FORECOURT FUEL PUMPS

Abstract: A pump unit (10) for a garage forecourt fuel pump has a pump mechanism (17) provided with an inlet valve (27) and an outlet valve (33). The valves (27, 33) are biased by a respective spring (29, 35) to the closed position, and a respective solenoid (30, 36) is arranged fully to open the associated valve whenever the pump mechanism (17) is in operation. This allows a number of separate pump units (10) to be connected to a single suction line from a storage tank, without operation of one pump unit affecting the operation of the others.

Description: FORECOURT FUEL PUMPS This invention relates to a pump unit for use in a forecourt fuel pump (as defined hereinafter) . The invention also relates to a forecourt fuel pump incorporating such a pump unit and further to a fuel delivery system having a plurality of such forecourt fuel pumps. A typical garage forecourt may have a number of fuel pumps each arranged to draw fuel from a storage tank and deliver that fuel to a flexible hose having at its free end a delivery nozzle and shut-off valve, whereby the nozzle may be inserted into the fill-pipe of a motor vehicle fuel tank, the pump then delivering a measured quantity of fuel into that tank. For this purpose, the fuel pump includes a pump unit and a metering arrangement, as well as a display device on which is displayed both the quantity of fuel delivered since the last reset and the value of that fuel, at a pre-set rate per unit quantity. Such a forecourt fuel pump will hereinafter be referred to as a fuel pump as defined herein. The pump unit of a fuel pump as defined herein usually includes a power-driven positive displacement liquid pump mechanism which is operated whenever the fuel pump is required to deliver fuel. The pump unit is provided with automatically-operating spring-loaded one-way inlet and outlet valves, the former primarily serving to ensure an inlet chamber of the pump unit remains full so that delivery may start more or less as soon as the pump unit is operated, and the latter serving to ensure the delivery hose and metering unit, remain full. Whenever the pump unit is operating and yet no fuel delivery is taking place, fuel is recirculated from the pump mechanism outlet to the pump mechanism inlet, through a pressure relief valve. The automatically-operating spring-loaded one-way valves referred to above open to an extent sufficient to allow the required fuel flow rate to pass therethrough. Having regard to the construction of those valves, the flow area in the immediate vicinity of the valve member may be significantly less than the flow area of the pipes along which the fuel flows, resulting in significantly higher fuel velocities through the valves, leading to the likelihood of at least some cavitation in that fuel. Particularly in the case of pumping petrol, which has a very low vapour pressure, the higher velocities and cavitation is likely to generate petrol vapour. Though most pump units include arrangements to separate vapour from liquid fuel, to prevent that vapour passing into the metering system, any vapour produced at the outlet valve will be passed to the metering system and this can lead to metering inaccuracies. Moreover, vapour produced at the inlet valve or within the pump mechanism itself may lead to reduced pumping efficiency. So far as the inlet valve is concerned, the extent of opening is dependent upon the pressures on both sides of the valve. If a common pipeline is used to connect a number of similar forecourt fuel pumps as defined herein to a single storage tank, it is found that the turning on or off of one fuel pump when another is already in operation is likely significantly to affect the operating pump. In particular, a closed valve of a pump not in use can be caused to lift momentarily, giving rise to the likelihood of leakage from that pump, or of air being drawn into the pipework. As a consequence, it is the usual practice to connect each forecourt fuel pump by a separate pipeline back to the storage tank so as to obviate the possibility of the interference of the operation of one pump, by turning on or off another. An alternative solution to the above problem is to employ a pressurised manifold system, with each forecourt fuel pump drawing fuel from the pressurised manifold. The disadvantage of this system is however that should there be any failure in the system, there will be leakage of fuel under pressure out of the pipework, and that will give rise to pollution and possibly also a significant safety hazard. With a suction system, any leakage will be of air into the pipework and fuel leakage would be minimised. In an attempt to mitigate the above-discussed disadvantages of the known forecourt fuel pumps and fuel delivery systems, one aspect of the present invention provides a pump unit for use in a forecourt liquid fuel pump (as defined herein), which pump unit includes a power-driven liquid fuel pump mechanism, an inlet valve through which passes fuel to be pumped and an outlet valve through which passes pumped fuel, at least one of said valves being provided with opening means arranged to open fully said at least one valve during operation of the fuel pump mechanism irrespective of the fuel flow rate through the valve. Most preferably, both of said valves are arranged to open fully during operation of the fuel