Abstract:
The invention concerns a sensor for detecting leaks in a liquid hydrocarbon dispenser, said sensor comprising a sealed plate arranged at the dispenser base and provided with a collecting container for receiving said liquid hydrocarbons collected by said sealed plate and coming from leaks in the dispenser, said collecting container comprising a sensor at the level of said hydrocarbons, capable of stopping the operation of the dispenser when the hydrocarbon level sensed reaches a predetermined level (N). The invention is useful for protecting the environment against hydrocarbon pollution.

Description:
FIELD OF INVENTION 
     The present invention relates to a sensor for detecting leaks in a dispenser for liquid hydrocarbons. 
     The invention can be applied to particular advantage in the field of environmental protection against hydrocarbons, especially fuels for motor vehicles. 
     BACKGROUND OF THE INVENTION 
     In view of growing concerns to preserve the quality of the environment, it appears essential to fit liquid hydrocarbon dispensers with a sensor for detecting leaks, regardless of where they originate within the dispenser. 
     Several detection systems have been proposed for this purpose. 
     Firstly, it is possible to detect the vapours from liquid hydrocarbons inside the dispenser. This can be achieved either by means of biological, optical or combined sensors or by measuring the density of vapours contained in the dispenser. However, in view of the very marked variety of temperatures, humidity and quality of installation at service stations, this type of detection triggers numerous false alarms or, even worse, no alarm at all. Biological sensors, furthermore, have a tendency to become poisoned by additives. When it comes to liquid hydrocarbons of the gas oil type, these generate no or little vapour and it is difficult to detect their presence other than by the odours of the additives which they contain. 
     It would be conceivable to detect leaks by taking pressure measurements at different points in the pipework system for the hydrocarbons. However, to detect slight leaks, it is necessary to have a perfect knowledge and model of the distribution of pressure in the passages depending on the conditions under which the dispensers are installed on site and the sensors need to be extremely sensitive, in order of several mbars, and be capable of withstanding pressure surges of more than 15 bars, which require extremely expensive equipment. Moreover, the software must exhibit a high degree of intelligence to be able to process data from the sensors. Finally, sensors operating in hazardous areas also need to be security-protected and are therefore very expensive. 
     SUMMARY OF THE INVENTION 
     Accordingly, the technical problem to be resolved for the purposes of the invention is that of proposing a sensor for detecting leaks in a liquid hydrocarbon dispenser that would be simple in design and cost-effective whilst providing perfect efficiency and the requisite security. 
     This technical problem is resolved for the purposes of the invention due to the fact that said sensor comprises a sealed plate, arranged on the base of said dispenser and fitted with a catchment container designed to receive the liquid hydrocarbons collected by said sealed plate and coming from leaks in the dispenser, said catchment container having a level detector for said hydrocarbons, capable of halting operation of the dispenser if the detected level of hydrocarbons reaches a given level. 
     This provides a perfectly reliable sensor due to the presence of the sealed plate in the base of the dispenser where liquid hydrocarbons emanating from all leaks, regardless of their origin, are collected and detected. Furthermore, the sensor proposed by the invention uses components (plate, catchment container and level detector) which are cheap and easy to install in the dispensers. 
     By virtue of another advantageous feature of the leakage sensor proposed by the invention, said dispenser has a pump, a flow-rate counter and a computer, said computer being capable of detecting a flow rate of liquid hydrocarbons in said counter after the dispensing process because said pump continues to operate for a given period. 
     As a complement to overall detection of leaks inside the dispenser, this particular feature pinpoints any leaks which might occur downstream of the flow-rate counter. In practice, after dispensing, immediately after the gun is replaced, rather than halting the motor of the pump in the dispenser as usually happens, operation of said motor is continued for a period in the order of a few seconds during which the computer continues to monitor the data from the counter so that if a flow rate is detected by the computer, it can only be attributable to a leakage downstream of the counter, and an indication of this fault can then be given to the service station manager, pinpointing where the dispenser is faulty. This detection system is particularly useful in the case of dispensers fitted with double hose vapour recovery devices as a means of detecting any leaks of liquid hydrocarbons which might be sucked in by the recovery device. 
     The description outlined below with reference to the appended drawings, given by way of illustration and not restrictive in any respect, should provide an understanding of what the invention comprises and how it can be operated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a liquid hydrocarbon dispenser fitted with a leakage sensor as proposed by the invention. 
     FIG. 2 is a side view of a level detector of the leakage sensor of FIG.  1 . 
     FIG. 3 is a side view of a first variant of the embodiment of the level detector illustrated in FIG.  2 . 
     FIG. 4 is a side view of a second variant of the embodiment of the level detector illustrated in FIG.  2 . 
     FIG. 5 is a side view of a level detector fitted with a water-level detector. 
