Abstract:
An auxiliary canister operates with a storage canister of an evaporative emissions control system to reduce the amount of fuel vapor emitted from a vehicle to very low levels. The storage canister contains a first sorbent material and has a vent port in communication therewith. The auxiliary canister comprises an enclosure, first and second passages, a heater and a connector. Inside the enclosure, a second sorbent material is in thermal contact with the heater. Attached at one end to the bottom of the enclosure, the first passage is connectable at its other end to the vent port to allow flow between the storage and auxiliary canisters. Attached at one end to a top of the enclosure, the second passage is connectable at its other end to a vent valve of the control system to allow flow between the auxiliary canister and the vent valve. Incorporated into the enclosure, the connector is used to convey electrical power from the vehicle to the heater. During a regenerative phase of operation for the control system, the heater can be used to heat the second sorbent material and the passing purge air. This enables the second and first adsorbent materials to more readily release the fuel vapor they adsorbed during the previous storage phase of operation so that they can be burned during combustion.

Description:
FIELD OF THE INVENTION 
     The present invention relates, in general, to the reduction of evaporative emissions from motor vehicles. More specifically, the invention relates to an evaporative emission control system employing a heated adsorber. 
     BACKGROUND OF THE INVENTION 
     Evaporative emissions of fuel vapor from a vehicle having an internal combustion engine occur principally due to venting of the fuel tank of the vehicle. When the vehicle is parked, diurnal changes in temperature or pressure of the ambient atmosphere cause air to waft into and out of the fuel tank. Some of the fuel inevitably evaporates into the air within the tank and thus takes the form of a vapor. If the air emitted from the fuel tank were allowed to flow untreated into the atmosphere, it would inevitably carry with it this fuel vapor. The fuel vapor, however, is a pollutant. For that reason, federal and state governments have imposed increasingly strict regulations over the years governing how much fuel vapor may be emitted from the fuel system of a vehicle. 
     One approach that automobile manufacturers have long employed to reduce the amount of fuel vapor that a vehicle emits to the atmosphere involves the use of a storage canister. In this approach, a tube, often referred to as a “tank tube,” is used to connect the air space in the fuel tank to the storage canister. Inside the storage canister is contained a sorbent material, typically activated carbon, whose properties enable it to adsorb the fuel vapor. Consequently, when air flows out of the tank, the tank tube carries it to the storage canister wherein the fuel vapor is adsorbed into the sorbent material There the fuel vapors are temporarily stored so that they can be burned later in the engine rather than being vented to the atmosphere when the engine is not operating. 
     FIGS. 1 and 2 illustrate one type of storage canister, generally designated  10 , typically used in the automotive industry. FIG. 1 shows the canister in a perspective view, whereas FIG. 2 shows it in cross-section. The storage canister  10  comprises a container  18  that is partially divided by partition  24  into two compartments  20  and  22 . An intercompartmental flow passage  26  connects these compartments. 
     The storage canister  10  has a tank port  12  and a purge port  14 , both of which communicate with the first compartment  20 . The tank port  12  connects to the tank tube  7 , and thereby allows the air space in the fuel tank  8  to communicate with the first compartment  20 . To the left of the tank port  12  as viewed from the perspective of FIG. 2, the purge port  14  connects to a purge line  19 . Through a purge valve  15 , the purge line  19  connects to the air intake passage  9  of the vehicle  11 . (Air flowing into the air intake passage  9  is mixed with fuel, and the mixture eventually drawn into the cylinders for combustion.) The purge valve  15  is closed when the engine is not running. When the engine is running, however, purge valve  15  is opened in and thereby allows the storage canister  10  via the first compartment  20  to communicate with the air intake  9 . 
     The storage canister  10  also features a vent port  16  that communicates with the second compartment  22 . The vent port  16  connects to a vent line  6 . The vent line  6  communicates with the ambient atmosphere through a vent valve  17 . Typically controlled via a solenoid, the vent valve  17  is normally held open. When opened, the vent valve  17  allows the storage canister  10  via the second compartment  22 , vent port  16  and vent line  6  to communicate with the atmosphere. The vent valve  17  is closed when the storage canister  10  is being tested for leaks. 
