Patent Publication Number: US-6666277-B2

Title: Low pressure pneumatic and gate actuator

Description:
RELATED APPLICATION 
     This is a continuation-in-part application of U.S. application Ser. No. 09/535,599, filed Mar. 27, 2000 now U.S. Pat. No. 6,293,348. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to actuators for controlling the operation of valves and especially for valves used in sprinkler systems for fire protection. 
     BACKGROUND OF THE INVENTION 
     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. 
     Of the various types of automatic sprinkler systems available, the preaction systems find widespread use. Preaction systems use an actuator which responds to a combination of signals from different detectors to trip a valve which provides water to the sprinkler piping network. Similar to the so-called “dry-pipe” systems, the piping network in the preaction system is normally filled with air or nitrogen (and not water) prior to actuation. The preaction 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. 
     When sufficiently pressurized, the behavior of the gas within the piping network may be used to indicate a fire condition and trigger actuation of the preaction 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 system. Actuation of the system may be effectively triggered by this pressure drop. 
     Specifically, double interlock preaction systems are further advantageous because an alarm may be sounded to provide a warning before the sprinklers operate. Furthermore, failure, breakage or accidental opening of the sprinklers or a pipe in the piping network will not result in an unintentional discharge of water, since there is no water in the network until the system is actuated. Actuation for double interlock preaction systems requires that two or more separate signals be sensed. 
     Preaction systems are not without their disadvantages however. Traditional preaction systems, described above, which are triggered by a drop in air pressure within the piping network as the result of a sprinkler head opening in response to heat (along with a confirming signal from another sensor) usually maintain the sprinkler piping network at a relatively high internal pressure, typically on the order of 20% of the maximum water pressure in the system. The air pressure in such systems is used to control the release of the water to the piping network, and the valves typically operate at a mechanical advantage of about 1 to 5 air pressure to water pressure. The use of relatively high-air pressures becomes a problem with larger systems which tend to have a relatively large volume of air within the piping network. Higher air pressures and volumes require more powerful compressors, having higher capital and operating costs. Furthermore, the higher pressures mean that more air must be forced out of the piping network upon activation. The air in the network inhibits the free flow of water and, thus, increases the reaction time of the system. More air in the piping network also means that more moisture will be present, accelerating corrosion of the pipes. 
     There is clearly a need for a preaction sprinkler system having the ability to operate at relatively low system air pressures for providing a signal which activates the sprinkler system. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention concerns a purely pneumatic actuator for actuating a fire sprinkler system. The system is actuated when the actuator depressurizes a piston holding a valve controlling the flow of water to the sprinkler system closed. The actuator behaves like an AND gate in a logic circuit in that it will depressurize the piston and release the valve only when two separate pressure drops are manifest in the actuator. The actuator is thus connected to two separate sources of compressed air, one being the piping network of the sprinkler system, the other being a pilot line substantially co-located with the piping network. During a fire, heat-sensitive sprinkler heads on both networks open and release pressurized air within each network to the ambient. This causes pressure drops to occur in both networks which is sensed by the actuator. In response to the pressure drops, the actuator depressurizes the piston which allows the valve to open and supply water to the piping network for release through the open sprinkler heads onto the fire. 
     In the preferred embodiment, the actuator has a first chamber with a flexible first diaphragm mounted therein. The first diaphragm sealingly divides the first chamber into first and second chamber portions, both the chamber portions being in fluid communication with the cylinder. The second chamber portion has an opening providing fluid communication with the ambient, the opening being surrounded by a seat facing the first diaphragm. The first diaphragm is deflectable into sealing engagement with the seat to seal the opening when the cylinder is charged with a fluid, such as water from a pressurized source. 
     A second chamber having a flexible second diaphragm mounted therein which sealingly divides the second chamber into third and fourth chamber portions is preferably positioned above the first chamber. The third chamber portion is in fluid communication with a source of compressed air, for example, the pilot line network, and the fourth chamber portion is in fluid communication with the ambient. The fourth chamber portion has an aperture providing fluid communication with the first chamber portion, the aperture being surrounded by a second seat facing the second diaphragm. The second diaphragm is deflectable into sealing engagement with the second seat to seal the aperture when the third chamber portion is charged with compressed air from the pilot line network. 