     FIG. 6 is a side view of a pipe passage through the sealed plate of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a dispenser  1  for liquid hydrocarbons having a pump  10  which extracts said hydrocarbons from a storage tank  2  and conveys them into a gas-release device  20 , the purpose thereof being to remove the gases incorporated in the liquid, which is then fed to a flow-rate counter  30 , generally capable of producing a movement in rotation, the angular speed of which is proportional to the hydrocarbon flow-rate. A transducer  31  of the wheel encoder type enables the mechanical position of the counter to be converted into electric pulses. Said pulses are transmitted to a computer  32  in order to establish the volume of hydrocarbons dispensed and the amount payable on the basis of the unit price. 
     Having passed through the flow-rate counter  30 , the liquid is conveyed through a member  40  providing a connection to a flexible hose  50  terminating in a dispenser gun  51 . 
     As may be seen from FIG. 1, the dispenser  1  has a leakage sensor  100  essentially comprising a sealed plate  101  arranged on the base of the dispenser  1  and a catchment container  102  designed to receive the liquid hydrocarbons collected by the plate  101  and coming from leaks in the dispenser. In the embodiment illustrated in FIG. 1, the catchment container  102  is positioned substantially at the centre of the plate  101 , this latter being of a flared design to facilitate the flow of hydrocarbons collected to the catchment container  102 . 
     As illustrated in FIG. 1, the catchment container  102  has a level detector  103  capable of halting operation of the dispenser  1  if the detected level of hydrocarbons reaches a given level N. In the example given in FIG. 1, the level sensor  103  is connected to the motor of pump  10  of the dispenser, If the given level is reached, the detector  103  sends a signal commanding that operation of the motor of the pump  10  be halted. 
     FIG. 2 illustrates a specific embodiment of the level detector  103  in which a float  1031  is placed in the catchment container  102 . The position of said float  1031  is detected by a position sensor comprising a magnet  1032  disposed at the non-immersed end of the float  1031  and an element  1033  sensitive to the magnetic field, such as a Reed relay or a Hall effect sensor, and connected to the pump  10 . As the catchment container  102  fills up, the level of the float  1031  rises and the magnetic field detected by the sensitive element  1033  increases until it reaches a high enough value to actuate said sensitive element and trigger the shutdown of the motor of the pump  10 . The level N at which the leakage sensor  103  is triggered is calibrated so as to correspond to a given volume of leakage, for example less than 100 cm 3 . 
     FIG. 3 illustrates an embodiment of the level detector  103  comprising a piezoelectric transducer  1034  designed to emit an ultrasound wave and detect the echo reflected from the surface of the liquid hydrocarbons in the catchment container  102 . The time which elapses between emission of the ultrasound wave and detection of the echo is directly proportional to the position of the liquid level in the container  102 . 
     Another embodiment is illustrated in FIG.  4 . This is an optical level detector comprising an optical fibre  1035  which emits a light wave and a receiving optical fibre  1036 , positioned in alignment on either side of the catchment container  102 . If the level of liquid hydrocarbons has reached the level N of FIG. 4, the light wave is deflected by reflection and refraction and the receiving optical fibre  1036  no longer receives light radiation and this situation is detected by an optical sensor, not illustrated, located at the end of the optical fibre  1036 , which sends a signal to shut down the pump  10 . 
     In view of the fact that water may accidentally get into the catchment container  102 , means must be provided to overcome this problem, which is likely to distort operation of the leakage sensor proposed by the invention. 
     A first approach is to make the catchment container  102  so that it can be moved, enabling the service station manager to purge said recipient of any water each time the dispenser  1  is inspected. 
     In the case of service stations unattended by personnel, the level detector illustrated in FIG. 5 may be used. This latter detector uses a piezoelectric transducer  1034 , identical to that of FIG. 3, designed to detect the echoes of the ultrasound wave produced on the one hand at the air/hydrocarbon interface and on the other hand at the hydrocarbon/water interface. The time separating these two echoes is directly proportional to the height h of hydrocarbons. 
     Clearly, in view of its position in the dispenser  1 , the plate  101  has passages through it, such as that shown by reference  21  in FIG. 1, coming from the storage tank  2 . In order to ensure that the leakage sensor proposed by the invention is sealed, the passage of any pipes running through the plate  101  must be sealed in turn and this can be effected by means of a flexible bellow expansion joint  104  such as that illustrated in FIG.  6 . 
     The computer  32  may be provided with software which, instead of halting the pump  10  when the gun  51  is replaced, i.e. at the end of the dispensing operation, prolongs operation of said pump for a given period, a few seconds. In this manner, if there are any leaks of liquid hydrocarbon downstream of the counter  30 , a flow rate will be detected by the computer  32  and the anomaly will be indicated to the service station manager. As already mentioned above, this option of detecting leaks downstream of the flow-rate counter  30  has the advantage of highlighting induction of liquid hydrocarbons by the vapour recovery devices fitted to the dispensers.