Abstract:
The present invention combines the gasoline vapor recovery efficiency advantages of a flirt “Partial Seal System”, as disclosed, for example, in U.S. Pat. No. 4,680,004 to flirt, with the customer convenience advantages of gasoline vapor recovery systems employing “bootless” nozzles. The use of bootless nozzles in combination with strict environmental vapor emissions compliance is made possible because of specific system advantages, which include the use of a burner designed to operate at two different flow rates, a coaxial processor stack which permits second and third stage combustion of excess gasoline vapor generated by the system before it is released to atmosphere, and a remote sensor which continually monitors system vacuum pressure to ensure that a sufficient vacuum is maintained at all times. A major advantage of the present system is that the processor unit is adaptable for installation into existing gasoline vapor recovery systems and into other systems, including other manufacturer&#39;s systems.

Description:
This application is a continuation under 35 U.S.C. 120 of U.S. application Ser. No. 09/258,041, filed on Feb. 25, 1999, now U.S. Pat. No. 6,193,500, which in turn claims the benefit under 35 U.S.C. 119(e) of the filing date of Provisional Application Ser. No. 60/076,157, filed on Feb. 26, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a system for controlling gasoline vapor emissions at a service station or stations where liquid gasoline is transferred from one container or tank to another, and more particularly to a bootless nozzle system for preventing the escape of vapors from the fuel tank of a vehicle during refueling, while at the same time preventing ingestion of fresh air into the fuel storage tank of a service station. 
     When a vehicle has consumed its supply of gasoline, its gasoline tank is full of gasoline vapors plus a lesser amount of liquid gasoline. During the process of dispensing a fresh supply of liquid gasoline into the tank, the vapor in the tank is displaced into the atmosphere. At the same time, fresh air is drawn down into the service station gasoline storage tank through provided vent pipes. 
     Gasoline vapors escaping into the atmosphere are a major source of smog and ozone. Fresh air, drawn into the storage tank, stimulates evaporation of the stored gasoline, which converts valuable gasoline into more polluting vapor. 
     The purpose of state of the art gasoline station vapor control systems is to solve both problems simultaneously; i.e. to prevent the escape of vapors from the vehicle tank and to prevent the ingestion of fresh air into the storage tank. 
     Because the volume of vapors escaping and the volume of fresh air ingested are approximately equal, the purpose of the system mechanism is to capture the vapors emitted from the vehicle tank and lead them through a conduit to the storage tank. As gasoline is dispensed from the storage tank, the storage tank ingests the vapor displaced from the vehicle tank instead of fresh air. 
     Pollution control agencies have increasingly mandated strict control standards for release of gasoline vapors into the atmosphere. For example, the California Air Resources Board (CARB) has mandated the following standards for vapor control systems: 
     1) Highest vapor efficiency in all weather conditions; 
     2) Zero fugitive emissions (emissions of vapor through unmonitored openings or gaps in a gasoline delivery system); 
     3) Automatic continuous self-diagnosis; 
     4) System tolerant of leaks in service station hardware; 
     5) System simple, tough, reliable, and economical; and 
     6) System must use best available control technology. 
     One gasoline vapor recovery system well known in the art is the so-called “Balance System”. Such a system consists of a tight sealing vapor recovery nozzle  1   a  (FIG.  2 ), a vapor return hose, and vapor return piping. To prevent fugitive emissions, all vent pipes are equipped with a p/v valve (pressure/vacuum valve), which will not permit venting until the tank pressure exceeds approximately +3 inches w.c.g. (water column gauge). 
     The “Balance System” is simple and inexpensive, but has several disadvantages. Foremost among these are its failure to meet tough control standards such as those outlined above. For example, its vapor collection efficiency is often much less than 95% (typically its efficiency runs between 60 and 95%, depending upon ambient conditions and system maintenance), which is a government mandate in many localities. This loss of efficiency is caused by the fact that gasoline vapor is very sensitive to changes in temperature; i.e. when the temperature of the vehicle tank is colder than the storage tank, vapor transferred to the storage tank will expand. This expansion causes vapor to escape through any leak or opening it can find, usually due to poor system maintenance, thus destroying the vapor collection efficiency. 
     The “Balance System” requires a tight vapor seal at the nozzle/vehicle interface. Typically, this seal is created by employment of a vapor collecting bellows boot  2   a  (FIG.  2 ), which is adapted to fit tightly about the vehicle tank filler neck (not shown). This type of nozzle, however, is heavy, complicated, expensive, and difficult to use. Additionally, because of the tight seal, several internal safety devices are required so as not to overpressure the vehicle tank, and to prevent recirculation of gasoline back through the nozzle and hence back to the storage tank. Also, to contain vapor, all service station components must continuously remain leaktight. 
