Abstract:
A leak detector for an insulated duct carrying pressurized hot air comprises a cover secured over a circumferential cut in the insulation of the duct, or over a joint connecting duct sections, thereby creating a reservoir of hot air which has leaked from the duct or joint, a manifold block defining a conduit therein in communication with the hot air reservoir and a cap for securing heat sensitive wires to manifold at the end of the conduit such that the hot air from the hot air reservoir impinges directly on the heat sensitive wires. The leak detector includes flow control mechanisms in the body of the manifold block, to prevent false alarms arising from nominal leakage resulting from ordinary operation of the duct system.

Description:
FIELD OF THE INVENTION 
     This invention is related to the field of aerospace, and, in particular, to modern aircraft which utilize the flow of hot compressed bleed air from the engines for various on-board functions. 
     BACKGROUND OF INVENTION 
     The present invention relates to the use of ducting systems in aircraft structures. Amongst the prior art, it is well known in the art to use high temperature bleed air from the engines for various on-board purposes in a modern aircraft. Typically, a stream of hot air bled from the engines is used to provide an anti-icing function on the leading edge of the wings and empennage of the aircraft and is also used by the air conditioning units to supply fresh air to the passenger cabin. The bleed air must therefore be transported from the engines to various other areas of the aircraft, and this is typically accomplished utilizing insulated metallic ducts ranging in diameter from 1.00″ to 6.50″ and ranging in length from at least 6″. The air in the duct can reach pressures up to 450 psig and temperatures of 1200° F., but is typically at a pressure of 60 psig and 800° F. in temperature. 
     The ducts carrying the engine bleed air are insulated to prevent damage to the aircraft. An insulation blanket is wrapped around the exterior of the duct. This insulation blanket may be composed of a material of the type sold under the tradename Q-Felt® and manufactured by the Johns-Manville Corporation of Denver, Colo. The insulation blanket is capable of lowering the exterior temperature of the duct from 800° F. to about 400° F. or less. A fiberglass impregnated silicon-rubber, textured metal foil, or fiberglass impregnated polyimide resin insulation shell is then wrapped around the exterior of the duct to contain the insulation blanket. 
     The ducts of the type mentioned can develop leaks from the cracking of the inner metallic duct. If such cracks go undetected, catastrophic failure of the duct can result. Therefore, it is necessary to have sensors positioned along the length of the duct to detect any leakage from the duct. 
     Prior art leak detection sensing systems consisted of a vent disk, which is a disk having a hole therein, which allowed a stream of hot air to escape the silicon-rubber, texturized foil, or polyimide resin insulation shell. In the event that a duct developed a crack, hot bleed air will flow from the metallic duct wall through the insulation blanket and to the vent disk, then through the hole in the vent disk. The vent disk hole is designed to spread the flow of hot air in a cone-like spray pattern impinging on a pair of heat detection wires spaced approximately 1.0″ apart and positioned approximately 1.00″ to 1.75″ from the outer circumference of the duct. The heat detection wires are of the type sold under the tradename Firewire® and manufactured by Kidde Graviner Limited of the United Kingdom. The heat sensing wires which change their electrical characteristics when exposed to a predetermined temperature. In the case of typical prior art systems used in aircraft, the detection circuit will trip when the wire is exposed to a temperature of approximately 255° F. It is required that both wires of the pair of wires in proximity to the duct be exposed to this temperature before an alarm will be raised to the pilot of the aircraft, to prevent false alarms. 
     It is desirable that the leak detectors be able to detect a leak in the metallic duct through a crack having the equivalent area of a 5 mm diameter hole. In practice, it has been found that the prior art leak detection systems fail to detect such leaks. The primary reason for the failure of the prior art design is that there is insufficient air flow through the vent disk hole. This results in the hot air stream having insufficient temperature to trip the heat detection wires. First, the temperature of the hot air through the leakage in the metal duct is significantly reduced as the hot air passes through the insulation blanket. Second, the insulation blanket impedes the passage of the hot air from the site of the leak to the vent disk hole, underneath the silicon-rubber, texturized foil, or polyimide resin insulation shell. Further, it has been found that, by the time the air has traversed the distance between the vent disk hole and the sensor wires, it has fallen to a temperature well below the 255° F. necessary to trip the leak detection wires. 
