Abstract:
A method for monitoring vapor-to-liquid flow rate in a fuel dispensing system with a vacuum assisted vapor recovery system having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor includes the steps of: determining vapor flow rate in the inner vapor conduit; issuing a signal indicative of the vapor flow rate; determining liquid fuel flow rate in the outer fuel conduit; issuing a signal indicative of the liquid fuel flow rate; comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate; and, when vapor-to-liquid flow rate is outside a predetermined range, issuing a signal. A vacuum assist vapor recovery system, and a fuel dispensing system equipped with such a vapor recovery system are also described.

Description:
TECHNICAL FIELD  
       [1]    1. This application is a continuation-in-part of U.S. Ser. No. 09/272,479, filed Mar. 19, 1999, and now pending, and a continuation-in-part of International Patent Application No. PCT/US99/01932, having an International filing date of Mar. 18, 1999, and now pending. This application also claims the benefit of U.S. Provisional Application No. 60/154,617, filed Sep. 17, 1999.  
         [2]    2. This invention relates to vapor flow indicators for fuel dispensing systems.  
     
    
     
       BACKGROUND  
         [3]    3. Systems for dispensing fuel into vehicles, e.g. at gasoline stations, typically employ a coaxial hose, which, in so-called inverted arrangement, has an outer conduit for delivery of fuel to the vehicle and an inner conduit for recovery of fuel vapors displaced from the vehicle tank. Recent field testing by the California Air Resources Board (CARB) of vacuum assist vapor recovery systems for use in fuel dispensing systems uncovered a problem with the inverted coaxial hose. They found that the internal vapor hose can kink during normal operation, causing substantial blockage of the vapor return pathway. Once kinked, these hoses tend to remain in a tube-collapsed condition, thus permanently reducing the cross sectional area of the vapor flow path.  
           [4]    4. Vacuum assist systems which employ a variable speed vane pump, or other flow control device mounted in the dispenser, use the electronic pulses related to the liquid gasoline flow rate to control the vane pump speed or the orifice size of a variable orifice restrictor. Using this technique, the volumetric rate of vapor recovery is maintained in proportion to the rate of liquid gasoline delivery.  
           [5]    5. A kink in the vapor hose will act to restrict vapor flow, thus changing the absolute pressure on the inlet side of the vapor flow control device. The reduction in pressure results in a reduction in throughput for both the vane pump and the variable orifice flow control device. A kink in the vapor hose can therefore result in escape of gasoline vapor in the vehicle tank fillpipe to the extent that the vapor recovery throughput is reduced at the flow control device.  
           [6]    6. In practice, the detection of a damaged vapor hose in the service station is not easy, since the outer hose might not show any physical sign of kinking. This type of defect can only be found through extensive testing or by a process of elimination of other vapor recovery related components.  
         SUMMARY  
         [7]    7. According to one aspect of the invention, a method for monitoring vapor-to-liquid flow rate in a fuel dispensing system with a vacuum assisted vapor recovery system having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor comprises the steps of: determining vapor flow rate in the inner vapor conduit; issuing a signal indicative of the vapor flow rate; determining liquid fuel flow rate in the outer fuel conduit; issuing a signal indicative of the liquid fuel flow rate; comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate; and, when vapor-to-liquid flow rate is outside a predetermined range, issuing a signal.  
           [8]    8. Preferred embodiment of this aspect of the invention may include the following additional features. The method comprises the steps of: issuing the signal to adjust flow of vapor; comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate; and, if vapor-to-liquid flow rate remains outside a predetermined range, issuing a signal to further adjust flow of vapor. The method comprises the step of issuing the signal to adjust flow of vapor.  
           [9]    9. According to another aspect of the invention, a vacuum assist vapor recovery system for a fuel dispensing system having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor comprises: an indicator assembly for providing indication of vapor flow reduction in the inner vapor conduit, the indicator assembly comprising a detector element in communication with the inner vapor conduit for detection of vapor flow within the inner vapor conduit and an indicator element of vapor flow for indication of vapor flow and vapor flow reduction within the inner vapor conduit detected by the detector element, the detector element comprising a Venturi device disposed in communication with the inner vapor conduit, a diaphragm responsive to the pressure between the Venturi throat and the upstream inner vapor passageway, and a magnet associated with, i.e. reflecting the movement of, the diaphragm, and the indicator element comprising a signal indicative of the vapor flow rate from a Hall Effect device.  
