Patent Publication Number: US-6901786-B2

Title: Fueling system vapor recovery and containment leak detection system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 09/725,727, filed on Nov. 30, 2000 now U.S. Pat. No. 6,622,751, which is an application that relates to and claims priority to (1) U.S. Provisional Patent Application Ser. No. 60/168,029, filed on Nov. 30, 1999, entitled “Fueling System Vapor Recovery Performance Monitor;” (2) U.S. Provisional Patent Application Ser. No. 60/202,054, filed on May 5, 2000, entitled “Fueling System Vapor Recovery Performance Monitor;” and (3) U.S. Provisional Patent Application Ser. No. 60/202,659, filed on May 8, 2000, entitled “Method of Determining Failure of Fuel Vapor Recovery System.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a fueling system vapor recovery and containment leak detection system. 
     BACKGROUND OF THE INVENTION 
     Gasoline dispensing facilities (i.e. gasoline stations) often suffer from a loss of fuel to the atmosphere due to inadequate vapor collection during fuel dispensing activities, excess liquid fuel evaporation in the fuel and vapor containment system storage tank (hereinafter referred to as “storage tank”), and inadequate reclamation of the vapors during tanker truck deliveries. Lost vapor is an air pollution problem that is monitored and regulated by both federal and state governments. Attempts to minimize losses to the atmosphere have been effected by various vapor recovery methods. Such methods include: “Stage-I vapor recovery” where vapors are returned from the vapor containment system to the delivery truck; “Stage-II vapor recovery” where vapors are returned from the refueled vehicle tank to the vapor containment system; vapor processing where the fuel/air vapor mix from the vapor containment system is received and the vapor is liquefied and returned as liquid fuel to the vapor containment system; burning excess vapor off and venting the less polluting combustion products to the atmosphere; and other fuel/air mix separation methods. 
     A “balance” Stage-II vapor recovery system may make use of a dispensing nozzle bellows seal to the vehicle tank filler pipe opening. This seal provides an enclosed space between the vehicle tank and the vapor recovery system. During fuel dispensing, the liquid fuel entering the vehicle tank creates a positive pressure which pushes out the ullage space vapors through the bellows sealed area into the nozzle vapor return port, through the dispensing nozzle and hose paths, and on into the storage tank. 
     It has been found that even with these measures, substantial amounts of hydrocarbon vapors are lost to the atmosphere, often due to poor equipment reliability and inadequate maintenance. This is especially true with Stage-II systems. One way to reduce this problem is to provide a vapor recovery system monitoring data acquisition and analysis system to provide notification when the system is not working as required. Such monitoring systems may be especially applicable to Stage-II systems. 
     When working properly, Stage-II vapor recovery results in substantially equal or designed exchanges of air or vapor (A) and liquid (L) between the storage tank and the consumer&#39;s gas tank. The notation “A” and the terms “air” and “vapor” are used loosely and interchangeably herein (and throughout) to refer to air and fuel vapor mix being returned from the refueled vehicle tank to the storage tank. Ideally, Stage-II vapor recovery produces an air-to-liquid (A/L) ratio very close to 1. In other words, returned vapor replaces an equal or substantially equal amount of liquid in the storage tank during refueling transactions. When the A/L ratio is close to 1, refueling vapors are collected, the ingress of fresh air into the vapor containment system is minimized and the accumulation of an excess of positive or negative pressure in the vapor containment system is prevented. This minimizes losses at the dispensing nozzle and fuel evaporation in the storage tank and leakage of excess vapors from the vapor containment system. Measurement of the A/L ratio thus provides an indication of proper Stage-II vapor collection operation. A low ratio means that vapor is not moving properly through the dispensing nozzle, hose, or other part of the system back to the storage tank, possibly due to an obstruction or defective component. 
     Recently, the California Air Resources Board (CARB) has been producing new requirements for Enhanced Vapor Recovery (EVR) equipment. These include stringent vapor recovery system monitoring and In-Station Diagnostics (ISD) requirements to continuously determine whether or not the systems are working properly. CARB has proposed that, when the A/L ratio drops below a prescribed limit for a single or some sequence of fueling transactions, an alarm be issued and the affected fueling point be disabled to allow repair to prevent further significant vapor losses. The proposed regulations also specify an elaborate and expensive monitoring system with many sensors that will be difficult to wire to a common data acquisition system. 
     The CARB proposal requires that A/L volume ratio sensors be installed at each dispensing hose or fuel dispensing point and pressure sensors be installed to measure the containment system vapor space pressure. The sensors would be wired to a common data acquisition system used for data logging, storage, and pass/fail analysis. It is likely that such sensors would comprise air-flow sensors (AFSs). 