     Evaporative emission control systems of this type essentially have two phases of operation. During the storage phase when the engine is off, the system operates with the purge valve  15  closed and the vent valve  17  opened. When the pressure in the fuel tank  8  is high relative to atmospheric pressure, air from the tank and the fuel vapor it carries flows into tank tube  7  and through tank port  12  into storage canister  10 . Inside the storage canister  10 , the fuel vapor is adsorbed by the sorbent material  28  as the air that carried it flows not only through the first compartment  20  but also through the second compartment  22  via intercompartmental flow passage  26 . Although a high percentage of the fuel vapor is adsorbed into the sorbent material  28 , the air as it exits the canister  10  via vent port  16  carries with it some unadsorbed fuel vapor to atmosphere. 
     During the regenerative phase of operation when the engine  90  is running, the system operates with both the purge valve  15  and the vent valve  17  opened. A vacuum is developed within the intake manifold as a result of the combustion occurring within the cylinders of the engine  90 . This vacuum ultimately causes fresh air from the atmosphere to be drawn through vent valve  17  and into the storage canister  10 . Specifically, the air is pulled by vacuum through vent port  16 , second compartment  22 , flow passage  26 , first compartment  20  and out purge port  14 . Inside the storage canister  10 , as the fresh air flows through the sorbent material  28 , it strips it of the fuel vapor that it had adsorbed during the previous storage cycle. The sorbent material  28  is thus regenerated for the next storage phase. The purged fuel vapors are carried by the air stream through purge line  19 , purge valve  15 , air intake passage  9  and to the cylinders where they are consumed as fuel during combustion. 
     During the storage phase, the fuel vapors previously adsorbed by the sorbent material  28  may also return to the fuel tank  8  when the pressure in the tank lowers relative to atmospheric pressure. This happens when the temperature inside the fuel tank  8  drops and the fuel vapors condense. Being normally open, the vent valve  17  under such conditions allows air into the storage canister  10  and relieves any vacuum. 
     Due to the increasingly stringent air quality standards, the automotive industry has pondered several ways of further reducing the emissions of evaporated fuel. Thought has been given to increasing the size or number of compartments in the storage canister  10 . Those approaches have been deemed undesirable due to excessive cost and bulk. Various proposals for heating the storage canister  10  electrically have also been considered. Those approaches have also proved undesirable due to the electrical power they would require. 
     OBJECTIVES OF THE INVENTION 
     It is therefore an objective of the invention to reduce emissions of evaporated fuel from a motor vehicle to levels lower than previously achievable. 
     Another objective is to provide an evaporative emission control system having improved diurnal performance. 
     Still another objective is to capture minute breakthrough emissions from an evaporative emission control system. 
     A further objective is to enable the use of modern internal combustion engine fuels having increased volatility without increasing evaporative emissions. 
     An additional objective is to provide heat to assist the endothermic desorption process in an evaporative emission control system. 
     Yet another objective is to desorb adsorbed water from high retentivity carbon in an evaporative emission control system. 
     Yet another objective is to provide an evaporative emission control system for a motor vehicle having a superabsorber that is protected from contamination during fueling. 
     An additional objective is to provide an evaporative emission control system that employs heat to assist desorption of vapor and which minimizes electrical heating requirements. 
     Another objective is to provide an evaporative emission control system that reduces emissions to ultra-low levels, and one that is rugged and easy to maintain. 
     A further objective is to reduce the amount of partitioning needed in storage canisters used in such evaporative emission control systems. 
     Yet a further objective is to reduce the size of storage canisters used in such evaporative emission control systems. 
     An additional objective is to reduce the volume of purge air required in such evaporative emission control system. 
     Another objective is to achieve ultra-low evaporative emission levels while reducing the need to use fuel having low values of REID vapor pressure. 
     A further objective of the invention is to provide a refueling bypass to reduce air pressure in the fuel tank during refueling to prevent shutoff of the refueling nozzle. 
     An additional objective of the invention is to reduce contamination of the auxiliary canister by refueling vent flow. 
     In addition to the objectives and advantages listed above, various other objectives and advantages of the invention will become more readily apparent to persons skilled in the relevant art from a reading of the detailed description section of this document. The other objectives and advantages will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein. 
