Abstract:
An actuator for use with a negative pressure fire suppression sprinkler system is disclosed. The actuator has three chambers, each chamber having a flexible diaphragm. One chamber is connected to the sprinkler system piping network. Its diaphragm moves in response to an increase in pressure in the piping network signaling a fire. The diaphragm in the second chamber opens an orifice in response to the motion of the first diaphragm. The open orifice allows water to flow from the third chamber to the ambient. The diaphragm in the third chamber moves in response to the water flow from the third chamber. The third chamber is connected to a valve controlling water flow to the piping network. Motion of the diaphragm in the third chamber actuates the valve, releasing water to the system.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to pneumatic actuators for actuating valves in response to a change in gas pressure. 
       BACKGROUND OF THE INVENTION 
       [0002]    Automatic sprinkler systems for fire protection of structures such as office buildings, warehouses, hotels, schools and the like are required when there is a significant amount of combustible matter present. The combustible matter may be found in the materials from which the building itself is constructed, as well as in the building contents, such as furnishings or stored goods. 
         [0003]    Of the various types of automatic sprinkler systems available, the “dry-pipe” system finds widespread use. Dry-pipe systems use an actuator which responds to a signal or combination of signals from different detectors to trip a valve which provides water to the sprinkler piping network. Most dry-pipe systems are of the positive pressure type, meaning that the piping network is normally filled with compressed air or nitrogen (and not water) prior to actuation. The dry-pipe system can thus be used in unheated environments which are subject to below freezing temperatures without fear of pipes bursting due to water within the pipes expanding upon freezing. 
         [0004]    When sufficiently pressurized, the behavior of the gas within the piping network of a positive pressure dry-pipe system may be used to indicate a fire condition and trigger actuation of the system. Heat from the fire will cause sprinkler heads to open, allowing pressurized gas to escape from the piping network and resulting in a pressure drop within the piping network. Actuation of the system may be effectively triggered by this pressure drop. 
         [0005]    Positive pressure dry-pipe systems are not without their disadvantages however. Such systems use compressed air drawn from the ambient atmosphere to pressurize the piping network. This introduces moisture and oxygen into the piping network, creating conditions within the pipes which favor microbiological influenced corrosion (MIC). 
         [0006]    MIC can lead to significant problems in piping networks of fire suppression systems. Microbiological entities, such as bacteria, molds and fungi introduced into the piping network with untreated water or compressed air, feed on nutrients within the piping system and establish colonies in the stagnant water or moisture within the system. 
         [0007]    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. 
         [0008]    In addition to MIC, other forms of corrosion are also of concern. For example, the presence of moisture 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. 
         [0009]    One way to mitigate MIC and other forms of corrosion is to maintain the piping network at a negative pressure relative to the ambient atmosphere and draw air having little or no entrained moisture through the system. This will dry the piping network and starve the biological entities of their required water, rendering them inert, and largely preventing MIC. 
         [0010]    When maintaining negative as opposed to positive pressure within the piping network, it is still possible to use the change in pressure within the system, which results when one or more sprinkler heads open, as a signal to trigger the system. For a negative pressure system, it is, of course, an increase in pressure within the system which constitutes the actuating signal. This will require different actuators from those which are currently used for positive pressure systems, which detect a decrease in the system pressure as the triggering event. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention concerns a device for depressurizing a fluid contained in a first enclosed space, such as a latch valve used in a sprinkler system, in response to an increase in fluid pressure in a second enclosed space, such as the piping network of a negative pressure dry-pipe sprinkler system. The device comprises a first chamber having a flexible first diaphragm mounted therein. The first diaphragm sealingly divides the first chamber into first and second chamber portions. Both of the chamber portions are in fluid communication with the first enclosed space. The first chamber portion has an opening which provides fluid communication with the ambient. The opening is surrounded by a seat which faces the first diaphragm. The first diaphragm is deflectable into sealing engagement with the seat to seal the opening when the first enclosed space is pressurized with the fluid. A second chamber has a flexible second diaphragm mounted therein. The second diaphragm sealingly divides the second chamber into third and fourth chamber portions. The fourth chamber portion is in fluid communication with the ambient. The third chamber portion is also in fluid communication with the ambient and has an aperture which provides fluid communication with the second chamber portion. The aperture is surrounded by a second seat which faces the second diaphragm. The second diaphragm is deflectable into sealing engagement with the second seat to seal the aperture. A third chamber has a flexible third diaphragm mounted therein. The third diaphragm sealingly divides the third chamber into fifth and sixth chamber portions. The sixth chamber portion is vented to the ambient. The fifth chamber portion is in fluid communication with the second enclosed space. An elongated plunger has one end positioned within the fifth chamber portion. The one end of the plunger is engageable with the third diaphragm. The other end of the plunger is positioned within the fourth chamber portion and is engageable with the second diaphragm. The third diaphragm is deflectable into engagement with the one end of the plunger when the second enclosed space, and thereby the fifth chamber portion, is at a pressure lower than the sixth chamber portion. The plunger is thereupon forced into engagement with the second diaphragm and thereby forces the second diaphragm into sealing engagement with the second seat. 