     However, one issue that may occur in such a vapor recovery system employing AFS&#39;s is that a leak may occur in the vapor return passage or vapor return pipe where vapors are recovered and returned to the storage tank. If a leak occurs in the vapor return passage or vapor return pipe for a dispensing point, vapors are likely to escape outside of the vapor containment system to atmosphere thereby defeating the purpose of containing such vapors and returning them back to the underground storage tank. One method of detecting a possible leak in a vapor recovery system is to monitor the A/L ratio using an AFS for an active dispensing point to determine if the actual vapor being recovered is equal or substantially equal to the expected amount. However, this method does not always work. 
     For example, a defective air valve in the nozzle or vapor return pipe of a dispensing point may not close properly to block reverse vapor flow (i.e. out of the nozzle) when the dispensing point is idle. In such a case, the A/L ratio for the defective dispensing point will not be affected, because when the dispensing point is active, the vapor flow is normal and as expected. 
     Therefore, it may be desirable to include as part of a vapor recovery system employing AFS&#39;s the ability to detect leak conditions for dispensing points where determination of the A/L ratio for a dispensing point will not effectively detect such a leak. 
     SUMMARY OF THE INVENTION 
     The present invention relates to detection of a leak in a dispensing point, including the vapor return passage or a vapor return pipe coupled to the dispensing point, in a fuel dispenser vapor recovery system. An air-flow sensor (AFS), which may also be termed a “vapor flow sensor,” is used to detect either vapor or air flowing in either the vapor return passage or the vapor return pipe of the vapor recovery system. The vapor return passage is the conduit for each individual dispensing point where recovered vapors are passed. All vapor return passages for each dispensing point are coupled into a common vapor return pipe coupled to the storage tank. In this manner, recovered vapors are captured and placed in the vapor return passage, which in turn transports the vapors to the vapor return pipe and on to the storage tank. 
     In general, if vapor is detected flowing at a dispensing point either in the direction of the nozzle to the storage tank, called “forward vapor flow,” or in the direction of the storage tank to the nozzle, called “reverse vapor flow,” this is an indication that a leak is present at such dispensing point. The AFS registers air from the leaking dispensing point as either the ingestion of air at the dispensing point or the egress of air out of the dispensing point depending on the pressure differential between the leak point in the dispensing point and the storage tank. The leak may be due to a defective air-valve in the nozzle, or a loose or defective fitting or coupling at the nozzle or in the hose and fuel conduit coupled to the nozzle, that does not properly close when the dispensing point is idle, or the leak may be due to a leak in the hose connected to the nozzle or anywhere in the vapor return passage between the nozzle and the AFS. 
     In one embodiment of the present invention, the AFS is placed in each vapor return passage coupled to one or more dispensing points in a fuel dispenser. In this manner, the AFS registers vapor flow recovered by each individual dispensing point. If the AFS registers vapor flow when such one or more dispensing points are idle, a leak is present at a dispensing point coupled to the AFS. If the vapor or air flow detected by the AFS is “forward vapor flow,” this is indicative of outside air being ingressed into the leak point of the dispensing point. If the vapor flow detected by the AFS is “reverse vapor flow,” this is indicative of vapor from the storage tank being egressed out of the leak point of the dispensing point. 
     In a second embodiment of the present invention, an AFS is placed in the common vapor return pipe that is coupled to one or more vapor return passages of the individual dispensing points. In this manner, the AFS registers vapor flow for each of the vapor return passages coupled to the vapor return pipe and where such vapor flow passes through the AFS before reaching the storage tank. If the AFS registers vapor flow when all of the dispensing points are idle, then a leak is present at one or more of the dispensing points. If the vapor or air flow detected by the AFS is “forward vapor flow,” this is indicative of outside air being ingressed into the leak point of the dispensing point. If the vapor flow detected by the AFS is “reverse vapor flow,” this is indicative of vapor from the storage tank being egressed out of the leak point of the dispensing point. 
