This invention relates to apparatus for and methods of blending of two or more liquids- in predetermined proportions. The invention further relates to liquid dispensing apparatus whenever incorporating blending apparatus of this invention.

The invention particularly - but not exclusively - relates to the blending of two different grades of liquid fuel to permit the dispensing of an intermediate grade, from a forecourt fuel pump. A common form of forecourt fuel pump is arranged to draw fuel from two storage tanks containing different grades of fuel, to permit the dispensing of either one of those two grades, separately. It is also known to provide within such a pump a blending arrangement, whereby the two grades of fuel drawn from the two storage tanks are blended to provide a grade of fuel intermediate that of the two pumped grades. For example, in the United Kingdom, fuel of two-star and four-star grades may be drawn from respective storage tanks and blended to allow the dispensing of an approximation to a three-star grade of fuel.

One known form of blending arrangement for use in a fuel pump includes a blending chamber having inlets connected to the pumped fuel lines of the two grades to be blended, the inlets being provided with a pair of balance pistons arranged to adjust the relative amounts of the two fuels to the required predetermined proportion (typically 1:1) for the blend. The use of balance pistons in this way has a relatively slow response time to changes in the pumped fuel quantities and takes no account of any error which may accumulate during a period of dispensing. Though the error may not significantly affect the characteristics of the dispensed fuel, if more of the higher grade of fuel is

consistently dispensed over a period of time, this could represent a significant financial less.

In an attempt to improve on a balance piston system, it is known to use adjustable valves to control the flow rates of the two grades of fuel to be blended, the valves being operated by stepper motors responsive to flow rate measurements in the respective fuel supply lines, so as to allow fine adjustment of the blending. The stepper motors must be fully flame-proofed, having regard to the environment within which those motors are employed. Consequently, such an arrangement is relatively complex and expensive to implement, though it does allow more accurate dynamic control of the blend of the two grades of fuel. It is a principal aim of the present invention to provide apparatus for and a method of blending at least two liquids, and particularly liquid fuels, in pre¬ determined proportions and which at least reduces the disadvantages mentioned above. According to one aspect of the present invention, there is provided apparatus for blending at least two liquids in predetermined proportions, which apparatus comprises a respective supply line for each liquid to be blended and leading from a source of the respective liquid to a blended liquid duct, each supply line including a respective pair of electrically-operated on/off valves arranged in parallel and through at least one of which the respective liquid to be blended passes, each supply line further having respective flow monitoring means which provides a respective output signal indicative of the flow along the associated supply line, and control means which receives the output signals of the flow monitoring means and controls the operation of the electrically-operated on/off valves dependent thereon.

According to a second aspect of the present invention, there is provided a method of blending at least two liquids in predetermined proportions, comprising pumping the liquids to be blended along respective supply lines to a blended liquid duct, each of the supply lines including a pair of electrically- operated on/off valves arranged in parallel and through at least one of which the respective pumped liquid passes, monitoring the flow along each of the supply lines, and controlling the operation of the electrically-operated on/off valves of the supply lines dependent upon the monitored flow therethrough.

In the present invention, the control means controls the operation of the pair of electrically- operated on/off valves in each liquid supply line, in order to control the blend to fall within predetermined limits . The normal operation is with both valves in each supply line open, the flow along each supply line being continuously monitored to ensure the blend falls within a preset range. As soon as the proportions blended lie outside the preset range, one of the on/off valves of the supply line delivering a greater quantity of liquid is closed, so reducing the flow through that supply line. When the blend falls back within the required range, the closed valve may be re¬ opened.

The present invention thus allows a relatively simple arrangement for blending liquids in a pre¬ determined proportion, which allows good control of that proportion and also permits the blending history to be accumulated over any given period of time and corrections made to ensure that over that period, the average blend will fall closely within preset limits, even if there may be an instantaneous deviation from the required proportion.

The invention will hereinafter be described expressly with reference to the blending of two grades of petrol for dispensing from a forecourt fuel pump, though it is to be understood that the invention is not limited to this particular use.

