Patent Publication Number: US-9429120-B2

Title: Detecting leaks in a feedthrough device

Description:
BACKGROUND 
     This specification relates to detecting leaks in a feedthrough device, for example, in a fuel injector system. Electro-mechanical fuel injectors are controlled by electrical signals carried by conductors that extend from a low pressure environment into a high pressure zone. The high pressure zone contains a combustible fuel mixture. To prevent the combustible fuel mixture from leaking to the environment, a feedthrough provides a seal around the conductors at the interface where the conductors enter the high pressure zone. 
     Some conventional feedthroughs include groups of soldered, crimped, or otherwise connected wire strands, with each group of wire strands contained within a solid conductor that is sealed on its outer diameter. A nonconductive body around the conductors seals the conductors relative to each other and ensures insulative spacing between the conductors. When the feedthrough is installed in a fuel injector system, an O-ring seals around the nonconductive body of the feedthrough. 
     SUMMARY 
     In one general aspect, a feedthrough device includes an internal leak-detection zone. In some instances, the feedthrough device can be included in a fuel injector system. 
     In some aspects, a feedthrough device includes first and second opposing outer end faces. The feedthrough device includes an opening, between the first and second opposing outer end faces, that allows fluid communication between an interior and an exterior of the feedthrough device. A conductor extends through the feedthrough device from the first end face, through the interior, to the second end face. 
     In some aspects, the feedthrough device is adapted for installation between a high pressure zone and a low pressure zone of a fuel injector system. The feedthrough device includes a feedthrough body. The feedthrough body includes a first outer end face and a second outer end face opposite the first outer end face. The feedthrough body includes an outer surface between the first outer end face and the second outer end face. The feedthrough body includes an interior surface defining a cavity. The cavity is disposed between the first outer end face and the second outer end face. The feedthrough body includes a fluid passage through the outer surface that allows fluid communication between the cavity and an exterior of the feedthrough body. The feedthrough device includes a conductor extending through the feedthrough body from the first end face, through the cavity, to the second end face. 
     Implementations may include one or more of the following features. The feedthrough device includes a first seal between the first outer end face and the fluid passage. The feedthrough device includes a second seal between the second outer end face and the fluid passage. The outer surface includes a cylindrical outer face of the feedthrough body. The first outer end face is a first axial end of the feedthrough body. The second outer end face is a second axial end of the feedthrough body. The first seal and the second seal are both O-rings. 
     Additionally or alternatively, these and other implementations may include one or more of the following features. The conductor defines a solid conductive cross-section through the cavity. The feedthrough device includes a second conductor extending through the feedthrough body from the first end face, through the cavity, to the second end face. The second conductor defines a second solid conductive cross-section through the cavity. The body is an integral structure made of nonconductive material. 
     In some aspects, a fuel injector system includes a partition between a high pressure zone and a low pressure zone. The fuel injector system includes a feedthrough device disposed in the partition between the high pressure zone and the low pressure zone. The feedthrough device includes a first end face exposed to the high pressure zone and a second end face exposed to the low pressure zone. The feedthrough device includes a first seal that isolates an interior volume of the feedthrough device from the high pressure zone. The feedthrough device includes a second seal that isolates the interior volume of the feedthrough device from the low pressure zone. The fuel injector system includes a conductor extending through the feedthrough device from the high pressure zone, through the first end face, through the interior volume, through the second end face, to the low pressure zone. The fuel injector system includes a fluid passage that allows fluid communication between the interior volume and an exterior. 
     Implementations may include one or more of the following features. The fuel injector system includes a sensor. The sensor includes a pressure sensor, a fuel sensor, or both. The low pressure zone includes an internal volume of the fuel injector system. The fuel injector system includes a solenoid assembly in the high pressure zone. The conductor is configured to communicate a control signal between the solenoid assembly in the high pressure zone and an external control system in the low pressure zone. The partition includes a chamber that contains inert gas. The inert gas is contained within the chamber at a pressure that is higher than the pressure of the high pressure zone of the fuel injector system. 
     In some aspects, an electrical signal is sent from a low pressure zone of a fuel injector system to a high pressure zone of the fuel injector system through a feedthrough device. The feedthrough device has an internal volume that is sealed from the low pressure zone and the high pressure zone. A condition of the internal volume of the feedthrough device is sensed. 