     A combined data acquisition system/in-station diagnostic monitor receives the AFS readings in the aforementioned embodiments and detects the leak condition at the dispensing point. The monitor may generate an alarm and may report the condition to a point-of-sale (POS) system and/or a remote reporting system. The monitor and/or the POS may shut down one or more dispensing points if configured to do so when a leak condition is detected. 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is a schematic view of a fueling system vapor recovery performance monitor in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic view of a fueling system vapor recovery performance monitor in accordance with another embodiment of the present invention; 
         FIG. 3  is a schematic view of a communication architecture between the monitor, the POS controller and a remote reporting system; 
         FIG. 4  is a flowchart diagram of one embodiment of a leak detection system that may be performed in accordance with the embodiment illustrated in  FIG. 1  of the present invention; and 
         FIG. 5  is a flowchart diagram of another embodiment of a leak detection system that may be performed in accordance with the embodiment illustrated in  FIG. 2  of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 09/725,727, filed on Nov. 30, 2000 and incorporated herein by reference in its entirety, which is an application that relates to and claims priority to (1) U.S. Provisional Patent Application Ser. No. 60/168,029, filed on Nov. 30, 1999 entitled “Fueling System Vapor Recovery Performance Monitor” incorporated herein by reference in its entirety; (2) U.S. Provisional Patent Application Ser. No. 60/202,054, filed on May 5, 2000, entitled “Fueling System Vapor Recovery Performance Monitor” incorporated herein by reference in its entirety; and (3) U.S. Provisional Patent Application Ser. No. 60/202,659, filed on May 8, 2000, entitled “Method of Determining Failure of Fuel Vapor Recovery System” incorporated herein by reference in its entirety. 
     The present invention relates to detection of a leak at a dispensing point in in a fuel dispenser vapor recovery system. An air-flow sensor (AFS), which may also be termed a “vapor flow sensor,” is used to detect vapor or air flowing in either the vapor return passage or the vapor return pipe of the vapor recovery system. The vapor return passage is the conduit for each individual dispensing point for a fuel dispenser where recovered vapors are passed. All vapor return passages for each dispensing point are coupled into a common vapor return pipe coupled to the storage tank. In this manner, recovered vapors are captured and placed in the vapor return passage, which in turn transports the vapors to the vapor return pipe and on to the storage tank. The terms “vapor” and “air” are used interchangeably in this application and its claims, and use of one term is also used to represent the other term. 
     In general, if vapor is detected flowing at an idle dispensing point in the direction of the nozzle to the storage tank, called “forward vapor flow,” and the dispensing point is not “active” (i.e. idle), this is an indication that a leak exists at a dispensing point coupled to the AFS. If vapor or air flow is detected flowing at an idle dispensing point in the direction of the nozzle to the storage tank, called “forward vapor flow,” and the dispensing point is not “active,” this is an indication that outside air is being ingressed into the leaking dispensing point. If vapor is detected flowing at a dispensing point in the direction of the storage tank to the nozzle, called “reverse vapor flow,” and the dispensing point is not “active,” this is an indication that vapor from the storage tank is being egressed out of the leaking dispensing point to atmosphere. These aspects of the invention will be further discussed in this application. 
     Before further discussing the details of the leak detection system of the present invention, which are described below and operationally illustrated in  FIGS. 4 and 5 , one embodiment of the vapor recovery and containment monitoring system for use in a liquid fuel dispensing facility of the present invention is described first in FIG.  1 . As illustrated in  FIG. 1 , a dispensing facility  10  is provided that may include a station house  100 , one or more fuel dispenser units  200 , a main fuel storage system  300 , means for connecting the dispenser units  200  to the main fuel storage system  400 , and one or more of the air (or vapor) flow sensors (AFS&#39;s)  500 . 
     The station house  100  may include a central electronic control and diagnostic arrangement  110  that includes a dispenser controller  120 , dispenser current loop interface wiring  130  connecting the dispenser controller  120  with the dispenser unit(s)  200 , and a combined data acquisition system/in-station diagnostic monitor  140 . The dispenser controller  120  may be electrically connected to the monitor  140  by a first wiring bus  122 . The interface wiring  130  may be electrically connected to the monitor  140  by a second wiring bus  132 . The monitor  140  may include standard computer storage and central processing capabilities, keyboard input device(s), and audio and visual output interfaces among other conventional features. 
     The fuel dispenser units  200  may be provided in the form of conventional “gas pumps.” Each fuel dispenser unit  200  may include one or more dispensing points typically defined by the nozzles  210 , also called dispensing points  210 . The fuel dispenser units  200  may include one coaxial vapor/liquid splitter  260 , one vapor return passage  220 , and one fuel supply passage  230  per nozzle  210 . The nozzle  210  or vapor return passage  220  may contain an air-valve  213  that opens when fuel is being dispensed so that the vapor return passage  220  is not open to atmosphere when a dispensing point  210  is not active and recovering vapor. An examples of an air-valve  213  that may be used in the present invention is disclosed in U.S. Pat. No. 5,195,564, which is incorporated herein by reference in its entirety. 
