WO2007036754A1

WO2007036754A1 - Fuel dispensing apparatus and method thereof

Info

Publication number: WO2007036754A1
Application number: PCT/IB2005/002845
Authority: WO
Inventors: André Sylvere Joseph VAN COILLIE; Frank Jan Nijhof
Original assignee: M.I.T.Z.I. S.R.L.
Priority date: 2005-09-27
Filing date: 2005-09-27
Publication date: 2007-04-05

Abstract

The present invention relates to a fuel dispensing apparatus comprising one or more pumping units. Advantageously each pumping unit comprises a foam breakdown rotor for applying a centrifugal force to the fuel and the fuel foam. 5 Leaks are promptly detected by way of fuel level sensors monitored by suitable control means. Strainers are cleaned at each pumping cycle by a fuel back flow.

Description

"FUEL DISPENSING APPARATUS AND METHOD THEREOF"

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FIELD OF THE INVENTION

The present invention refers to a fuel dispensing apparatus, in particular to a multiproduct fuel dispensing (MPD) apparatus for supplying different fuels to motor vehicles, and to the operating method thereof. BACKGROUND OF THE INVENTION

The invention relates to a fuel dispensing apparatus, in particular for different relatively volatile vehicle fuels, such as gasoline (leaded or unleaded), diesel, etc. to be delivered in a gas station. Such a dispensing apparatus is known as multiproduct dispenser (MPD) and contains generally 2, 3 or 4 pumping units, one per product. Generally each of the pumping units feeds two dispensing nozzles to be operated by the user. Traditionally each pumping unit comprises a volumetric type pump, for instance a vane pump, for drawing the fuel from a storage tank and delivering the same to a vehicle through a nozzle. Each pump is normally operated by a corresponding electric motor. Thus a MPD dispenser may comprise several electric motors, this leading to high purchase, operating and maintenance costs. The European patent application n. EP 1065384, from the same inventor, discloses a MPD dispenser wherein each pumping unit is provided with a closed pump housing having an intake connected to a supply of one of the fuels, for instance a storage tank, and comprising at least one discharge connected to a delivery means of a vehicle fuel station, i.e. a nozzle. Advantageously the pump is a hydrodynamic fuel pump having a fuel inlet drawing from the interior of the pump housing and a pressure outlet connected to the discharge. All the pumps of the MPD dispenser can be operated by a single motor, this allowing for minimizing of the costs for assembling, operating and maintaining the dispenser. The hydrodynamic pumps of the dispenser are primed by a single gas pump having a gas inlet drawing from the pump housing of each of the pumping units. In particular only the pumps which deliver the fuels selected by the user are primed, while the remaining pumps are not primed and run idle.

A drawback of the dispenser according to EP 1065384 is in that foam is generated in the pump housing by the fuel when it passes through the respective hydrodynamic pump, especially when the fuel is diesel. In other words foam is generated by the fuel due to the interaction between the diesel and the blades/vanes of the pump. Thus there is the necessity for breaking down the foam and avoiding the foam from being dispensed together with the liquid fuel. Also the foam would lead to incorrect flow rate measures of the dispensed fuel operated by a flow meter. Traditional pumps are provided with a container to be filled with the liquid fuel wherein breaking down of the foam is achieved slowly by action of the gravity force.

Usually known MPD dispensers are provided with a strainer for filtering impurities from the fuel drawn from the respective storage tank. For instance the strainer may be arranged in the intake line connecting a pump to an underground storage tank. A problem, which is common to all the MPD dispenser, is in that the strainer soils easily, this increasing the resistance of the fuel flow in the intake line. Thus it is desirable to keep the strainer clean as long as possible. In fact cleaning of the strainer is periodically operated by a technician with evident increasing in the maintenance costs of the MPD dispenser.

Another drawback of known fuel dispensing apparatuses is in that fuel leaks may occur which must be timely blocked for security reasons. Leaks are difficult to detect and to isolate. It is therefore desired to provide the fuel dispensing apparatuses with effective devices for detecting fuel leaks and isolating the defective portion. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fuel dispensing apparatus, in particular a MPD apparatus, which overcomes the drawbacks of known fuel dispensing apparatuses in a simple and inexpensive way.

It is a further object of the present invention to provide a fuel dispensing apparatus which allows for the breakdown of the fuel foam. It is still an object of the present invention to provide a fuel dispensing apparatus which allows for the prompt fuel leak detection, locally as well as remotely, and for the automatic shutdown of the defective portion of the apparatus.

It is another object of the present invention to provide a fuel dispensing apparatus which allows for minimizing of the soiling of the fuel strainers. These and other objects are achieved by the present invention which concerns a fuel dispensing apparatus comprising one or more pumping units each having a closed pump housing with an inlet connected to a fuel supply, at least one discharge connected to a fuel delivery means, and a hydrodynamic fuel pump with a fuel intake drawing from the interior of the pump housing and a pressure outlet connected to said discharge, and further comprising at least one separate vacuum pump having a gas inlet drawing from the pump housing of each of said one or more pumping units, wherein fuel foam may be generated by the pumping action on the fuel, characterized in that for at least one pumping unit it further comprises a foam breakdown rotor having an intake drawing from said pump housing and an outlet connected to said vacuum pump, said foam breakdown rotor applying a centrifugal force to said fuel and fuel foam.