     A third chamber having a flexible third diaphragm mounted therein and sealingly dividing the third chamber into fifth and sixth chamber portions is preferably positioned above the second chamber. The fifth chamber portion is in fluid communication with a second source of compressed fluid, for example, the piping network. An elongated plunger having one end positioned within the sixth chamber portion and engagable with the third diaphragm, and the other end positioned within the third chamber portion and engagable with the second diaphragm is slidably movable between the sixth and third chamber portions. The third diaphragm is deflectable into engagement with the one end of the plunger when the fifth chamber portion is charged with compressed air form the piping network, and the plunger is thereupon forced into engagement with the second diaphragm, thereby forcing the second diaphragm into sealing engagement with the second seat. The second diaphragm will be deflected out of engagement with the second seat only when both the fifth and the third chamber portions are vented to a lower pressure, as when sprinkler heads on both the pilot line network and the piping line network are open concurrently and vent the compressed air from these networks to the ambient. As a result, fluid pressure in each the third and fifth chamber portions falls to a predetermined value which allows fluid in the first chamber portion to enter the fourth chamber portion and exit to the ambient. This allows the first diaphragm to deflect out of engagement with the first seat and allows water to flow from the cylinder through the second chamber portion and exit to the ambient, thereby depressurizing the piston and allowing it to move within the cylinder and release the valve which moves to the open position and supplies water to the piping network. 
     The invention also includes a reset valve for manually resetting the sprinkler system and preventing unintentional resetting during a fire. The reset valve has a valve body and a conduit extending through the valve body. One end of the conduit is in fluid communication with the third chamber portions and the other end is vented to the ambient. A valve seat is positioned in the one end of the conduit and a valve closing member is movably mounted within the conduit adjacent to the seat. The valve closing member is movable into sealing engagement with the seat to close the reset valve. The reset valve also has means for biasing the valve closing member out of engagement with the seat when fluid pressure within the one end of the conduit falls below a predetermined value. The biasing means thereby opens the reset valve and vents the third chamber portion to the ambient. Preferably, there is an identical reset valve in fluid communication with the fifth chamber portion as well. The reset valves prevent spurious pressure surges from pressurizing either of the third or fifth chamber portions and thereby accidentally resetting the system and, thus, cutting off the water supply during a fire. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic depiction of a preaction fire protection system using a low pressure pneumatic actuator according to the invention; 
     FIG. 2 is a longitudinal sectional view of a valve and control piston used in the preaction fire protection system shown in FIG. 1; and 
     FIG. 3 is a longitudinal sectional view of a low pressure pneumatic actuator according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a preaction fire protection sprinkler system  10  having a low pressure AND gate actuator  12  according to the invention. System  10  comprises a piping network  14  having a plurality of automatic sprinkler heads  16  which open when the air surrounding the head reaches a predetermined temperature due to a fire. Network  14  is normally dry and is connected to a valve  18  which controls the flow of water from a water supply source  20  to the network  14 . 
     As shown in FIG. 2, the valve closing member of valve  18  is preferably a pivoting clapper  22  held in the closed position against the pressure of the water supply  20  by a latch  24  controlled by a piston  26  reciprocable within a cylinder  28 . Cylinder  28  is in fluid communication with water supply  20  via a conduit  30 , the water supply  20  pressurizing piston  26  to hold the latch in position keeping the clapper  22  closed. As shown in both FIGS. 1 and 2, cylinder  28  is also in fluid communication with the low pressure actuator  12  via a conduit  32 , the actuator hydraulically controlling the action of the piston  26  to actuate valve  18  as described below. 
     Sprinkler system  10  also includes a pilot line network  34  of pipes having automatic sprinkler heads  36  distributed along the pilot line network. Similar to sprinkler heads  16 , sprinkler heads  36  open in response to a fire when the air surrounding the head reaches a predetermined temperature. Unlike the piping network  14 , however, the pilot line network is not in fluid communication with the water supply  20  but is in fluid communication with a supply of compressed air  38 . The piping network  14  is also in fluid communication with compressed air supply  38  at a point  40  downstream of the clapper  22 . Both the piping network  14  and the pilot line network  34  are connected to the low pressure actuator  12  by conduits  42  and  44  as described below. 