     Therefore, it is desirable to improve the design of the leak detection system such that a leak through a crack in the metallic duct having an equivalent area of a 5 mm diameter hole is successfully detected. It is also desirable that the new design be able to be economically retrofitted into existing aircraft. In particular, it is desirable that the same existing sensor wires be used and that it not be necessary to remove the existing insulation and to re-insulate the ducts to install the improved leak detection system. 
     At the joints between adjacent sections of duct, such as bleed air ducts in aircraft wings, the joints are typically constructed by abutting connection flanges between adjacent duct sections, and then by clamping those connection flanges together through the use of a band clamp or similar mechanism. Because this is a clamped arrangement, and not, e.g., a weld or other sealing structure, a certain amount of leakage is permitted and anticipated. Inasmuch as temperature sensor wires and temperature sensing systems have attained a high degree of sensitivity and responsiveness, it is desirable to provide a bleed leak detection system which is capable of discriminating between the low-level leakage that is part of ordinary and acceptable operating conditions, and the higher-level leakage which indicates either a failure of a joint, or failure of the ducting, not necessarily at the joint but in its vicinity, or even at a distance from the joint. 
     SUMMARY OF INVENTION 
     To produce air flow with adequate velocity, the laws of fluid dynamics dictate the necessity for both air pressure and volume. If sufficient air pressure exists at low volume, air flow velocity cannot be sustained once the volume is quickly depleted. If sufficient air volume is present without pressure, there is practically no movement of air from a high to a low pressure environment. 
     When the metallic duct develops a crack, the hot air leaks from duct interior to the insulation blanket. The insulation blanket changes the characteristics of the hot air leakage 1) by absorbing the thermal energy and reducing the air temperature; 2) by reducing the effective pressure due to pressure drop; and 3) by reducing the volume by diffusing the air in the annulus between metal duct and insulation shell throughout the length of the duct. 
     In one embodiment of the invention, this problem is solved by recapturing or recollecting the degraded air into an air reservoir after the air has passed through the insulation blanket. This is accomplished by circumferentially cutting the insulation shell 360°, at one or more locations along the length of the duct. The circumferential cuts will be covered by installing a “U”-shaped cuff or cover made from multi-ply silicone-rubber impregnated fiberglass cloth centered over each of the circumferential cuts and sealed at both ends to the insulation shell. The cuff re-collects the leakage of degraded hot air and acts as an air reservoir. A vent hole of the proper size and shape, similar to the hole in the vent disc, is provided for the air to be directed to the existing sensor wires. The vent hole will be supported by a silicone rubber pad on the inside of the cuff to stabilize the flow direction of the air through the vent hole. The pressure inside the cuff will begin to rise once the cuff is filled with air. The pressure will reach a steady state value when the flow from the crack in the duct and the flow through the vent hole reach a steady state condition. 
     With the just-described embodiment of the invention, it has been found, depending upon the distance between the vent hole in the cuff and the sensor wires, that, although there is a steady stream of air being expelled from the vent hole at a temperature sufficient to trip the detector, the air may still have insufficient heat once reaching the sensor wires as the result of its movement between the vent hole and the sensor wires due to a nozzle ejector effect mixing with ambient air around the duct. 