The centrifugal force acting on the foam bubbles can be about 300 times greater than the gravity force responsible for the breaking down of the foam bubbles in conventional fuel pump systems. This results in a dramatically increasing of the foam breaking down speed. Advantageously the bubbles generated by the pumping of the fuel, for instance diesel fuel, rapidly break under the centrifugal force exerted by the rotor. The liquid fuel resulting from the bubble breakdown is recovered in the pump housing through a passage provided at the periphery of said rotor. Preferably the foam breakdown rotor intake draws from an upper portion of the pump housing.

According to one embodiment, the foam breakdown rotor is mounted on the same shaft together with the hydrodynamic fuel pump and is arranged between the vacuum pump and the vacuum pump inlet. Advantageously the fuel dispensing apparatus according to the invention allows for the effective pumping of different types of fuel regardless of fuels generating foam when processed by the hydrodynamic pump. For instance, the apparatus may be a MPD for delivering different kinds of diesel fuel in petrol stations. The apparatus of the present invention allows for a simple and inexpensive breakdown of the fuel foam. The rotor may have a simple design to minimize production costs and may be easily mounted on the pump shaft to minimize the apparatus encumbrance and achieve a compact configuration and simple actuation. On the contrary in the traditional systems the longer time needed to break down the foam bubbles requires the container to have large dimensions. Moreover all the advantages of using hydrodynamic pumps for delivering fuel are maintained.

The foam breakdown rotor operates as a barrier for the foam between the pump container and the vacuum pump, in such a way that only liquid fuel is supplied to the delivery means, for instance the nozzle of the petrol station. The present invention relates also to a fuel dispensing apparatus comprising one or more pumping units each having a closed pump housing with an inlet connected to a fuel supply, at least one discharge connected to a fuel delivery means, and a hydrodynamic fuel pump with a fuel intake drawing from the interior of the pump housing and a pressure outlet connected to said discharge, and further comprising at least one separate vacuum pump having a gas inlet drawing from the pump housing of each of said one or more pumping units and a gas discharge outlet, characterized in that for at least one pumping unit it further comprises a vacuum shut off valve in the connection with the vacuum pump and a discharge shut off valve in a connection with said gas discharge outlet, an upper level fuel detector, arranged at an upper portion of said pump housing, and a lower level fuel detector, arranged at a lower portion of said pump housing, both detectors being connected to control means for the actuation of said shut off valves. The control means may be monitored remotely, for instance from a remote control centre.

At each pumping operation, for example each time a nozzle is operated to supply fuel to a vehicle in a gas station, the control means checks the time occurred for the fuel to fill the pump housing when the vacuum pump is priming the hydrodynamic pump. The control means may also check the level of the fuel in the pump housing continuously. For instance the control means monitors the condition of the upper level fuel detector to check if the fuel is periodically at the maximum level within the pump housing.

In this way it is possible to immediately detect leaks or malfunctions of the apparatus and to quickly isolate the same. In fact if the time between the triggering of the detectors by the fuel exceeds a threshold value the control means actuates the shut off valves to achieve isolation of the defective pumping unit.

The control means may also check the rate at which the fuel fills the pump housing when the vacuum pump starts.

It is evident that the apparatus allows for the prompt detection of failures and leaks and for the shut down of the defective pumping unit. This can be achieved automatically and can be monitored remotely when the control means is connected to a remote operative headquarter. This case is particularly advantageous when the apparatus is used to pump fuel in gasoline stations. In fact leaks or failures of any pumping unit may be immediately detected by a central operative headquarter with evident improving in the security and lowering the maintenance costs of the apparatus.

The fuel dispensing apparatus may comprise a strainer or filter in the connection line between the pump housing and the fuel supply, for instance a storage tank. In order to minimize the build up of impurities within the strainer, the apparatus provides a sort of auto-cleaning function. At the end of each pumping operation the control means closes the vacuum shut off valve and opens the discharge shut off valve to let the fuel contained in said pump housing flowing back in the underground storage tank through the strainer, thus washing the same from impurities. This allows for a sensible reduction of the maintenance costs related to the strainer and to the apparatus. Preferably the control means operates in such a way that at least an amount of fuel flows back in the fuel supply through the intake of the pump housing until the fuel in said pump housing reaches a set level. Cleaning of the strainer is important since impurities or the like may compromise the operation of the pump or valves. In known apparatuses the strainer is frequently renewed by a technician. The apparatus according to the invention allows for a sensible increasing in the time between successive attends of the technician with evident reduction in the maintenance costs of the apparatus. BEST WAY TO CARRY OUT THE INVENTION Further advantages and features of the present invention will become apparent from the following detailed description with reference to the drawing enclosed as a non-restrictive example, where:

- figure 1 is a sectional view of a part of a first embodiment of the fuel dispenser apparatus according to the present invention; - figure 2 shows a schematic layout of a fuel dispenser apparatus according to the present invention;

- figure 3 is a partial schematic sectional view of a part of a second embodiment of the fuel dispenser apparatus according to the present invention. The fuel dispenser apparatus according to the present invention comprises at least a pumping unit 1 as shown in figure 1 , but preferably the apparatus is a multi-product dispenser MPD provided with several pumping units, for instance 1-3, as shown in figure 2, for delivering as many types of fuel, for instance low-octane unleaded petrol (gasoline), high-octane unleaded petrol, diesel, etc..

