fig1 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 . 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 . 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 . 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 . control valve 20 is shown in detail in fig2 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 . when the flapper 22 is closed as shown in fig2 , 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 fig1 ). 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 . negative pressure actuator 22 is shown in detail in fig3 . 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 . 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 . 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 . 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 fig1 ). 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 . the system 10 shown in fig1 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 . 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 . because , as shown in fig1 , 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 fig3 , 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 . 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 . in the absence of water pressure within the system , flapper 42 in control valve 20 ( see fig2 ) 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 . as shown in fig3 , 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 fig1 ), 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 . 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 fig2 ), 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 . 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 . 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 .
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 .