     In another embodiment of the invention, a manifold has been added between the cuff and the sensor wires to direct the stream of hot air directly from the vent hole to the sensor wires without the loss of heat to the ambient environment. The design of the preferred embodiment comprises adding a manifold block and a manifold cap installed on top of the cuff and inline with the vent hole in the cuff. The manifold block is designed to route the hot air from a single conduit in the manifold, to a “Y” where the conduit divides into two conduits, which lead directly to the sensor sires. Hot air impingement is accomplished by installing a cap on the manifold block that secures each of the sensor wires in a channel groove. The channel groove in the cap for each sensor wire is designed to align with the outlet of the one of the two conduits running through the manifold from the “Y”. As such, the hot air flows directly from the vent hole to the sensor wires with sufficient heat to trip the sensor wires. 
     In yet another improved embodiment of the invention, for applications in which the temperature sensor wires, and manifold, are located above, or in the immediate vicinity of a clamped joint between adjacent duct sections, the manifold is located in a structure referred to as a coupling cover, which is typically clamped in place over and around the joint between adjacent duct section ends. In this embodiment, the leak detection system sensitivity issue discussed hereinabove is addressed through the use of a flow control mechanism in the manifold, to accommodate the allowable “leakage” which is expected and acceptable at such locations. The use of a flow control mechanism in the manifold block enables the leak detection system to differentiate between the maximum allowable leakage that is part of ordinary operation from leakage that is indicative of actual structural failure. Accordingly, an embodiment of the present invention incorporates a mechanism for providing this desired discrimination, in the form of a valve structure disposed within the manifold block, to prevent duct gases from impinging on the temperature sensitive wires of the temperature sensor system, unless the duct gases are at such a pressure, as to override the valve structure, and thus confirm their source as being a structural failure. 
     While the aforementioned flow control mechanism or valve structure may typically be employed in manifold blocks located above or in the immediate vicinity of joints between adjacent duct sections, in yet alternative improved embodiments of the invention, the manifold blocks located at positions further removed from joints between duct sections, i.e., in manifold blocks located in the previously-mentioned cuffs, may also be provided with such flow control mechanisms, if desired. 
     Accordingly, the present invention comprises, in part, a joint cover apparatus, for a ducting system for transporting high temperature pressurized gases, for covering a joint between adjacent duct sections, wherein the ducting system is provided with a leak detection system using one or more temperature-responsive sensor wires 
     The joint cover apparatus may comprise a split joint cover body, operably configured to be expanded, to permit the split joint cover body to be positioned circumferentially around a joint between adjacent duct sections, the split joint cover body having an aperture therethrough, to permit the passage of gases emanating from the joint to a location external to the split joint cover body. At least one clamping mechanism may be provided to releasably engage the split joint cover body, to cause the split joint cover body to be contracted around the joint. 
     In these embodiments, a manifold block may be positioned within the aperture of the split joint cover body, for maintaining the at least one sensor wire in fixed position, relative to the aperture in the split joint cover body, for directing gases emanating from the joint into contact with the sensor wires, the manifold block having one or more gas passages disposed therein to conduct gases through the block and into contact with the one or more temperature-responsive sensor wires. The manifold block further may have a flow control mechanism for controlling flow of gases through the one or more gas passages to preclude the flow of gases through the one or more gas passages when the gases emanating from the joint have a pressure that is below a preselected numerical value. 
     The present invention also comprises, in part, a manifold block, for a ducting system for transporting high temperature pressurized gases, for placement in a cover surrounding at least part of at least one duct section in the ducting system, wherein the ducting system is provided with a leak detection system using one or more temperature-responsive sensor wires. 
     The manifold block may comprise a manifold block body. Sensor wire notches may be formed in the manifold block body for restrainably receiving temperature-responsive sensor wires. Gas passages may be disposed in the manifold block body and extending along a fluid path from an interior-facing surface of the manifold block body to an exterior facing surface of the manifold block body, the gas passages intersecting the sensor wire notches. A flow control mechanism may be disposed in the fluid path between the interior-facing surface and the exterior-facing surface, for controlling flow of gases through the gas passages to preclude the flow of gases through the gas passages when the gases have a pressure that is below a preselected numerical value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows side, cross sectional and isometric views of the cuff. 
         FIG. 2  shows top, side and isometric views of the pad. 