Each pumping unit 1 , 2 and 3 has a pump housing H intended to be filled with fuel and a fuel intake, respectively 11 , 21 , 31 , connected to a fuel tank (not shown) for drawing a specific fuel into the housing H. The tank may be an underground fuel tank usually provided in the petrol stations. The pump of the pumping units 1 , 2 and 3 is a hydrodynamic pump P arranged within the respective housing H, mounted horizontally as shown in the figures 1-2 or vertically on a shaft. Preferably all the pumps P of the pumping units 1 , 2 and 3 are driven by a single motor M. for instance by way of pulleys 12, 22, 32 and belts B. The pumps P supply the pumped fuel to a discharge 13, 23, 33 connected to a fuel delivery means, preferably a fuel nozzle of the type normally provided in gas stations for dispensing fuel to a vehicle tank. In particular the pumps P have a fuel intake Pl drawing from the interior of the pump housing H and a pressure outlet PO connected to said discharge 13, 23, 33. The pump pressure outlet PO can be a single discharge 13, 23, 33 for one high flow rate nozzle or a double discharge for two nozzles with standard 40 l/min flow rate. A non return valve 4 avoids the emptying of the outlet pipe (not shown) from the fuel when the pumping unit 1 , 2 and 3 is not pumping. A vacuum pump VP is provided for drawing the fuel gas from the pump housings H and for priming the hydrodynamic pumps P, i.e. for filling the housing H with fuel to have the pump P immersed. The vacuum pump VP may have also operate for the vapour recovery as normally required for actual gas stations. The vacuum pump VP may be driven by the motor M as shown in figure 2. The vacuum pump VP is connected to all the pump housings H through a common line 50 and respective gas inlets 14, 24 and 34. The same vacuum pump VP supplies the recovered fuel gas to a storage tank for processing through the line 60.

Preferably the hydrodynamic fuel pump P is a two-stage centrifugal pump comprising two impellors I and two stators S. The number of stages may be different in order to deliver different fuel flow rates at different pressures. The impellors I and the stators S are mounted on a shaft 5 and a flange so to form altogether a cartridge which is tested and pre-aligned before mounting in the pump housing H. In this way the cartridge can easily be replaced in case of failure with no need for dismounting other parts of the pumping unit 1 , 2 or 3. The shaft 5 rotates supported by two ball bearings 6 which are mounted in the front flange to resist axial and radial forces.

The pulley 12 is fixed on the shaft 5 and is designed to minimize the momentum transferred by the shaft 5 to the ball bearings 6. This momentum is due to the traction of the belt(s) B on the pulley 12. The MPD apparatus shown in the figures 1 and 2 allows for the simultaneous delivery of fuel through two nozzles, typically one nozzle on each side of the apparatus. If the two nozzles deliver the same product, only one pumping unit 1 , 2 or 3 is activated. If the two nozzles deliver a different product, two pumping units 1 , 2 or 3 are activated. Normally MPDs do not provide activation of more than two pumping units. Normally the total flow rate of a MPD is thus maximum 80 l/min (40 l/min. on each side of the MPD). The work needed to run a centrifugal pump, such as the pump P, is approximately proportional with the fuel flow rate, which means that the work (and the power) needed to run the centrifugal pump P when the nozzles connected to the discharge 13 are closed is limited to the liquid friction losses. This is not valid for volumetric pumps which require always almost the maximum work and power even when nozzles are closed. Advantageously the pumping units 1 , 2, 3, etc., are coupled to one motor M. In the worse case the motor M shall operate two pumping units 1 , 2 or 3, each with a maximum flow rate of about 40 l/min.

Several fuels, such as the diesel, easily generate foam when pumped in the housing H. Thus there is the need for breaking down the foam and avoiding the same from being delivered to the vacuum pump VP. The apparatus overcomes this problem by providing a foam breakdown rotor R associated at each pump P. The foam breakdown rotor R has an intake 8 drawing from the correspondent pump housing H and an outlet 9 connected to said vacuum pump VP through the connection 14.

The foam breakdown rotor R applies a centrifugal force to the mixture of fuel and fuel foam in order to breakdown the foam, i.e. in order to rupture the foam bubbles and recover the fuel liquid. In other words the foam breakdown rotor R operates as a barrier for the foam.