     In operation, both the piping network  14  and the pilot line network  34  act as sensors to trigger the sprinkler system in the event of a fire. Heat from the fire causes the automatic sprinkler heads  16  and  36  nearest the fire to open substantially concurrently. Concurrent opening of the heads from both the piping and pilot line networks permits a drop in the pressure of the compressed air in both networks which is sensed by the low pressure actuator  12 . Upon sensing the combination of pressure drops, actuator  12  depressurizes piston  26  which releases latch  24  permitting clapper  22  to open and supply water to the piping network  14 . Upon reaching the open sprinkler head or heads  16 , the water is discharged onto the fire. The operation of the low pressure sensor  12  is described in detail below. 
     As shown in cross-section in FIG. 3, low-pressure actuator  12  has a housing  46  preferably comprised of brass. Housing  46  has three chambers, a top chamber  48 , a middle chamber  50  and a bottom chamber  52 . Although the chambers are shown positioned one above another and are named top, middle and bottom, it is understood that the orientation of the actuator is irrelevant to its operation and the naming of its parts is for convenience and by way of example only and places no limitations on the structure or configuration of the actuator. 
     Each chamber is divided into upper and lower chamber portions by a respective top, middle and bottom diaphragm  54 ,  56  and  58 . Preferably, each of the diaphragms comprise a metal ring  60  surrounding a metal plate  62 . Both the plate  62  and ring  60  are encapsulated in a flexible sheath  64  and are attached to one another by a membrane portion  66  of the sheath  64  which extends between the plate and the ring. Ring  60  stiffens the perimeter of the diaphragm and provides a means for attaching it to the housing, the ring being sandwiched between various segments  68 ,  70 ,  72  and  74  forming the housing. The sheath is preferably EPDM or a similar flexible polymer and provides for a fluid tight seal between the segments. Plate  62  stiffens the diaphragm and the sheath surrounding it ensures a fluid tight seal between the diaphragm and various seats as described below. The membrane portion  66  provides flexibility allowing the diaphragm to deflect in response to fluid pressure on one side or another. 
     While the diaphragms as described above are preferred, it is understood by those of skill in the art that other types of diaphragms may also be used without adversely affecting the operation of the actuator. 
     Bottom chamber  52  is divided by bottom diaphragm  58  into an upper chamber portion  76  and a lower chamber portion  78 . Both chamber portions  76  and  78  are in fluid communication with cylinder  28  through conduit  32 . Conduit  32  has a large diameter duct  80  which interfaces with the lower chamber portion  78 , and a smaller diameter duct  82  which connects to the upper chamber portion  76 . Lower chamber portion  78  has a hole  86  surrounded by a seat  88 , the hole  86  allowing the lower chamber portion to vent to the ambient through a port  89 , the seat  88  being engageable by the bottom diaphragm  58  to seal the hole  86  when the force exerted by the pressure in the upper chamber portion  76  is greater than the force exerted by the pressure in the lower chamber portion  78 . Preferably, a biasing means in the form of a spring  90  is positioned within upper chamber portion  76  to bias bottom diaphragm  58  into sealing engagement with seat  88 . 
     Middle chamber  50  is divided into upper and lower chamber portions  92  and  94  respectively by middle diaphragm  56 . Upper chamber portion  92  is in fluid communication with pilot line network  34  through conduit  44  (see FIG.  1 ), and lower chamber portion  94  is in fluid communication with the ambient through a duct  98  connecting to port  89 . Lower chamber portion  94  is further in fluid communication with upper chamber portion  76  through an aperture  100 . A seat  102  surrounds aperture  100 , the seat being engageable by middle diaphragm  56  to seal the aperture  100 . A biasing means in the form of a spring  104  is positioned within the lower chamber portion  94  to normally bias the diaphragm out of engagement with seat  102 . 
     Top chamber  48  is divided into upper and lower chamber portions  106  and  108  by top diaphragm  54 . Upper chamber portion  106  is in fluid communication with piping network  14  through conduit  42  (see FIG.  1 ). Lower chamber portion  108  is in fluid communication with the ambient through duct  110 . An elongated plunger  112  extends between lower chamber portion  108  and upper chamber portion  92 . One end  114  of the plunger is engageable with top diaphragm  54 . The other end  116  of the plunger is engageable with middle diaphragm  56 . The plunger is slidably movable within the housing  46 , and the lower chamber portion  108  is isolated from the upper chamber portion  92  by a seal  118  surrounding the plunger  112 . 