pump mechanism, irrespective of the fuel flow rate through those valves. This arrangement maximises the flow areas through the two valves and so minimises the likelihood of cavitation and the generation of vapour. Moreover, the problems association with a number of forecourt pumps drawing fuel from a common non- pressurised manifold may be greatly reduced. The inlet and outlet valves may each be provided with electromagnetic actuators arranged fully to open the valves whenever the pump mechanism is operating. Alternatively, the valves may be provided with hydraulic actuators arranged to respond to the fuel pressure prevailing during operation of the pump mechanism, so as thereby fully to open the associated valves. Another possibility would be mechanically to link the valves to the pump mechanism, so as to be opened thereby when the pump mechanism is operating. In a preferred pump unit of this invention, there is provided an inlet chamber from which the pump mechanism draws fuel and an outlet chamber to which the pump mechanism delivers fuel, the inlet valve being located at an inlet to said inlet chamber and the outlet valve being located at an outlet from the outlet chamber. In this arrangement, vapour separating means may be provided in the outlet chamber, to separate vapour from the liquid fuel delivered by the fuel pump mechanism. Moreover, a by-pass valve may be arranged between the outlet and inlet chambers, to permit the recirculation of fuel during pump mechanism operation, when there is to be no delivery from the forecourt fuel pump. This invention extends to a forecourt fuel pump as defined herein whenever incorporating a pump unit of this invention, as described above. This invention further extends to a fuel delivery system comprising an underground storage tank for fuel, a plurality of separate forecourt fuel pumps each for delivering measured quantities of fuel lifted from the tank, and each incorporating a pump unit of this invention as described above, and there being a common fuel supply pipe extending from the tank and along which all of said plurality of forecourt fuel pumps draw fuel for delivery thereby. By way of example only, one specific embodiment of pump unit constructed and arranged in accordance with the present invention, and also of a fuel delivery system, will now be described in detail, reference being made to the accompanying drawings in which:- Figure 1 is a vertical section through the embodiment of pump unit, when not operating; Figure 2 is a vertical section through the unit of Figure 1, but with the pump unit operating; and Figure 3 is a diagrammatic view of a fuel delivery system having four forecourt fuel pump assemblies, each of which is able to deliver four different fuel products drawn from four separate underground tanks. Figures 1 and 2 show a pump unit for use in a garage forecourt fuel pump (i.e. a fuel pump as defined herein) . This pump unit 10 has a main housing 11 including dividing walls 12 and 13 which separate the housing into inlet and outlet chambers 14 and 15, and a vapour chamber 16. Mounted in the wall 12 is a positive displacement rotary pump mechanism 17 which draws fuel from the inlet chamber 14 and discharges that fuel into a duct 18 which leads through opening 19 into the outlet chamber 15. A centrifugal air separator 20 is mounted in the duct 18 and discharges into the vapour chamber 16. An air separator valve 21 is mounted in wall 13 between the outlet chamber 14 and vapour chamber 16, to permit vapour collecting in the outlet chamber 15 to pass into the vapour chamber 16. A float 22 is mounted in the vapour chamber 16 and opens a valve 23 arranged between the vapour chamber 16 and inlet chamber 14, when the quantity of fuel collected in the vapour chamber 16 reaches a pre¬ determined level. Whenever the pump mechanism 17 is operating, there will be a reduced pressure in the inlet chamber 14, which will hold valve 23 closed. When the pump mechanism is not operating, there will be atmospheric pressure in chambers 14 and 16 and so the valve 23 may be opened by float 22 upon the fuel level in chamber 16 rising to the pre-determined level. An overflow float valve 24 is also provided in the vapour chamber 16, including an air vent to a flame trap, over-flowing fuel being directed from this valve back to a storage tank. A filter unit 25 is mounted on a side wall of the housing 11 and includes a flange 26 for the connection of a suction line (not shown) from an underground fuel storage tank. An inlet poppet valve 27 is arranged between the filter 25 and the inlet chamber 14 which poppet valve includes a valve member 28 and a spring 29 biasing the valve member to its closed position. When energised, a solenoid (shown diagrammatically at 30) moves the valve member against spring 29, to the fully- opened position. An outlet poppet valve 33, including a valve member 34, spring 35 and solenoid 36, is arranged between the outlet chamber 15 and an outlet pipe 37 leading to a fuel metering unit (not shown). As with the inlet valve, when the solenoid 36 of the outlet valve 33 is energised, the valve will be fully opened. A by-pass valve 38 is fitted into wall 12 and has a spring 39 biasing a valve member 40 into engagement with a port 41 in wall 12. If the pump mechanism 17 is operating and yet no fuel is being delivered by the fuel pump, the