           [10]    10. According to still another aspect of the invention, a fuel dispensing system with a vacuum assisted vapor recovery system having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor and further comprises an indicator assembly for providing indication of restriction of flow cross-section for the inner vapor conduit, the indicator assembly comprising a detector element in communication with the inner vapor conduit for detection of vapor flow within the inner vapor conduit and an indicator element of vapor flow for indication of vapor flow and detection of vapor flow reduction within the inner vapor conduit detected by the detector element, the detector element comprising a Venturi device disposed in communication with the inner vapor conduit, a diaphragm responsive to the pressure between the Venturi throat and the upstream inner vapor passageway, and a magnet associated with, i.e. reflecting the movement of, the diaphragm, and the indicator element comprising a signal indicative of the vapor flow rate from a Hall Effect device.  
           [11]    11. According to another aspect of the invention, a vacuum assist vapor recovery system, e.g. in or for a fuel dispensing system, having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor comprises an indicator assembly for providing indication of vapor flow reduction in the inner vapor conduit, e.g., due to restriction of flow cross-section in the inner vapor conduit or failure of a vacuum pump or other vacuum control device, the indicator assembly comprising a detector element in communication with the inner vapor conduit for detection of vapor flow within the inner vapor conduit and an indicator element of vapor flow for indication of vapor flow within the inner vapor conduit detected by the detector element.  
           [12]    12. Preferred embodiments of the invention may include one or more of the following additional features. The indicator assembly further comprises a housing defining a chamber in communication with the inner vapor conduit, a paddle mounted to pivot in the chamber between a first position indicating relatively low or no flow and a second position indicating relatively higher flow, spring means biasing the paddle toward the first position, and a window for viewing into the chamber from external of the housing, the paddle having a first end portion disposed in a flow of vapor through the inner vapor conduit, the first end portion being moved from the first position toward the second position by vapor flow in the inner vapor conduit for detection of vapor flow within the inner vapor conduit, and the paddle having a second end portion disposed in view of the window, the second end portion being moved from the first position toward the second position in response to movement of the first end portion in detection of flow of vapor for indication of vapor flow within the inner vapor conduit. The indicator assembly further comprises a housing defining a chamber in communication with the inner vapor conduit, a paddle wheel comprising a body with a plurality of paddles extending therefrom generally radially in a plane of rotation, the paddle wheel being mounted to rotate in the chamber in response to flow of vapor in the inner vapor conduit, and a window for viewing into the chamber from external of the housing, at any time, one or more of the plurality of paddles being disposed in a flow of vapor through the inner vapor conduit, the one or more paddles being moved and the paddle wheel being rotated by vapor flow in the inner vapor conduit for detection of vapor flow within the inner vapor conduit, and one or more other of the plurality of paddles being disposed in view of the window, the one or more other of the plurality of paddles being moved relative to the window in response to movement of the one or more paddles of the plurality of paddles in detection of flow of vapor for indication of vapor flow within the inner vapor conduit. The indicator assembly further comprises a module, the module being reversible 180E relative to the housing to permit alternative placement of the housing, including where vapor flows in an opposite direction. The detector element comprises a Venturi device disposed in communication with the upstream inner vapor conduit, the indicator assembly comprises a differential pressure gauge, and the indicator element comprises an electronic display of flow rate. The detector element comprises a Venturi device disposed in communication with the inner vapor conduit, the indicator assembly comprises a differential pressure transducer, and the indicator element comprises an electronic display of flow rate. The detector element comprises a paddle wheel comprising a body with a plurality of paddles extending therefrom generally radially in a plane of rotation with signal elements mounted to one or more of the paddles of the paddle wheel, and the indicator element comprises a proximity sensor responsive to the signal elements mounted upon the paddle wheel and an electronic display of flow rate. The indicator assembly further comprises a housing defining a chamber in communication with the inner vapor conduit and adapted for mounting vertically, and a float ball rotameter comprising a precision float ball disposed for movement between a lower pin and a spaced apart upper pin, the upper and lower pins defining a chamber therebetween, the precision float ball adapted to move in the chamber between a first position in proximity to the lower pin indicating relatively low or no flow and a second position in proximity to the upper pin indicating relatively higher flow, and a window for viewing into the chamber from external of the housing, the precision float ball being lifted from the first position toward the second position by vapor flow in the inner vapor conduit for detection of vapor flow within the inner vapor conduit, and movement of the precision float ball between first position and the second position in response to flow of vapor providing indication of vapor flow within the inner vapor conduit. The detector element comprises a Venturi device disposed in communication with the inner vapor conduit and a diaphragm responsive to a differential of pressure between the Venturi throat and the upstream inner vapor passageway, and the indicator element comprises a pointer associated with a scale and moveable relative to the scale in response to movement of the diaphragm. The detector element comprises a Venturi device disposed in communication with the inner vapor conduit, a diaphragm responsive to the pressure between the Venturi throat and the upstream inner vapor passageway, a magnet associated with, i.e. reflecting the movement of, the diaphragm, and an indicator element comprising a signal indicative of the vapor flow rate from a Hall Effect device. The detector element comprises a Venturi device disposed in communication with the inner vapor conduit and a differential vapor transducer responsive to a differential of pressure between the Venturi throat and the upstream inner vapor passageway, and the indicator element comprises a signal indicative of the vapor flow rate from the differential pressure transducer.  