     Preferably, both the upper chamber portion  106  and the upper chamber portion  92  also vent to the ambient through respective reset valves  120  and  120   a . The reset valves are substantially the same in construction and operation, and therefore, only one is described in detail. Reset valve  120  has a valve body  122  through which a conduit  124  extends providing fluid communication between the associated upper chamber portion and the ambient. A valve seat  126  is positioned at the end of the conduit which interfaces with the upper chamber portion  106 , and a valve closing member  128  is movably mounted within the conduit and is movable into sealing engagement with the valve seat  126 . In the example shown in FIG. 3, valve closing member  128  is mounted on the end of a shaft  130  which is slidably movable within the valve body  122 , although other configurations are also feasible. 
     Shaft  130  extends outwardly from the valve body  122  and has a knob  132  which may be manually grasped to pull valve closing member  128  into engagement with valve seat  126 . A biasing means in the form of spring  134  is positioned around shaft  130  to bias the closing member  128  out of engagement with seat  126 . Preferably, conduit  124  is sized larger than the valve closing member over a region  136  between seat  126  and the upper chamber portion  106  or  92  for reasons explained below. 
     Low Pressure AND Gate Actuator Operation 
     The low pressure AND gate actuator  12  according to the invention is used in the preaction fire protection system  10  to reset the system (make it ready for actuation) and to actuate the system upon receipt of the appropriate signals. The appropriate signals preferably comprise a pressure drop in both the sprinkler piping network  14 , and the pilot line network  34  which occurs in response to a fire which causes heads  16  on the piping network and heads  36  on the pilot line network to open. 
     System Reset Function 
     With compressed air being supplied to the actuator  12  from the system air supply  38 , to reset the system  10 , an operator pulls upwardly on the reset knobs  132  and  132   a  on the reset valves  120  and  120   a , moving the valve closing members  128  and  128   a  against biasing spring  134  and  134   a  and seating the valve closing members against valve seat  126  and  126   a  respectively. When the valve closing members are in the unseated positions as shown in FIG. 3, compressed air normally flows around them due to the enlarged regions  136  and  136   a  of conduits  124  and  124   a . Enlarged conduit regions  136  and  136   a  on each reset valve prevent an air pressure surge in the system from unintentionally resetting the system during a fire (and thereby cutting off the water to the sprinkler heads) by inadvertently seating the valve closing members. Because of the enlarged conduit region, the valve closing members in each valve  120  and  120   a  must be held in the seated position until the pressure within upper chamber  106  (for reset valve  120 ) and upper chamber  92  (for reset valve  120   a ) exerts a force on the valve closing members  128  and  128   a  which exceeds the biasing force of springs  134  and  134   a . The springs  134 ,  134   a  and valve closing members  128  and  128   a  are designed such that a pressure above about 6.5 psi in respective upper chambers  106  or  92  is sufficient to keep the valve closing member seated. The reset valves are thus used to establish a relatively low pressure trip point for the system as described in more detail below. 
     With the reset valve  120  closed, air pressure increases in the upper chamber portion  106 , deflecting top diaphragm  54  into the lower chamber portion  108 . Air in the lower chamber portion  108  is preferably vented to the ambient through duct  110 . The top diaphragm  54  engages end  114  of plunger  112 , forcing the opposite plunger end  116  into engagement with the middle diaphragm  56  and causing it to deflect into lower chamber portion  94  against biasing spring  104 . Middle diaphragm  56  sealingly engages seat  102  to close the aperture  100  between the lower chamber portion  94  and the adjacent upper chamber portion  76 . Air in lower chamber portion  94  is vented to ambient through duct  98  and port  89 . 
     Middle diaphragm  56  is also deflected into lower chamber portion  94  by air pressure from the pilot line network  34  entering the upper chamber portion  92  through conduit  44 . Because conduit  44  also preferably has a reset valve  120   a  substantially identical to reset valve  120 , upper chamber portion  92  is thus pressurized with air only when knob  132   a  is pulled to engage valve closing member  128   a  with seat  126   a  and held in place until sufficient pressure is reached within chamber portion  92  to keep the reset valve  120   a  closed. The pressure is preferably the same as for reset valve  120 , but could also be higher or lower, thus, yielding a different trip point pressure for the system. Together the top and middle diaphragms  54  and  56  provide the AND gate logic function of the actuator  12  in that both diaphragms must be allowed to independently deflect to allow the lower diaphragm  58  to unseat and open aperture  100  to actuate the main valve  18  supplying water to the sprinkler heads as described further below. Either diaphragm alone, however, can exert sufficient force to keep the bottom diaphragm seated and prevent actuation of the system. 