     A better solution is a loose fitting nozzle bellows boot  2   b  in a partial seal nozzle  1   b  (FIG. 3) which helps collect the vapor but does not seal tightly. In such a system, in order to prevent escape of vapors around the loose fit bellows boot, the prior art teaches that it is necessary to impose a vacuum on the vapor side of the nozzle. This is done in some prior art systems, sometimes referred to as Healy systems, by placing a vapor pump in the gasoline vapor return line between the underground gasoline storage tank and the dispensing nozzle  1   b . A significant disadvantage to this approach is that the gasoline vapor is pressurized on the downstream side of the vapor pump, increasing its propensity to escape through any available leak, and making compliance with environmental regulations virtually impossible. 
     In other prior art systems, sometimes referred to as Hasselman systems, a vapor pump is placed in a line disposed between the gasoline vapor return line and a vapor vent line which exits the underground storage tank. In this prior art approach, a vapor burner is disposed at the discharge end of the vapor vent line. The burner actuates upon the sensing of a positive pressure in the gasoline storage tank. The disadvantage of this type of prior art system is that the magnitude of the positive pressure necessary to actuate the burner is too high to prevent leakage (fugitive emissions) of the pressurized vapor, but too low to properly feed a nozzle mixing type burner. 
     A significant problem with all of the foregoing systems is the operator&#39;s inability to actually measure the vapor recovery efficiency of the system. For example, still another prior art system is one presently in use in Mexico, which employs a monitoring system known as the ENVIROSENTRY ™. This system is an electronic system which monitors the gasoline storage tank for negative or positive pressure levels. The operating theory is that if any portion of the system, such as the vent lines, vapor pumps, or nozzles, fails, typically creating a blockage in the system, a vacuum will be created in the system. The vacuum is generated because gasoline is pumped at a greater rate than vapor is collected, due to the blockage. The system is set so that when the vacuum pressure reaches −6 to −8 water column, a switch will open, cutting a signal to the control panel. The loss of signal indicates to the control panel that there is a failure and an alarm will be activated. If the condition persists for more than sixty (60) minutes, the control panel will cut current to the pumps and the service station will be shut down. 
     The problem with this system is that the extreme vacuum pressure of −6 to −8 water column will never be reached by the typical poorly maintained service station. At about −0.5 water column, p/v valves in the vent risers, Stage I fittings, and other components will begin to leak, permitting air into the system to reduce the negative pressure without solving the malfunction. 
     The ENVIROSENTRY system also theoretically operates to detect a leak of gasoline vapor in the system. The operating theory is that during normal operation some type of pressure, positive or negative, will be generated. This will vary due to climatic conditions. If the pressure is zero for a long period of time, that indicates a problem. Therefore, when the system monitor detects a zero system pressure for a specified period of time, an alarm sequence will be triggered. After a predetermined period of time of continued zero pressure, the system will cut power to the pumps and the service station will be inoperative. 
     Again, the problem with this approach is that, due to leaks in the system, the pressure will never remain at zero for a long period of time. 
     A third system condition which ENVIROSENTRY is designed to monitor is a system overpressure of greater than 2.5 inches water column. If such a condition is detected, an alarm will sound, followed by system shutdown after continued overpressure conditions for a specified period of time. Again, the problem is that leaks will activate to release vapor to the environment, lowering the system pressure before +2.5 inches water column is attained, so the system will not operate as designed. As is the case with most existing systems, it is designed to placate government regulators rather than to effectively solve real problems. 
     Still another prior art approach is disclosed in U.S. Pat. No. 4,680,004 to Hirt. In this patent, which is also a thermal oxidation system employing a vapor burner, it is disclosed that placement of the vapor pump at the discharge end of the vent line, just upstream of the vapor burner, is a superior approach. This arrangement, known as the “Hirt partial seal system”, permits the pump to create a vacuum in all vapor spaces (the nozzle, the hose, the vapor return piping, the storage tank, and the vent line), to thereby minimize vapor escape through leaks, and producing sufficient pressure on the burner which makes a clean, sharp flame. This is a superior design to the foregoing prior art systems, but requires a moderately well sealed system including a vapor collection boot at the nozzle/vehicle interface. 
     The booted nozzle, as shown in FIGS. 2 and 3, has been a problem for the self-serve customer, resulting in public rejection of the entire gasoline vapor control program. Furthermore, the booted nozzles are often misused by customers, by improperly “topping off” their vehicle tanks or improperly inserting the nozzle into the vehicle fill pipe. Both of these misuses result in the escape of vapor which causes the system to fail to comply with gasoline vapor recovery regulations. This public reaction has given rise to a requirement for a bootless nozzle, as shown in FIG.  4 . But the bootless nozzle has no seal at the nozzle/vehicle interface. It is obvious, therefore, that a bootless nozzle which forms no seal would be completely incompatible with the partial seal system approach taught by the Hirt U.S. Pat. No. 4,680,004. 
