Abstract:
Apparatus for protecting a confined space having a vent aperture for relief of an overpressure condition and provided with a vent unit having a pressure relief portion normally closing the vent aperture is provided with recloser structure for generally closing off the vent aperture in the event of opening of the pressure relief portion of the vent unit. The recloser structure includes a resilient, flexible, spring steel recloser panel that is normally held in a bent condition out of closing relationship to the vent aperture. Releasable mechanism engages the recloser panel for normally retaining the panel in its open position. An actuator is connected to the releasable mechanism for actuating the latter to release the recloser panel for movement as a function of its inherent resilience into substantially closing relationship to the vent aperture after the relief portion of the vent unit has opened. The vent apparatus including the spring steel recloser panel may be of either rectangular or circular configuration.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to improvements in vent apparatus for protecting a confined space having a vent aperture for relief of an overpressure condition. Conventional vent apparatus is especially useful for covering relief openings in enclosures subject to rapid pressure build-ups such as may occur during explosions or uncontrolled combustion events in bag houses, duct work communicating with the bag houses, processing equipment, duct work leading to and from the processing equipment, buildings, pressure vessels, and other types of commercial and industrial installations where explosions or uncontrolled combustion events producing high overpressures may occur. 
   Vents of the type described have a vent unit including a vent portion that completely opens when a predetermined overpressure condition, such as an explosion or an uncontrolled fire, occurs in the protected area, thereby relieving the excessive overpressure and preventing untoward damage to equipment, vessels, duct work, building structures, and the like that would otherwise be subjected to potentially catastrophic overpressure events. 
   More particularly, the invention concerns high overpressure vent structure having a pressure relief portion that is in closing relationship to the vent aperture of the protected area, and that includes recloser structure for at least generally closing off the vent aperture in the event of opening of the pressure of the vent unit under a preselected overpressure condition. The recloser structure includes a spring steel vent aperture recloser panel that is normally maintained in a location out of closing relationship to the vent aperture, but may move into a position closing the vent aperture following opening of the pressure relief portion of the vent unit as a function of its inherent resilience of the spring steel. 
   Advantages of reclosing of the vent aperture by the recloser structure after opening of the primary vent unit include:
         elimination or reduction of the ingress of air and thereby oxygen, thus mitigating the effects of a secondary explosion if the protected area remained exposed to the surrounding atmosphere via the vent opening;   prevention of continuation of combustion of process materials that could cause permanent damage to the protected installation;   improvement of suppression of flames/fire, where inert gas, water mist, or the like, is used as an extinguishment agent, by virtue of the fact that the resulting combustion gases/flames cannot escape through venting holes; and   reduction/elimination of contamination of the protected process zone.       

   Releasable mechanism is provided in engagement with the panel normally maintaining the panel in the bent condition thereof, out of the location closing the vent aperture. An actuator is connected to the releasable mechanism for effecting release of the panel upon from command from a sensor unit that senses opening of the vent unit from an overpressure condition. 
   2. Description of the Prior Art 
   Explosion vents traditionally have been provided with arupturable sheet of metal that has score lines or interrupted slits that define a line of weakness presenting the relief area of the vent. The amount of overpressure required to open the relief area of the vent is determined by, among other things, the type, thickness, and physical properties of the metal selected for fabrication of the explosion vent, the shape and nature of the line of weakness, the location of the line of weakness in the overall area of the vent, and oftentimes the provision of a series of spaced cross-tabs overlying the line of weakness in predetermined relative dispositions. 
   An exemplary explosion vent of this type is shown and described in U.S. Pat. No. 6,070,365, wherein a rectangular pressure relief panel is mounted in a frame adapted to be secured across a pressure relief opening. The unitary relief panel is formed from a single sheet of steel, stainless steel, Inconel, or other similar metal, and has a three-sided line of weakness defined by a plurality of interrupted slits. The series of spaced rupture tabs positioned over the line of weakness as shown in the &#39;365 patent, must rupture before the relief area of the panel gives away under a predetermined high overpressure resulting from an explosion or a fast-burning fire. 