Advantageously the foam breakdown rotor R allows for an accelerated breakdown of the fuel foam bubbles and for the setting of a centrifugal force, preventing the fuel resulting from the broken foam bubbles to be sucked into the vacuum pump VP. The foam bubbles may be thought as a small sphere of gas surrounded by a film of liquid fuel, which is kept around the gas sphere by its surface tension. In stationary conditions the fuel foam breaks down by the gravity force acting on the foam bubbles. In fact due to the gravity force, the film of liquid becomes thicker at the lower portion of the bubbles, while the film becomes thinner at the upper portion of the same bubbles. When the upper portion of the film becomes so thin that the surface tension of the liquid is not able to keep the film complete, the foam bubbles explode and the film becomes a liquid droplet. Thus the "breaking down speed" of the foam depends on the surface tension of the liquid and on the gravity force acting on the foam. The foam breakdown rotor R increases the effect of the gravity force and, thus, increases the "breaking down speed" of the foam.

The foam breakdown rotor R is lodged within a casing 40 and comprises at least one blade 10, but preferably it comprises several blades 10 intended to centrifuge the foam or the mixture of foam and liquid fuel which enters the intake 8 at an upper level of the pump housing H. The liquid fuel obtained by the breaking down of the foam or drawn from the housing H is directed by the blades 10 toward the casing 40 of the rotor R. A passage 41 is provided on the casing 40 to deliver the liquid fuel back into the housing H. The fuel gas is sucked by the vacuum pump VP through the outlet 9 of the rotor R and the connection 14. When the fuel dispensing apparatus is operated a pressure difference is kept between the pump housing H and the vacuum pump VP suction side in order to impede the same vacuum pump VP from sucking liquid fuel with the gas. The maximum pressure difference is preferably about 400 mbar. For example, if the foam breakdown rotor R rotates at 3000 rpm the centrifugal force applied on the fuel droplets at the periphery of the rotor R may result in a pressure on the liquid fuel equal to about 500 mbar. The centrifugal force on the liquid fuel is consequently bigger than the sucking force applied on the same liquid by the vacuum pump VP, i.e. the pressure difference between the rotor R periphery and the vacuum pump VP is sufficient to avoid the liquid fuel from being sucked by the vacuum pump VP.

In this way the apparatus provides a protection against the introduction of liquid fuel in the vacuum pump VP even when one or more electrovalves provided on the connection 14 are defective.

The skilled man will appreciate that the fuel dispensing apparatus of the present invention allows for the effective breaking down of the foam generated by a fuel. The rotor R is simple to manufacture and to assemble in the respective pumping unit 1 , 2 or 3 together with the pump P, preferably on the same shaft 5. The design of the blades 10 of the rotor R may be simple since their function is to apply a centrifugal force. Thus production costs of the rotor R do not affect in a sensible way the production costs of the apparatus. Moreover the rotor R does not affect the operation of the apparatus when the pumped fuel does not generate foam. The fuel dispensing apparatus can be utilized not only for assembling MPDs for vehicle gas stations but it may serve to deliver fuel to boats, trains, airplanes, etc. wherein dispensed fuels generate foam when pumped. Preferably a shut off valve is provided downstream of each gas inlet 14, 24 or

34 to block the gas passage. The pumping units 1-3 are provided with the vacuum shut off electrovalves A1 , A2 and A3 respectively. A by-pass 15, 25,

35 is provided which connects each gas inlet 14, 24 or 34 to the gas discharge outlet line 60 communicating the vacuum pump VP to the storage tank. Electrovalves B1 , B2 and B3 are provided also within each by-pass 15, 25, 35 for shutting off the discard flow rate through the same. The electovalves A1-A3 and B1-B3 are controlled by suitable control means (not shown) such as a circuitry, a computer, etc., which may be itself monitored remotely, for instance by a remote operative centre. Each pumping unit 1 , 2 or 3 is provided with an upper level fuel detector respectively C1 , C2 or C3, arranged at an upper portion of the pump housing H, and a lower level fuel detector respectively D1 , D2 or D3, arranged at a lower portion of the pump housing H. The detectors C1-C3 and D1-D3 are intended to be triggered by the fuel when it reaches the level of the detector and are connected to the control means for the actuation of shut off valves A1-A3 and B1-B3. The pumping unit 1 shown in figure 1 is provided with the upper level detector C1 at the top of the housing H and the lower level detector D1 at the bottom of the housing H.

When the fuel is sucked into the housing H the lower level detector D1 is triggered and a correspondent signal is input to the control means. When the fuel fills completely the housing H, i.e. when it reaches the top of the container H, the upper level detector is triggered and a correspondent signal is input to the control means. In this way the control means monitors the level of the fuel within the pumping unit 1.

