RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/056,528, filed May 28, 2008, the entire disclosure of which is expressly incorporated by reference herein. 
     This application is related to U.S. Provisional Patent Application Ser. No. 61/056,522, filed May 28, 2008, the entire disclosure of which is expressly incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This invention relates to a method and apparatus for detecting vapor leaks in a Stage II vapor recovery system. 
     BACKGROUND OF INVENTION 
     Historically as fuel was being dispensed into a vehicle&#39;s fuel tank, typically from an underground storage tank (UST), vapor in the vehicle&#39;s fuel tank would escape into the atmosphere. In order to prevent this, Stage II vapor recovery systems were developed to collect this vapor and return it to the UST. 
     Stage II vapor recovery systems recover fuel vapor released from a vehicle&#39;s fuel tank as fuel is being dispensed into the vehicle&#39;s fuel tank. As is known, Stage II vapor recovery systems may be a balance type system or a vacuum-assist type system. Stage II vapor recovery systems typically are only installed in urban areas where the escaping fuel vapors can pose a greater threat to the environment. 
     It is desirable to detect whether there is a leak in the vapor recovery system. However current procedures typically require one to first pressurize the system to a predetermined pressure. 
     SUMMARY 
     In an exemplary embodiment of the present disclosure, a system for detecting a leak in a stage II fuel vapor recovery system is provided. In another exemplary embodiment of the present disclosure, a method for detecting a leak in a stage II fuel vapor recovery system is provided. In an exemplary embodiment of the present disclosure, a computer readable medium is provided including instructions which when executed by a controller are used to detect a leak in a stage II fuel vapor recovery system. 
     In another exemplary embodiment of the present disclosure, a system which monitors for leaks in a vapor recovery system of a fuel dispensing system including an underground storage tank and a plurality of dispensing points in fluid communication with the underground storage tank is provided. The system comprising: a controller which continuously monitors the vapor recovery system for leaks by monitoring the vapor recovery system for a quiet time period wherein there is the absence of external changes to vapor recovery system; recording pressure data during the quiet time period; and based on the recorded pressure data determining whether the vapor recovery system contains a leak. In one example, the determination of whether the vapor recovery system contains a leak is based on the recorded pressure data from a plurality of spaced apart quiet time periods. In one variation thereof, the controller classifies each of the plurality of spaced apart quiet time periods as one of positive and negative and the controller determines that the vapor recovery system contains the leak when a percentage of negative quiet time periods exceeds a threshold value. In one refinement thereof, the threshold value is 66 percent. In another refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure and the ending pressure are both negative and the ending pressure is more negative than the starting pressure. In still another refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure is negative and the ending pressure is positive. In yet another refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure is zero and the ending pressure is positive. In yet still another refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure is zero and the ending pressure is negative. In a further refinement thereof, the controller classifies a given quiet time period as negative based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure is zero and the ending pressure is zero. In still a further refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure is positive and the ending pressure is negative. In yet a further refinement thereof, the controller classifies a given quiet time period as positive based on a starting pressure of the quiet time period and an ending pressure of the quiet time period when the starting pressure and the ending pressure are both positive and the ending pressure is more positive than the starting pressure. In another variation, the controller classifies a given quiet time period as one of positive and negative based on a degree of linearity of the recorded pressure data of the given quiet time period. In a refinement thereof, the degree of linearity is an R 2  value, the given quiet time period is classified as one of positive and negative when the R 2  value is below a threshold amount. In another refinement thereof, the threshold amount is 0.90. In still another refinement thereof, the controller classifies a given quiet time period as positive based on the recorded pressure data when a starting pressure of the quiet time period and an ending pressure of the quiet time period are both negative, the ending pressure is less negative than the starting pressure, and the R 2  value of the pressure data is below the threshold amount. In yet still another refinement thereof, the controller classifies a given quiet time period as negative based on the recorded pressure data when a starting pressure of the quiet time period is negative, an ending pressure of the quiet time period is zero, and the R 2  value of the pressure data is below the threshold amount. In still a further refinement thereof, the controller classifies a given quiet time period as negative based on the recorded pressure data when a starting pressure of the quiet time period is positive, an ending pressure of the quiet time period is zero, and the R 2  value of the pressure data is below the threshold amount. In