     The vapor return passages  220  may be joined together before connecting with a common vapor return pipe  410 . The units  200  may also include one liquid fuel dispensing meter  240  per nozzle  210 . The liquid fuel dispensing meters  240  may provide dispensed liquid fuel amount information to the dispenser controller  120  via the liquid fuel dispensing meter interface  270  and interface wiring  130 . 
     The main fuel storage system  300  may include one or more storage tanks  310 . It is appreciated that the storage tanks  310  may typically be provided underground, however, underground placement of the tank is not required for application of the invention. An underground or aboveground fuel storage tank is commonly referred to as a “UST” or “AST”, respectively. It is also appreciated that the storage tank  310  shown in  FIGS. 1 and 2  may represent a grouping of multiple storage tanks tied together into a storage tank network. 
     Each storage tank  310 , or a grouping of storage tanks, hereinafter referred to as “storage tank  310 ”, may be connected to the atmosphere by a vent pipe  320 . The vent pipe  320  may terminate in a pressure relief valve  330 . A vapor processor  340  may be connected to the vent pipe  320  intermediate of the storage tank  310  and the pressure relief valve  330 . A pressure sensor  350  may also be operatively connected to the vent pipe  320 . Alternately, it may be connected directly to the storage tank  310  or the vapor return pipe  410  below or near to the dispenser  200  since the pressure is normally substantially the same at all these points in the vapor containment system. 
     The storage tank  310  may also include an Automatic Tank Gauging System (ATGS)  360  used to provide information regarding the fuel level in the storage tank  310 . The vapor processor  340 , the pressure sensor  350 , and the automatic tank gauging system  360  may be electrically connected to the monitor  140  by third, fourth, and fifth wiring busses  342 ,  352 , and  362 , respectively. The storage tank  310  may also include a fill pipe and fill tube  370  to provide a means to fill the tank with fuel and a submersible pump  380  to supply the dispensers  200  with fuel from the storage tank  310 . 
     The means for connecting the dispenser units  200  and the main fuel storage system  400  may include one or more vapor return pipelines  410  and one or more fuel supply pipelines  420 . The vapor return pipelines  410  and the fuel supply pipelines  420  are connected to the vapor return passages  220  and fuel supply passages  230 , respectively, associated with multiple dispensing points  210 . As such, a “vapor return pipeline”  410  designates any return pipeline that carries the return vapor of two or more vapor return passages  220 . 
     In this embodiment, the AFS  500  is operatively connected to a common vapor return pipeline  410 . Thus, the AFS  500  must be operatively connected to the vapor return system downstream of the vapor return passages  220  for each of the fuel dispensers  200 . Each AFS  500  may be electrically connected to the monitor  140  by a sixth wiring bus  502 . 
     In order to determine the acceptability of the performance of vapor recovery in the facility  10 , the ratio of vapor flow to dispensed liquid fuel is determined for each fuel dispensing point  210  included in the facility  10 . This ratio may be used to determine if the fuel dispensing point  210  in question is in fact recovering an equal volume of vapor for each unit volume of liquid fuel dispensed by the dispensing point  210 . 
     In  FIG. 1 , each dispensing point  210  is served by an AFS  500  that is shared with at least one other dispensing point  210 . Mathematical data processing may be used to determine an approximation of the vapor flow associated with each dispensing point  210 , as is described in the parent application of the present invention, U.S. patent application Ser. No. 09/725,727, filed on Nov. 30, 2000, entitled “Fueling System Vapor Recovery and Containment Performance Monitor and Method of Operation Thereof,” incorporated herein by reference in its entirety. 
     The amount of fuel dispensed by each dispensing point  210  is known from the liquid fuel dispensing meter  240  associated with each dispenser unit  200 . Amount of fuel (i.e. fuel volume) information may be transmitted from each dispensing meter  240  to the dispenser controller  120  for use by the monitor  140 . In an alternative embodiment of the invention, the dispensing meters  240  may be directly connected to the monitor  140  to provide the amount of fuel information used to determine the A/L ratio for each dispensing point  210 . 
     The AFS  500  measures multiple (at least two or more) dispensing point  210  return vapor flows. In the embodiment of the invention shown in  FIG. 1 , a single AFS  500  measures all the dispensing point  210  vapor flows for the facility  10 . In the case of a single AFS  500  per facility  10 , the AFS  500  is installed in the single common vapor return pipeline  410  which runs between all the dispensers  200  as a group, which are all tied together into a common dispenser manifold pipe, and all the storage tanks  310  as a group, which are all tied together in a common tank manifold pipe. Various groupings of combinations of feed dispensing point  210  air flows per AFS  500  are possible which fall between these two extremes described. 