It is evident that a larger number of fuel level detectors may be provided to check different fuel levels. Advantageously the apparatus allows for the effective checking of fuel leaks. In fact if a leak occurs in a portion of the apparatus, the fuel level within the housing H changes, i.e. drops. The unexpected variation in the fuel level is monitored by the control means through the detectors C1-C3 and D1-D3. The control means generates an alarm signal, for instance by transmitting an electronic signal to a remote operation centre, and isolate the defective pumping unit 1 , 2 or 3 by actuating the shutting off electrovalves A1-A3, BIBS. When the electrovalve A1 is open, the vacuum pump VP sucks the air/gas mixture out of the pump housing H trough the connection 14, the outlet 9 and the rotor R as indicated by the arrows in figure 1.

Due to the very low density of the air/gas mixture, no significant centrifugal force acts on the air/gas mixture when the foam breaking down rotor R is operating.

When the fuel level, topped with a more or less thick layer of foam, rises in the pump housing H, the foam is sucked in the intake 8 and enters the rotor R where it is suddenly accelerated by the rotational speed of the blades 10 and pushed to the periphery by virtue of the centrifugal force. Both the rotational and the centrifugal acceleration increase the "breaking down speed" of the foam.

The centrifugal force acts as a gravity amplifier which pushes the liquid originated from the broken down foam bubbles in the collector gap 42 and out of the rotor R through the passage 41 back in the housing H. The air/gas mixture, not affected by the rotation of the rotor R is sucked from the outlet 9 and delivered to the vacuum pump VP through the open valve A1. Priming of a pumping unit. Now the priming of a pumping unit will be explained with reference to the sole pumping unit 1 since operation of the other pumping units is the same.

When electrovalve A1 is open, the vacuum pump VP sucks the air/gas mixture out from the pump housing H through the intake 8, the rotor R and the outlets 9 and 14. The pressure within the pump housing H and in the inlet 11 coming from the underground storage tank drops and fuel is sucked from the underground storage tank into the housing H.

The pump housing H fills up with fuel until its level reaches the upper level detector C1. When the upper level detector C1 is triggered, the control means closes the vacuum shut off electrovalve A1 , thus blocking further filling of the housing H by the vacuum pump VP. The pump stages I and S are now immersed in the fuel and the pump P generates the necessary pressure for pumping. Operation of a pumping unit.

Now the standard operation of a pumping unit will be explained with reference to the sole pumping unit 1 since operation of the other pumping units is the same. During normal operation of the fuel dispensing apparatus, the pumping units 1 , 2 or 3, which are not pumping fuel are emptied in order to save power consumption and to avoid heating of the fuel by friction. The lower level of the fuel is monitored by the control means through the lower level detector D1 , D2 or D3 and the electrovalves A1-A3 and B1-B3. Once the nozzle connected to the pumping unit 1 is taken out of the nozzle booth, for instance for serving a vehicle in a gas station, the vacuum shut off electrovalve A1 is opened and the fuel level in the pumping unit 1 rises. Within a few seconds the fuel level in the unit 1 has immersed the pump P and the apparatus is in operating mode. The electrovalve A1 stays open until the fuel level reaches the upper level detector C1 which is triggered and initiates to close.

The pumping unit 1 is now delivering fuel to the nozzle, through the discharge 13, but also some gas bubbles which accumulate above the fuel in the housing H. This makes the fuel level to lower until the upper fuel detector C1 is not triggered. Then the control means opens the electrovalve A1.

By this, and similar as in the priming mode, the gases accumulated in the upper part of the pump housing H are evacuated by the vacuum pump VP until the upper level detector C1 is triggered again and the electrovalve A1 is closed. Consequently, the fuel level increases and decreases around the level corresponding to the upper level detector C1. Continuous leak detection with remote error signal.

The objective of the MOCs (Major Oil Companies) is to diagnostic on-line their filling gasoline stations from their central headquarters for leaks in the dispensing apparatuses and other errors such as malfunctioning or failures of the vapour recovery devices.

An error occuring during the functioning of an MPD in one or more pumping units may not influence the proper functioning of the other pumping units of the same MPD. This means that the pumping unit presenting a leak must be detected and isolated from the vacuum pump VP, enabling the latter to continue to degas the other pumping units when needed. The fuel dispensing apparatus according to the present invention includes an auto-diagnostic feature for remote leak detection, i.e. the apparatus allows for the effective detection of fuel leaks, for the transmission of an alarm signal to a remote headquarter and for the shut off of the defective part of the apparatus with evident improvements in the safety of the system. Checking of the fuel level by the control means is preferably continuous. Alternatively the monitoring may be operated at a preset rate. The fuel dispensing apparatus may detect leaks in several ways. In a first case, when the flow rate of the air/gas leakage in a suction pipe is larger than the flow rate of the air/gas extraction by the vacuum pump VP, the liquid level in the pump housing H lowers. An error signal is generated by the control means after for instance five seconds from when the upper level detector C1 is not triggered and the pump P is isolated from the vacuum source VP and emptied together with its housing H. The leak may occur in the pump housing H or in the supply line 11 or also in the underground storage tank (the underground tank may also run dry while the apparatus is drawing fuel from it). This can happen while the MPD delivers fuel through one or, simultaneously, through two nozzles. If the two nozzles deliver from the same tank (i.e. they deliver the same fuel), and thus through one single pumping unit 1 , 2 or 3, the pump P stops and is isolated from the vacuum source VP by the control means activating the vacuum shut off valve A1 , A2 or A3. An error signal is generated and transmitted to the headquarter.