yet another refinement thereof, the controller classifies a given quiet time period as positive based on the recorded pressure data when a starting pressure of the quiet time period and an ending pressure of the quiet time period are both positive, the ending pressure is less positive than the starting pressure, and the R 2  value of the pressure data is below the threshold amount. In still another variation, the controller classifies a given quiet time period as one of positive and negative based on a pressure decay slope of an ullage of the vapor recovery system without pressurization of the vapor recovery system. In a refinement thereof, based on a number of dispensing points, a starting pressure of the ullage, and a volume of the ullage a threshold slope is determined. In another refinement thereof, when the pressure decay slope is less than the threshold slope the given quiet time period is classified as positive. In another example, the controller first attempts to classify a given quiet time period as one of positive and negative based on the starting pressure and the ending pressure, if inconclusive then further on a degree of linearity of the pressure data, and, if still inconclusive, then further on a pressure decay slope of an ullage of the vapor recovery system, without the need to pressurize the vapor recovery system or to limit fuel dispensing from the fuel dispensing system. In still another example, monitoring the vapor recovery system for a quiet time period includes monitoring whether any dispensing points are active and monitoring whether fuel is being delivered to the underground storage tank, wherein if either a dispensing point is active or fuel is being delivered to the underground storage tank a quiet time period does not exist. in yet still another example, monitoring the vapor recovery system for a quiet time period includes monitoring whether any dispensing points are active, whether a vapor processor of the vapor recovery system is active, and monitoring whether fuel is being delivered to the underground storage tank, wherein if either a dispensing point is active, the vapor processor is active, or fuel is being delivered to the underground storage tank a quiet time period does not exist. In still a further example, a given quiet time period is at least twelve minutes. In a variation thereof, the given quiet time period is up to sixty minutes. 
     In still another exemplary embodiment of the present disclosure, a method for monitoring a vapor recovery system of a fuel dispensing system including an underground storage tank and a plurality of dispensing points in fluid communication with the underground storage tank for a leak is provided. The method comprising the steps of continuously monitoring the vapor recovery system for a quiet time period wherein there is the absence of external changes to vapor recovery system; recording pressure data during the quiet time period; and based on the recorded pressure data determining whether the vapor recovery system contains a leak. 
     In a further exemplary embodiment of the present disclosure, a system which monitors for leaks in a vapor recovery system of a fuel dispensing system including an underground storage tank and a plurality of dispensing points in fluid communication with the underground storage tank is provided. The system comprising: a controller which monitors the vapor recovery system for leaks by monitoring the vapor recovery system for a quiet time period wherein there is the absence of external changes to vapor recovery system; recording pressure data during the quiet time period; and based on the recorded pressure data determining whether the vapor recovery system contains a leak without pressurizing the vapor recovery system. 
     In yet still another exemplary embodiment of the present disclosure, a method for monitoring a vapor recovery system of a fuel dispensing system including an underground storage tank and a plurality of dispensing points in fluid communication with the underground storage tank for a leak is provided. The method comprising the steps of monitoring the vapor recovery system for a quiet time period wherein there is the absence of external changes to vapor recovery system; recording pressure data during the quiet time period; and based on the recorded pressure data determining whether the vapor recovery system contains a leak without pressurizing the vapor recovery system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of a fuel dispensing system in accordance with the present invention. 
         FIGS. 2-4  represent processing sequences of a controller of the fuel dispensing system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail, a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiment illustrated. 
     A fuel dispensing system  10 , such as one for use at a conventional retail gasoline station, is illustrated in  FIG. 1 . The fuel dispensing system  10  typically includes multiple fuel dispensers  12  (only one illustrated), each having two dispensing points  14  (i.e., two assemblies, each comprising a conventional hose  16  and a nozzle  18 ), for dispensing fuel from a UST  20 . UST  20  is filled with fuel through a fuel pipe  31  which introduces the fuel into a lower portion of UST  20  through pipe end  33 . The UST  20  includes a conventional fuel level sensor  22  to measure the level of fuel  24  in the UST  20 . Electrical signals from the fuel level sensor  22  are communicated to a microprocessor based controller  26 , such as Franklin Electric Co., Inc.&#39;s TS-5 automatic tank gauge, which runs software in a conventional manner. This permits the controller  26  to monitor the level of fuel  24  in the UST  20 , and thus inversely to monitor the ullage volume of the UST  20 . This also permits the controller  26  to monitor when fuel  24  is being delivered to the UST  20 . In one embodiment, controller  26  is located within a central location, such as a station house. 