         FIG. 3  shows top, bottom, side, cross sectional and isometric views of the manifold block. 
         FIG. 4  shows top, side and isometric views of the cap. 
         FIG. 5  shows an exploded view of the invention showing the cuff pad, manifold and cap and their placement with respect to each other. 
         FIG. 6  shows the preferred embodiment of the invention installed on a duct. 
         FIG. 7  is a perspective view of an improved embodiment of the invention showing a cuff/coupling cover with integrated manifold block. 
         FIG. 8  is a perspective view, in section, of the cuff/coupling cover with integrated manifold block, according to the embodiment of  FIG. 7 . 
         FIG. 9  is a perspective view, in section, of the manifold block according to the embodiment of  FIGS. 7 and 8 , showing the leakage flow check valve. 
         FIG. 10  is a perspective exploded view of the manifold block of  FIGS. 8 and 9 . 
         FIG. 11  is a side elevation of the manifold block of  FIGS. 8-10 . 
         FIG. 12  is an exploded side elevation, in section, of the manifold block of  FIGS. 8-11 . 
         FIG. 13  is an end elevation of the manifold block of  FIGS. 8-12 . 
         FIG. 14  is a top view of the manifold block of  FIGS. 8-13 . 
         FIG. 15  is a side elevation, in section, of the assembled manifold block of  FIG. 13 , taken along line  15 - 15  thereof. 
         FIG. 16  is a bottom view of the assembled manifold block of  FIGS. 8-15 . 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail, several embodiments with the understanding that the present disclosure should be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments so illustrated. Further, to the extend that any numerical values or other specifics of materials, etc., are provided herein, they are to be construed as exemplifications of the inventions herein, and the inventions are not to be considered as limited thereby. 
     A typical duct assembly  2  of the type with which the invention is intended to be used is shown in  FIG. 6  and comprises an inner metal duct  3 , typically composed of steel and 1.00″ to 6.50″ in diameter, covered by insulation blanket  4 , and secured by outer insulation shell  5 . Insulation blanket  4  and outer insulation shell  5  are composed of materials as previously discussed. 
       FIG. 1  shows the cuff  10  portion of the invention. Cuff  10  is positioned circumferentially around outer insulation shell  5  of duct assembly  2  as shown in  FIG. 6 . Preferably, cuff  10  is composed of multiple plies of silicon rubber impregnated with fiberglass (to limit stretch), and, in the most preferred embodiment, three plies are used to avoid having cuff  10  rupture due to excessive pressure build-up when installed in situ around duct assembly  2 . Before securing cuff  10  to duct assembly  2 , at least outer insulation shell  5  is cut circumferentially around duct assembly  2 . A small amount of outer insulation shell  5  may also be removed to form a narrow gap in outer insulation shell  5 . 
     To secure cuff  10  to duct assembly  2 , cuff  10  is situated circumferentially around the portion of duct assembly  2  in which the cut in outer insulation shell  5  has been made, and the tongue and groove arrangement  11 , as shown in  FIG. 1 , at the ends of cuff  10  are engaged. 