         [0012]    The second diaphragm is deflected out of engagement with the second seat when pressure in the second enclosed space, and thereby the fifth chamber portion, increases to a predetermined value. Fluid in the second chamber portion is permitted to enter the third chamber portion and exit to the ambient, thereby allowing the first diaphragm to deflect out of engagement with the first seat and allowing the fluid to flow from the first enclosed space through the first chamber portion and exit to the ambient, thereby depressurizing the first enclosed space. 
         [0013]    The device also includes a set point trigger which comprises a body and a conduit which extends through the body. One end of the conduit is in fluid communication with the fifth chamber portion and the other end of the conduit is in fluid communication with the second enclosed space. An opening in the body provides fluid communication between the conduit and the ambient. A valve seat surrounds the opening. A valve closing member is movably mounted within the body. The closing member is movable into sealing engagement with the seat to close the opening. Biasing means, such as a spring is provided for biasing the valve closing member out of engagement with the seat when fluid pressure within the second enclosed space, and thereby the conduit, rises to a predetermined value thereby opening the conduit and venting the fifth chamber portion to the ambient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic view of a negative pressure dry-pipe sprinkler system having a negative pressure actuator according to the invention; 
           [0015]      FIG. 2  is a sectional view of a valve actuated by the negative pressure actuator according to the invention; and 
           [0016]      FIG. 3  is a sectional view of a negative pressure actuator according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0017]      FIG. 1  shows a schematic representation of a negative pressure dry-pipe sprinkler system  10  according to the invention. System  10  comprises a piping network  12  which extends throughout the structure (not shown), such as a building or warehouse, in which the system is installed. Sprinkler heads  14  are mounted on the piping network throughout the structure for the discharge of water or other fire suppressing fluid in the event of a fire. The sprinkler heads have a heat sensitive element which opens the sprinkler in response to heat generated by a fire. Other triggering methods are also feasible. 
         [0018]    Piping network  12  is connected to a source of pressurized water  16  or other fire suppressing fluid. In an example system, the source of water  16  may be a municipal water service water main. Water flow from the source  16  to the piping network  12  is controlled by a service valve  18  and a control valve  20 . Service valve  18  is used to isolate the entire system  10  from the source  16  so that the components can be serviced, replaced, repaired or reset after actuation due to a fire or a test. When the system is in operation, the service valve  18  is open, allowing pressurized water to the control valve  20 . A trim valve  19  is used to provide fluid communication between the source  16  and the mechanisms of control valve  20  and is used to set and reset the control valve during operation as described below. 
         [0019]    Control valve  20  controls the flow of water to the piping network  12 . In the dry-pipe system  10 , the control valve  20  is normally closed and is opened by a negative pressure actuator  22  in response to a fire as described in detail below. Negative pressure actuator  22  is in fluid communication with the control valve  20  through a pipe  24 . Both the control valve  20  and the actuator  22  are in fluid communication with pressurized water source  16  through a pipe  26 . (Flow of water through pipe  26  is controlled by the aforementioned trim valve  19 .) Negative pressure actuator  22  is also in fluid communication with piping network  12  through a pipe  28 . 
         [0020]    The piping network is maintained at a negative pressure (below atmospheric pressure) by a vacuum pump  30 . The vacuum pump is in fluid communication with the piping network through a cut-off valve  31  which is normally open but is closed to protect the pump  30  when water enters the system during test or actuation. The piping network may be substantially fluid tight when all of the sprinkler heads  14  are closed, or it may be a vented system which permits ambient air to be drawn into and flow through the piping network at a controlled rate. For example, the piping network may have one or more vents  32  which comprise a filter  34  for filtering out particulate matter from the ambient air, a desiccant dryer  36  for removing moisture from the ambient air, and an orifice  38  for controlling the rate of flow of ambient air into the system. The piping network in both the fluid tight and vented systems is considered an “enclosed space” as that term is used herein. 