     In one embodiment, the ullage volume is the common vapor space volume of a plurality of USTs. In this embodiment, respective USTs deliver respective octane levels of gasoline to dispensing points based on a selection by the user at the dispenser. The vapor recovery system returns vapors to the USTs through piping which is coupled to each of the USTs; thereby providing a common vapor ullage space for the USTs. This results in a single ullage pressure across all USTs. In one embodiment, each UST has an independent ullage volume and thus the vapor recovery system must analyze each ullage volume independently. This results in potentially different ullage pressures in the different USTs. 
     The fuel dispensing system  10  also includes a fuel delivery system  30  for transferring fuel  24  from the UST  20  to each of the dispensing points  14 . The fuel delivery system  30  typically includes a fuel supply line  32  to provide a common conduit for fuel delivery from the UST  20  to a branch fuel line  34  associated with a respective one of each of the dispensers  12 . A pump  35  is provided in UST  20  to pump fuel through a fuel supply line  32  to dispensers  12 . Each of the branch fuel lines  34  then splits into two fuel delivery lines  36  to provide fuel to each of the dispensing points  14  of a particular one of the dispensers  12 . Each of the fuel delivery lines  36  includes a fuel flow sensor  38 . Each of the fuel flow sensors  38  generates an electrical signal indicative of the quantity of fuel flowing through the sensor  38 , and thus dispensed into a vehicle (not shown). In one embodiment, sensors  38  are volume meters. The signals from the fuel flow sensors  38  are also communicated to the controller  26 . 
     Each dispenser  12  provides signals to the controller  26  indicating whether either one of the dispensing points  14  is in a hook-off condition (i.e., when the dispensing points  14  is not authorized to dispense fuel, and is therefore “idle”) or whether the dispensing points  14  is in a hook-on condition (i.e., when the dispensing points  14  is authorized to dispense fuel, and is therefore “active”). In one embodiment, each dispenser  12  includes pump electronics  11  which monitor the condition (active or idle) of each of the dispensing points  14 , sensors  38  and  48 , and the customer display outputs of the dispenser  12 . 
     The fuel dispensing system also includes a Stage II vapor recovery system  40 . The vapor recovery system  40  may be either a balance type system or a vacuum-assist type system. 
     Similar to the fuel delivery system  30 , the vapor recovery system  40  includes a common vapor return line  42  to provide a common vapor return conduit to return fuel vapor from each of the dispensing points  14  to the UST  20 . Each of the dispensing points  14  has an associated dispensing point vapor return line  44 . The two dispensing point vapor return lines  44  for each of the dispensing points  14  associated with a respective one of the dispensers  12  connect to a dispenser vapor return line  46 . Each of the dispenser vapor return lines  46  connects with the common vapor return line  42 . 
     A vapor return flow sensor  48  is placed in-line with each of the dispenser vapor return lines  46  (i.e., a single return flow sensor is associated with each of the dispensers). The return flow sensors  48  generate electrical signals indicative of the magnitude of vapor return flow through their associated dispenser vapor line  46  towards the UST  20 . In one embodiment, sensors  38  are volume meters. These electrical signals from the return flow sensors  48  are also electrically transmitted to the controller  26 . 
     The vapor recovery system  40  also includes a pressure sensor  50  to measure the vapor pressure in the vapor recovery system  40 . Pressure sensor  50  monitors the pressure of the ullage. In one embodiment, pressure sensor  50  is provided in line  42 . In one embodiment, pressure sensor  50  is located on a vent pipe connected with pressure/vacuum valve  55 . In either location, pressure sensor  50  is coupled to controller  26 . The vapor pressure sensor  50  generates an electrical signal, indicative of the vapor pressure of the ullage, which is communicated to the controller  26 . 
     The vapor recovery system  40  may include a conventional vapor processor  52 , particularly if the vapor recovery system  40  is a balance type vapor recovery system, to prevent build-up of excessive pressure in the fuel dispensing system  10 . Vapor processor  52  may process vapors to convert them to liquid. Vapor processor  52  may burn the vapors and vent the resultant products thereof to atmosphere through vent pipe  53 . The operation of vapor processor  52  affects the pressure of the ullage in storage tank  20 . Vapor processor  52  is an active system. In contrast to vapor processor  52 , vapor recovery system  40  may instead include a clean air separator (CAS). The CAS includes an internal bladder which may either reduce or increase the volume of the ullage. The CAS is a passive system. In one embodiment, the bladder does not expand until a positive pressure is present in the ullage volume. For the system described herein, negative pressure is all pressures up to and including −0.1″ wc, zero pressure is all pressures between −0.1″ wc and 0.1″ wc, and positive pressure is all pressures above and including 0.1″ wc. The bladder of the CAS system does not move to expand the ullage volume until the ullage pressure is at least 0.1″ wc. Likewise, the bladder of the CAS system does not move to reduce the ullage volume until the ullage pressure is −0.1″ wc and below. A pressure/vacuum relief valve  55  is provided to prevent the ullage pressure from becoming too high or too low. Electrical signals from the vapor processor  52  are communicated to the controller  26 , so that the controller  26  can monitor when the vapor processor  52  is active. Further, electrical signals from the vapor processor  52  are communicated to the controller  26 , so that the controller  26  may monitor when the vapor processor  52  is in an alarm condition indicating that the vapor processor  52  is not functioning correctly. In one embodiment, when vapor processor  52  is in an alarm condition all dispensing points  14  are shut down for the fuel dispensing system  10 . 