The electrically-operated on/off valves used in the apparatus and method of this invention should not normally be adjustable to an intermediate setting, part -way between fully open and fully closed. Thus, it is highly preferred that each valve comprises a solenoid-operated shut-off valve. Such valves are widely used in the petrol pump business and are relatively cheap. The valves have no electrical contacts which could give rise to fire risks and so are approved for use in hazardous environments such as the interior of a petrol pump. Consequently, the use of such valves allows a relatively low cost blending arrangement to be provided within a petrol pump, which nevertheless allows accurate control over the blending. It will be appreciated that it is relatively easy to modify a conventional modern fuel pump adapted to dispense two different grades of fuel, so as additionally to allow the dispensing of a third grade blended from the two different grades. The flow monitoring means used in the present invention may be the conventional flow monitoring means for dispensing either one of the two grades of fuel, separately. Moreover, a modern fuel pump includes a computing unit having a microprocessor appropriately programmed to perform the required control and display functions. That computing unit may easily be modified to serve as the control means of the present invention. The microprocessor should be reprogrammed so as simul¬ taneously to monitor the flow rates for the two grades of fuel, and to provide outputs which control the operation of the on/off valves of the two fuel supply

lines, to maintain the blend within the required limits.

It is preferred for the two on/off valves of each pair to have substantially the same flow area, and for the combined flow area of those two valves to be of the same order as the flow area of the supply line in which the valves are installed in parallel. In this way, when both valves are open, there will be no significant restriction to the flow, but when one valve is closed, the flow rate will be reduced to a significant extent. It would be possible to provide two valves of different flow areas, and for the control means to decide which of the two valves is to be operated to effect a correction to the blending, depending upon the determined error.

The on/off valves advantageously are rapid acting, so as to give an immediate response to a detected blending error. All of the flow will thus be through both fully-open valves, or through one fully-open valve, for both supply lines.

This invention extends to a forecourt fuel pump whenever provided with blending apparatus of this invention as described above. Such a fuel pump may have three separate dispensing nozzles, one for each of the two basic grades of fuel supplied to the pump and the third for a blended grade of fuel. Each pumped fuel line leading to the respective nozzle should be provided with a shut-off valve, the control means serving to allow only one of those shut-off valves to be opened at any one time. For this purpose, the pump may be provided with nozzle detector switch means, the removal of a nozzle from the pump housing actuating the respective switch means . The control means may then react to that, to provide the required functionality for dispensing the grade of fuel associated with that nozzle.

By way of example only, one specific embodiment of a forecourt fuel pump incorporating blending apparatus of this invention will now be described in detail, reference being made to the accompanying drawing, which diagrammatically shows the principal components of that pump.

The fuel pump 10 is arranged to draw fuel from two separate storage tanks 11 and 12, respectively storing two different grades of fuel. Fuel is drawn from tank 11 by a pump 13 of a known construction, the inlet to and outlet from that pump being fitted with respective check valves 14 and 15. The pumped fuel supply line 16 from the pump 13 is fitted with a pair of solenoid- operated shut-off valves 17 and 18 arranged in parallel, the outlets from those two valves 17 and 18 being connected to a metering device 19 of a known construction. The outlet of the metering device 19 is connected to a solenoid-operated valve 20 in the pumped fuel line leading to a dispensing nozzle 21. The pump includes a nozzle detector switch 22, which is opened when the nozzle 21 is removed from its holster.

The arrangement associated with the pumping of fuel from tank 12 is essentially identical to that described above for the pumping of fuel from tank 11; like components with those identified above by the reference numerals 13 to 22 are given the reference numerals 23 to 32 in the arrangement associated with tank 12 and will not be described further, here.

