry climates where the ambient air has low relative humidity it may be possible to dispense with the dryers. Similarly, for large systems formed of pipes having relatively small diameters, discrete flow restrictors may not be necessary, as the lengths and diameter of the pipes themselves may provide the desired air flow rates for effective drying. 
         [0032]    In another system embodiment  50 , shown in  FIG. 2 , the air pump  24  is a compressor which forces ambient air  30  into the piping network  12 . Air  30  passes through a dryer  44 , positioned either at the intake  52  of the compressor or between the compressor and the cut-off valve  26 , where the moisture is removed. The dry air then passes through the various piping network branches  14 , absorbing the residual water and exiting each branch at an air vent  28 . The compressor  24  is operated intermittently in a feed back control loop by the control system  22  which receives signals from the pressure sensor  32  and operates the compressor to maintain the piping network at a positive pressure between an upper and a lower limit. The rate of air flow through the system is controlled largely by the flow restrictors  34  as described above, in conjunction with the system pressure. Valves  54 , under the control of the control system  22  are advantageously positioned between the last sprinkler head  16  in each branch and the air vents  28 , and are closed by the control system when the sprinkler system is activated to suppress a fire, thereby preventing water from exiting through the air vents. 
         [0033]    The sprinkler system according to the invention is advantageously used with dry systems, but will also find use with wet systems that are seasonally converted to dry systems as, for example, in an unheated warehouse where the sprinkler system is operated as a wet system in the summer and as a dry system in the winter.