     SUMMARY OF THE INVENTION 
     The foregoing objectives and advantages are attained by an evaporative emissions control system that reduces the amount of fuel vapor emitted from a vehicle to very low levels. The vehicle has an engine with an intake passage and a fuel system. According to the invention, the control system comprises a primary canister and an auxiliary canister. The primary canister has a purge port, a tank port and a vent port in communication with a first sorbent material disposed within the primary canister. The purge port communicates with the intake passage via a purge valve. The tank port communicates with the fuel system and allows a mixture of air and the fuel vapor it carries to be conveyed between the fuel system and the primary canister. The auxiliary canister has a first flow passage and a second flow passage in communication with a second sorbent material disposed within the auxiliary canister. The first flow passage connects to the vent port of the primary canister, and the second flow passage connects to one end of a vent valve whose other end communicates to atmosphere. The auxiliary canister has a heater and an electrical connector connected to a source of electrical power onboard the vehicle. During at least one predetermined time interval, electrical power is supplied to the heater to heat the second sorbent material when the control system is operated in a regenerative phase of operation. During a storage phase of operation, the control system allows the mixture of air and fuel vapor to flow from the fuel system through the tank port and into the primary canister. As the mixture flows through the primary canister, the first sorbent material adsorbs a first percentage of the fuel vapor. The mixture of air and any unadsorbed fuel vapor then flows out the vent port and through the first flow passage into the auxiliary canister. As the once filtered mixture flows through the auxiliary canister, the second sorbent material adsorbs a second percentage of the fuel vapor, with the now twice-filtered air flowing out the second flow passage and through the vent valve it to atmosphere. During the regenerative phase, the control system allows air drawn in from atmosphere to flow through the vent valve and second flow passage into the auxiliary canister. As the air flows through the auxiliary canister, fuel vapor is desorbed from the second sorbent material, particularly during the predetermined interval when it is heated. The warmed mixture of air and fuel vapor is then drawn through the first flow passage and vent port into the primary canister. As the mixture flows through the primary canister, fuel vapor is desorbed from the first sorbent material. The mixture is drawn out through the purge port and into the intake passage by and for combustion within the engine of the vehicle. 
     In a related aspect, the invention provides an auxiliary canister for use with a storage canister of an evaporative emissions control system to aid in reducing the amount of fuel vapor emitted from a vehicle. The storage canister has a vent port in communication with a first sorbent material housed in the storage canister. The auxiliary canister comprises an enclosure, a second sorbent material, first and second flow passages, a heater and an electrical connector. The second sorbent material is disposed within the enclosure and is in thermal contact with the heater. The first flow passage at one end is attached to a bottom of the enclosure. At its other end, the first flow passage is connectable to the vent port so as to allow flow between the storage and auxiliary canisters. Attached at one end to a top of the enclosure, the second flow passage is connectable at its other end to a vent valve of the control system so as to allow flow between the auxiliary canister and the vent valve. Incorporated into the enclosure, the electrical connector is used to convey electrical power from the vehicle to the heater to heat the second adsorbent material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art storage canister used to reduce emissions of evaporated fuel. 
     FIG. 2 is a schematic cross-sectional view showing the interior of the prior art storage canister shown in FIG.  1 . 
     FIG. 3 is a perspective view of the prior art storage canister shown in FIG. 1 deployed with an auxiliary canister according to the invention. 
     FIG. 4 is a perspective view of the case of the auxiliary canister illustrated in FIG.  3 . 
     FIG. 5 is a perspective view of a cover and one flow passage of the auxiliary canister shown in FIG.  3 . 
     FIG. 6 is a perspective view of a preferred embodiment of a heater for the auxiliary canister. 
     FIG. 7 is a perspective view of an alternative embodiment of a heater for the auxiliary canister. 
     FIG. 8 is a view of another embodiment of a heater for the auxiliary canister. 
     FIG. 9 is a cross-sectional view of an additional embodiment of a heater within the auxiliary canister. 
     FIG. 10 is a cross-sectional view of an embodiment of the invention showing the auxiliary canister and the prior art storage canister deployed as shown in FIG.  3 . 
     FIG. 11 is a cross-sectional view of another embodiment of the invention illustrating a refuel-bypass valve deployed as a bypass to protect the sorbent material in the auxiliary canister from contamination during refueling. 
     FIG. 12 is a cross-sectional view of another embodiment illustrating the refuel-bypass valve deployed to protect the auxiliary canister during refueling and to simplify testing of the overall system for leaks. 
     FIG. 13 is a cross-sectional view of another embodiment of the invention showing a purge-bypass valve deployed to reduce contamination of the auxiliary canister during the purge cycle. 