   U.S. Pat. No. 5,036,632 is another example of a conventional rectangular metal sheet explosion vent that has a three-sided line of weakness defined by interrupted slits. A layer of synthetic resin material or the like may be provided in covering relationship to the line of weakness slits. Rupturable tabs are also provided in the type of vent shown and described in the &#39;632 patent that must break before the central section of the panel ruptures along the slit line to relieve an overpressure. An elastomeric sealing gasket or gaskets may be provided around the periphery of the rupturable metal sheet. 
   U.S. Pat. No. 4,498,261, referred to in the disclosure of the &#39;632 patent, is a rectangular vent panel that opens under a relatively low pressure in which the thin sheet structure is described as being medium impact polystyrene, a relatively soft metal such as aluminum alloy, or a fully annealed stainless steel. Interrupted X-pattern slits extend through the vent panel and define individual lines of weakness that terminate at the apex of the X. A thin sealing membrane having the same area as the rupture panel is adhesively bonded to the rupture panel, and may be formed of polyethylene, stainless steel, or aluminum. Similar structure is shown and described in U.S. Pat. No. 4,612,739. 
   Although prior art pressure relief vents of the type described do satisfactorily open and relieve predetermined overpressure condition in protected spaces, these vents have remained open, thereby allowing the confined space to have continuing access to the surrounding atmosphere. Following out rush of products of combustion from the explosion or fire and relief of the high pressure, oxygen from the atmosphere is immediately available through the vent aperture that can produce a secondary explosion, exacerbation of a fire, or re-ignition of the fire. 
   SUMMARY OF THE INVENTION 
   It is conventional to provide apparatus for protecting a confined space having a vent aperture for relief of an overpressure condition. Apparatus of this type includes a vent unit having a pressure relief portion across the vent aperture in closing relationship thereto. The pressure relief portion of the vent unit opens when subjected to a preselected overpressure in the protected space. 
   This invention improves conventional vent apparatus for relieving high overpressure conditions by the provision of recloser structure for at least generally closing off the vent aperture in the event of opening of the pressure relief portion of the vent unit under a preselected overpressure condition. The reclosure structure includes a resilient flexible spring steel panel that in its normal state is of a configuration and in a position to at least substantially close the vent aperture. The spring steel panel is bent away from and disposed in a location out of a position substantially closing the vent aperture. Releasable mechanism engages the panel for normally maintaining the panel in the location thereof out of closing relationship to the vent aperture. An actuator is connected to the releasable mechanism for actuating the mechanism to release the panel for movement as a function of its inherent resilience from said location to said position thereof substantially closing the vent aperture after the relief portion of the vent unit has opened as a result of said preselected overpressure in the protected area. 
   A sensor is preferably provided in association with the vent unit of the vent apparatus that is operable to sense opening of the pressure relief portion of the vent unit resulting from an untoward high overpressure condition such as an explosion or products of combustion from a fast-burning fire. The sensor is operably connected to the actuator for effecting operation thereof to release the panel for return to a position closing the vent aperture when the sensor detects opening of the pressure relief portion of the vent unit. Operation of the actuator in response to a signal from the sensor may be controlled so that the spring steel panel normally held in a position away from the vent aperture is released for swinging movement into closing relationship to the vent aperture only after a predetermined variable time delay. 