     The present system  10  includes an in-station diagnostic system (ISD) wherein the controller  26  conducts a pressure test to monitor pressure in the vapor recovery system  40  to detect fuel vapor leaks. In one embodiment, the pressure test is based on a plurality of pressure test evaluations, each made during a quiet time. 
     A “quiet time” is a period of time when there are no external changes to the vapor recovery system  40 , as such changes would affect the pressure in the system  40 . These external changes occur at times such as when fuel is being dispensed, when fuel is being delivered to the UST  20 , and when the vapor processor  52  is active. 
     The controller  26  continuously monitors the system  10  to determine the presence or absence of a quiet time. A minimum quiet time of twelve minutes is required to complete a pressure quiet period evaluation, the first two minutes to permit the system to stabilize and a subsequent minimum ten minute period to conduct the evaluation procedure. 
     During the evaluation procedure, pressure samples are taken once per minute and stored in conventional memory  27  of the controller  26 . In order to monitor the presence or absence of a quiet time, the controller  26  utilizes a “quiet sample” register located in conventional memory  27  of the controller  26 . The controller  26  sets the “quiet sample” register to “true” when all of the dispensing points  14  are in a hook-off condition (i.e., idle), when no fuel is being delivered to the UST  20  and when the vapor processor  52  is inactive, (i.e., when all three conditions are satisfied). Similarly the controller  26  sets the quiet sample register to “false” when any of the dispensing points  14  are in a hook-on condition (i.e., active), when fuel is being delivered to the UST  20  or when the vapor processor  52  is active, (i.e., when any one of the three conditions are satisfied). 
     If the controller  26  determines that a quiet time has ended prior to completion of the minimum twelve minute test period, the pressure evaluation is terminated and the pressure data is cleared from memory  27 . Otherwise, the controller  26  continues collecting data for the pressure evaluation for a maximum of sixty minutes. 
     Specifically the controller  26  continuously executes a first software sub-routine  100  (see  FIG. 2 ) to determine the presence or absence of a quiet time. The quiet sample value is set to false and the quiet time period is reset, as represented by block  102 . Controller  26  executes a series of checks, collectively represented by block  104 . The controller  26  first determines if the ullage has decreased by forty liters, to determine whether fuel is being delivered to the UST  20  (as represented by block  106 ). The controller  26  then determines if any of the dispensers  12  are in a hook-on condition (as represented by block  108 ). The controller  26  then determines if the vapor processor  52  is active (as represented by block  110 ). The controller  26  then determines if the pressure is less than (i.e., more negative than) −7.8″ wc (as represented by block  112 ). If any of these determinations are true, the controller  26  sets the quiet register sample value to false and the quiet time period is reset. The controller  26  also determines whether the evaluation period has met the quiet time period minimum, for example twelve minutes (as represented by block  114 ). If the minimum time period has been met, controller  26  evaluates the next sample (as represented by block  116 ) for the conditions represented in block  104 . Pressure values are recorded (as represented by block  118 ) until a quiet time maximum value is reached (as represented by block  120 ). The quiet sample value is set to true (as represented by block  122 ) and controller  26  begins an evaluation of the recorded pressure data which is represented by block  122 . Once the evaluation is completed, controller  26  returns to block  124  and monitors for a subsequent quiet time. 
     The controller  26  also executes a second sub-routine which monitors the status of the quiet register. If the controller  26  determines that the quiet register is false, the quiet time evaluation is terminated and started again. The controller  26  continues to monitor the quiet register and begins a quiet time pressure evaluation as soon as the status of the quiet register is determined to be true. 
     During the quiet time pressure evaluation, the controller  26  makes a pressure reading every minute. Once complete, the readings are electronically profiled and a status of the pressure evaluation is determined by controller  26  through the processing sequence  200  represented in  FIG. 3 . The profiles are described in Table 1, below. It has been found that there are 15 possible resulting situations: 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Case # 
                 Start P 
                 End P 
                 Other 
                 R 2  &gt; 0.90 
                 Result 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Negative 
                 Negative 
                 Start P (i.e., more 
                 No 
                 Positive 
               