     FIG. 14 is a cross-sectional view of another embodiment in which both the refuel-bypass valve and the purge-bypass valve protect the auxiliary canister from contamination during both the purge cycle and refueling. 
     FIG. 15 is a cross-sectional view of another embodiment in which the refuel-bypass and purge-bypass valves are deployed to protect the auxiliary canister from contamination during both refueling and the purge cycle and to simplify leak testing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before describing the invention in detail, the reader is advised that, for the sake of clarity and understanding, identical components having identical functions have been marked where possible with the same reference numerals in each of the Figures provided in this document. 
     As noted in the background section of this document, FIGS. 1 and 2 show a prior art storage canister  10  and its various ports. Attention is now directed to FIGS. 3 through 5, which show a presently preferred embodiment of the invention. An auxiliary canister  30  is shown in these figures. The purpose of auxiliary canister  30  is to function in cooperation with the primary storage canister  10  to reduce emissions of fuel vapor to in levels much lower than was possible with the canister  10  alone. The sorbent material contained within the auxiliary canister  30  is heated during at least one time when the engine  90  of vehicle  11  is running, to facilitate purging of sorbed fuel vapors. 
     The auxiliary canister  30  has an enclosure  29  inclusive of a case  32  and a lid  38 . Viewed from the perspective of FIG. 4, case  32  has a first flow passage  34  attached to its bottom and an electrical connector  36  incorporated within its side. The first flow passage  34  is designed to attach to vent port  16  of storage canister  10 , as shown in FIG.  3 . The electrical connector  36  is connected to a heater located inside the case  32 . As described further below, electrical power is conveyed from the vehicle to the heater through this electrical connector  36 . The lid  38  affixes atop case  32 . Projecting from the top of lid  38  is a second flow passage  40 , as shown in FIG.  5 . 
     FIGS. 6 through 9 show alternative designs for the heater and sorbent material to be used within the auxiliary canister  30 . FIG. 6 shows the presently preferred embodiment, which is a honeycomb heater  42  having surfaces  48  and a layer of sorbent material  46  on surfaces  48 . Preferably, the heater  42  is an electrically conducting ceramic and the sorbent material  46  is an activated carbon. Persons skilled in the automotive engine arts will recognize that heater  42  may be made by technology available in positive temperature control devices. Preferably, sorbent material  46  consists of granules of activated carbon cemented to surfaces  48  by an acrylic cement. 
     The sorbent material  46  may be standard automotive carbon. Preferably, however, the sorbent material  46  has a higher surface (i.e., a greater surface area per unit mass) and lower density than standard automotive carbon. Sorbent material  46  may, for example, be the type of activated carbon that is usually employed in gas masks. Because the density of the sorbent material is low, its thermal conductivity is also low. The design of the heater  42  places the sorbent material  46  in direct thermal contact with surfaces  48  to ensure heating of the sorbent material  46 . 
     FIG. 7 shows an alternative design for the heater, one employing a cylindrical shape. The cylindrical heater  44  has an inner surface  50  and an outer surface  52 . Sorbent material  46  is placed on one or both of the surfaces  50  and  52 . This design places sorbent material  46  in direct thermal contact with one or both surfaces  50  and  52 . The cylindrical heater  44  itself is preferably composed of an electrically conducting ceramic. 
     FIG. 8 depicts another design for the heater, one having a planar portion  82  from which one or more fin(s)  84  project. The planar portion  82  is preferably an electrical resistor. From the resistor  82  projects at least one fin  84  having sorbent material  46  adhered to one or both of its surfaces  85 . The fin(s)  84  of this planar heater  80  are preferably made of a high conductivity material, such as aluminum. 
     FIG. 9 shows yet another heater design, one that employs convection to carry heat from the heater  86  to the sorbent material  46 . Again, the sorbent material  46  is preferably a low density, high surface activated carbon. 