     It would be desirable, therefore, to develop a gasoline vapor recovery system which combines the vapor processing advantages of the system disclosed by the Hirt U.S. Pat. No. 4,680,004 with the customer convenience advantages of a bootless nozzle. 
     SUMMARY OF THE INVENTION 
     The present invention combines the gasoline vapor recovery efficiency advantages of a Hirt “Partial Seal System”, as disclosed, for example, in U.S. Pat. No. 4,680,004 to Hirt, with the customer convenience advantages of gasoline vapor recovery systems employing “bootless” nozzles. The use of bootless nozzles in combination with strict environmental vapor emissions compliance is made possible because of specific system advantages, which include the use of a burner designed to operate at two different flow rates, a coaxial processor stack which permits second and third stage combustion of excess gasoline vapor generated by the system before it is released to atmosphere, and a remote sensor which continually monitors system vacuum pressure to ensure that a sufficient vacuum for vapor retention and collection is maintained at all times. A major advantage of the present system is that the processor unit is adaptable for installation into existing gasoline vapor recovery systems. 
     More particularly, the present invention provides a gasoline vapor emission control system which comprises a gasoline storage tank and a dispenser with a nozzle and a hose for dispensing gasoline into a vehicle. A first conduit is disposed between the gasoline storage tank and the nozzle for supplying gasoline from the storage tank to the nozzle, and a second conduit is disposed between the nozzle and the gasoline storage tank for returning gasoline vapor from the nozzle to the gasoline storage tank. A third conduit is disposed between the gasoline storage tank and a processor unit for removing excess gasoline vapor from the gasoline storage tank. The processor unit is provided for processing excess gasoline vapor accumulating in the gasoline storage tank. The processor unit comprises a system for abating excess gasoline vapor and a pump for maintaining a vacuum pressure on the system. Advantageously, a remote self-zest monitor is provided for detecting and recording, in real time, the presence of vacuum pressure in the system. 
     In another aspect of the invention, there is provided a gasoline vapor emission control system which comprises a gasoline storage tank and a dispenser for dispensing gasoline into a vehicle. A first conduit is disposed between the gasoline storage tank and the dispenser for supplying gasoline from the storage tank to the dispenser, and a second conduit is disposed between the dispenser and the gasoline storage tank for returning gasoline vapor from the dispenser to the gasoline storage tank. A third conduit is disposed between the gasoline storage tank and atmosphere for removing excess gasoline vapor from the gasoline storage tank. A processor unit is provided for processing excess gasoline vapor accumulating in the gasoline storage tank. The processor unit comprises a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining a vacuum pressure on the system, and further advantageously comprises a coaxial processor stack assembly for releasing combustion products emitted from the burner, wherein the stack assembly comprises an inner stack and a coaxial outer stack disposed about the inner stack. 
     In yet another aspect of the invention, there is provided a gasoline vapor emission control system which comprises a gasoline storage tank and a dispenser for dispensing gasoline into a vehicle. The dispenser advantageously includes a bootless nozzle. A first conduit is disposed between the gasoline storage tank and the bootless nozzle for supplying gasoline from the storage tank to the bootless nozzle, and a second conduit is disposed between the bootless nozzle and the gasoline storage tank for returning gasoline vapor from the bootless nozzle to the gasoline storage tank. A third conduit is disposed between the gasoline storage tank and a processor unit for removing excess gasoline vapor from the gasoline storage tank. The processor unit is provided for processing excess gasoline vapor accumulating in the gasoline storage tank. The processor unit comprises a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining the presence of vacuum pressure in the system. 
     In still another aspect of the invention, there is provided a gasoline vapor emission control system which comprises a gasoline storage tank and a dispenser for dispensing gasoline into a vehicle. A first conduit is disposed between the gasoline storage tank and the dispenser for supplying gasoline from the storage tank to the dispenser, and a second conduit is disposed between the dispenser and the gasoline storage tank for returning gasoline vapor from the dispenser to the gasoline storage tank. A third conduit is disposed between the gasoline storage tank and atmosphere for venting excess gasoline vapor from the gasoline storage tank. A processor unit is provided for processing excess gasoline vapor accumulating in the gasoline storage tank. The processor unit comprises a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining a vacuum pressure on the system. Advantageously, the system includes a multipath pipetrain for directing the excess gasoline vapor to the processor unit, which permits the burner to operate at two different volumetric flow rates, thereby ensuring that an adequate vacuum pressure can be maintained on the entire system during all operating regimes. 