If the two nozzles deliver fuel from different tanks (i.e. they deliver different fuels), the pumping unit 1 , 2 or 3 which is suffering from the leak is isolated by the control means from the vacuum source VP within for instance five seconds and is emptied. An error signal is transmitted remotely to the headquarter, for instance by way of a RF interface, a GSM interface, via internet, etc.. The other pumping units continues to deliver fuel. The time lapse of five seconds is an example. Another reference value may be set. Operation of the control means with respect to the leak detection.

Lets assume that the pumping units 1 , 2, or 3 of the MPD are in stand-by and one or two nozzles are taken out of their nozzle booths. The first nozzle taken out of the nozzle booth activates, by means of its nozzle booth micro- switch, the motor M of the pumping units 1 , 2 or 3 and the vacuum pump VP. The corresponding electrovalve A1 , A2 or A3 is activated and opens, allowing the respective pumping unit to be filled with fuel. At the same time a counter of the control means starts and checks the time lapse between the opening of the valve A1 , A2 or A3 and the signal coming from the triggering of the corresponding lower level detector D1 , D2 or D3 indicating that the fuel has reached the lower level in the housing H.

If the time lapse is shorter than, for instance, five seconds, the pumping unit 1 , 2 or 3 continues to fill until the fuel level reaches the corresponding upper level detector C1 , C2 or C3 and the electrovalve A1 , A2 or A3 is closed setting the pumping unit in its normal working mode. If not, an error signal is generated, meaning that a leak occurred in the pump housing H or in the supply line 11 , or that the tank is empty. In this case the relative electrovalve A1 , A2 or A3 is immediately closed. This isolates the pumping housing H from the vacuum pump VP. The electrovalve B1 , B2 or B3 is opened and air/gas enters the pump housing H. The fuel level in the housing H lowers until the corresponding lower level detector D1 , D2 or D3 is activated. At this point the control means closes the electrovalve B1 , B2 or B3. The defective pumping unit 1 , 2 or 3 is now in "empty tank/leakage mode". The MPD continues to operate with the other pumping units until the problem which caused the leak is fixed by a maintenance intervention. During the pumping operation, due to gas bubbles production in the supply intake 11 , the fuel in the pump housing H lowers slowly, and when the upper level detector C1 , C2 or C3 is no more immersed in the fuel the corresponding electrovalve A1 , A2 or A3 is activated to open so that the vacuum source VP sucks the air/gas accumulated in the upper part of the housing H. At the same time a counter of the control means starts and monitors the time lapse between the opening of the valve A1 , A2 or A3 and the generating of the signal from the triggering of the upper level detector C1 , C2 or C3 indicating that the fuel has reached the upper level in the housing H. If the time lapse is shorter than, for instance, five seconds, the pump P continues to pump in its normal working situation, otherwise an error signal is generated, meaning that a leak occurred either in the pump housing or in the supply line 11 or that the underground storage tank is empty. The control means closes the electrovalve A1 , A2 or A3 and the corresponding defective pumping unit 1 , 2 or 3 is isolated from the vacuum pump VP and emptied. For instance, when the nozzle(s) of the pumping unit 1 is (are) put back in the nozzle booth, and the two nozzle switches are activated, the control means sets the following sequence for emptying the pump housing H and driving the pumping unit 1 back in stand-by:

- the electrovalve A1 is closed; - the electrovalve B1 is opened;

- the pumping unit 1 is emptied until the liquid level activates lower level detector D1 ;

- the electrovalve B1 is closed to stop further emptying of the housing H; - the pumping unit 1 is now in stand-by.

The skilled man will appreciate that the fuel dispensing apparatus according to the present invention allows for the prompt detection of the leaks occurring at any part of the same apparatus at any time during its operation and also for the detection of the storage tanks being empty. Emptying the pump at the end of the pumping operation.

The fuel dispensing apparatus may be provided with at least one filter or strainer 70 for intercepting impurities contained in the fuel. In order to reduce the soiling of the strainers 70 the apparatus provides a backwash feature. With reference to figure 1 a strainer 70 is arranged within the intake 11 to filter the fuel coming from the storage tank. At the end of each pumping operation, when the nozzle is placed back in the nozzle booth, the electrovalve A1 is closed (in the case it was open) and the electrovalve B1 is opened, letting atmospheric air/gas to enter the pump housing H. The fuel level in the housing H lowers, as the fuel flows through the strainer 70 in the opposite direction until the lower level detector D1 generates a signal which triggers the closing of valve B1. The fuel still lowers a small amount until the underpressure generated in the pump housing H stops the fuel from flowing further back to the underground storage tank through the intake 11. Now the pumping unit 1 is in stand-by for another pumping cycle. In this way at each pumping cycle the strainer is cleaned by the fuel flowing back to the storage tank. This feature allows for a sensible increasing of the time normally needed for the strainer to get completely soiled. In this way the costs for periodically replacing the strainer are reduced. The following description refers to an alternative second embodiment of the fuel dispensing apparatus according to the present invention. In some cases there is no need for a control over the leakage and the fuel dispensing apparatus can have a simpler structure than the one disclosed above. Figure 3 refers to a simpler embodiment of the apparatus according to the invention wherein the valves A and B and the level detectors C and D (which are expensive components) are respectively replaced by a single three-way electrovalve (not shown) and by a check valve 100 that automatically closes when the pump container is empty. In particular figure 3 schematically shows a portion of the pump container H and some components shown in figure 1 wherein like numbers refer to similar elements. The pump P, which is best shown in figure 1 , is schematically indicated in dotted line.