     Implementations may include one or more of the following features. Sensing the condition includes sensing a pressure of the internal volume. Sensing the condition includes sensing a fuel content of the internal volume. An internal leak in the feedthrough device is identified based on the condition. Sending the electrical signal operates a solenoid assembly in the high pressure zone. The electrical signal is received from a controller in the low pressure zone. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-section of an example fuel injector system. 
         FIGS. 2A and 2B  are diagrams of an example feedthrough device. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram of an example fuel injector system  100 . The example fuel injector system  100  shown in  FIG. 1  includes low pressure zones  101 ,  102 , high pressure zones  103 ,  104 , and a partition  105  between the low pressure zone  102  and the high pressure zone  104 . The example fuel injector system  100  includes a solenoid assembly  106  in the high pressure zone  104 . A pair of conductors  107   a ,  107   b  are conductively connected to the solenoid assembly  106  in the high pressure zone  104 . The pair of conductors  107   a ,  107   b  extend from the low pressure zone  102  into the high pressure zone  104  through a feedthrough device  108 . The feedthrough device  108  includes an internal leak-detection zone in fluid communication with a leak-detection port  110 . A sensor  112  is positioned to receive fluid from the leak-detection port  110 . 
     A fuel injector system can include additional or different features; and the features of the example fuel injector system  100  can be arranged in the manner shown in  FIG. 1  or in another manner. In some implementations, the example fuel injector system  100  shown in  FIG. 1  can be used in engines that must meet regulations set forth by various Marine compliance agencies. A common regulation required by such agencies is the ability to detect or prevent external gas leakage. The example fuel injector system  100  can be included in other types of systems, including systems that meet other types of regulations, or systems that do not meet any specified regulations. 
     In the example shown in  FIG. 1 , the low pressure zones  101 ,  102  are internal to the fuel injector system  100 . In some examples, the low pressure zone  101  includes an external environment of the fuel injector system  100 . The low pressure zones  101 ,  102  can be at the same pressure or they can be at different pressures. In some cases, the low pressure zones  101 ,  102  are sealed from each other, or fluid communication may be permitted between the low pressure zones  101 ,  102 . The low pressure zone  102  can include fluid pressures that are lower (e.g., significantly lower) than the fluid pressure in the high pressure zone  104 . For example, the low pressure zone can include fluids at atmospheric pressure. Portions of the conductors  107   a ,  107   b  extend through the low pressure zone  102 . Although not shown in  FIG. 1 , the conductors  107   a ,  107   b  typically connect the controller  114  to the solenoid assembly  106 . 
     The high pressure zones  103 ,  104  include the solenoid assembly  106 , portions of the conductors  107   a ,  107   b , and possibly other components of the fuel injector system  100 . The high pressure zones  103 ,  104  can be at the same pressure or they can be at different pressures. For example, when solenoid assembly  106  is pressure-balanced, the high pressure zones  103 ,  104  can be at different pressures, when solenoid assembly  106  is not pressure-balanced, the high pressure zones  103 ,  104  can be at the same pressure. In some cases, the high pressure zones  103 ,  104  are sealed from each other, or fluid communication may be permitted between the low pressure zones  103 ,  104 . The high pressure zone  104  can contain a combustible fuel mixture at high pressure during operation of the fuel injector system  100 . For example, the high pressure zone  104  can contain fluids at pressures that are significantly higher than the low pressure zone  102 . In some implementations, the high pressure zone  104  contains fluids at pressures on the order of 160 psi; or the high pressure zone  104  can contain fluids at different (lower or higher) pressures. 
     The partition  105  can prevent fluid communication between the low pressure zone  102  and the high pressure zone  104 . For example, the partition  105  can be part of a housing or another structure of the fuel injector system  100 . The partition  105  can be made of aluminum, steel, plastics, a different material, or a combination of materials. The partition  105  can be made of one or more parts formed by machining, casting, molding, other manufacturing processes. The partition  105  includes a port that houses the feedthrough device  108 . The partition  105  also includes the leak-detection port  110  that provides fluid communication between the sensor  112  and the port that houses the feedthrough device  108 . 