     In yet still another aspect of the invention, a processor subsystem for use in a gasoline vapor recovery system is provided, the gasoline vapor emission control system comprising a gasoline storage tank, a dispenser for dispensing gasoline into a vehicle, and a conduit disposed between the gasoline storage tank and atmosphere for venting excess gasoline vapor from the gasoline storage tank. The inventive processor subsystem comprises a processor unit for processing excess gasoline vapor accumulating in the gasoline storage tank. The processor unit includes a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining a vacuum pressure on the system. The subsystem advantageously further comprises a remote self-test monitor for detecting and recording, in real time, the pressure of the system. 
     In another aspect of the invention, a processor subsystem is provided for use in a gasoline vapor emission control system which comprises a gasoline storage tank, a dispenser for dispensing gasoline into a vehicle, and a conduit disposed between the gasoline storage tank and atmosphere for venting excess gasoline vapor from the gasoline storage tank. The inventive processor subsystem comprises a processor unit for processing excess gasoline vapor accumulating in the gasoline storage tank, which includes a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining a vacuum pressure on the system, and a coaxial processor stack assembly for releasing combustion products emitted from the burner. The stack assembly comprises an inner stack and a coaxial outer stack disposed about the inner stack. 
     In still another aspect of the invention, a processor subsystem is provided for use in a gasoline vapor emission control system which comprises a gasoline storage tank, a dispenser for dispensing gasoline into a vehicle, and a conduit disposed between the gasoline storage tank and atmosphere for venting excess gasoline vapor from the gasoline storage tank. The inventive processor subsystem comprises a processor unit for processing excess gasoline vapor accumulating in the gasoline storage tank, which includes a burner for thermally oxidizing excess gasoline vapor and a pump for maintaining a vacuum pressure on the system. The processor subsystem further comprises a multipath pipetrain for directing the excess gasoline vapor to the processor unit. 
    
    
     The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying illustrative drawing. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a system for controlling gasoline vapor emissions constructed in accordance with the principles of the present invention; 
     FIG. 1 a  is a perspective view of the system shown in FIG. 1; 
     FIG. 2 is a plan view of a booted balance system gasoline dispensing nozzle as is known in the prior art; 
     FIG. 3 is a plan view of a booted partial-seal gasoline dispensing nozzle as is known in the prior art; 
     FIG. 4 is a plan view of a bootless gasoline dispensing nozzle for use in the inventive gasoline vapor recovery system; 
     FIG. 5 is a schematic view illustrating the processor portion of the system shown in FIG. 1; 
     FIG. 6 is a table illustrating the control parameters for the processor of FIG. 5 in typical operation in three different modes, particularly with respect to actuation of the three flow valves in the vapor recovery system; 
     FIG. 7 is a schematic view illustrating a coaxial processor stack constructed in accordance with the principles of the invention for use in a system for controlling gasoline vapor emissions as shown in FIG. 1; and 
     FIG. 8 is a schematic view illustrating a monitoring panel for use in the system as shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIGS. 1 and 1 a , a service station is provided with facilities for storage and dispensing of fuel, such as liquid gasoline and for control and abatement of fuel vapors by burning. In FIGS. 1 and 1 a , a system  10  for control and abatement of gasoline vapors includes a plurality of gasoline dispensers  12 , each having a coaxial liquid gasoline dispensing hose  14  provided with a nozzle  16  for insertion into a fill pipe of a gasoline tank  17  (FIG. 1) of a vehicle  18 . The coaxial hose  14  includes two hose lines connected to the nozzle  16 , one hose line providing for passage of liquid gasoline through pipe  20  from a storage tank  22  to dispensers  12  and nozzles  16 . A gasoline delivery pump  24  (FIG. 1) is provided for pumping the liquid gasoline from the tank  22  to the dispensers  12 . The other hose line provides for passage of gasoline vapors from the vehicle tank  17  through pipe  26  to the storage tank  22 . 
     FIG. 1 a  also schematically illustrates the filling of the underground tank  22  by a gasoline tank truck  28  having a fuel line  30  entering the underground tank  22  through an upstanding fill riser  32  which discharges liquid gasoline adjacent to the bottom of tank  22 . Tank  22  also has an upstanding vent riser  34  which may be connected to a vapor return line  36  leading to the upper chamber portion of the tank so that vapor from the underground tank will be displaced and returned to the truck  28 . 