       FIG. 1 , section A-A, shows a cross sectional view of cuff  10  showing a raised middle portion  15  with shoulders  12  on either side thereof. Shoulders  12  will rest against outer insulation shell  5  of duct assembly  2 , while raised middle portion  15  remains above insulation shell  5 , thereby defining an annular-shaped void thereunder. Cuff  10  is secured to duct  2  by wrapping shoulders  12  and the adjoining area of outer insulation shell  5  with a heat-resistant, silicon-rubber compound tape,  13 , as shown in  FIG. 6 . One example of an appropriate heat-resistant, silicon-rubber tape  13  is sold under the tradename MOX-Tape™ and manufactured by Arlon Corporation of Santa Ana, Calif. In lieu of heat resistant tape  13 , any known method of securing cuff  10  to duct assembly  2  may be used, as long as the passage of air through insulation layer  4  to the void under cuff  10  is not restricted. Cuff  10  should be situated on duct assembly  2  such that hole  14  is in a convenient orientation with respect to the position of existing sensor wires  8  such that air escaping hole  14  will impinge on both of the sensor wires  8 . Because pressures within the inner metal portion  3  of duct assembly  2  can reach up to 60 psig, it can be expected that pressure within the void created between cuff  10  and duct assembly  2  may also experience similar pressures. As a result, it is possible that middle portion  15  of cuff  10  may deform because of bowing due to pressure buildup in the void inside cuff  10 . As a result, it is possible that hole  14  may not direct the air escaping therefrom to impinge onto sensor wires  8  when middle portion  15  of cuff  10  is deformed. Therefore, to assist in keeping hole  14  pointed toward sensor wires  8 , pad  20  is situated on the inside of cuff  10  between cuff  10  and outer insulation shell  5  of duct assembly  2 . Pad  20  is configured with two “legs”  26  which may rest on the outer surface of duct assembly  2  and channel  24  between legs  26  which has been provided to allow pressurized air within the void created by cuff  10  to reach the underside of hole  22 . Pad  20  is adhered to the inner surface of cuff  10  using any means known in the prior art, such as with room temperature vulcanizing silicon rubber (RTV) adhesive sold by Dow-Corning. Pad  20  is composed of a flexible silicon rubber compound having a durometer of between 20 and 50 Shore hardness, such that pad  20  should align with hole  14  in cuff  10  such that air can flow from the void created by cuff  10  through channel  24 , hole  22  and out of hole  14 . 
     The configuration of cuff  10  and pad  20  comprise one embodiment of the invention which is functional as long as sensor wires  8  are in close enough proximity to the outer surface of cuff  10  such that the air being forced from hole  14  has enough heat by the time it impinges on sensor wires  8  such as to trip the detector. This temperature is approximately 255° F. In the event that sensor wires  8  are too far away from duct  2  to be tripped by the escaping air, then the second, and preferred, embodiment of the invention may be used. 
     The preferred embodiment of the invention includes cuff  10  and pad  20  already discussed in addition to manifold block  30  and cap  40 . Manifold block  30  is shown in various views in  FIG. 3  and in situ in  FIG. 6 . Manifold  30  is a block of silicon rubber compound having channels defined therein to route the air from hole  14  in cuff  10  directly to sensor wires  8 , which will be captured by channels  42  in cap  40  at the top of manifold block  30 . 
     Manifold block  30  is provided with a defined radius  33  on the bottom thereof which matches the outer radius of cuff  10  when in place on duct assembly  2 . Naturally, radius  33  will vary depending upon the size of duct assembly  2  upon which cuff  10  is installed. The bottom of manifold block  30  is also configured to match the outer shape of cuff  10 . Shoulders  37  on the bottom of manifold block  30  will sit in shoulders  12  on cuff  10  and channel  35  will accept the raised middle portion  15  of cuff  10 . Wings  36 , defined on the outer edges of manifold block  30  at the bottom thereof, extend past the outer edge of cuff  10  and are used to secure manifold block  30  to cuff  10  through the use of heat-resistant tape  13  of the same type used to secure cuff  10  to the outside of duct assembly  2 . 
     Defined within manifold  30  is a conduit  34  which, when manifold block  30  is place over cuff  10 , aligns with hole  14  in cuff  10 . Conduit  34  splits into two separate conduits  32  which extend to the top of manifold block  30  and emerge through holes  31  defined thereon, thereby forming a “Y” shaped conduit in the interior of manifold block  30 . Sensor wires  8  are captured in channels  42  of cap  40 , which lock them into place directly above holes  31 . Posts  38  defined on the top of manifold block  30  are used to hold cap  40  in place and to keep sensor wires  8  positively aligned with holes  31  in manifold  30 , thereby allowing hot air coming from conduits  32  through holes  31  to impinge directly on sensor wires  8 , without the loss of heat experienced in the prior art when the hot air was forced through an environment of much lower temperature. 