     Bottom diaphragm  58  is normally biased into engagement with seat  88  by spring  90 , thus, sealing hole  86  which would otherwise vent the lower chamber portion  78  to the ambient through port  89 . As shown in FIGS. 1 and 2, water pressure taken from upstream of valve  18  through conduit  30  pressurizes the piston  26  within cylinder  28  into engagement with latch  24 , keeping clapper  22  closed and cutting water off from the sprinkler piping network  14 . The cylinder  28  is in fluid communication with lower chamber portion  78  of actuator  12  through conduit  32 , and with upper chamber portion  76  through the small diameter duct  82  fed from conduit  32 . Water pressure within the cylinder  28  which keeps clapper  22  closed also forces bottom diaphragm  58  against seat  88  to close hole  86 . Specifically the water pressure in upper chamber  76  exerts greater force on the diaphragm than the same pressure in lower chamber portion  78  since the water pressure in the lower chamber portion  78  does not act over the entire area of the diaphragm as it does in the upper chamber portion  76 . This is because the central portion of diaphragm  58  is exposed to atmospheric pressure through hole  86  when the diaphragm  58  is seated against seat  88 , and the water pressure within chamber  78  cannot act against this central portion isolated by seat  88 . 
     The system is now set and ready to supply water to sprinkler heads  16  as called for to suppress a fire. 
     System Actuation 
     Heat from a fire will cause sprinkler heads  16  on the piping network  14  and sprinkler heads  36  on the pilot line network  34  in the immediate vicinity of the fire to open. This allows compressed air within both the piping network and the pilot line network to vent to the ambient, causing a pressure drop in both networks. As shown in FIGS. 1 and 3, the upper chamber portion  106  is in fluid communication with the piping network  14  through conduit  42  and the upper chamber portion  92  is in fluid communication with the pilot line network  34  through conduit  44 . Pressure drops in each network will thus be communicated to the respective associated chamber portions  106  and  92  within the actuator  12 . (The system would work equally well if upper chamber portion  106  were in fluid communication with the pilot line network and the upper chamber portion  92  were in fluid communication with the piping network. The actual connections shown and described are by way of example only and are not intended as limiting in any way.) 
     When the pressure in each chamber portion drops to a predetermined value (preferably about 6.5 psi), the reset valves  120  and  120   a  open (valve closing elements  128  and  128   a  unseat from seats  126  and  126   a  and are biased into enlarged conduit regions  136  and  136   a ) venting both upper chamber portions  106  and  92  to the ambient and causing a rapid pressure drop in both chamber portions. As the pressure in upper chamber portions  106  and  92  drops, it falls below a second predetermined value which allows biasing spring  104  to deflect both the top and middle diaphragms  54  and  56  upwardly, unseating middle diaphragm  56  from seat  102  and opening aperture  100 . This allows water under pressure in upper chamber portion  76  to flow through aperture  100 , into lower chamber portion  94  and out to the ambient through duct  98  and port  89 . With the water pressure in upper chamber portion  76  thus relieved, the bottom diaphragm  58  is deflected by water pressure within lower chamber portion  78 , the bottom diaphragm is unseated from seat  88 , allowing water from conduit  32  to vent to the ambient. Deflection of the bottom diaphragm  58  away from seat  88  is ensured by making the diameter  80  of conduit  32  feeding lower chamber portion  78  relatively large as compared with the diameter of duct  82  which feeds the upper chamber portion  76 . Despite being at the same pressure, water from conduit  32  cannot flow fast enough through small diameter duct  82  to pressurize upper chamber portion  76  and deflect the bottom diaphragm  58  into engagement with seat  88 . 
     Conduit  32  is in fluid communication with cylinder  28  (see also FIG.  2 ). Thus, when the conduit  32  is vented to ambient by the action of bottom diaphragm  58 , piston  26  is depressurized. This releases latch  24  allowing clapper  22  to open under the pressure of water source  20  and supply water to the piping network  14  where the water is released from the open sprinkler heads  16  onto the fire. 