     Since the system  10  is a substantially vapor-tight system, provision must be made for processing gasoline vapors accumulating in upper portions of underground storage tank  22 . Accordingly, such vapors may flow through vent pipes  38  to a manifold  40  (FIG. 1 a ), and then through a tie  42  between the vent pipes  38  and a processor unit  44 . Under conditions of nondispensing of gasoline from service dispensers  12  or nonfilling of the tanks by the tank truck  28 , the vapor piping systems or that which contains gasoline vapors includes the space above the liquid level in each of the tanks  22 , the vent pipes  38  leading from the tanks  22  to the manifold  40 , tie  42 , the vapor carrying pipes in the processor unit  44 , the dispensing hose  14 , and the vapor return line  26 . Under conditions of filling the tanks  22  by tank truck  28 , the vapor piping system includes the vapor return line  36 . In the dispensing of gasoline to a vehicle  18  the vapor piping system includes the bootless nozzle  16 . 
     The processor unit  44  may be installed on top of a service station  46  as illustrated in FIG. 1 a , or elsewhere as fire safety rules permit. Adjacent manifold  40  may be a pressure/vacuum valve  48  in communication with the manifold  40 . Preferably the horizontally disposed tie pipe  42  is pitched away from the processor unit  44  so that condensate which may appear in pipe  42  will be drained toward the manifold  40  and the tanks  22 . A remote control panel  50  (FIGS. 1 a  and  8 ) may be located in the service station building, the remote control panel  50  being connected to the processor unit  44  by suitable cable  52 . 
     The processor unit  44  and associated control systems and valving may be generally constructed in the manner disclosed in U.S. Pat. No. 4,680,004, herein expressly incorporated by reference, except for the inventive features as described hereinbelow. Within the processor unit housing  54  is a turbine  56  (FIGS.  1  and  5 ), which may comprise a small electric regenerative turbine as disclosed in the aforementioned Hirt &#39;004 patent. Such an exemplary turbine utilizes a fractional (such as a {fraction (1/16)} or ⅛) horsepower motor and is capable of moving 2¼ cubic feet per minute at 1 pound pressure per square inch. This is in contrast to prior art systems which often utilize ½ horsepower or greater motors, because a lot more vapor must be pumped. The turbine  56  has the capacity for quickly moving the vapor through the vapor piping system and is quickly responsive to changes from selected vacuum conditions in the vapor piping system. Downstream of turbine  56 , vapor pipe  58  (FIG. 5) conducts the discharge vapor to a main and high flow burner  60  (FIGS. 1,  6  and  7 ), and by a pipe  62  (FIG. 5) connected to pipe  58  upstream of the main burner  60 , vapor is conducted to a pilot burner  64 . 
     An important feature of the present invention is the implementation of a coaxial processor stack  66  (FIGS.  1  and  7 ). As is apparent from the foregoing description, in the design of a gasoline vapor control system, the primary component is the vapor processor  44 . Inside the processor  44  is a thermal oxidizer (burner  60 ), the purpose of which is to destroy vapors which are so excess to the vapor storage capacity of the system that, if they are not destroyed, they would pressurize and escape to the atmosphere. Thus, we can immediately specify several functions for the burner and its exhaust stack: 
     1. The system must burn clean (i.e minimal oxides of nitrogen, hydrocarbons, ozone, and carbon monoxide); 
     2. The system must not make a visible flame or night-glow out of the top of its stack  66 , in order not to alarm service station patrons; 
     3. The stack itself must not glow visibly; 
     4. The system must not give off sufficient heat to overheat the other components in the processor housing; 
     5. The system must resolve two problems which are unique to the inventive application; i.e. it must burn vapor which has a concentration varying from full lean to full rich, and it also must not permit the prevailing wind to blow its fire out (it is particularly susceptible to this, since it is typically exposed on the roof of a service station building); 
     6. Advantageously, the outer stack should be kept cool enough so that it may be made of mild steel instead of stainless steel; and 
     7. The vertical height of the stack must be kept to a minimum because of aesthetics and to ease compliance with local zoning ordinances. 
     As shown particularly in FIG. 7, coaxial stack  66  of the present invention is constructed such that gasoline vapor  68  enters the main pillbox burner  60  under pressure of the turbine vapor pump  56 , having a minimum pressure of 15 inches water column (w.c.). Vapor is forced out through orifices  70  of the vapor manifold (pillbox)  71  at high velocity. High velocity serves two functions. First, it induces an increased flow of combustion air, as illustrated by arrows  72 , which represent the flow of primary combustion air. Second it prevents the flame from burning back into the orifice and into the vapor pipe train because the velocity in the orifice throat is higher than the velocity of the propagation of flame through vapor. 