The check valve 100 closes the inlet 11 of the container H, through which the fuel is sucked from an underground storage tank.

A passage 200 is provided for communicating the discharge 13, i.e. the outlet of the second stage of the hydrodynamic pump P, with the check valve 100. The passage 200 extends vertically within the housing H and is connected to an horizontal passage 201 which opens into a guide 800. The check valve 100 has a portion 101 sliding within the guide 800. Between the vertical passage 200 and the horizontal passage 201 operates a non-return valve 300. When the pump P is operating, the fuel exits the pump P under pressure at the outlet 13 and is pushed into the passage 200. The non-return valve 300 remains open as long as the fuel is pressurized. In this configuration a fuel flow reaches the guide 800 of the check valve 100 through the vertical passage 200, the valve 300 and the horizontal passage 201. After the fuel pumping operation, the three-way electrovalve is set to let air in the pump container H so as to diminish the fuel level. As long as there is enough fuel in the pump P impellors to build up pressure at the outlet 13, the check valve 100 will be kept open by the pressurized fuel flow through the by-pass connection formed by the passages 200 and 201. When the fuel level in the container H becomes lower than the input level of the first pump impeller, the pressure at the output 13 drops and so does the pressure within the passages 200 and 201. In these conditions the check valve 100 slides downwardly within the guide 800 and closes the fuel inlet 11. The check valve 100 can be set to operate so as to close when the container H is substantially empty. The non-return valve 300 isolates the container H and the fuel in the passage 201 from the atmospheric pressure. A strainer 70 is located in the inlet manifold 11. The system operation will now be described.

When a nozzle is taken out from the nozzle booth the motor M starts to run as well as the fuel pumps and the vacuum pump. The three-way electrovalve (not shown), which is used instead of the electrovalves A and B (see Fig. 1 ), opens the connection between the pump container H and the vacuum pump VP. The fuel is sucked from the underground tank and fills the pump container H.

When the fuel and/or the foam reaches the level of the rotor R inlet 8, the fuel enters the rotor R, i.e. it is sucked in the foam barrier, and forms a liquid ring in the collector 42 by virtue of the centrifugal force applied by the rotor R. As the centrifugal force exerted on the fuel by the foam barrier rotor R is bigger than the pressure difference between the pressure in the container H and the pressure in the outlet collector pipe 14, no fuel will be sucked into the vacuum pump VP. The foam barrier R operates in this way also as a liquid barrier and obviates the need of the electrovalve A shown in figure 1.

When, after pump operation, the nozzle is placed back in the nozzle boot, the three-way valve closes the connection between the pump container H and the vacuum pump VP and opens the connection between the pump container H and the line 60 (see figure 2). The level of the fuel in the container H lowers until the latter is empty.

In order to keep the proper fuel pressure at the pump outlet 13 after the nozzle is back in its nozzle booth, a delay of a few seconds is foreseen between the inlet of the air in the container H and the stopping of the pump motor M.

Claims

1. A fuel dispensing apparatus comprising one or more pumping units (1- 3) each having a closed pump housing (H) with an inlet (1 1 , 21 , 31 ) connected to a fuel supply, at least one discharge (13, 23, 33) connected to a fuel delivery means, and a hydrodynamic fuel pump

(P) with a fuel intake (Pl) drawing from the interior of the pump housing (H) and a pressure outlet (PO) connected to said discharge (13, 23, 33), and further comprising at least one separate vacuum pump (VP) having a gas inlet (14, 24, 34) drawing from the pump housing (H) of each of said one or more pumping units (1 , 2, 3), wherein fuel foam may be generated by the pumping action on the fuel, characterized by comprising, for at least one pumping unit (1 , 2, 3), a foam breakdown rotor (R) having an intake (8) drawing from said pump housing (H) and an outlet (9) connected to said vacuum pump (VP), said foam breakdown rotor (R) applying a centrifugal force to said fuel and fuel foam.

2. The fuel dispensing apparatus according to claim 1 , characterized in that said centrifugal force is set to break said foam bubbles.

3. The fuel dispensing apparatus according to any claim from 1 to 2, characterized in that said foam breakdown rotor comprises a passage (41 ) which opens in said pump housing (H) for delivering the centrifuged fuel.