       FIG. 2  illustrates a second embodiment of the vapor recovery and containment monitoring system for use in a liquid fuel dispensing facility  10  according to the present invention. In  FIG. 2 , multiple AFS&#39;s  500  are illustrated as deployed to measure various groupings of dispensing point  210  vapor flows, down to a minimum of only two dispensing point  210  vapor flows. One AFS  500  is installed in each dispenser housing  200 , which typically contains two dispensing points  210  (one dispensing point per dispenser side) or up to 6 dispensing points  210  (hoses) in Multi-Product Dispensers (MPDs) (3 dispensing points  210  per side of the dispenser  200 ). The vapor flows piped through the vapor return passage  220  may be tied together to feed the single AFS  500  in the dispenser housing  200 . 
     As stated above, the monitor  140  may connect to the dispenser controller  120 , directly to the current loop interface wiring  130  or directly to the liquid fuel dispensing meter  240  to access the liquid fuel flow volume readings. The monitor  140  may also be connected to each AFS  500  at the facility  10  so as to be supplied with vapor flow amount (i.e. vapor volume) information. The liquid fuel flow volume readings are individualized fuel volume amounts associated with each dispensing point  210 . The vapor flow volume readings are aggregate amounts resulting from various groupings of dispensing point  210  vapor flows, which therefore require mathematical analysis to separate or identify the amounts attributable to the individual dispensing points  210 . This analysis may be accomplished by the monitor  140  and may include processing means. 
     Once the vapor flow information is determined for each dispensing point  210 , the A/L ratios for each dispensing point  210  may be determined and a pass/fail determination may be made for each dispensing point based on the magnitude of the ratio. It is known that the ratio may vary from 0 (bad) to around 1 (good), to a little greater than 1 (which, depending upon the facility  10  design, can be either good or bad), to much greater than 1 (typically bad). This ratio information may be provided to the facility operator via an audio signal and/or a visual signal through the monitor  140 . The ratio information may also result in the automatic shut down of a dispensing point  210 , or a recommendation for dispensing point  210  shut down. 
     The embodiments of the invention shown in  FIGS. 1 and 2  may provide a significant improvement over known systems due to the replacement of the multiple AFSs  500  (one per dispensing point, typically anywhere from 10 or 12 up to 30 or more per site) and their associated wiring with a single, or fewer AFSs  500  (about 2 as many or less, depending upon dispensing point groupings). 
       FIG. 3  illustrates a possible communication architecture that is used to report information and alarms by the monitor  140  to another system. For example, the monitor  140  may be communicatively coupled to a point-of-sale (POS)  600  using a communication line  602 . The communication line  602  may be any type of communication line, including but not limited to a current loop, LAN, or Ethernet. In this manner, the monitor  140  can report information and other alarms, including information received from AFSs  500 , to the POS  600 . The monitor  140  can also retrieve metering data relating to the fuel dispensers  200  from the POS  600  since the monitor  140  uses this information for fuel storage system  300  calibration as is described in U.S. Pat. Nos. 4,977,528; 5,544,518; and 5,665,895, which are incorporated herein by reference in their entireties. The POS  600  can in turn communicate such information to a remote reporting system  604  over a communication line  606 , which may be a physical line or wireless or satellite communication. Alternatively, the monitor  140  may communicate directly to the remote reporting system  604  using its own dedicated communication line  608 . Again, communication lines  606 ,  608  may be any type including but not limited to a current loop, LAN, and Ethernet. The remote reporting system  604  may be located anywhere including off site from the fueling facility  10 . It is desired to detect any leaks that occur in the vapor return passage  220  at any of the dispensing points  210  so that such leaks can be reported and repaired as soon as possible. The leak at a dispensing point  210  may be present anywhere between the nozzle  210  and an AFS  500 , including the vapor return passage  220  and the vapor return pipeline  410 . In  FIG. 1 , the AFS  500  registers any vapor flow that occurs as a result of any of the dispensing points  210  recovering vapor. For instance, in  FIG. 1 , the AFS  500  is placed in the common vapor return pipe  410  in between the vapor return passages  220  of the dispensing points  210  and the storage tank  310 . In this manner, any vapor that is recovered by any of the dispensing points  210  enters into the vapor return pipe  410  and passes through the AFS  500  for registering vapor flow before such vapors reach the storage tank  310 . If the AFS  500  registers vapor flow when all of the dispensing points  210  coupled to the AFS  500  are idle, meaning not actively recovering vapor, this is indicative of a leak somewhere in one or more of the dispensing points  210  coupled to the AFS  500 . This is because vapor flow should not be registered by the AFS  500  when the dispensing points  210  coupled to the AFS  500  are idle. The leak may be anywhere in the dispensing point  210  between the nozzle  210  and the AFS  500 . 