     The solenoid assembly  106  is contained in the high pressure zone  104  of the example fuel injector system  100 . The solenoid assembly  106  can control a flow of fuel into an internal combustion engine. In some cases, the solenoid assembly  106  can include a plunger or another type of actuator that opens and closes a fuel injection port. In some cases, the actuator of the solenoid assembly  106  moves at an operating frequency of the solenoid (e.g., 5 Hz, 10 Hz, 50 Hz, 100 Hz, etc.). Movement of the actuator can be controlled, for example, by a magnetic field produced by a conductive coil of the solenoid assembly  106 . The conductive coil can produce the magnetic field based on an electrical signal (e.g., a direct current signal that is modulated over time, etc.) carried by the conductors  107   a ,  107   b.    
     The conductors  107   a ,  107   b  carry an operating signal from the external controller  114  to the solenoid assembly  106 . For example, the conductors  107   a ,  107   b  can form a closed-loop circuit with the solenoid assembly  106  and the controller  114 . The conductors  107   a ,  107   b  can carry an alternating current, direct current, or another type of signal. The conductors  107   a ,  107   b  can be configured to carry a signal having a voltage in the operating range of the solenoid assembly  106 . In some implementations, the conductors  107   a ,  107   b  carry a signal having a maximum voltage between 90 and 140 Volts; or the conductors  107   a ,  107   b  can carry a signal having a lower or higher maximum voltage (e.g., 18 Volts, 180 Volts). Although two conductors are shown in  FIG. 1 , a different number of conductors (e.g., one, three, four, ten, etc.) may be used. 
     The conductors  107   a ,  107   b  can be made of copper, brass, gold, a different conducting material, or a combination of them. The conductors can include lengths of braided wire, solid wire, leads, soldered junctions, or a combination of these and other components. In some implementations, the conductors  107   a ,  107   b  are each conductively connected (e.g., soldered) to a first pair of terminals at the controller  114  and a second pair of terminals at the solenoid assembly  106 . 
     The conductors  107   a ,  107   b  extend from the low pressure zone  102 , through the feedthrough device  108 , into the high pressure zone  104 . The feedthrough device  108  provides a pressure-sealed conductive path through the partition  105 . The example feedthrough device  108  shown in  FIG. 1  resides in a port in the partition  105  between the low pressure zone  102  and the high pressure zone  104 . The feedthrough device  108  can be the example feedthrough device  200  shown in  FIGS. 2A and 2B  or another type of feedthrough device. 
     The example feedthrough device  108  includes a provision to allow detection of leakage in the feedthrough device  108  itself. For example, an internal cavity in the feedthrough device  108  can function as a leak-detection zone. The leak-detection zone can be exposed to all conductors within the feedthrough device  108 , and it can be isolated from both the fuel source and the ambient environment. In some examples, the feedthrough device  108  includes two independent seals, such that fuel leaking through the first seal cannot travel from the first seal to the second seal without passing through the leak-detection zone. Moreover, the leak-detection zone can be connected to a leak detection system, a pressurized leak-prevention system, or another mechanism. 
     In the event that the feedthrough device  108  develops a leak, high pressure fluids from the high pressure zone  104  can be collected in the leak-detection zone of the feedthrough device  108 , and the leak-detection zone of the feedthrough device  108  can communicate the high pressure fluids through the leak-detection port  110  to the sensor  112 . As such, a leak in the feedthrough device  108  can be detected, in some cases, by sensing an increased pressure in the leak-detection port  110 . In some instances, the fluids leaked from the high pressure zone  104  contain fuel (e.g., hydrocarbon gas). As such, a leak in the feedthrough device  108  can be detected, in some cases, by sensing a fuel concentration or fuel content in the leak-detection port  110 . 
     In some example implementations, the feedthrough device  108  includes an internal cavity and a fluid passage; the fluid passage provides fluid communication between the internal cavity and the leak-detection port  110 . In the event that the feedthrough device  108  develops a leak, fluids leaked from the high pressure zone  104  can be communicated through the internal leak-detection zone the feedthrough device  108  and into the leak-detection port  110 . For example, the feedthrough device  108  can be configured to accumulate any such leaked fluids in the internal cavity, and the fluid passage of the feedthrough device  108  can communicate the leaked fluids from the internal cavity into the leak-detection port  110 . The leak-detection port  110  provides a fluid communication path from the feedthrough device  108  to the sensor  112 . In the event that the feedthrough device  108  develops a leak, the leak-detection port  110  can communicate the leaked fluids from the feedthrough device  108  to the sensor  112 . 