         [0021]    Control valve  20  is shown in detail in  FIG. 2  and includes a housing  40  in which a flapper closing member  42  is mounted. Flapper  42  is pivotally mounted for rotation about an axis  44 . The flapper is sealingly engageable with a seat  46  to prevent water flow from the source  16  to the piping network  12 . The flapper is biased in a closed position by a spring  48  but is more positively held in the closed position against the pressure of source  16  by a latch  50 . Latch  50  pivots about another axis  52  and is biased by a spring  54  into a position away from the flapper  42 . 
         [0022]    When the flapper  22  is closed as shown in  FIG. 2 , it is held in position against the pressure of source  16  by the latch  50 , which in turn, is held in position against the force of flapper  42  and the biasing of spring  54  by a diaphragm  56 . Diaphragm  56  is positioned within a chamber  58  (comprising another “closed space” as used herein) mounted on the valve housing  40 . Chamber  58  is in fluid communication with the source of pressurized water  16  through pipes  24  and  26  (see also  FIG. 1 ). Water pressure from the source  16  within the chamber  58  acts against the diaphragm  56  to maintain the flapper in the closed position shown. To open the control valve  20 , the enclosed space defined by the chamber  58  must be depressurized. A drop in pressure within chamber  58  allows the latch  50  to pivot about axis  52  away from the flapper under the biasing force of spring  54  and the force of the flapper  42 . This releases the flapper which pivots about axis  44  into an open position in response to the pressure from source  16  to release water to the piping network  12 . The operation of control valve  20  is effected by the negative pressure actuator  22  operating in response to an increase in pressure within the piping network  12  caused by an opening of one or more sprinkler heads  14  allowing ambient air into the network as described in detail below. 
         [0023]    Negative pressure actuator  22  is shown in detail in  FIG. 3 . Actuator  22  comprises a housing  60  having an inlet  62  that is connected to pipe  24 . Inlet  62  is in fluid communication with a first chamber  64  defined within the housing  60 . First chamber  64  is divided into respective first and second chamber portions  64   a  and  64   b  by a flexible diaphragm  66  sealingly located within the first chamber. The inlet  62  is in fluid communication with both chamber portions  64   a  and  64   b,  with a duct  68  extending from the inlet  62  into the second chamber portion  64   b.  First chamber portion  64   a  is in fluid communication with the ambient through an outlet  70 . A duct  72  connects the first chamber portion  64   a  to the outlet, the duct having an opening  74  in the first chamber portion defined by a seat  76 . Seat  76  is in facing relation with diaphragm  66 , which is deflectable into and out of sealing engagement with the opening to open and close it during operation of the actuator  22  as described below. A biasing spring  78  is positioned within the second chamber portion  64   b  to bias the diaphragm  66  into engagement with the seat  76 . Biasing spring  78  is used to help control the pressure differential between chamber portions  64   a  and  64   b  at which the diaphragm will move out of engagement with the seat to allow water to flow from the inlet  62  through the opening  74  and through the duct  72  to the outlet  70  during actuator operation. 
         [0024]    A second chamber  80  is positioned adjacent to the first chamber  64 . Second chamber  80  is sealingly divided into third and fourth chamber portions  80   a  and  80   b  by a second diaphragm  82 . An aperture  84 , located between the first and second chambers  64  and  80  provides fluid communication between the second chamber portion  64   b  and the third chamber portion  80   a.  A second seat  86  surrounds the aperture  84 . Second seat  86  is in facing relation with the second diaphragm  82 , which is flexible and may therefore be deflected into and out of engagement with the seat to open and closed aperture  84 . A second biasing spring  88  is located in the third chamber portion  80   a  to bias the diaphragm out of engagement with seat  86 . Spring  88  is used to help control the pressure in chamber portions  80   a  at which the diaphragm  82  will engage the seat  86  and sealingly close aperture  84 . The fourth chamber portion  80   b  is vented to the ambient through a duct  90  to permit movement of the diaphragm  82  unencumbered by pressure within the fourth chamber portion  80   b.  A duct  92  extends between the third chamber portion  80   a  and the outlet  70  to allow water which enters the third chamber portion  80   a  through aperture  84  to escape to the ambient during actuator operation. 