           [13]    13. Preferred embodiments of a fuel dispensing system of the invention may also include one or more of the following additional features. The fuel dispensing system further comprises a comparator adapted to receive the signal indicative of vapor flow rate and a corresponding signal indicative of liquid flow rate. Preferably, the comparator is further adapted to issue a signal when vapor-to-liquid flow rate outside a predetermined range is detected. More preferably, fuel dispensing system further comprises a signal receiver adapted to receive the signal issued by the comparator and discontinue flow of liquid fuel.  
           [14]    14. According to another aspect of the invention, a method for monitoring vapor-to-liquid flow rate in a fuel dispensing system with a vacuum assisted vapor recovery system having a coaxial hose with an outer fuel conduit for delivery of fuel and an inner vapor conduit for recovery of vapor comprises the steps of: determining vapor flow rate in the inner vapor conduit; issuing a signal indicative of the vapor flow rate; determining liquid fuel flow rate in the outer fuel conduit; issuing a signal indicative of the liquid fuel flow rate; comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate; and, when vapor-to-liquid flow rate is outside a predetermined range, issuing a signal.  
           [15]    15. Preferred embodiments of this aspect of the invention may also include one or more of the following additional features. The method comprises the steps of issuing the signal to adjust flow of vapor; comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate; and, if vapor-to-liquid flow rate remains outside a predetermined range, issuing a signal to adjust flow of liquid fuel. The method comprises the step of issuing the signal to adjust, i.e. shut off, flow of liquid fuel.  
           [16]    16. An object of the invention is to provide a device for indication of vapor flow within the inner conduit of a coaxial fuel dispensing hose in order to detect restriction of the vapor flow path, e.g., due to kinking of the inner hose or faulty performance of the vapor flow control device or pump.  
           [17]    17. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.  
       
    
    
     DESCRIPTION OF DRAWINGS  
       [18]    18.FIG. 1 is a somewhat diagrammatic view of one embodiment of a fuel dispensing system with a vacuum assist vapor recovery system and employing a coaxial vapor recovery flow indicator of the invention;  
         [19]    19.FIG. 2 is a side view, partially in section, of a coaxial hose for use in a fuel dispensing system, e.g., as shown in FIG. 1 (and also as shown in FIG. 3);  
         [20]    20.FIG. 3 is a somewhat diagrammatic view of another embodiment of a fuel dispensing system with a vacuum assist vapor recovery system and employing the coaxial vapor recovery flow indicator of FIG. 1;  
         [21]    21.FIG. 4 is a side section view of the coaxial vapor flow indicator of FIG. 1;  
         [22]    22. FIG.  5  is a bottom plan view of the coaxial vapor flow indicator of the invention, taken at the line  5 - 5  of FIG. 4; and  
         [23]    23.FIG. 6 is an end section view of the coaxial vapor flow indicator of the invention, taken at the line  6 - 6  of FIG. 4.  
         [24]    24.FIG. 7 is a side section view of an alternate embodiment of the coaxial vapor flow indicator of the invention.  
         [25]    25.FIG. 8 is a side section view of another alternate embodiment of the coaxial vapor flow indicator of the invention.  
         [26]    26.FIG. 9 is a side section view of another embodiment of the coaxial vapor flow indicator of the invention;  
         [27]    27.FIG. 10 is an end section view of the coaxial vapor flow indicator of FIG. 9, taken at the line  10 - 10  of FIG. 9; and  
         [28]    28.FIG. 11 is a top section view of the coaxial vapor flow indicator of FIG. 9, taken at the line  11 - 11  of FIG. 10.  