     In some example implementations, each of the conductors  107   a ,  107   b  is sealed from the fuel pressure source (i.e., the high pressure zone  104 ) by a first seal at or near a point where the conductor enters the internal cavity of the feedthrough device  108 ; and each of the conductors  107   a ,  107   b  is sealed from the low pressure zone  102  by a second seal at or near the point where the conductor exits the internal cavity of the feedthrough device  108 . Upon failure of the first seal, leakage through the feedthrough device  108  can be detected via a passage connected to the internal cavity, while the second seal prevents leakage to the external environment. As such, the internal cavity can operate as a leak-detection zone for the feedthrough device  108 . 
     The sensor  112  can be configured to detect a condition that indicates a leak in the feedthrough device  108 . In some implementations, the sensor  112  is a pressure sensor. For example, the sensor  112  can be configured to detect static pressure, pressure changes, or other types of pressure conditions. In some implementations, the sensor  112  is a fuel sensor. For example, the sensor  112  can be configured to detect fuel content, fuel concentration, or other types of fluid properties. The sensor  112  may be connected to the controller  114 , another type of processor, or an external monitoring system. The example sensor  112  is disposed in a position where it can sense a condition of the internal volume of the feedthrough device  108 . The sensor  112  can be installed within the leak-detection port  110 , in a low pressure or high pressure zone outside of the leak-detection port  110 , or in another area. In some cases, the sensor  112  is omitted from the fuel injector system  100 . 
     The sensor  112  can be part of a monitoring system that includes other components (not shown in the figure). The sensor  112  can be part of a pressure detection system. The pressure detection system can include a fixed volume in which the pressure increase from the accumulation of the leaking fuel can be detected using a pressure sensor. The sensor  112  can be included in a fuel detection system (e.g., a methane detector, etc.). 
     In some examples, the sensor  112  is a dedicated sensor for the leak-detection port  110 . As such, the conditions detected by the sensor  112  may directly indicate whether a leak has formed in the feedthrough device  108 . In some examples, the sensor  112  receives fluid from the leak-detection port  110  and other leak-detection ports at other locations in the fuel injector system  100 . As such, the conditions detected by the sensor  112  may indicate whether a leak has formed at any of several locations in the fuel injector system  100 . In some implementations, the fuel injector system  100  is contained in an external housing or another type of external enclosure (not shown in the figure), and the sensor  112  is configured to detect any leakage within the enclosure. 
     In some implementations, the leak-detection port  110  is filled with high pressure inert gas (e.g., air, nitrogen, etc.). The high pressure inert gas in the leak-detection port  110  can prevent or reduce leaking of fuel through the feedthrough device  108  to an external environment. The high pressure inert gas in the leak-detection port  110  can be maintained at a pressure that is higher than the pressure within the high pressure zone  104 . If a leak occurs in the feedthrough device  108 , the pressure of the inert gas in the leak-detection port  110  can, in some cases, minimize or reduce the amount of fuel that escapes from the high pressure zone  104  through the leak. As such, a leak in the feedthrough device  108  can be rendered inert through the introduction of the high pressure inert fluid. In some cases, the inert gas in the leak-detection port  110  can flood the internal volume of the feedthrough device  108 . 
     In some aspects of operation, the controller  114  sends an electrical signal from the low pressure zone  102  to the high pressure zone  104  through the feedthrough device  108 . The electrical signal from the controller  114  (in the low pressure zone  102 ) operates the solenoid assembly  106  (in the high pressure zone  104 ). The feedthrough device  108  has an internal cavity that is sealed from the low pressure zone  102  and the high pressure zone  104 . The internal cavity can communicate fluid into the leak-detection port  110 , so that the sensor  112  can sense a condition of the internal volume of the feedthrough device  108 . 
     In some aspects of operation, the sensor  112  can produce an output that indicates (e.g., directly or indirectly) whether there is a leak in the feedthrough device  108 . For example, if the feedthrough device  108  develops a leak, the combustible, high pressure fuel from the high pressure zone  104  is collected in the internal cavity of the feedthrough device  108  and communicated to the sensor  112 . In some instances, the sensor  112  senses the pressure, fuel content, or another condition of the internal cavity of the feedthrough device  108 . The conditions sensed by the sensor can be communicated to the controller  114  or another external system, which can produce a signal or another appropriate output to indicate whether a leak has been detected. If a leak is detected, an appropriate action can be initiated, such as, for example, powering down all or part of the system. In some examples, potential external leak paths of the fuel valve can be pressurized to a pressure that is equal to, or higher than, the inlet pressure of the fuel valve. In such cases, a fuel valve “leak” would simply result in flow of the leak system pressurized media into the fuel valve. 