     Vapor and primary combustion air (oxygen bearing fresh air) mix and ignite in the throat  73  (first stage combustion zone) of ceramic tiles  74  which are venturi-shaped to promote mixing and ceramic to hold heat and flame. The holding of heat in the ceramic tiles of the burner  60  is vitally important to the burner&#39;s ability to remain burning while the concentration of the vapor changes. 
     The issue of accommodation of vapor concentration changes arises because of the employment in the present inventive system of a bootless nozzle  16 , as illustrated in FIG.  4 . Bootless nozzles of this type are known in the prior art, and comprise a coaxial spout  76  having an inner tube (not shown) for carrying liquid gasoline to the vehicle tank and an outer tube (not shown) for returning gasoline vapor to the coaxial dispensing hose  14 . Vapor ingestion ports  78  in the distal end of the spout  76  function to draw the gasoline vapor being displaced from the vehicle tank into the outer tube of the spout  76  for return to the underground tank  22 . Because there is no boot to seal against the vehicle filler spout and ensure the return of substantially all gasoline vapors to the vapor recovery system, it is necessary to operate a bootless system under a substantial vacuum pressure (in an exemplary system, the optimal level of vacuum is {fraction (1/10)} psi for a bootless nozzle system, versus {fraction (1/100)} psi for a booted nozzle system). This vacuum pressure at the ports  78  functions to draw the gasoline vapors into the ports  78  rather than permitting them to escape to atmosphere. 
     As discussed supra, the concentration of the vapor changes because the bootless nozzle  16 , having no seal, ingests some fresh air through the ports  78  as a result of the imposed vacuum pressure, and because the maintained vacuum level induces air ingestion through any existing leak. This variation in vapor concentration is a problem not encountered by designers of burners which burn natural gas, because the quality of natural gas is very constant. 
     Referring once again to FIG. 7, combustion flame is emitted from the tile venturi  74  and is mixed with secondary combustion air  80 , which increases the probability that all hydrocarbons will be oxidized in the flame. Secondary combustion takes place inside an inner stack  82 , in the second stage combustion zone  83 . Additionally, fresh air flow  84  is induced through an annulus  86  between the inner stack  82  and an outer stack  88 . This air  84  keeps the outer stack  88  cool, and the air  84  is preheated during its journey along the hot inner stack to become heated fresh air  90  at the top end of the inner stack  82 . The heated fresh air  90  supplies warm oxygen to burn any residual hydrocarbon, in third stage combustion zone  91 , not combusted during the first two combustion stages. Simultaneously, the air  90  quench-cools the burning stream  92  as it exits the outer stack  88 , thereby reducing the probability that a glow or visible flame will be visible from the top of the outer stack. 
     The inventive coaxial stack burner design, affording three stage combustion and quench cooling of exhaust gases to eliminate flare-off, is superior to anything known or used in the industry, and solves problems related to the inventive gasoline vapor recovery system which were not known in connection with any other application. 
     Still referring to FIG. 7, the inventors have discovered an advantageous approach for constructing the pillbox burner  60 . A pipe  94  is disposed through the manifold for entry of a portion of the primary combustion air  72  into the first stage combustion zone  73 . The pipe  94  divides the pillbox manifold  71  into an annulus, as illustrated, which permits even distribution of the gasoline vapor to the spud holes  70 , and a low pressure drop. Also, with this approach, the remaining primary combustion air  72  which does not traverse the pipe  94  can flow evenly around the periphery of the venturi mouths. The inventors have found that such a configuration permits the use of a smaller standard blower  56 , and gives the turndown stability necessary for an open system. 
     The inventors have found that, with the open style system for Stage II vapor recovery, which uses the “bootless” dispensing nozzles discussed supra, a high turndown burner  60  is necessary. In situations where many people are dispensing gasoline into their vehicles during a bulk fill delivery from a tanker truck  28  (FIG. 1 a ), a high processing rate is needed. However, in instances where few or no people are dispensing fuel, a low processing rate is required to keep hydraulic shock from wearing out the vacuum switches utilized in the system. 
     Conventional design would call for using a larger blower  56  with a throttling flow control valve to obtain the desired turndown. However, this approach tends to complicate the system and the control logic required to keep it operational, and is therefore relatively expensive. Alternatively, the inventive system employs the standard turbine blower  56  employed by the closed system disclosed in the Hirt &#39;004 patent, in conjunction with a multi-path pipetrain as illustrated in FIG.  5 . 
     Referring now more particularly to FIG. 5, a high flow valve  96  is disposed in the main vapor pipe  58 . A high flow solenoid  98  actuates the high flow valve  96  between its open and closed states. A pilot valve  100  is disposed in the pilot vapor pipe  62 . A pilot solenoid  102  actuates the pilot valve  100  between its open and closed states. A main flow pipe  104  branches from the vapor pipe  58 , bypassing the high flow valve  96 . A main flow valve  106  is disposed in the main flow pipe  104 , which is actuated between its open and closed states by means of a main flow solenoid  108 . 