         [29]    29.FIG. 12 is a block flow diagram of the flow comparison logic for a gasoline dispenser system with vacuum assist Phase II vapor recovery.  
         [30]    30.FIG. 13 is a somewhat diagrammatic view of a coaxial vapor flow indicator including a Hall Effect device for measuring magnetic field.  
         [31]    31. Like reference symbols in the various drawings indicate like elements.  
     
    
     DETAILED DESCRIPTION  
       [32]    32. Referring to FIG. 1, a multi-product fuel dispenser  10  is mounted on an island  12  above a driving surface  14 , e.g. at a typical gasoline or vehicle fueling station. Extending from the dispenser is a coaxial hose assembly  16  consisting of a coaxial whip hose  18 , a coaxial vapor flow indicator  20  of the invention (to be described more fully below), a coaxial breakaway assembly  22 , e.g. as described in my U.S. Pat. No. 5,297,574, and a segment of flexible coaxial hose  24 , terminating in a fuel dispensing, vacuum assist vapor recovery nozzle  26 .  
         [33]    33. Referring to FIG. 2, the coaxial hose assembly  16  defines an outer conduit  28  for delivery of fuel, e.g. gasoline (arrow, G), to a vehicle, and an inner conduit  30  for vacuum assisted recovery of vapor (arrow, V) displaced from the vehicle fuel tank by delivery of fuel.  
         [34]    34. Referring to FIG. 3, another multi-product fuel dispenser  10 ′ is mounted on island  12  above driving surface  14 . Extending from the dispenser is a coaxial hose assembly  16 ′ consisting of a coaxial hose  24 ′, a coaxial vapor flow indicator  20  of the invention (again, to be described more fully below), and a dual plane, coaxial swivel breakaway assembly  22 ′, e.g. as described in my U.S. Provisional Patent Application No. 60/117,584, filed Jan. 27, 1999, and entitled “Fuel Dispensing Swivel Breakaway Assembly.” The breakaway system  22 ′ is attached to a fuel dispensing, vacuum assist vapor recovery nozzle  26 ′.  
         [35]    35. Referring next to FIGS.  4 - 6 , in one embodiment, a coaxial vapor flow indicator assembly  20  of the invention consists of a flow indicator module insert  31 , with o-ring seal  33 , mounted in a one-piece cast metal body structure  32  having a male inverted hose connection  34  at one end and a female connection  36  at the other end. The indicator device  20  is adapted to be threaded into the dispenser side of a coaxial hose breakaway assembly  22  (FIG. 1), or into the dispenser side of a coaxial hose, dual plane, swivel hose breakaway assembly  22 ′ (FIG. 3), or directly into the dispenser side of fuel dispensing nozzle  26 ,  26 ′.  
         [36]    36. The indicator device  20  provides visual indication of vapor flow rate in the inner vapor conduit  30 . Referring again to FIGS.  4 - 6 , in this embodiment of a coaxial, vapor flow indicator  20  of the invention, a flow indicator paddle  36  is mounted to pivot on pin  48  between a low flow position, FL (represented in solid line in FIG. 4) and a high flow position, FH (represented in dashed line in FIG. 4). The paddle has a first end  38  extending into the vapor flow path  30  and an opposite, second end  40  which is usually enhanced, e.g., by enlargement, to provide a visual indication of vapor flow rate. The indicator end  40  of the paddle is viewed through the transparent cover  42  that has external gradation markings  44  to indicate flow rate. The indicator end  40  of the paddle  36  is biased to the low flow end, FL, of the graduated scale by a torsion spring  46  installed coaxially with the pin  48 , which provides a pivot axis for the paddle. The flow-sensing end  38  of the paddle is therefore in its minimum (FL) upstream (solid line) position. As vapor flow increases, force on the flow sensing paddle overcomes the torsion spring force, causing the paddle  36  to rotate about its pivot, toward its high flow (FH) downstream (dashed line) position, until the force applied on the paddle by vapor flow is in balance with the opposing force applied by the torsion spring. The torsion spring design is dictated by the need to indicate flow rates of up to at least 10 gym (gallons per minute) in order to match the maximum permitted rate of gasoline flow.  
         [37]    37. Other embodiments of coaxial vapor flow indicators of the invention, e.g., for detection of a kinked vapor hose, are contemplated. These include, in FIG. 7, an indicator assembly  20 ′ with a housing  50  containing a flow indicator module  31 ′ with a paddle wheel  52  mounted to indicate flow without reference to flow rate. In FIG. 8, an indicator assembly  20 ″ suited for vertical mounting has a housing  60  with a flow indicator module  31 ″ containing a float ball rotameter  62  to provide a flow rate reference. The rotameter  62  contains a rotameter-type glass or other precision float ball  64  disposed for movement between pins  66 ,  67  in response to vapor flow.  