     Either “forward vapor flow” or “reverse vapor flow,” as previously described above, will occur at the AFS  500  if a dispensing point  210  coupled to the AFS  500  contains a leak, and there is a pressure differential between the storage tank  310  and the dispensing point  210 . If the storage tank  310  is under a lower pressure than a dispensing point  210  containing a leak, outside air will be ingressed through the leak in the dispensing point  210  thereby causing the AFS  500  to register “forward vapor flow.” If the dispensing point  210  containing a leak is under a lower pressure than the storage tank  310 , vapor from the storage tank  310  will egress out of the leak at the dispensing point  210  thereby causing the AFS  500  to register “reverse vapor flow.” 
     By way of additional examples, if the pressure in the vapor return pipe  410  is negative, excess air from the outside may be drawn into or ingressed into the vapor return pipe  410  and possibly returned to the storage tank  310  thereby causing the pressure inside the storage tank  310  to rise. In this instance, the AFS  500  will register “forward vapor flow,” as previously described above. If an air-valve  213  in a dispensing point  210  is defective by remaining open when the dispensing point  210  is idle and the pressure in the storage tank  310  is higher than the pressure at the dispensing point  210 , vapor from the storage tank  310  may egress through the defective air-valve  213  to atmosphere. In this instance, the AFS  500  will register “reverse vapor flow,” as previously described above. Note that a defective dispensing point  210  may also be a leak caused by a loose or defective fitting or coupling at the nozzle, in the hose and fuel conduit coupled to the nozzle, or anywhere between the nozzle  210  and the AFS  500 , which will also cause vapor from the storage tank  310  to egress through the defective dispensing point  210 . The term defective dispensing point  210  encompasses all of the aforementioned types of leaks at a dispensing point  210 . 
     The flowchart in  FIG. 4  illustrates the embodiment performed by the monitor  140  illustrated in  FIG. 1  wherein one AFS ( 500 ) is located in the vapor return pipe  410  for all dispensing points  210 , but such processing could also be performed by any control system that is capable of communicating with the AFS  500  to determine vapor flow as well as having knowledge of the state, idle or active, of the dispensing points  210 . As illustrated in  FIG. 4 , the process starts (block  1000 ), and the monitor  140  determines if all dispensing points  210  coupled to an AFS  500  are idle (decision  1002 ). If not, the process goes back to decision  1002  again in a repeating fashion. If all of the dispensing points  210  coupled to an AFS  500  are idle (decision  1002 ), the monitor  140  determines if the AFS  500  is or has registered vapor flow (decision  1004 ). If not, this means that no leak indication is present since no vapor flow is occurring at an idle dispensing point  210 , and the process goes back to decision  1002  to continue repeating the process. 
     If the monitor  140  determines that vapor or air flow is or has been registered by the AFS  500  (decision  1004 ), the monitor  140  sets a leak alarm for the dispensing points  210  that are coupled to the AFS  500  (block  1006 ). This is because a registered vapor or air flow by the AFS  500  when all dispensing points  210  coupled to such AFS  500  are idle is indicative of a leak. The monitor  140  may also be configured, in response to detection of a leak at a dispensing point  210 , to cause such dispensing point  210  where a leak is detected to shut down or remain idle until the leak detection condition can be further analyzed and/or repaired. 
     Next, the monitor  140  determines if the vapor flow is flowing in the forward or reverse direction via vapor or air flow direction information received from the AFS  500  (decision  1008 ). If the AFS  500  detects “forward vapor flow,” the monitor  140  additionally reports a “forward vapor flow” as being indicative that outside air is being ingested through the leak in the dispensing point  210  and being returned to the vapor return pipe  410  and storage tank  310  (block  1010 ). “Forward vapor flow” is caused by the pressure at the dispensing point  210  being at a higher pressure level than the pressure level in the vapor return pipe  410  and the storage tank  310 . If the AFS  500  detects a “reverse vapor flow,” the monitor  140  reports a “reverse vapor flow” as being indicative that vapor from the storage tank  310  is being egressed to the environment though the leak in a dispensing point  210  coupled to the AFS  500  (block  1012 ). “Reverse vapor flow” is caused by the pressure at the dispensing point  210  being at a lower pressure level than the pressure level in the vapor return pipe  410  and/or the storage tank  310 . 