   In a preferred embodiment, cable structure may be connected to the flexible spring steel panel for maintaining the latter out of closing relationship to the vent aperture of the protected structure, with actuating mechanism being provided in association with the cable structure for releasing the cable upon command, thereby allowing the flexible spring steel panel to swing back into a position substantially closing the vent aperture of the protected area. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of vent apparatus having a vent unit provided with a pressure relief portion normally closing a vent aperture of protected structure, wherein the apparatus includes vent aperture recloser structure having a flexible spring steel panel bent away from the vent aperture and held in its normally open position by selectively releasable mechanism, that includes a cable-severing guillotine device forming a part of the releasable mechanism; 
       FIG. 2  is an essentially schematic side elevational view of the vent apparatus of  FIG. 1 , showing the flexible spring steel recloser panel in its restrained bent position; 
       FIG. 3  is a schematic side elevational view of the vent apparatus of  FIGS. 1 and 2  showing the spring steel panel in its vent aperture closing position after opening of the vent unit under a predetermined overpressure; 
       FIG. 4  is a fragmentary enlarged view of one of the panel-restraining members that is connected to the selectively releasable mechanism; 
       FIG. 5  is an enlarged fragmentary view of a portion of the flexible spring steel panel illustrating the manner in which the panel is mounted on the vent unit of the vent apparatus; 
       FIG. 6  is an enlarged, essentially schematic, cross-sectional view of a portion of a retaining cable for the flexible spring steel panel, and a solenoid device for selective release of the cable, and thereby the panel, upon command; 
       FIG. 7  is a fragmentary, enlarged, horizontal cross-sectional view of the cable restraining and release mechanism as shown in  FIG. 6 , and 
       FIG. 8  is a perspective view of an alternate vent apparatus having a circular configuration. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The vent apparatus  10  of this invention, illustrated in  FIGS. 1 and 2 , is adapted to be mounted in normal closing relationship to the vent aperture of structure presenting an area requiring protection from an untoward overpressure event. 
   A rectangular metal frame element  12  may, for example, be mounted on and secured to the protected area structure in surrounding relationship to a vent aperture of the structure. Frame element  12  may typically have a box-defining leg segments  14  that are secured to the protected area structure in surrounding aligned relationship to the vent aperture of the structure, while the flange segments  16  of frame element  12  are unitary with and project outwardly from the extremities of leg segments  14  remote from the protected area structure. It is to be understood in this respect that the frame element  12  is exemplary only, and a number different components may be provided for securing vent apparatus  10  on structure to be protected in alignment with a respective vent aperture therefor. 
   A rectangular vent unit hold-down member  18  may be provided in overlying relationship to the flange segments  16  of frame element  12 . A series of threaded studs  20  secured to the outer face of flange segments  16  and that extend through respective openings therefor in flange segments  16 , are provided, with associated hold-down nuts  22 . 
   A conventional, composite, laminated vent unit  24  is trapped between flange segments  16  and hold-down member  18  and has outer dimensions approximately equal to the peripheral dimensions of flange segments  16  and hold-down member  18 . Vent unit  24 , as shown in  FIG. 5 , may, for example, include a pair of vent panels  26  and  28  of stainless steel, Inconel, titanium, nickel, or Hastelloy, or similar metals, separated by an intermediate cover sheet  30  of, for example, fluorinated ethylene propylene (FEP), or alternatively, polytetrafluoroethylene (PTFE), or perfluoroalkoxy polymer (PFA). Suitable stainless steel stock may include types 301, 304, 316, 316L, and 316LT. The vent panels  26  and  28  typically have a series of spaced, end-to-end slits defining a substantially U-shaped line of weakness  32  presenting a pressure relief portion  34  of each vent panel  26  and  28 . The terminal ends of each line of weakness  32  remote from the bight portion thereof, present respective hinge areas for the pressure relief portions  34 . The sheet  30  serves to cover and close the slits defining the lines of weakness  32  in vent panels  26  and  28 . 
   In preferred embodiments of vent apparatus  10 , as is well known to those skilled in the explosion vent panel art, vent panels  26  and  28  may be fabricated from metal stock of varying type, thickness, and physical properties, and the spacing between the slits making up lines of weakness  32  adjusted to assure opening of the pressure relief portion  34  of vent panels  26  and  28  by severing of the space between adjacent slits when the pressure buildup within the protected area reaches a predetermined overpressure value. Exemplary vent panels  26  and  28  may be fabricated of a selected metal, with a preferred material being 1.4301 stainless steel having a thickness of from about 0.2 mm to about 0.6 mm and preferably about 0.4 mm. The sheet  30  may, for example, be of a thickness of about 0.250 mm and preferably is from about 0.0125 mm to about 0.30 mm. 