increase in pressure in the outlet chamber 15 will open valve 38 and allow recirculation of fuel into the inlet chamber 14. The solenoids 30 and 36 are arranged to be energised whenever the pump mechanism 17 is operating. As shown in Figure 2, both valves will immediately open fully, irrespective of whether any fuel is being metered and delivered by the fuel pump. Even if only a relatively small quantity of fuel is being delivered, the flow area through the valves 27 and 33 is not restricted and so there will be relatively low flow rates through those valves, leading to a lessened likelihood of cavitation and vapour generation. Any vapour which is generated either prior to the fuel being pumped or by the pump mechanism itself will be trapped by the separators 20 and 21 and fuel will collect in the chamber 16, for recirculation. The metering unit may also be provided with a vapour trap, to separate any small quantity of vapou which may be generated after the fuel has passed through the pump unit 10. In general, unless use is made of a pressurised feed line from a storage tank, it is not possible to link together a number of separate fuel pumps all drawing fuel along a common suction line from a storage tank, because the commencement and cessation of the operation of any one pump is likely to cause leakage of fuel or ingress of air at an adjacent, non-operating fuel pump. This is because the conventional automatic one-way inlet valve will momentarily open if a pressure pulse appears in the common suction line. This may occur when an adjacent operating pump ceases operation. It has therefore been the practice to connect each separate forecourt fuel pump by an individual suction line to the storage tank from which fuel is drawn. With pump units of the present invention installed in forecourt fuel pumps, it is possible to have a single common suction line from an underground storage tank to all of the fuel pumps, each fuel pump being connected to that common line. Figure 3 shows such an installation; four underground fuel storage tanks 45 to 48 supply fuel to four separate fuel pumps 49 to 52 each of which has four separate pump units so that the fuel pump is able to dispense metered quantities of any one of the grades of fuel stored in the tanks 45 to 48. In a typical forecourt installation having a layout of tanks and fuel pumps as shown in Figure 3, the adoption of fuel pump mechanisms according to the present invention permits the use of a piping arrangement as shown in that Figure. This results in a total pipe length of approximately one-third of that which would be required were each fuel pump to be connected separately by an individual suction line to each of the four fuel tanks 45 to 48.

Claims: CLAIMS 1. A pump unit for use in a forecourt liquid fuel pump (as defined herein), which pump unit includes a power-driven liquid fuel pump mechanism, an inlet valve through which passes fuel to be pumped and an outlet valve through which passes pumped fuel, at least one of said valves being provided with opening means arranged to open fully said at least one valve during operation of the fuel pump mechanism irrespective of the fuel flow rate through the valve. 2. A pump unit as claimed in claim 1, wherein both of said valves are arranged to open fully during operation of the pump mechanism irrespective of the fuel flow rate therethrough. 3. A pump unit as claimed in either of the preceding claims, wherein said opening means associated with at least one of said valves comprises an electromagnetic actuator arranged fully to open the associated valve whenever the pump mechanism is operating. 4. A pump unit as claimed in any of the preceding claims, wherein said opening means associated with at least one of said valves comprises a hydraulic actuator arranged to respond to the fuel pressure prevailing during operation of the pump mechanism so as thereby fully to open the associated valve. 5. A pump unit as claimed in any of the preceding claims, wherein each said valve comprises a poppet valve member co-operating with a static valve seat. 6. A pump unit as claimed in claim 5, wherein the valve member of each valve is spring-biased to a closed position. 7. A pump unit as claimed in any of the preceding claims, wherein there is provided an inlet chamber from which the pump mechanism draws fuel and an outlet chamber to which the pump mechanism delivers fuel, the inlet valve being located at an inlet to said inlet chamber and the outlet valve being located at an outlet from the outlet chamber. 8. A pump unit as claimed in any of the preceding claims, wherein there is provided vapour separating means to separate vapour from liquid fuel delivered by the pump unit. 9. A forecourt fuel pump (as defined herein) whenever incorporating a pump unit as claimed in any of the preceding claims. 10. A fuel delivery system comprising an underground storage tank for fuel, a plurality of separate forecourt fuel pumps each for delivering measured quantities of fuel lifted from the tank, and there being a common fuel supply pipe extending from the tank and from which all of said plurality of forecourt fuel pumps draw fuel for delivery thereby.

Inventors: OSBORNE GRAHAM WILLIAM, OSBORNE, GRAHAM, WILLIAM
Applicants: OSBORNE GRAHAM WILLIAM, OSBORNE, GRAHAM, WILLIAM
Application year: 1996
Main classification: B67D5
IPC codes: B67D5