     Note that the monitor  140  may be configured to indicate a leak at a dispensing point  210  based on either no vapor or air flow registration by the AFS  500  or more than a threshold amount of vapor flow being registered by the AFS  500  depending on sensitivity of the AFS  500 . For instance if, according to testing, a leak at a dispensing point  210  is certain to always register a vapor or air flow by the AFS  500  of a certain threshold amount due to certain inherent inaccuracies in either the AFS  500  or the system, the monitor  140  may be configured in decision  1004  to not indicate a registration of vapor or air flow by the AFS  500  for leak detection purposes unless vapor or air flow is above such threshold amount even if vapor or air flow is greater than a zero amount. Configuring the monitor  140  to register a leak at a dispensing point  210  only if vapor or air flow detected by the AFS  50  is greater than a threshold flow amount may be important if the AFS  500  is capable of registering some flow due to sensitivity or pressure variations in the system when no leak is present at a dispensing point  210 . Such may be necessary to reduce and/or eliminate false leak detections. 
     After the tank monitor reports the leak condition at a dispensing point  210 , whether it be due to “forward vapor flow” or “reverse vapor flow” detection by the AFS  500  (blocks  1010  and  1012 , respectively), the monitor  140  may also communicate such leak alarm to the POS  600  and/or the remote reporting system  604  (block  1014 ). The monitor  140 , the POS  600  and/or the remote reporting system  604  may cause the dispensing points  210  where a leak may be present to shut down or remain idle until the leak detection condition can be further analyzed and/or repaired. The monitor  140  then repeats the leak detection process (block  1000 ). 
     In  FIG. 2  as previously discussed, the AFS  500  is located in the vapor return passage  220  inside the fuel dispenser unit  200  in between the nozzle  210  and the vapor return passage  220  instead of in the common vapor return pipe  410 , as illustrated in FIG.  1 . In this manner, any vapor or air flow that is recovered by the particular dispensing point  210  where a particular AFS  500  for such dispensing point  210  is provided will pass through such AFS  500  for registering vapor flow. If a leak occurs in the vapor return passage  220  in a particular fuel dispenser unit  200  employing an AFS  500  and such dispensing point  210  is idle, vapor flow will be registered by the AFS  500 . This is indicative of a leak in a dispensing point  210  coupled to the AFS  500  that registered vapor or air flow since vapor or air flow should not be registered by the AFS  500  when the dispensing points  210  coupled to the AFS  500  are idle. 
     Either “forward vapor flow” or “reverse vapor flow,” as previously described above, will occur at the AFS  500  if a dispensing point  210  coupled to the AFS  500  contains a leak, and there is a pressure differential between the storage tank  310  and the dispensing point  210 . In the embodiment illustrated in  FIG. 2 , since the AFS  500  is located in the vapor return passage  220  instead of the vapor return pipe  410 , the pressure differential that will cause registered flow at the AFS  500  is between the vapor return pipe  410  and the dispensing point  210 . The pressure level in the vapor return pipe  410  and the storage tank  310  should be substantially the same during normal operation. 
     By way of example, if the pressure in the vapor return passage  220  is negative, excess air from the outside may be drawn into or ingressed into the vapor return passage  220  and possibly returned to the storage tank  310 , via the vapor return pipe  410 , thereby causing the pressure inside the storage tank  310 . In this instance, the AFS  500  will register “forward vapor flow,” as previously described above. If an air-valve  213  in a dispensing point  210  is defective by remaining open when the dispensing point  210  is idle and the pressure inside the storage tank  310  is higher than the pressure at the dispensing point  210 , vapor recovered in the vapor return pipe  410  from another active dispensing point  210  may egress through the defective air-valve  213  to atmosphere instead of returning to the storage tank  310  or vapor from the storage tank  310  may egress through the defective air-valve  213  to atmosphere. In this instance, the AFS  500  will register “reverse vapor flow,” as previously described above. 
     The flowchart in  FIG. 5  illustrates one embodiment of the vapor return pipe  410  leak detection system of the present invention where an AFS  500  is placed in the vapor return passage  220  in a fuel dispenser unit  200  like that illustrated in FIG.  2 . In this manner, a registered vapor flow by the AFS  500  when the dispensing point  210  is idle is indicative of a leak somewhere in the vapor return passage  220  between the nozzle  210  and the AFS  500 . The flowchart in  FIG. 5  illustrates processing performed by the monitor  140 , but such processing could also be performed by any control system that is capable of communicating with the AFS  500  to determine vapor flow as well as having knowledge of the state, idle or active, of a dispensing point  210  employing an AFS  500 . 