     In a preferred embodiment, gasoline vapor is supplied at pressure by the blower  56 , with a maximum flow rate of 4.4 Standard Cubic Feet per Minute (SCFM). The main tie pipe  42  and main vapor pipe  58  upstream of the high flow valve  96  each have preferred diameters of 1 inch. Downstream of the valve  96 , the diameter of the pipe  58  is preferably ⅜ inch. Pilot pipe  62  is preferably comprised of a ⅜ inch tube upstream of the pilot valve  100 , and ¼ inch tubing downstream of the valve  100 . Main flow pipe  104  is preferably comprised of ⅜ inch tubing along its entire length. 
     The multi-path pipetrain configuration herein described is efficiently operated using a set of vacuum switches to control the processing rate. In that regard, high flow vacuum switch  110 , lesser vacuum switch  112 , and greater vacuum switch  114  are provided (FIG.  5 ). 
     One additional important feature of the inventive system  10  is the implementation of a remote self-test monitor  116  on the remote control panel  50  (FIGS. 1 a  and  8 ) in the interior of the service station  46 . In prior art systems, there has not been any effective self-test capability, so it has been difficult to determine whether a system has been working correctly or not. Diagnosis of the system operation required the use of special test equipment, tools, and a knowledge of the behavior of the system, and no analysis could be conducted without physical access to the rooftop processor. However, with the increasing vigilance of governmental authorities, who have become more likely to regulate, inspect, cite, fine and shut down service stations whose pollution control equipment is not functioning properly, it has become more important to service station owners to have conveniently located monitoring equipment. Locating the remote self-test monitor in the building, convenient to the operator, and providing for an audible alarm in the event of improper system operation, creates three major advantages. First, the station owner/operator can hear the alarm, indicating improper operation of the system, and know immediately that corrective action is necessary. The system can even be configured for remote monitoring (i.e. an operator could monitor via phone or internet from a remote location). Second, a governmental inspector can learn all he needs to learn about system operation from the monitor screen, and does not have to access the roof. Finally, the processor housing can be sealed shut, thereby denying access to vandals, tinkerers, and others who do not have proper tools or authorization for repair. Two additional advantages of a sealed housing involve the alleviation of worry on the part of the station owner/operator that 1) a governmental inspector might measure something in the processor and announce that the system is not working properly and that a citation must be issued or the station shut down, or 2) that the inspector might not first come to the office to announce his arrival and intent to inspect. With the housing sealed and the monitoring equipment inside the station, the inspector must first announce his arrival to the owner/operator, and the owner/operator already knows (presumably) that the system is operating properly, or else alarms would have sounded. In many instances, because regulatory agencies typically permit a “fix-it” period of time before requiring shutdown, early diagnosis of a problem which is then promptly reported to authorities will innoculate an operator from citation during such a random inspection visit 
     In a preferred embodiment, as illustrated in FIG. 8, the self-test monitor  116  comprises an audible alarm  118 , a power switch  120 , power and vacuum indicator lights  122  and  124 , respectively, alarm silence and alarm indicator light  126  and  128 , respectively, a fuse  130 , and a paperless recorder  132  having a liquid crystal display  134 . A significant advantage of the present system is that only one parameter need be monitored—total system pressure (vacuum pressure). As long as a vacuum persists during operation, even if there are leaks in the system, vapor collection efficiency will approach 100%. 
     In operation, referring in particular to the table shown in FIG. 6, the system  10  is advantageously designed to operate efficiently in three modes. In the idle mode, when no product dispensing occurs, the lesser vacuum switch  112  is in control and the system preferably maintains a vacuum setting of approximately −4.2 inches w.c. 
     When customers drive up to the dispensers  12  and begin dispensing gasoline into their vehicle tanks, demand on the system increases. As long as the vacuum level is below −4.35 inches w.c., the high flow vacuum switch  110  energizes to turn on the high flow valve  96 . This will approximately double the flow rate to the burner  60  to approximately −4 SCFM, thereby giving the processor  44  a greater ability to generate vacuum. When the vacuum level reaches a predetermined setpoint (approximately −4.35 inches w.c. in the preferred embodiment), the high flow valve  96  is switched off and the main flow valve  106  remains actuated to take the vacuum level to −4.5 inches w.c. In the product dispensing mode, the vacuum level will be maintained at approximately −4.5 inches w.c. by the greater vacuum switch  114 . 