     Based upon the foregoing description of the actuator and its operation, it is possible to view the actuator as comprised of a plurality of pressure actuated valves. Bottom chamber  52  and its associated bottom diaphragm  58  comprise an example of a first pressure actuated valve controlling the flow of the pressurized fluid through the actuator. This first valve has a first valve closing member (diaphragm  58 ) with opposite sides both in fluid communication with the pressurized fluid. The first valve is normally closed and prevents the fluid flow which depressurizes the piston  26 . The first valve closing member opens to permit the depressurizing flow when the fluid pressure on one side of the first valve closing member exceeds the fluid pressure on the opposite side of the first valve closing member. 
     The middle chamber  50  and its middle diaphragm  56  comprise an example of a second pressure actuated valve controlling the fluid pressure on the opposite side of the first valve closing member. The second valve has a second valve closing member (diaphragm  56 ) which is movable from a closed position, which maintains fluid pressure on the opposite side of the first valve closing member, to an open position, which releases fluid pressure from the opposite side of the first valve closing member. The second valve closing member has a side in fluid communication with a first source of compressed fluid and is movable from the closed to the open position in response to a decrease in pressure of the first source of compressed fluid. 
     The top chamber  48  and its top diaphragm  54  comprise an example of a third pressure actuated valve. The third pressure actuated valve has a third valve closing member (diaphragm  54 ) with a mechanical link to the second valve closing member. The third valve closing member has a side in fluid communication with a second source of compressed fluid and is movable from a first position which maintains a force through the mechanical link onto the second valve closing member (thereby maintaining the second valve closing member in the closed position) to a second position removing the force from the second valve closing member. The third valve closing member moves to the second position in response to a decrease in pressure of the second source of compressed fluid. However, both the third and second valve closing members move into their respective second and open positions only upon a concurrent pressure decrease of both the first and second sources of compressed fluid, as occurs when both the pilot line network  34  and the piping network  14  are vented in the event of a fire. Motion of both the second and third valve closing members allows the first valve closing member to move into its open position and permit flow of the pressurized fluid through the actuator, thereby depressurizing piston  26  and triggering the sprinkler system. 
     Use of the actuator according to the invention provides the following advantages. First, the system is entirely pneumatic, thus eliminating dependence on electrical power for actuation. Once set, the system will continue to maintain its ready state and operate even during an electrical power failure. Second, the sprinkler system may operate at a relatively low air pressure, the air pressure design parameters being chosen independently of the source water pressure needed. This is made possible by controlling the ratio of the area of the middle diaphragm  56  to the cross-sectional area of the aperture  100 . By keeping this ratio relatively large, for example, substantially greater than 8/1, a modest air pressure may be used to control a much larger water pressure. Preferably, the ratio is on the order of 20/1 or greater and may range between 20/1 and 700/1 in practical applications. Other ranges of this area ratio, for example, from about 20/1 to about 100/1 or 20/1 to about 600/1 are also useful in practical sprinkler system designs. A preferred embodiment of the actuator uses a ratio of about 528/1. For the various ranges of ratios described above, the system air pressure is effectively independent of the system water pressure. Thus, regardless of the system water pressure (typically 100-120 psi) the system air pressure may be kept relatively low (preferably about 10 psig maximum), and the volume of air in the piping network  14  may be kept to a minimum. This results in less corrosion due to the presence of water vapor in the piping system. Furthermore, water traveling from the source to the sprinkler heads also will arrive sooner because there will be less air under lower pressure to displace out of the system. Third, the actuator acts as an AND gate in a logic circuit in that both the top diaphragm  54  and middle diaphragm  56  must deflect for actuation to occur. Since the top diaphragm is in fluid communication only with the piping network  14  and the middle diaphragm is in fluid communication only with the pilot line network  34 , depressurization must occur in both the piping network and the pilot line network for actuation to occur. Inadvertent depressurization in either network alone, such as may occur if a sprinkler head is damaged, will not trip the system in error. Fourth, unintended resetting of the system, for example, during a fire, is prevented by the use of the reset valves  120  and  120   a , which must be manually held in place until sufficient pressure is achieved to hold the valve closing members  128  and  128   a  seated. This is accomplished by the enlarged conduit regions  136  and  136   a  which permit relatively large surges of compressed air to flow without closing the reset valves and shutting down the system. Fifth, the reset valves also eliminate the need for auxiliary means to accelerate system activation since they rapidly depressurize the chamber portions with which they are associated upon opening.