4. The fuel dispensing apparatus according to any previous claim 1-3, characterized in that said foam breakdown rotor intake draws from an upper portion of said pump housing.

5. The fuel dispensing apparatus according to any previous claim 1-4, characterized in that said foam breakdown rotor is mounted on the same shaft (5) with said hydrodynamic fuel pump and is arranged between said vacuum pump (VP) and said intake (8).

6. The fuel dispensing apparatus according to any previous claim 1-5, characterized in that said foam breakdown rotor rotates at about 3000 rpm.

7. The fuel dispensing apparatus according to any previous claim 1-6, characterized in that the maximum pressure difference between said pump housing (H) and said vacuum pump inlet (14) is about 400 mbar.

8. A fuel dispensing apparatus comprising one or more pumping units (1 , 2, 3) each having a closed pump housing (H) with an inlet (11 ) connected to a fuel supply, at least one discharge (13) connected to a fuel delivery means, and a hydrodynamic fuel pump (P) with a fuel intake (Pl) drawing from the interior of the pump housing (H) and a pressure outlet (PO) connected to said discharge (13), and further comprising at least one separate vacuum pump (VP) having a gas inlet (14, 24, 34) drawing from the pump housing (H) of each of said one or more pumping units (1 , 2, 3) and a gas discharge outlet (60), characterized by comprising, for at least one pumping unit (1 , 2, 3), a vacuum shut off valve (A1 , A2, A3) in the connection with the vacuum pump (VP) and a discharge shut off valve (B1 , B2, B3) in a connection to said gas discharge outlet (60) of said vacuum pump (VP), an upper level fuel detector (C1 , C2, C3), arranged at an upper portion of said pump housing (H), and a lower level fuel detector (D1 , D2, D3), arranged at a lower portion of said pump housing (H), both detectors being connected to control means for the actuation of said shut off valves (C1 -C3, B1-B3).

9. The fuel dispensing apparatus according to claim 8, characterized in that said control means are monitored remotely.

10. The fuel dispensing apparatus according to claim 8 or claim 9, characterized in that it comprises at least one foam breakdown rotor (R) according to any claim from 1 to 7.

1 1.A method for operating a fuel dispensing apparatus comprising at least one pumping unit provided with an hydrodynamic pump arranged within a pump housing to be filled with a fuel, said hydrodynamic pump being primed by an external vacuum source drawing gas from said pump housing, the method comprising the steps of: - monitoring the time needed for filling said pump housing with a fuel at a set level.

12.A method for operating the fuel dispensing apparatus according to any claim from 8 to 10, characterized in that it comprises the steps of:

- monitoring the time lapsed between the triggering of said fuel delivery means and the triggering of said lower level fuel detector (D 1-

D3) by the fuel drawn in said pump housing (H), and

- monitoring the time lapsed between successive triggerings of said upper level fuel detector (C1-C3) by the fuel varying its level in said pump housing during the fuel delivering, and - actuating said vacuum shut off valve (A1-A3) and said discharge shut off valve (B1-B3) in dependence on either of said times lapsed.

13.A method for breaking down the fuel foam generated by the pumping action on fuel operated in a fuel dispensing apparatus, the method comprising the step of applying a centrifugal force to the fuel foam.

14. The method according to any claim from 11 to 12, characterized in that it comprises the step of applying a centrifugal force to the fuel foam.

15.A fuel dispensing apparatus comprising one or more pumping units (1 , 2, 3) each having a closed pump housing (H) with a fuel inlet (11 ) connected to a fuel supply, at least one discharge (13) connected to a fuel delivery means, and a hydrodynamic fuel pump (P) with a fuel intake (Pl) drawing from the interior of the pump housing (H) and a pressure outlet (PO) connected to said discharge (13), and further comprising at least one separate vacuum pump (VP) having a gas inlet (14, 24, 34) drawing from the pump housing (H) of each of said one or more pumping units (1 , 2, 3) and a gas discharge outlet (60), wherein a strainer (70) is provided in said fuel inlet (11 ), characterized by further comprising a vacuum shut off valve (A1-A3) in the connection with the vacuum pump (VP), a discharge shut off valve (B1-B3) in a connection with said gas discharge outlet (60) and control means to close said vacuum shut off valve (A1-A3) and open said discharge shut off valve (B1-B3) at the end of each pumping operation to let at least an amount of the fuel contained in said pump housing (H) flowing back in said fuel supply through said strainer (70).

16.A method for operating the fuel dispensing apparatus according to claim 8 or claim 15, characterized in that it comprises the steps of:

- closing the vacuum shut off valve and opening the discharge shut off valve at the end of each pumping operation to let the fuel flowing back in said fuel supply through said fuel inlet until the fuel in said pump housing reaches a set level 17. The fuel dispensing apparatus according to any previous claim, characterized in that it comprises a check valve (100) intended to isolate said pump housing (H) from said fuel supply, the check valve (100) being in fuel fluid communication with said pressure outlet (PO) and being operated in dependence on the fuel pressure.