     When, in addition to dispensing product into vehicle tanks, a gasoline delivery truck arrives to replenish the supply of gasoline into the underground tank  22  (a “bulk drop”), the system functions to compensate for this extreme demand in the same manner as described supra in connection with the higher demand generated by the dispensing of fuel into several vehicle tanks simultaneously. Again, the high flow switch  110  and valve  96  energize to give the processor a greater ability to generate vacuum and increase the vacuum level to −4.35 inches w.c., after which the high flow vacuum switch  110  will shut off, closing the high flow valve  96 , and the greater vacuum switch  114  throttles the main flow valve  106  to maintain a vacuum level of −4.5 inches w.c. This state, with its higher vacuum setpoint of −4.5 inches w.c. will be maintained until demand on the system returns to an idle level, thereby causing the processor to return the system to the idle mode, and its lower vacuum setpoint of −4.2 inches w.c. 
     Important to the successful operation of the foregoing system is that the high flow vacuum switch  110  is a slave to either of the other two switches  112  and  114 . Thus, regardless of the system mode, high flow volume may be activated on demand in order to ensure that desired vacuum level may be maintained continuously, so that the system is virtually never out of operational compliance with emissions regulations. 
     The monitor  116  functions by recording in real time, preferably in one minute increments, via the paperless recorder, the total system pressure. Preferably, this merely involves monitoring the status of the lesser vacuum switch. The status of the lesser vacuum switch is recorded periodically (in the preferred embodiment, once each minute) for an entire year. If the vacuum is sufficient to open the switch (i.e. in the preferred embodiment approximately −4.2 inches w.c. or greater), the recorder marks (0) VAC. If the vacuum decays below this setpoint level, thereby causing the lesser vacuum switch to close, the monitor notes the closed status of the switch. Should the switch  112  be detected in the closed status for a predetermined amount of time, such that it is presumable that the system has developed a leak which renders the processor incapable of generating sufficient vacuum pressure to overcome the loss of vacuum in the system due to the leak, the remote monitor  116  sounds the alarm horn  118 , lights the alarm lamp  128 , and the recorder marks the house voltage of approximately 120 VAC for the duration of the outage. The horn can be silenced by depressing button  126 . However, if the malfunction has not been repaired, the horn will sound again after an hour has elapsed to remind the operator of the unresolved problem. 
     A plot of the recorded vacuum switch status checks may be displayed in LCD display  134 , and may be printed out for any time increment up to one year earlier upon demand, using a supplied printer (not shown). Thus, the previous year&#39;s system history is available instantly if desired. 
     Leaks anywhere between the vapor valves and the storage tank will cause the processor to run excessively. Once the leak becomes large enough to overcome the processor, the vacuum condition will be lost and the monitor will sound the horn, light the alarm lamp, and record the outage. Leaks anywhere between the storage tank and the processor allow entrained air to dilute the vapor. By nature of its design, the processor cannot thermally oxidize an excessively diluted vapor stream. The processor thus shuts down to allow the vacuum to decay. Again, when the vacuum decays, the monitored vacuum switch is not actuated to its open position, and the alarm will be activated. Similarly, a bulk delivery conducted with poorly maintained equipment or performed with improper connection/disconnection procedures will also dilute the vapor stream sent to the processor. As a result, the processor will shut down and the monitor will go into alarm mode. 
     Thus, the processor  44  in the present inventive system functions to create a total system vacuum, by operation of the pump or turbine  56 , monitor the vacuum pressure, by means of the monitor  116 , and to process excess vapor, by means of he burner  60 . The system is “foolproof”, in that, as long as a negative system pressure is maintained, no leaks to atmospheric pressure will occur (all leaks will be into the lower region of pressure, i.e. inwardly into the underground tanks and related piping), and if the vacuum pressure falls below a predetermined parameter, indicating a system malfunction, such as leaky vapor valves, poorly maintained tank tops, processor malfunctions, improperly performed bulk deliveries, leaky Stage I hoses, leaky dispenser piping, leaky underground vapor return piping, and leaky P/V valve, an alarm is sounded. 
     Thus, the inventive system has at least the following advantages, among others: 1) an operator of a gasoline dispensing facility has a way to detect leaks in the vapor recovery system immediately upon occurrence; 2) an operator of a gasoline dispensing facility can determine when a bulk delivery driver uses worn out Stage I equipment or follows improper connect/disconnect procedures; and 3) the local inspector can inspect the record and determine whether operators and bulk delivery drivers are working diligently to keep the Stage I/II systems operational and leak-free throughout the year. 
     Accordingly, although an exemplary embodiment of the invention has been shown and described, it is to be understood that all the terms used herein are descriptive rather than limiting, and that many changes, modifications, and substitutions may be made by one having ordinary skill in the art without departing from the spirit and scope of the invention.