     Holes  44 , defined in cap  40 , mate with posts  38  disposed on the top of manifold block  30 , to form a snap type fitting to secure cap  40  firmly in place on the top of manifold block  30  without the use of tools. Manifold block  30  is preferably composed of a silicon rubber compound having a durometer reading between 65 and 85. Alternatively, manifold block  30  may be made of other materials, such as aluminum, however, care must be taken to avoid excessive heat transfer through the metal body of manifold block  30  such as to lower the temperature of the hot air emerging from holes  31 . Also, preferably, cap  40  will be softer than manifold block  30 , having a durometer reading of between 30 and 50 Shore hardness, such that the cap can be removed from snap posts  38  without damaging the manifold block. 
     Tests of this design were conducted in a lab wherein an original prior art vent disk design and the design of the embodiments of the invention disclosed herein were installed adjacent to one another on a duct assembly. A partial cut measuring approximately 0.025″ wide by 1.25″ long was made in the metal portion  3  of duct assembly  2  to simulate a crack-like failure having an area equivalent to a 5 mm diameter hole, and the metal portion  3  of duct assembly  2  was pressurized. The air flow through the original vent disk was undetectable, while the air flow through vent  14  in cuff  10  was of significant velocity throughout a range of duct pressures ranging from 5 psi to 40 psi. The pressure in the void created by cuff  10  was measured and was found to be approximately 12% of the pressure in the metal portion  3  of duct assembly  2 . The pressure combined with the volume in cuff  10  provided a visual and a measurable flow of air through vent hole  14  in cuff  10 , thereby meeting the objective of the invention. 
       FIGS. 7-16  illustrate an improved alternative embodiment of the invention, wherein the manifold block incorporates a check valve. In ducting structures of the type described herein, the specifications for the ducts allow for a small amount of leakage, particularly at the locations where two sections of duct are joined together by a coupling. Accordingly, in order to prevent false alarms resulting from such small, accounted for leakage, it is desirable to provide a way to prevent leaking gases from reaching the highly sensitive temperature sensing wires, unless the volume and/or pressure of the leaking gases exceeds a preselected value. 
     Therefore, coupling covers employed in accordance with the principles of the present invention, particularly those covering duct couplings, may be provided with a check valve, which is biased in a closed position, against leakage gas pressures which are below a preselected threshold level. 
     Coupling cover  100  is shown in perspective view in  FIG. 7 , in the form of a split ring, having, at the split, a first inner portion  101  that is overlapped by a second outer portion  102  in the vicinity of the split. First inner portion has wedge-shaped or ramp-shaped outer contours. Coupling cover  100  is held in place by band clamps  106 . Each band clamp may be in the form of a conventional hose-type clamp, having a band  108 , and a screw drive section  110 . As band clamps  106  are tightened, second outer portion  102  is forced to ride up first inner portion  101 , creating a binding fit, so as to inhibit leakage of gases therebetween. Coupling cover  100  is preferably fabricated from silicone rubber impregnated fiberglass cloth, which may be pre-molded, and cured in a temperature-controlled environment. Opening  112  in coupling cover  100  permits manifold block  114  to be inserted therethrough from the inside, and held in place, e.g., by an RTV (“Room Temperature Vulcanization”) adhesive. In preferred embodiments of the invention, coupling cover  100  is fabricated from the same material and cured in the same manner as cuff  10 . 
       FIG. 8  is a lengthwise or longitudinal sectional view of a duct joint surrounded by a coupling cover  100  according to the this embodiment of the invention. Duct sections  116 ,  118  are connected to one another by joint flanges  120  affixed to the ends of the respective duct sections  116 ,  118 . Joint flanges  120  are, in turn, held together by V-band coupling  122 , formed from V-band  124  and strap  126 . V-band coupling will have a screw drive section (not shown), such as used with band clamps  106 , to tighten strap  126 , to create radially inwardly directed clamping pressure against flanges  120 . Standoffs  128  are used to provide radial spacing between duct sections  116 ,  118 , and insulation shells  130 . Insulation (not shown) may typically be provided in the annular gap between insulation shells  130  and duct sections  116 ,  118 . 