     FIG. 10 illustrates a cross-sectional view of the preferred embodiment of the invention showing how the auxiliary canister  30  and the prior art storage canister  10  are deployed together. Although heater  42  is depicted, it should be apparent that any of the others heaters described above may take its place. During the storage phase when the engine  90  is off, the system operates with the purge valve  15  closed and the vent valve  17  opened. When the pressure in the fuel tank  8  is high relative to atmospheric pressure, air from the tank and the fuel vapor it carries flows into the tank tube  7  and through tank port  12  into storage canister  10 . Inside the storage canister  10 , the fuel vapor is adsorbed (as described above) as the mixture of fuel vapor and air flows through the sorbent material  46 . Although the storage canister  10  adsorbs a high percentage of the fuel vapor, the air stream still carries some fuel vapor as it passes from vent port  16  into the auxiliary canister  30  via first flow passage  34 . The sorbent material  46  in case  32  of the auxiliary canister  30  extracts even more fuel vapor, as the air passes through the enclosure  29  out second flow passage  40  through vent valve  17  to atmosphere. 
     During the regenerative phase of operation when the engine  90  is running, the vacuum developed by the engine draws in air from the vent valve  17  through vent line  6  and second flow passage  40  into the auxiliary canister  30 . Before this “purge air” is pulled into the vent port  16  of storage canister  10 , it passes through the case  32  of the auxiliary canister  30 . There it flows through whichever one of the heaters  42 ,  44 ,  80  or  86  is deployed in case  32 . The heater is preferably activated only during one or more predetermined time intervals when the engine is running. The engine control module (ECM) or other control component (not shown) in the vehicle  11  may be used to define or otherwise control the time interval during which power is supplied to the heater. Selecting an interval that encompasses the period of time soon after the engine is first started is just one option. During the selected interval, electrical power is supplied to the heater  86  via electrical connector  36 . The resulting heat is carried to the sorbent material  46 , further enhancing its ability to give up the fuel vapors it previously adsorbed. As the air passes over the sorbent material  46 , it carries with it the evaporated fuel. Some of the heat generated by the heater is also imparted to the passing air stream. 
     The vacuum drives the air and fuel vapor it collected from the auxiliary canister  30  through first flow passage  34  into the storage canister  10  via vent port  16 . The warmed purge air continues through second compartment  22 , flow passage  26 , first compartment  20  and out purge port  14 . Inside the storage canister  10 , the warmth of the passing purge air enables the sorbent material  28  to give up its fuel vapors more readily. Stripped of the fuel vapor that it had adsorbed during the previous storage cycle, the sorbent material  28  is thus regenerated for the next storage phase. The purged fuel vapors are carried by the air stream through purge line  19 , purge valve  15 , air intake passage  9  and ultimately to the cylinders where they are consumed as fuel during combustion. 
     Deployed together, the auxiliary canister  30  and the prior art storage canister  10  may be viewed as essentially two containment portions  18  and  29 . As shown in perspective in FIG.  3  and in cross-section in FIGS. 10-15, the two containment portions  18  and  29  are interconnected by vent port  16  and first flow passage  34 . As is apparent from the foregoing paragraphs, the auxiliary canister  30  operates in such a way as to improve the efficiency of the storage canister  10  with which it is used. Moreover, it also reduces evaporative emissions by itself through its heater and sorbent material  46 . The improvement in the operation of the storage canister  10  is due mostly to the heated purge air that the auxiliary canister  30  passes to the sorbent material  28  during the regenerative phase of operation. Together, the two canisters  10  and  30  further reduce the amount of fuel vapor that a vehicle emits to the atmosphere, as compared to prior art approaches. 
     To reduce power requirements, it is preferred that the mass of the sorbent material  46  in auxiliary canister  30  be substantially smaller than the mass of sorbent material  28  in storage canister  10 . Preferably, the mass of sorbent material  46  is less than one tenth of the mass of sorbent material  28 . For the embodiments shown in FIGS. 6-8 in which the sorbent material  46  is a thin layer on surfaces  48 ,  50 ,  52  or  85 , the mass of sorbent material  46  may be less than one percent of the mass of sorbent material  28 . 
     FIG. 11 shows a refuel-bypass valve  60  added to the embodiment of the invention shown in FIG.  10 . The storage canister  10  of FIG. 10 is also modified to include a first bypass port  61 . Preferably, a flow restrictor  35 , such as an orifice, is provided within either the first flow passage  34  of canister  30  or the vent port  16  of canister  10 . The bypass port  61  communicates with the second compartment  22  preferably to the left of vent port  16 , as viewed from the perspective of FIG.  11 . The bypass valve  60  is connected at one end to the bypass port  61 , and its other end is open to atmosphere. Deployed as shown, the bypass valve  60  should be normally closed, opening only when a slight positive pressure exists within the second compartment  22  of storage canister  10 . 