               
                   
                   
                   
                 negative than) &lt; End P 
               
               
                 2. 
                 Negative 
                 Negative 
                 Start P (i.e., more 
                 Yes 
                 Inconclusive 
               
               
                   
                   
                   
                 negative than) &lt; End P 
               
               
                 3. 
                 Negative 
                 Negative 
                 Start P (i.e., less 
                 No or Yes 
                 Positive 
               
               
                   
                   
                   
                 negative than) &gt; End P 
               
               
                 4. 
                 Negative 
                 Zero 
                   
                 Yes 
                 Inconclusive 
               
               
                 5. 
                 Negative 
                 Zero 
                   
                 No 
                 Negative 
               
               
                 6. 
                 Negative 
                 Positive 
                   
                 No or Yes 
                 Positive 
               
               
                 7. 
                 Zero 
                 Negative 
                   
                 No or Yes 
                 Positive 
               
               
                 8. 
                 Zero 
                 Zero 
                   
                 No or Yes 
                 Negative 
               
               
                 9. 
                 Zero 
                 Positive 
                   
                 No or Yes 
                 Positive 
               
               
                 10. 
                 Positive 
                 Negative 
                   
                 No or Yes 
                 Positive 
               
               
                 11. 
                 Positive 
                 Zero 
                   
                 No 
                 Negative 
               
               
                 12. 
                 Positive 
                 Zero 
                   
                 Yes 
                 Inconclusive 
               
               
                 13. 
                 Positive 
                 Positive 
                 Start P &gt; End P 
                 No 
                 Positive 
               