       FIG. 9  is a transverse sectional view of manifold block  114 . Manifold block  114  incorporates block body  115 , from which emanates block flange  132  to provide overlap surface area between manifold block  114  and the surrounding coupling cover  100 , for placement of a suitable adhesive material, to permanently affix manifold block  114  to coupling cover  100 . Manifold block  114  is preferably fabricated from silicone rubber. 
     To assemble manifold block  114 , coil spring  146  is inserted into coil spring pocket  152 , followed by the insertion of valve ball  148 . Block insert  134 , which is preferably fabricated also from silicone rubber, like block body  115 , is then inserted into rectangular recess  117  (compressing spring  146  against ball  148  in the process), and held in place by adhesive. 
     Gas passages  136  in block insert  134 , and gas passages  138 ,  140  in manifold block  114  enable the flow of leakage gases, as described hereinafter. Passages  138 ,  140  are intentionally configured to be partially obstructed by sensor wires  142 ,  144  (see  FIG. 9 ), so as to cause any leakage gases to be forced to spread longitudinally along wires  142 ,  144 , to increase the amount of surface area contact made by the gases, to ensure increased exposure time, and thus more accurate sensor wire responses. 
     Manifold grooves  154 ,  156 , at the top of manifold block  114 , extend at an angle to the longitudinal/axial direction of ducts  116 ,  118 . See, e.g.,  FIGS. 10 and 14 . However, within the body of manifold block  114 , manifold grooves  154 ,  156  extend parallel to the longitudinal/axial direction, so as to create ledges or overhangs that serve to lock sensor wires  142 ,  144  in place within manifold block  114 , without having to use a cap or other separate retaining structure to fixedly position sensor wires  142 ,  144 . Fully assembled manifold block  114  is shown in  FIGS. 10 ,  13 - 16 . 
     In operation, once coupling cover  100  is in place over a duct joint, as sensor wires  142 ,  144  are strung along the ducting, at each such manifold block  114 , the sensor wires are deflected sufficient to align them with grooves  154 ,  156 . Upon full insertion of sensor wires  142 ,  144  down into grooves  154 ,  156 , the wires reach the portions of grooves  154 ,  156  which extend parallel to the longitudinal direction of the duct joint, and the overhanging portions of block body  115  that are above wires  142 ,  144  serve to prevent undesired “popping out” of the wires from the grooves. 
     As gases begin to flow through the duct joint, a certain amount of gases will escape through the interface between joint flanges  120  and will be exposed to the underside of valve ball  148 . Until the pressure of the escaping gases exceeds a certain predetermined value (which may vary from application to application), ball  148  will remain firmly seated, under the biasing action of coil spring  146 . Once the predetermined pressure has been exceeded, then ball  148  will be raised off its seat  150 , and the gases can enter passages  136 ,  138 ,  140 , and be conducted into contact with sensor wires  142 ,  144 . Depending upon the temperature which is sensed through action of the impingement of the gases on sensor wires  142 ,  144 , the control apparatus not shown, but which is known to those of skill in the art) may cause a warning signal to be generated and communicated, e.g., to the operator of the aircraft. A series of graduated warnings may even be possible, that would be a function of the gas temperature(s) which are being sensed. 
     The embodiments disclosed herein are exemplary in nature and are not intended to restrict the scope of the invention. Alternate materials, methods of securing the various parts on the invention, and different configurations and shapes for the cover, manifold block and cap are contemplated as being within the scope of the invention. 
     The foregoing description and drawings merely explain and illustrate the invention, and the invention is not limited thereto, except as those skilled in the art who have the present disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.