     During refueling of a fuel tank, pressure in the fuel tank rises. As the pressure rises, air from the tank carries fuel vapor into tank tube  7  and through tank port  12  into the storage canister  10 . As soon as the pressure in the second compartment  22  rises above a set threshold relative to atmospheric pressure, the bypass valve  60  opens. As long as it stays open, the bypass valve  60  and port  61  allow the air and the unadsorbed fuel vapor to flow from the second compartment  22  to atmosphere, largely bypassing the auxiliary canister  30 . Without bypass valve  60 , the fuel vapor that is not adsorbed by the sorbent material  28  within canister  10  would flow into the auxiliary canister  30 . By permitting some of the unadsorbed evaporate to bypass the auxiliary canister  30 , the bypass valve  60  reduces the degree to which the sorbent material  46  in auxiliary canister  30  is contaminated during refueling. 
     The bypass valve  60  serves an additional purpose. By providing a low impedance path to the atmosphere, the air pressure in the fuel tank during refueling is reduced. This is desirable because air pressure sensed by the refueling nozzle is, in some refueling stations, used to determine that the tank is full. Premature shutoff of the refueling nozzle may occur if air pressure in the fuel tank increases excessively. 
     FIG. 12 illustrates a variation on the embodiment shown in FIG.  11 . In this case, the bypass valve  60  is connected by bypass passage  62  to the vent line  6  leading to vent valve  17 . This arrangement simplifies testing the system for leaks. During a leak test, the purge valve  15  and the vent valve  17  are both closed after a partial vacuum has been applied to the system. By connecting the outlet of the bypass valve  60  to the vent valve  17 , the bypass valve  60  cannot leak to atmosphere, as would be the case for the embodiment shown in FIG.  11 . 
     FIG. 13 shows an optional purge-bypass valve  70  added to the embodiment shown in FIG.  10 . The canister  10  of FIG. 10 is also modified to include a second bypass port  71 . Preferably, the flow restrictor  35  is provided within either the first flow passage  34  of canister  30  or the vent port  16  of canister  10 . The bypass port  71  communicates with second compartment  22  preferably to the left of vent port  16 , as viewed from the perspective of FIG.  13 . The bypass valve  70  is connected at one end to bypass port  71  and at its other end via bypass line  72  to the vent line  6  leading to vent valve  17 . 
     The bypass valve  70  is normally closed, opening only when a slight negative pressure exists within the second compartment  22  of canister  10 . As soon as the pressure in the second compartment  22  falls below a preset threshold relative to atmospheric pressure, the bypass valve  70  opens and thereby reduces the volume of purge air passing through the auxiliary canister  30 . The restrictor  35  also contributes in that regard. Together, their main function is to reduce the degree to which the sorbent material  46  in canister  30  will be contaminated with. particulates and other outside matter drawn in from the atmosphere. This arrangement may be used to make it unnecessary to supply electrical power to auxiliary canister  30  during the entire time the engine of the vehicle is running. 
     FIG. 14 illustrates an embodiment in which both the refuel-bypass and purge-bypass valves  60  and  70  are added to the invention shown in FIG.  10 . The restrictor  35  is also featured. Bypass valve  60  is connected at one end to the bypass port  61  and at its other end to atmosphere. Bypass valve  70  is connected at one end to bypass port  71  and at its other end via bypass line  72  to the vent line  6  into vent valve  17 . This alternative embodiment protects the auxiliary canister  30  from contamination during refueling and the purge cycle. 
     FIG. 15 illustrates a variation on the embodiment shown in FIG.  14 . In this case, however, the outlet of both bypass valves  60  and  70  are connected via passage  62  and line  72  to the vent line  6 . This embodiment not only protects the auxiliary canister  30  from contamination during the purge cycle and refueling but also simplifies testing the system for leaks. 
     The preferred and alternative embodiments for carrying out the invention have been set forth in detail above according to the Patent Act. Persons of ordinary skill in the art to which this invention pertains may nevertheless recognize that the invention may be modified and/or adapted in various ways without departing from the spirit and scope of the following claims. Persons of such skill will also recognize that the foregoing description is merely illustrative and not intended to limit any of the claims to any particular narrow interpretation.