   Vent aperture recloser structure  36  preferably comprises a recloser panel  38  fabricated from hard rolled type 1.4310 stainless spring steel having a thickness of from about 0.6 mm to about 1.2 mm and most preferably about 0.8 mm. The difference between the yield point and the tensile strength of the recloser panel is no more than about 30%. Preferably, the yield point and tensile strength of the recloser panel are at least about 1200 N/mm 2  and about 1450 N/mm 2 , respectively. Exemplary spring steel materials useful in fabrication of vent unit  62  of vent apparatus  30  are available from Precision Metals M.V. B-2800 Mechelen, BE, including stainless steel austenitic 1.4310 C1300-hard rolled EN10088-2 having a tensile strength of 1404-1463 N/mm, a hardness of 431-446 HV, and an elongation (A80 mm %) 11.5-16.5; EN10151 AMS 5519 having a tensile strength of 1440-1460 N/mm 2 , a hardness of 465-468 HV, and an elongation (A80 mm %) 13-16; and EN 10151 types having (a) a tensile strength of 1325 N/mm 2 , a hardness of 403 HV, and an elongation (A80 mm %) A50:9; (b) a tensile strength of 1412-1428 N/mm 2 , a hardness of 429-431 HV, and an elongation (A80 mm %) 1.2; ©) a tensile strength of 1397 N/mm 2 , a hardness of 423 HV, and an elongation (A80 mm %) A50:4; (d) a tensile strength of 1410-1414 N/mm 2 , a hardness of 400-402 HV, and an elongation (A80 mm %) 1.4; and (e) a tensile strength of 1380-1382 N/mm 2 , a hardness of 441 HV, and an elongation (A80 mm %) 16-18. 
   An end marginal section  38   a  of recloser panel  38  is trapped between components comprising flange segment  16   a  of frame element  12  and leg portion  18   a  of hold-down member  18 . The studs  20  secured to flange segment  16   a  and nuts  22  thereon, serve to firmly affix marginal section  38   a  of recloser panel  38  to frame element  12  and hold-down member  18 . It is to be observed from  FIG. 2  that the remaining section  38   b  of recloser panel  38  is bent in a direction away from vent unit  24  and is of continuously curved configuration. The segment  38   b ′ of curved section  38   b  adjacent marginal section  38   a  of recloser panel is of greater curvature than the remaining segment  38   b ″ of section  38   b.    
   Releasable mechanism  39  is provided in engagement with the recloser panel  38  for normally maintaining the latter in its bent configuration as shown in  FIG. 2  out of closing relationship to the vent aperture. Mechanism  39  includes an elongated bar  40  is affixed to the outer face of segment  38   b ″ of section  38   b  of recloser panel  38 , opposite vent unit  34 , and preferably extends substantially the full width of recloser panel  38 . Bar  40  is provided with two widely-spaced openings  42  adjacent opposite ends thereof that receive respective members in the form of externally threaded studs  44   a  and  44   b  that are welded to the rear face of section  38   b  of recloser panel  38 . Each of the studs  44   a  and  44   b  extends beyond the outer face of bar  40 . A washer  46  is provided on each stud  44   a  and  44   b  adjacent bar  40 . A nut  48  is threaded onto each stud  44   a  and  44   b  adjacent washer  46 . Retainer structure  49  includes an elongated cable  50 , forming apart of the releasable mechanism  39 . One end of cable  50  is turned upon itself to form a loop  50   a  that is trapped between washers  52  and  54  on stud  44   a . An outer nut  56  engages the washer  54  on stud  44   a  and snugs washers  52  and  54  against end loop  50   a  of cable  50 . Similarly, a cable section  58  of retainer structure  49  has a loop turned upon itself that is trapped between nuts and washers on stud  44   b  in a manner similar to the entrapment of cable loop  50   a  on stud  44   a . The end of cable section  58  remote from stud  44   b  is connected to an intermediate portion of cable  50  by cable clamp  60 . 