The fuel pump further includes a microprocessor controlled computing and display unit 35, which receives inputs from the metering devices 19 and 29 and switches 22 and 32, and controls the operation of the pumps 13 and 23, solenoid-operated valves 17, 18, 27, 28 and the valves 20 and 30. In addition to the foregoing, the pump further includes a third nozzle 36, connected to a blended fuel

line 37, to which are connected the outputs from the metering devices 19 and 29, through respective non¬ return valves 38 and 39. As with the nozzles 21 and 31, there is a solenoid-operated valve 40 associated with the third nozzle 36 and provided in the blended fuel line 37, and also a nozzle detector switch 41 which is operated whenever the third nozzle 36 is removed from its holster. The computing and display unit 35 receives an input from switch 41 and controls operation of the solenoid valve 40.

The solenoid-operated valves 17, 18, 27, 28 are all of the same type, and so all have essentially the same flow area. The combined flow area of valves 17 and 18, or of valves 27 and 28, should be of the same order as the flow area of the supply line 16 or 26, so that when both valves are open, there will be no significant restriction to the pumped fuel flow. When only one valve is open, then there will be a significant reduction in the fuel flow. The fuel pump described above operates entirely conventionally whenever fuel is to be dispensed through either nozzle 21 or nozzle 31, respectively from tank 11 or tank 12. Lifting of the appropriate nozzle from its holster is detected by the associated switch 22 or 32 and the computing and display unit 35 causes operation of the appropriate pump 13 or 23 and opening of the associated solenoid valve 20 or 30. The unit 35 also opens both solenoid-operated shut-off valves 17 and 18 or 27 and 28, as appropriate. On fuel being dispensed, the flow is detected by the metering device 19 or 29 and a display thereof is given on a suitable display device (not shown). During such operation, the pump permits simultaneous dispensing of both grades of fuel, separately, through the nozzles 21 and 31, but prevents dispensing of blended fuel through nozzle 36,

by maintaining shut valve 40 even if nozzle 36 is removed from its holster.

On lifting the third nozzle 36 from its holster, and provided both nozzles 19 and 29 are in their holsters, the switch 41 is operated and the unit 35 causes operation of both pumps 13 and 23 and opening of the solenoid valve 40 associated with the third nozzle. The unit 35 also opens all four solenoid-operated shut- off valves 17, 18, 27, 28. On fuel being dispensed through the third nozzle 36, the flow rates as determined by the respective metering devices 19 and 29 are compared by the unit 35, and also the accumulated quantities delivered for that operation are compared. Should more of one grade of fuel be delivered than of the other grade (assuming a blend of 1:1 is desired), then one of the solenoid-operated shut-off valves associated with said one grade of fuel will be closed, so reducing the flow rate of that one grade. Monitoring continues and when the accumulated amounts blended are back within the required range, then the closed valve may be re-opened.

During dispensing of a blended grade of fuel through nozzle 36, the unit 35 prevents the dispensing of either grade, separately, through nozzle 21 or 31, by maintaining closed both valves 20 and 30 even should nozzle 21 or 31 be removed from its holster.

In the above way, close control over the proportions of fuel blended may be achieved. Though there will be a change in the flow rate through the nozzle 36 whenever one of the valves 17, 18, 27 or 28 is operated, this will not normally be noticeable by an operator, since there still will be simultaneous delivery of both grades of fuel. Also, over any given period of time which normally will be significantly shorter than the period of dispensing a typical quantity of the blended grade of fuel, there will be an

averaging function resulting in the total quantity of dispensed fuel being of the required blended pro¬ portion .

A further advantage of the blending arrangement described above results from there always being fuel f low of both grades during blending, since the normal operation when blending is with either three or four of the solenoid-operated shut-of f valves open . Thus , during blending both metering devices 19 and 29 should always provide an output showing flow of the respective grade of fuel , and should one of the grades of fuel not be del ivered f or any reason ( such as a blockage or other malfunction , or even emptying of one of the tanks 11 and 12 ) , this will immediately be detectable by no output from the associated metering device . The unit 35 may then shut down the pump and inhibit further dispensing of that grade of fuel or of a blended grade .