       FIGS. 2A and 2B  are diagrams of an example feedthrough device  200 . The example feedthrough device  200  can be used as the feedthrough device  108  of the fuel injector system  100  shown in  FIG. 1 . The feedthrough device  200  can be used in other contexts and in other types of applications. For example, the feedthrough device  200  and variations thereof can be used in other locations in a fuel injector system, in other components of an engine system, or in applications other than engine systems. 
     The feedthrough device  200  can be used or adapted to provide a pressure-sealed conductive pathway between any two zones of different pressures. The pressure difference between the two zones can range from small pressure differences (e.g., 10 psi) in some applications to larger pressure differences (e.g., 10,000 psi) in other applications. As such, in some instances, the dimensions, materials, and features of the example feedthrough device  200  can be adapted for particular applications other than a fuel injector system. 
     As shown in  FIG. 2A , the example feedthrough device  200  includes a feedthrough body  202  and two conductors  204   a ,  204   b . Features of the feedthrough body  202  are shown in  FIG. 2B . The feedthrough device  200  can enable leak prevention or leak detection by utilizing a feedthrough body  202  that includes a nonconductive housing with an internal cavity  216 , which can function as a leak-detection zone. The feedthrough device  200  can be configured such that all conductors pass through the internal cavity  216 . For example, both of the conductors  204   a ,  204   b  pass through the internal cavity  216  shown in  FIG. 2B . The feedthrough body  202  also includes a structural connection (other than the conductors  204   a ,  204   b ) between the high pressure side and the low pressure side of the feedthrough body  202  housing. This structural connection can increase the overall strength of the feedthrough device  200 , improving its robustness in environmentally challenging environments, such as, for example, those with high vibration levels, high structural loading, etc. 
     The example feedthrough body  202  includes a first outer end face  210   a  at a high pressure end of the feedthrough body  202 . The feedthrough body  202  includes a second outer end face  210   b  at a low pressure end of the feedthrough body  202 . The first outer end face  210   a  and the second outer end face  210   b  are at opposite ends of the feedthrough body  202 . The feedthrough body  202  includes an outer surface  208  between the first outer end face  210   a  and the second outer end face  210   b.    
     The example feedthrough body  202  has a generally cylindrical geometry, with the first outer end face  210   a  defining a first axial end of the feedthrough body  202  and the second outer end face  210   b  defining a second axial end of the feedthrough body  202 . The outer surface  208  generally defines an outer circumference of the feedthrough body  202 . In particular, the outer surface  208  includes cylindrical faces  212   a ,  212   b ,  212   c ,  212   d , and seals  206   a ,  206   b ,  206   c  between the cylindrical faces. In the example shown, the seals  206   a ,  206   b ,  206   c  are all O-rings. Other types of seals can be used. 
     The example feedthrough body  202  is a continuous structure between the first and second outer end faces  210   a ,  210   b . In some implementations, a feedthrough body includes multiple components. For example, a feedthrough body can be made of two components separated by a gap, where one of the components carries one or more seals (e.g.,  206   a ,  206   b ) on the high-pressure side and a separate component carries one or more seals (e.g.,  206   c ) on the low-pressure side. The two separate components can abut each other, or they can be separated by open space. 
     The feedthrough body  202  can include additional or different types of seals, including seals in other locations. In some implementations, the feedthrough body  202  includes an internal seal on each side of the feedthrough body. For example, the feedthrough body  202  can include seals about the conductors  204   a ,  204   b  at the first and second outer end faces  210   a ,  210   b , at the interior surface  214 , between an outer end face and the interior surface  214 , or in multiple locations within the feedthrough body. The seals about the conductors  204   a ,  204   b  can prevent high pressure gas from leaking between the feedthrough body  202  and the conductors  204   a ,  204   b . The seals can include, for example, O-rings, adherent compounds, compressive joints, etc. 