         [38]    38. The transparent cover flow indicator module, e.g. module  31  (FIG. 4), may be turned 180E in the housing for indicating vapor flow in the opposite direction, e.g., to permit attachment of an indicator device of the invention to the dispenser hose outlet  72  (FIG. 1).  
         [39]    39. Referring next to FIGS.  9 - 11 , according to another preferred embodiment of the invention, a coaxial, vapor flow indicator  80  has a Venturi section  82  formed in the vapor path  84  to provide measurement of pressure differential as an indication of vapor flow rate.  
         [40]    40. The coaxial vapor flow indicator  80  consists of a flow indicator assembly  86  mounted to a one-piece cast metal body  88 . The body has a male, inverted hose, threaded connection  90  (with an o-ring seal  92 ) and an opposite female threaded connection  94 . As above, the indicator device  80  is adapted to be threaded into the dispenser side of a coaxial hose breakaway assembly  22  (FIG. 1), or into the dispenser side of a coaxial hose, dual plane, swivel hose breakaway assembly  22 ′ (FIG. 3), or directly into the dispenser side of fuel dispensing nozzle  26 ,  26 ′. The body  88  defines an outer passageway  96  for flow of fuel and the inner, coaxial passageway  84  for flow of vapor, the inner passageway defining the Venturi section  82 . The male connection  90  includes an extension  98  defining the inner passageway  84 , about which is mounted a spring stop  100 , the inner passageway  84  being sealed from outer passageway  96  by quad rings  102 .  
         [41]    41. The flow indicator assembly  86  mounted to the body  88  consists of a diaphragm cover  104  and a spring housing  106 , secured to the body by retaining ring  108  and sealed by o-ring  110 . The diaphragm cover  104  and spring housing  106 , together with body  88 , define a cavity  112 . A flexible diaphragm  114  secured between the diaphragm cover  104  and the body  88  partitions the cavity  112  into a first chamber  116  (between the flexible diaphragm  114  and the diaphragm cover  104  and spring housing  106 ) and a second chamber  118  (between the flexible diaphragm  114  and the body  88 ).  
         [42]    42. The body  88  further defines a first passageway  120  in communication between the narrow, upstream neck of the Venturi section  82  and the first chamber  116 , and a second, branched passageway  122  (with one branch sealed by plug  124 ) in communication between the vapor passageway at a location upstream of the Venturi section  82  and the second chamber  118 . As a result, the position of the flexible diaphragm  114  within the cavity  112  is responsive to and an indication of the differential in pressure between the inlet from the vapor passageway  84  to the first passageway  120  and the inlet from the vapor passageway  84  to the second passageway  122 , which in turn is an indication of vapor flow rate in the vapor passageway. The flow indicator assembly  86  includes a shaft  132  which extends through the spring housing  106 , with a first end  134  attached to the flexible diaphragm  114  and an opposite, second end to which is mounted adjusting screw assembly  138 , secured to the body portion  140  (FIG. 11) of a pointer  142  for indicating vapor flow rate, as described below. A compression spring  144  positioned in the spring housing  106 , about the shaft  132 , bears between the housing  106  and the flexible diaphragm  114 .  
         [43]    43. The flow indicator assembly  86  further includes a cylindrical lens  146 , secured about and upon the diaphragm cover  104  by cover  148 , and sealed by o-rings  150 ,  151 . Mounted a diaphragm cover  104  by binder head screws  152 , and visible though lens  146 , is an indicator plate  154  marked with a vapor flow scale (FIG. 10) which is calibrated in units of vapor flow rate, e.g., in inches of Water Column (WC), as shown, or in gallons per minute or other flow rate units, with flow indicated on the scale by the tip  158  of pointer  142 . As seen in FIG. 11, the pointer  142  has a first end portion  160  terminating against a stainless steel ball  162  (acting in the manner of a jewel bearing) press fit within a bore  164  defined by the diaphragm cover  104  and a second, opposite end terminating in tip  158  disposed in front of the scale on indicator plate  154 , as viewed through lens  146 . The intervening serpentine body portion  140  of the pointer  142  is closely fitted in a circular slot in the second end of the shaft  132 , adjacent the adjusting screw assembly l 38 .  