         [0025]    A third chamber  94  is positioned adjacent to the second chamber  80 . Third chamber  94  is divided into fifth and sixth chamber portions  94   a  and  94   b  by a third flexible diaphragm  96 . A plunger  98  is positioned between the fifth chamber portion  94   a  and the fourth chamber portion  80   b  beneath it. The plunger  98  is slidably mounted between the chambers  94  and  80 , and opposite ends of the plunger are engaged with the third and second diaphragms  96  and  82  such that when the third diaphragm deflects downwardly (caused by a lower pressure in the fifth chamber portion  94   a  relative to sixth chamber portion  94   b ), it acts against the plunger which, in turn, acts against the second diaphragm  82  to force it into sealing engagement with the seat  86 , closing aperture  84 . The sixth chamber portion  94   b  is vented to the ambient by duct  100  to permit motion unencumbered by pressure within the sixth chamber portion. 
         [0026]    The fifth chamber portion  94   a  is in fluid communication with the piping network  12  through a duct  102  that is connected to pipe  28  (see also  FIG. 1 ). In some embodiments, it is advantageous to position a set point trigger  104  between the pipe  28  and the duct  102  as shown. Set point trigger  104  comprises a body  106  through which a conduit  108  extends providing fluid communication between the duct  102  and the pipe  28 . An opening  110  in the body  106  provides fluid communication between the conduit  108  and the ambient. A valve seat  112  surrounds the opening  110  and a valve closing member  114  is mounted in the body and engages the seat. The valve closing member is biased out of engagement with seat  112  by a biasing spring  116 . The spring constant of the biasing spring  116  may be chosen so that the valve closing member  114  remains closed as long as a negative pressure below a specific, predetermined value is maintained within the conduit  108  (and hence the piping network  12  and the fifth chamber portion  94   a  in which the conduit is in fluid communication). When the pressure within the conduit exceeds the specific, predetermined value (the “set point pressure”), the force of the biasing spring overcomes the ambient pressure which holds the valve closing member  114  closed and the closing member disengages from the seat  112  and conduit  108  is opened to the ambient, thereby allowing ambient air to rapidly enter the fifth chamber portion  94   a  and trigger the actuator  22 . A set point pressure of about 5 inches Hg is advantageous. The set point trigger acts as an accelerator, triggering the actuator more quickly than if air entered the fifth chamber from the piping network  12 . The set point trigger  104  also includes a manual reset knob  118  which is attached to the valve closing member  114 . To set or reset the set point trigger, the manual reset knob is grasped and pulled to engage the valve closing member  114  with the seat  112 . The knob is held in this position until the pressure within the conduit is below the set point pressure, at which point the ambient air pressure acting against the valve closing member from outside the body  106  can hold the valve closing member engaged with the seat against the biasing force of spring  116 . 
       Negative Pressure Actuator Operation 
       [0027]    The system  10  shown in  FIG. 1  must first be placed in the “ready” mode so that it is ready to detect and suppress a fire. To that end, service valve  18  and trim valve  19  are closed and any water in the piping network is drained through a drain valve  120 , usually positioned at the lowest point in the system. The drain valve is then closed. 
         [0028]    After the piping network  12  is drained, the vacuum pump cut-off valve  31  is opened and vacuum pump  30  is activated to draw a negative pressure within the network. As noted above, the piping network  12  could be substantially fluid tight or may be vented and draw in ambient air though a filter  34 , dryer  36  and orifice  38  at one or more branches. It is understood that even in vented systems negative pressure will be maintained by operation of the vacuum pump, drawing air at a greater flow rate than it is permitted to enter the system as controlled by the orifice or other throttling devices which may be used. 
         [0029]    Because, as shown in  FIG. 1 , the negative pressure actuator  22  is in fluid communication with the piping network  12  through pipe  28 , operation of the vacuum pump  30  will also draw a negative pressure in the actuator. As shown in detail in  FIG. 3 , pipe  28  is connected to the conduit  108  of set point trigger  104 . Ambient air will be drawn through opening  110  until the valve closing member  114  is pulled into engagement with valve seat  112  using reset knob  118 . This will result in negative pressure being created within body  106  and eventually the negative pressure will drop below the set point pressure, at which the ambient pressure of the atmosphere will hold the valve closing member closed against the biasing force of spring  116 . 
         [0030]    The set point trigger  104  is in fluid communication with the fifth chamber portion  94   a  through duct  102 , therefore, negative pressure will also be created in the fifth chamber portion. A negative pressure within chamber  94   a  of about 10 inches Hg is practical. Because the sixth chamber portion  94   b  is vented to the ambient through duct  100 , the third diaphragm  96  will be deflected into the fifth chamber portion by the differential pressure between the fifth and sixth chamber portions. As it deflects, the third diaphragm engages plunger  98  which, in turn, engages the second diaphragm  82 . Deflection of the third diaphragm is transmitted to the second diaphragm, forcing it into sealing engagement with seat  86  and closing aperture  84  against the biasing force of spring  88 . 