               
                 14. 
                 Positive 
                 Positive 
                 Start P &gt; End P 
                 Yes 
                 Inconclusive 
               
               
                 15. 
                 Positive 
                 Positive 
                 Start P &lt; End P 
                 Nor or Yes 
                 Positive 
               
               
                   
               
             
          
         
       
     
     In certain ones of the situations (cases 3, 6-10 and 15), based simply on the starting pressure (as represented by block  202 ) and the ending pressure (as represented by block  204 ) the controller  26  can make a reasonable conclusion that the system for the quiet time pressure evaluation has either a positive result or a negative result (as represented in Table 1 and by block  206 ). If the starting pressure and the ending pressure are conclusive, the quiet time pressure evaluation is stored as either positive or negative, as represented by block  208 . Otherwise controller  26  continues an evaluation of the pressure data. 
     For the remaining cases, the controller  26  performs a statistical R 2  analysis of the pressure data (represented by block  210 ) of the profiles, as represented by block  212 . The R 2  analysis provides an indication of how close the samples fit a straight line. This value helps for certain cases where one wants to determine if the pressure is decaying at a constant even rate, or just fluctuating. In theory, if the containment area is leaking, then it would in most cases have a constant pressure decay rate. However this may also be true if the ullage pressure is expanding and generating pressure at a constant rate. These situations would result both in an R 2  approximately equal to 1.0. 
     On the other hand, if the containment area is tight and the fuel vapors are saturated, then the pressure curve will typically stay steady or switch from positive to negative and back to positive slopes. This would result in an R 2  significantly less than 1.0. In the present embodiment, the controller  26  considers an R 2 &gt;0.90 as indicative of a sufficiently straight line. 
     The formula for R 2  is: 
               R   2     =       (       ∑       (     x   -     x   _       )     ⁢     (     y   -     y   _       )             ∑         (     x   -     x   _       )     2     ⁢     ∑       (     y   -     y   _       )     2               )     2           
where x and y represent the pressure value and corresponding time value for each of the pressure samples taken, and  x  and  y  represent the respective averages of all of the pressure samples and time values. The controller  26  calculates R 2  upon the completion of each test period.
 
     For cases 1, 5, 11 and 13, wherein the R 2  value is not greater than 0.90, the test is determinative, as noted in Table 1, above (as represented by block  214 ). If the R 2  value is not greater than 0.90, the quiet time pressure evaluation is stored as either positive or negative, as represented by block  216 . Otherwise controller  26  continues an evaluation of the pressure data. 
     For the remaining cases 2, 4, 12 and 14, wherein the R 2  value is greater than 0.90, the test is still inconclusive. For these cases, the controller  26  utilizes the ullage value and calculates a permissible pressure decay slope within which the actual decay slope must fall (as represented by block  218 ). As explained below, based on the pressure decay slope controller  26  may store the quiet time pressure evaluation as either positive or negative (as represented by block  220 ). 
     There is a known equation from which one can calculate an allowable final pressure to which the pressure can decay after a five minute test period. This equation is disclosed in the California Environmental Protection Agency Air Resources Board&#39;s (CARB) Vapor Test Procedure TP-201.3, amended Mar. 17, 1999. However use of this equation requires one to first pressurize the system to 2″ water column (wc). 
     The CARB equation is:
 
 P   p   =P   s   e   (x/V)  
 
where P p  is a permissible final pressure after the five minute test, P s  is the number 2, for 2″ water column (wc), the starting pressure on which the CARB data is based, e is the natural logarithm base, V is the ullage volume, in gallons and x is a variable depending upon the number of dispensing points. Table 2 below indicates the value for x stated in the above referenced CARB Test Procedure TP-201.3, for balance systems and vacuum-assist systems
 
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Vacuum-Assist 
               
               
                 Dispensing Points 
                 Balance Systems 
                 Systems 
               
               
                   
               
             
             
               