     As illustrated in  FIG. 5 , the process starts (block  2000 ), and the monitor  140  determines if all of the dispensing points  210  coupled to a particular AFS  500  are idle (decision  2002 ). If not, the process goes back to decision  2002  again checking to determine if all of the dispensing points  210  coupled to an AFS  500  are idle (decision  2002 ). Note that the flowchart process illustrated in  FIG. 5  may be used to detect a leak for any number of groups of dispensing points  210  that are coupled to an AFS  500  individually since the embodiment in  FIG. 2  may include more than one AFS  500  each for the dispensing points  210  in a fuel dispenser  200 . 
     If all of the dispensing points  210  are idle (decision  2002 ), the monitor  140  determines if the AFS  500  for such dispensing points  210  is or has registered vapor or air flow (decision  2004 ). If not, this means that no leak indication is present since no vapor or air flow is occurring, and the process goes back to decision  2002  to repeat the process. 
     Once the monitor  140  determines that vapor or air flow is or has been registered by the AFS  500  indicating a leak in a particular group of dispensing points  210  (decision  2004 ), the monitor  140  sets a dispensing point  210  leak alarm since a leak is occurring in one or more of the dispensing points  210  coupled to the AFS  500  that registered vapor or air flow (block  2006 ). This is because a registered vapor flow by the AFS  500  when all dispensing points  210  coupled to such AFS  500  are idle is indicative of a leak in the dispensing point  210  and/or the vapor return passage  220  on the nozzle  210  side of the AFS  500 . The monitor  140  may also be configured, in response to detection of a leak at a dispensing point  210 , to cause such dispensing point  210  where a leak is detected to shut down or remain idle until the leak detection condition can be further analyzed and/or repaired. 
     Next, the monitor  140  determines if the vapor flow is flowing in the forward or reverse direction via vapor flow direction information received from the AFS  500  (decision  2008 ). If the AFS  500  detected “forward vapor flow,” the monitor  140  additionally reports a “forward vapor flow” as being indicative that outside air is being ingressed through the leak in the dispensing point  210  and being placed the vapor return passage  220 , the vapor return pipe  410 , and the storage tank  310  (block  2010 ). “Forward vapor flow” is caused by the pressure at the dispensing point  210  being at a higher pressure level than the pressure level in the vapor return passage  220 , the vapor return pipe  410  and/or storage tank  310 . If the AFS  500  detected a “reverse vapor flow,” the monitor  140  reports a “reverse vapor flow” as being indicative that vapor from the storage tank  310  is being egressed to the environment though the leak in a dispensing point  210  coupled to the AFS  500  (block  2012 ). “Reverse vapor flow” is caused by the pressure at the dispensing point  210  being at a lower pressure level than the pressure level in the vapor return passage  220 , the vapor return pipe  410 , and/or storage tank  310 . 
     Note that the monitor  140  may be configured to indicate a leak at a dispensing point  210  based on either no vapor flow registration by the AFS  500  or more than a threshold amount of vapor flow being registered by the AFS  500  depending on sensitivity of the AFS  500 . For instance if, according to testing, a leak at a dispensing point  210  is certain to always register a vapor or air flow by the AFS  500  of a certain threshold amount due to certain inherent inaccuracies in either the AFS  500  or the system, the monitor  140  may be configured in decision  2004  to not indicate a registration of vapor or air flow by the AFS  500  for leak detection purposes unless vapor or air flow is above such threshold amount even if vapor or air flow is greater than a zero amount. Configuring the monitor  140  to register a leak at a dispensing point  210  only if vapor or air flow detected by the AFS  500  is greater than a threshold flow amount may be important if the AFS  500  is capable of registering some flow due to sensitivity or pressure variations in the system when no leak is present at a dispensing point  210 . Such may be necessary to reduce and/or eliminate false leak detections. 
     After the tank monitor reports the leak condition at a dispensing point  210 , whether it be due to “forward vapor flow” or “reverse vapor flow” detection by the AFS  500  (blocks  2010  and  2012 , respectively), the monitor  140  may also communicate such leak alarm to the POS  600  and/or the remote reporting system  604  (block  2014 ). The monitor  140 , the POS  600  and/or the remote reporting system  604  may cause the dispensing points  210  where a leak may be present to shut down or remain idle until the leak detection condition can be further analyzed and/or repaired. The monitor  140  then repeats the leak detection process (block  2000 ). 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. The embodiments described above are for illustration and enabling purposes, and the techniques and methods applied are equally applicable to any volatile liquid storage system. The words “air” and “vapor” may be used interchangeably in this application. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.