         [0031]    In the absence of water pressure within the system, flapper  42  in control valve  20  (see  FIG. 2 ) is closed by its biasing spring  48 . Next the trim valve  19  is opened, allowing water from source  16  to flow into chamber  58  and pivot latch  50  against the biasing force of its spring  54  into engagement with flapper  42  to hold the flapper in the closed position against its seat  46 , thereby isolating the piping network from the source of pressurized water  16  as is appropriate for a dry-pipe system. Opening of the trim valve  19  also sends water to the negative pressure actuator as described below. With the flapper  42  closed and locked by the latch  50 , the service valve  18  is opened to supply water to the control valve  20 . 
         [0032]    As shown in  FIG. 3 , with diaphragm  82  engaging seat  86 , water from source  16 , which is supplied to inlet  62  of the actuator  22  when trim valve  19  is opened (see also  FIG. 1 ), is prevented from passing through duct  68 , aperture  84  and duct  92  to the outlet  70 . The area ratio between the diaphragm  82  and the aperture  84  ranges between about 600:1 to about 1200:1 to ensure that false tripping of the actuator due to water pressure surges is avoided. The sealing of aperture  84  results in an increase in water pressure within the first chamber  64 . Although the water pressure is the same on both sides of the first diaphragm  66 , the force exerted by the water pressure on the diaphragm is greater on the side of the first diaphragm which faces the second chamber portion  64   b.  This is due to the fact that opening  74  is vented to the ambient. The water pressure within second chamber portion  64   b,  along with the biasing spring  78 , force the first diaphragm  66  into engagement with seat  76 , closing the opening  74  and preventing water from flowing through the inlet  62 , through the opening  74 , through the duct  72  and to the ambient through the outlet  70 . The system is now set and ready to detect and respond to a fire. 
         [0033]    During a fire, one or more of the sprinkler heads  14  open in response to the heat. This allows ambient air to flow into the piping network  12 , increasing the pressure otherwise held below atmospheric by the operation of vacuum pump  30 . The increase in pressure within the network  12  is conveyed to the set point trigger  104  though pipe  28 . When the set point pressure, determined substantially by the biasing spring  116  and the area of the valve closing member  114 , is reached, the valve closing member opens, venting the fifth chamber portion  94   a  to the ambient. This results in a pressure increase in the fifth chamber portion that causes the third diaphragm  96  to disengage from the plunger  98 . The absence of force on the plunger  98  permits the spring  88  within the third chamber portion  80   a  to deflect the second diaphragm  82  out of engagement with seat  86 , opening aperture  84  and allowing water to flow from the second chamber portion  64   b,  into the third chamber portion  80   a  and through duct  92  to the ambient through outlet  70 . The duct  68 , which allows water from the inlet  62  into the second chamber portion  64   b  is sized so that water flows more slowly into the chamber portion than out. This causes a reduction in pressure within the second chamber portion  64   b,  allowing the force exerted by the water pressure in the first chamber portion  64   a  to deflect the first diaphragm  66  out of engagement with the seat  76 . Water is thus permitted to exit the first chamber portion  64   a  through the opening  74 , the duct  72  and to the ambient through outlet  70 . The inlet  62 , the opening  74 , the duct  72  and the outlet are sized to allow water to flow out of the actuator  22  faster than it is supplied by the pipe  26 . Fluid flow to pipe  24  can be inhibited by using an orifice  122  or other flow restricting device in pipe  26  (see  FIG. 2 ), thereby ensuring that pressure is not maintained within the first chamber portion  64   a  when the first diaphragm  66  disengages from seat  76 . As the pressure drops within the first chamber portion  64   a  it also drops within chamber  58  of the control valve  20 , the chamber  58  being in fluid communication with the first chamber portion  64   a  through pipe  24 . 
         [0034]    Depressurization of chamber  58  reduces the force on diaphragm  56  and allows the latch  50  to pivot away from flapper  42 . Movement of the latch releases any constraint on the flapper, which opens under the water pressure from source  16 . Water is thereby provided to the piping network  12  where it is discharged from the open sprinkler heads  14  to suppress the fire. The vacuum pump cut-off valve  31  is closed to prevent water in the network  12  from entering the vacuum pump. 
         [0035]    Negative pressure actuators according to the invention allow negative pressure sprinkler systems to be employed enabling their advantages in inhibiting corrosion and scaling to be realized.