                 1-6 
                 −760.490 
                 −500.887 
               
               
                  7-12 
                 −792.196 
                 −531.614 
               
               
                 13-18 
                 −824.023 
                 −562.455 
               
               
                 19-24 
                 −855.974 
                 −593.412 
               
               
                 &gt;24 
                 −888.047 
                 −624.483 
               
               
                   
               
             
          
         
       
     
     If after a five minute test period the final pressure P f  is below a minimum value, as listed in Table 1B of the CARB Procedure, the system under test is deemed to have failed the test. One can also calculate the allowable slope b=(Δp/Δt) of the decay, where Δp is the change in pressure (P f −2) and Δt is five minutes. Any pressure decay having a slope less than the allowable slope would be allowable. 
     The present embodiment utilizes the same equation to calculate an allowable final pressure over a five minute test period, then calculates the allowable slope, then determines the actual slope of the pressure decay over the entire test period and then determines whether the actual slope is less than (i.e., closer to zero) the allowable slope. However instead of pressurizing the UST  20  to 2″ wc to begin the test, and using the number 2 in the equation, the controller  26  substitutes the actual starting pressure (provided the absolute value of the starting pressure is at least 0.5″ wc). 
     To calculate the actual slope, the controller utilizes the following equation: 
             b   =       ∑       (     x   -     x   _       )     ⁢     (     y   -     y   _       )           ∑       (     x   -     x   _       )     2               
As for the formula for R 2 , above, x and y represent the pressure value and corresponding time value for each of the pressure samples taken, and  x  and  y  represent the respective averages of all of the pressure samples and time values. The controller  26  calculates the slope b upon the completion of each evaluation period.
 
     For example: 
     Assume a starting pressure P s =3. 
     Assume a quantity of 12 dispensing points, thus x=−531,614. 
     Assume an ullage=10000 gallons. 
     This results in an allowable final pressure P p  of:
 
 P   p =(3)* e   (−531,614/10000) =2.84.
 