     When the feedthrough device  200  is installed (e.g., in a fuel injector system) between a high pressure zone and a low pressure zone, the feedthrough body  202  can prevent fluid communication between the low pressure zone and the high pressure zone. For example, the feedthrough body  202  can be installed in a port through a housing or another structure, and the seals  206   a ,  206   b ,  206   c  can form a pressure seal in the port. The feedthrough body  202  can be made of epoxy, a different kind of nonconductive material, or a combination of materials. In some cases, the feedthrough body  202  is an integral structure made of nonconductive material. The feedthrough body  202  can be formed by molding, machining, casting, or other manufacturing processes. 
     The example feedthrough body  202  includes an interior surface  214  defining the internal cavity  216 . The internal cavity  216  is disposed between the first outer end face  210   a  and the second outer end face  210   b . The internal cavity  216  is enclosed on multiple sides. For example, the internal cavity  216  is enclosed by the interior surface  214  that includes an internal face on the high pressure side of the feedthrough body  202  and an opposing internal face on the low pressure side of the feedthrough body  202 . The interior surface  214  also includes a cylindrical internal face between the opposing low pressure and high pressure sides. The internal cavity  216  is not fully enclosed. In particular, the feedthrough body  202  includes a fluid passage  218  through the outer surface  208 , which allows fluid communication between the internal cavity  216  and an exterior of the feedthrough body  202 . 
     Both conductors  204   a ,  204   b  extend through the example feedthrough body  202  from the first outer end face  210   a , through the internal cavity  216 , to the second outer end face  210   b . The example conductors  204   a ,  204   b  shown in  FIG. 2B  include a solid brass section that extends through the internal cavity  216 . Outside of the internal cavity  216 , the conductors  204   a ,  204   b  can include braided wires, soldered junctions, and other features. In some examples, each conductor includes braided wire outside the feedthrough body  202 , and each braided wire is connected to one of the solid brass sections that extend through the internal cavity  216 . For example, the braided wire can be soldered to leads or other connectors within the feedthrough body  202 , outside the feedthrough body  202 , or both. Because both example conductors are solid brass through the internal cavity  216 , both conductors define a solid conductive cross-section through the internal cavity  216 . In other words, between the opposing faces of the interior surface  214 , the conductor  204   a  has a solid conductive cross-section and the conductor  204   b  has a separate solid conductive cross-section. As such, neither conductor  204   a ,  204   b  has internal voids that would permit fluid leakage within the conductor across the internal cavity  216 . 
     The example feedthrough body  202  includes seals to prevent fluid leaks. The seal  206   a  provides a first seal on the high pressure side of the feedthrough body  202 . The seal  206   b  provides a second seal on the high pressure side of the feedthrough body  202 . The seals  206   a ,  206   b  seal between the first outer end face  210   a  and the internal cavity  216 . The seal  206   c  provides a third seal on the low pressure side of the feedthrough body  202 . The seal  206   c  seals between the second outer end face  210   b  and the internal cavity  216 . 
     The second and third seals ( 206   b ,  206   c ) define an internal volume of the example feedthrough body  202  between the first outer end face  210   a  and the second outer end face  210   b . The internal volume includes the internal cavity  216  and the fluid passage  218  through the outer surface  208 . When the example feedthrough device  200  is installed (e.g., in a fuel injector system), the internal volume can be placed in fluid communication with an external fluid passage (e.g., the leak-detection port  110  in  FIG. 1 ). As in the example shown in  FIG. 1 , the external fluid passage can contain or lead to a sensor  112  configured to detect leaks in the feedthrough device. 
     The internal volume of the example feedthrough device  200  can provide an internal leak-detection zone. In some instances, the structure of the feedthrough device  200  causes any fluid leaked from the high pressure side to flow into the internal volume (e.g., into the internal cavity  216 ). For example, the solid current-carrying interconnects within the internal cavity  216  in the example shown in  FIG. 2B  will not allow fuel to travel along the conductor surface without entering into the leak-detection zone. Similarly, leaks in the feedthrough body or seals will flow into the leak-detection zone. From the leak-detection zone, the leaked fluids can be detected, for example, by a sensor. 
     While this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular examples. Certain features that are described in this specification in the context of separate implementations can also be combined. Conversely, various features that are described in the context of a single implementation can also be implemented separately or in any suitable subcombination. 
     A number of examples have been shown and described. Nevertheless, it will be understood that various modifications can be made. Accordingly, other embodiments are within the scope of the following claims.