         [44]    44. Upon initiation of flow of vapor in the vapor passageway  84 , a differential of pressure is established between the first chamber  116  and the second chamber  118 , across the flexible diaphragm  114 . This differential of pressure acts to displace the flexible diaphragm  114 , overcoming the force of the compression spring  144 , displacing the shaft  132  (upward in the drawing) and flexing the pointer body  140  attached thereto to move the free end tip  158  of the pointer relative to the scale on the indicator plate  154  visible through the lens  146 , thereby providing an indication of vapor flow rate. The position of the pointer tip  158  relative to the scale may be adjusted, e.g. for calibration, by removing the button head screw  168  in the cover  148  and rotating the adjusting screw assembly  138  and the shaft  132 . This adjusts the position of the pointer relative to the scale without affecting the position of the diaphragm.  
         [45]    45. Referring now to FIG. 12, according to another embodiment of the invention, in a gasoline dispensing system  170  with vacuum assist Phase II vapor recovery, a Venturi device  172 , e.g., as described above with reference to FIGS.  9 - 11 , is placed in communication with a differential pressure transducer  174  for generating an electrical or other signal  176  proportionate to or otherwise indicative of vapor flow rate, e.g., to be transmitted to a flow comparator  178  and/or to drive an electronic display of vapor flow rate  180 .  
         [46]    46. In general, in a gasoline dispenser system  170  with vacuum assist Phase II vapor recovery system, as shown, liquid fuel (arrow, F) is delivered from an underground storage tank  182  into a vehicle tank (arrow, N) via a nozzle (not shown). The fuel delivered into the vehicle displaces vapor, which is recovered at the nozzle (arrow, R) for return by vapor vacuum pump  184  to the ullage space of the underground tank (arrow, V). The object of the system is to maintain a balance between the volume of fuel removed from the underground storage tank, into the vehicle, and the volume of vapor recovered and delivered into the storage tank as it is displaced from the vehicle tank.  
         [47]    47. In the system of FIG,  12 , vapor returning to the underground storage tank passes through the Venturi section  172 , which provides an indication of vapor flow rate through differential pressure monitoring, and results in issue of a signal  176  to the comparator  178 . Liquid fuel delivered from the underground storage tank  182  to the nozzle passes through the liquid flow meter  186 , which, via purser  188 , indicates liquid flow rate at The electronic flow meter  190 , and the flow meter  190  issues a signal  191  of liquid flow rate to the comparator  178 . The flow comparator then compares the respective vapor and liquid flow rates. If the vapor-to-liquid ratio is outside predetermined limits, e.g. due to an undetected kink in the vapor return hose or due to failure of the vapor vacuum pump or other vacuum flow control device, the comparator  178  issues a signal  192  to vapor vacuum pump  184  to adjust pump speed in a manner to return the vapor-to-liquid ratio to within the predetermined limits. If adjustment of pump speed fails to return the vapor-to-liquid ratio to within the predetermined limits within a preset period of time, a signal  192 ′ is issued by the comparator  178  to solenoid valve shut-off  194 , to shut down the system, thereby to limit escape of vapor to the environment.  
         [48]    48. A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, in another alternative embodiment of a coaxial, vapor flow indicator of the invention, a proximity sensor may be employed to detect the passing of signal elements mounted to individual blades on the paddle wheel, e.g. of the embodiment of FIG. 7. The signal rate would then allow electronic processing of this information, resulting in a visual display of the flow rate. The comparator  178  may be configured issue the signal  192 ′ to solenoid valve shut-off  194  to shut down the system whenever the vapor-to-liquid ratio is determined to be outside the predetermined limits.  
         [49]    49. In another embodiment, a detector element of the invention including a Venturi device disposed in communication with the inner vapor conduit and a diaphragm responsive to the pressure between the Venturi throat and the upstream inner vapor passageway, e.g. as shown in FIG. 9 et seq. and described above, may also include a magnet associated with, i.e. reflecting movement of, the diaphragm and an indicator element consisting of a signal indicative of the vapor flow rate issued from a Hall Effect device. Referring to FIG. 13, in this embodiment, movement of the diaphragm, D, in response to changes in pressure, P, between the Venturi throat and the upstream inner vapor passageway, moves an associated magnet, M, relative to Hall Effect device, H, which issues a signal, S, indicative of vapor flow rate, based on measurement of the proximity of the magnetic field, F, e.g. between 0-5 millivolts.  
         [50]    50. Accordingly, other embodiments are within the scope of the following claims.