     This results in an allowable slope of (2.84−3)/5=−0.032. 
     If the calculated decay slope is less than (i.e., closer to zero) the allowable decay slope, the quiet time pressure evaluation is indicated as positive. If the calculated decay slope is greater than the allowable decay slope, the quiet time pressure evaluation is indicated as negative. 
     Failure to pass a particular quiet time pressure evaluation does not indicate a failure of the vapor recovery system. The controller continually performs quiet time pressure evaluations over the course of a given time period, such as a week, which are used as data points for determining whether the vapor recovery system has failed. Controller  26 , in an exemplary test, determines if at least a threshold number of the quiet time pressure evaluations are negative for a given time period. If so, the vapor recovery system is determined to have failed. In one embodiment, the threshold value is 66% and the given time period is a week. In the event that the controller  26  determines that the vapor recovery system has failed, controller  26  generates an appropriate alarm. In one embodiment, an alarm is provided in the central location which includes controller  26 , such as the station house. The alarm may be one or more of audio, visual, and tactile. In one embodiment, there is an audio alarm and a visible light. In one embodiment, the alarm condition may be communicated to proper entity over a network. Examples include an e-mail message, a fax message, a voice message, a text message, an instant message, or any other type of messaging communication. The controller  26  also shuts down all of the dispensing points  14  until the alarm is cleared. 
     Referring to  FIG. 4 , a processing sequence  300  of controller  26  for a pressure test is shown. The quiet time pressure evaluation data is retrieved, as represented by block  302 . A threshold value, such as 66%, is also retrieved as represented by block  304 . Controller  26  determines the whether the vapor recovery system as passed or failed, as represented by block  306 . In one embodiment, if a percentage of the number of negative pressure evaluations to the total number of evaluations exceeds the threshold amount, the vapor recovery system has failed. If the vapor recovery system passes, the pressure evaluation data is cleared, as represented by block  308 . If the vapor recovery system fails, an alarm is generated as represented by block  310 . Also, controller  26  shuts down all dispensing points  14 , as represented by block  312 , until the alarm status is cleared, as represented by block  314 . 
     Discussed below is an analysis of each of the cases. 
     Case 1 
     In case 1, the pressure starts negative and ends less negative. The static pressure resulted in an R 2  that is less than 0.90. This indicates the pressure has saturated. Since the pressure remains in the negative region, it indicates that the system is not leaking, thereby resulting in a POSITIVE. 
     Case 2 
     Case 2 is similar to case 1 except the quiet time ended during the upward movement toward zero. Case 2 resulted in an inconclusive test based solely upon the R 2  value because the quiet time ended prematurely. One does not know if the slope would continue through the zero pressure region into the positive region or would flat line in the zero region. Therefore the controller will run the slope calculation, described above. 
     Case 3 
     Case 3 occurs when the ending negative pressure is more negative than the starting negative pressure. It is highly unlikely for a leaking tank to result in a more negative ending pressure from what it started at. There is thus no need for the controller to calculate the R 2  for this case because any value of R 2  would result in a POSITIVE. 
     Case 4 
     In case 4 the quiet time ended prematurely. Because the R 2  is greater than 0.90, it means the slope is fairly straight. However one does not know if the decay slope will continue through the zero region into the positive region. Therefore the pressure test is inconclusive based solely on the R 2  value, and the controller will execute the slope calculation described above. 
     Case 5 
     Case 5 is a classic case of a leaking vapor containment. The pressure begins in the negative region and results with a flat line in the zero region. 
     Case 6 
     Case 6 is a classic model for a tight vapor recovery containment. Here the pressure begins in the negative region and ends in the positive region without any regard for the zero region. A leaking tank will change its curve at the zero region rather than maintaining a high R 2 . 
     Cases 7 and 9 
     In these two cases the starting pressure begins in the zero region and either expands to the positive region or contracts to the negative region. A leaking tank would remain at the zero point during a quiet period. Both of these two cases will result in a POSITIVE. 
     Case 8 
     This is the other classic case of a leaking vapor containment, especially a gross leak where the tank rarely moves out of the zero region during fueling activity. This case results in a NEGATIVE. 
     Case 10 
     This case is the same as case 6 but begins and ends in opposite regions. 
     Case 11 
     This case is the same as case 5 but the beginning pressure is in the positive region. This is a classic case when the system is pressurized and leaking. 
     Case 12 
     This case is the same as case 4 but the beginning pressure is in the positive region. Since one cannot assume the future path for the slope of the pressure one cannot make a decision if it is passing or failing. Therefore the controller must execute the slope calculation. 
     Case 13 
     This case is the same as case 1, but the beginning pressure is in the positive region and ending in the positive region. With the R2 being less than 0.90, it indicates the pressure is remaining in the positive region for a while. This case results in a POSITIVE. 
     Case 14 
     This case is the same as case 2 but the beginning pressure is in the positive region and ends in the positive region. The R 2  is greater than 0.90 which indicates the slope is still moving toward the zero region but ended prematurely. One cannot predict the future direction of the slope. Therefore the controller must execute the slope calculation. 
     Case 15 
     This case ends with a pressure that is greater than the starting pressure, which results with an automatic POSITIVE. There is no need to for the controller to calculate R 2 . 
     The system and methods presented herein allow a vapor recovery system to be monitored for leaks during normal operation of the fueling facility. The system and methods monitor various aspects of a fuel dispensing system to determine a quiet time wherein there are no external changes to the vapor recovery system which would affect the pressure in the vapor recovery system. Exemplary external changes include the dispensing of fuel with one or more of the dispensing points, the delivery of fuel to the UST, and the active operation of a vapor processor. Further, the system and methods do not require a pressurization of the vapor recovery system to detect leaks of the vapor recovery system. The system and methods permit the continuous monitoring of the vapor recovery system for leaks. 
     From the foregoing, it will be observed that numerous variations and modifications may be affected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.
A system and method for detecting a leak in a Stage II vapor recovery system is disclosed. The system may monitor the Stage II vapor recovery system for the occurrence of quiet times and record pressure data during those quiet times. The system may make a determination of a leak based on the evaluation of the pressure data from a plurality of the quiet times.