   It can be seen from  FIG. 1 , for example, that the stretch  50   b  of cable  50  and cable section  58 , joined by cable clamp  60 , in association with bar  40 , form a generally triangular relationship of the components such that the restraining force on the outermost end of recloser panel  38  is substantially equalized thereby precluding canting of the recloser panel  38 . 
   The outermost free end of section  50   c  of cable  50  is re-bent upon itself and looped about a capstan  62 . Cable clamp  64  secures adjacent portions of cable section  50   c . A device  66  is provided for severing section  50   c  of cable  50  upon command. Device  66  may include a guillotine unit  68  having opposed blades that cooperate to sever cable section  50   c  at a point between clamp  60  and clamp  64 . 
   A sensor  70  of conventional construction is preferably provided in association with frame element  12 . Sensor  70  is operable to sense opening of the pressure relief portions  34  of vent panels  26  and  28  under a predetermined overpressure. Sensor  70  may be of the optical, magnetic, or severed wire type. An electrical signal is generated by sensor  70  upon opening of the pressure relief portions  34  of vent panels  26  and  28  that controls operation of device  66  to effect cutting of cable section  50   c . When the cable section  50   c  is severed, the inherent resiliency of recloser panel  38  causes the panel to move into the position shown in  FIG. 3 , where the outermost extremity of recloser panel  38  engages an inwardly-directed plate member  72  secured to the innermost surface of leg segment  14  opposite marginal section  38   a  of recloser panel  38 , thereby substantially closing the vent aperture. The vent panels  26  and  28  along with cover  30  are returned to their positions within frame element  12 , although normally in substantially deformed position, as schematically shown in  FIG. 3 , as a result of the violent forces imposed on the vent unit  24  during relief of an overpressure condition in the protected area. 
   Vent apparatus  10  may be programed such that the device  66  is not activated to sever cable  50  and thereby effect closing of the vent aperture by recloser panel  36  for a predetermined time interval following sensing of opening of pressure relief portions  34  by a predetermined overpressure condition. For example, in some installations of vent apparatus  10 , release of the recloser structure  36  and pivoting thereof into closing relationship to the vent aperture of the protected structure, may not occur for as long as five seconds, or an even longer time period if desired by a particular customer. 
   In the alternate embodiment of the invention illustrated in  FIGS. 6 and 7  an electro-mechanical device  166  is used as a replacement for device  66 . In this instance., the outer segment of section  150   d  of cable  150  is looped around a spring-biased, normally open armature  174  of solenoid  176 . When armature  174  is retracted against the force of spring  178  upon receiving an electrical command signal from sensor  70 , the loop  150   d  of cable section  150   c  is released from the armature  174 , thereby allowing recloser panel  38  to close as previously described. 
   The alternate vent apparatus  110  of the invention shown in  FIG. 8  differs from vent apparatus  10  only in that the frame element  112 , vent unit  124 , and recloser panel  138  are all of circular configuration rather than being rectangular, as in the other embodiments of the invention. Operation of vent apparatus  110  is essentially the same as the invention of  FIGS. 1-7  in that cable section  150 , connected to recloser panel  138 , is severed by guillotine mechanism or released by a solenoid, similar to solenoid  166 , upon command from a sensor such as sensor  70 . However, in view of the somewhat narrower marginal section  138   a  of recloser panel  138  of apparatus  110 , somewhat thicker spring steel material may be necessary to assure full closure of recloser panel  138  upon release thereof from its normally restrained position, as shown in  FIG. 7 .