Ipsofactoj.com: International Cases [2002] Part 4 Case 15 [Ch.D]




- vs -

MFI Furniture Centres Ltd


31 JULY 2001


Mr Justice Laddie


  1. This is the judgment in an action for patent infringement. The claimant, SABAF Spa ("SABAF"), is the registered proprietor of Patent GB 2,100,441 in respect of burners for gas hobs. The patent was applied for on 12 June 1981. It expired in June of this year at the end of its 20 year term. The acts of which complaint is made in these proceedings all occurred prior to expiry. As a result, the claimant's primary interest is in an order for damages or an account.

  2. There are two defendants to the proceedings. The first defendant, MFI Furniture Centres Ltd ("MFI"), sold in England burners for gas hobs made by the second defendant, Meneghetti Spa ("Meneghetti"), in Italy. MFI has not been represented at the trial because it has come to a settlement with SABAF. Meneghetti has not. It argues that the patent is invalid, that its burners do not fall within the scope of the patent even if it is valid and that it, Meneghetti, has never carried out any relevant activities in the jurisdiction nor is it liable as a joint tortfeasor with MFI. The only grounds of invalidity pursued with vigour at the trial were obviousness and an allegation that matter had been added to the patent during the course of prosecution contrary to the provisions of s 72(1)(d) of the Patents Act, 1977.

  3. I will refer below to various drawings. They are set out in an annex to this judgment.


  4. A burner for a gas hob must be capable of supporting a properly burning flame. This means that it must produce jets containing combustible gas in such circumstances that there will be complete and efficient combustion under the cooking utensil placed on the hob. Burning of a combustible gas on a kitchen hob involves the reaction of the gas with oxygen from the air. Some of that air will come from the atmosphere surrounding the jet of gas as it exits from the burner. This air is sometimes called "secondary air". However in many cases this secondary air will be incapable of supplying sufficient oxygen to the gas. For example the centre of a gas jet may be too far from the secondary air with the result it is starved of oxygen and burns incompletely. When that happens, particles of carbon are produced which give a yellow tinge to the flame. This carbon can be deposited on the underside of the cooking utensil. To avoid this, for many years it has been normal to pre-mix the combustible gas with air, called "primary air", so that what exits from the burner is a mixture which contains sufficient oxygen to ensure that, when ignited in the presence of the secondary air surrounding the burner, it burns completely. The flames in these two types of burning conditions are sometimes referred to respectively as "post-aerated flames" and "pre-aerated flames". They are illustrated at Figures 1 and 2 in the annex.

  5. The main combustible gases used in England have been town gas, a gas produced by heating coal in an oxygen-depleted vessel, and natural gas, derived from gas fields, for example in the North Sea. The chemical compositions of these two gases are different. Amongst other things, the former contains much more hydrogen than the latter and burns much more readily. This means that a burner which gives sufficient pre-mixing of the gas and air to work well with town gas, may not work as well if supplied with natural gas. It is for this reason that when the gas supply in England was converted from town gas to natural gas some 20 or so years ago, the changeover had to be accompanied by a mass programme of converting gas burners of various types to function properly with the new gas.

  6. Combustible gas can be mixed with air in a number of ways. For present purposes, only two need be considered. First this can be achieved by the use of a simple cylindrical tube such as that used in a bunsen burner. Gas is mixed inside the tube with primary air drawn in around the combustible gas injector. If the tube is long enough, sufficient mixing will take place within it to allow for complete combustion. A typical bunsen tube arrangement is illustrated in Figure 3.

  7. Second, gases may be mixed together in a tube which has a gentle flare. This type of arrangement, which is frequently referred to as a Venturi tube, is illustrated at Figure 4. This works as follows. The combustible gas from the injector draws primary air into the mouth of the tube. At the throat of the tube (marked as "A" in the Figure), the gas and air are moving comparatively fast. This means that they have comparatively high kinetic energy. From the throat onwards, the walls of the tube diverge gently, at between 3 and 8. Because the lumen of the tube is widening out, the air/gas flow slows down. That is to say, it loses kinetic energy. The lost kinetic energy changes into potential energy. In other words, the pressure of the air/gas stream increases. At first this seems to be counter-intuitive. It means that as the gas/air moves into the wider tube and slows down, its pressure goes up. Counter-intuitive or not, this is what happens. It is a well known phenomenon. The increase in pressure caused by the use of a Venturi tube is referred to sometimes as "pressure recovery". The increased pressure downstream of the Venturi is helpful. For the burner on a gas hob to work properly, it must not only produce an adequate mixture of combustible gas and air, but that mixture must also be made available at the outlet ports in the burner at a sufficient pressure to enable the mixture to pass through the holes to the outside, where it can be ignited. Therefore pressure recovery caused by the use of a Venturi tube can help generate sufficient pressure in the burner to force the gas/air mixture through the burner ports. The Venturi tube arrangement is particularly efficient at pressure recovery.

  8. It is necessary to have in mind that the increase in potential energy (pressure) generated by a decrease in kinetic energy (speed) of a gas stream is a general phenomenon. The Venturi tubes illustrated in Figures 4 to 7 are all of circular cross-section. Pressure recovery due to a reduction in speed of a gas stream is not restricted to Venturi tubes as illustrated here. In other words what happens in a Venturi tube is but one example of a general effect. The effect is the change of kinetic energy, as a gas stream loses speed, into potential energy, or pressure. For reasons which will become apparent hereafter, it is of importance to bear in mind the difference between this effect and the Venturi tube in which it can take place. The same effect can occur other than in Venturi tubes. Figure 8 illustrates what happens when a gas stream leaves a tube and enters a fan-shaped space. As the gas spreads out in that space, the forward front slows down. The speed of the gas at Front A will be higher than it is at Front B. This reduction of speed will be accompanied by an increase in pressure. Once again, the same effect is at work.

  9. Unfortunately the terminology used in the art is imprecise. This is apparent from the evidence given by Mr Angelo Bettinzoli, the Chief Executive Officer of SABAF, who described the type of burners in common use in the 1970's. In his witness statement he said:

    .... these designs of burner were of the traditional long tube mushroom style [see Figure 5 attached], or of the pipe design common in the late 1970s [see Figures 6 and 7 attached]. The tube of the mushroom style burner is a simple form of Venturi effect, long enough to mix the gas and air sufficiently to burn properly by the time it emerges from the tube. Because it looks like a school laboratory bunsen burner such a tube is commonly called a bunsen. The pipe design had a 90 bend in the tube to give a short vertical portion of the tube. This was essentially a variant designed to reduce the overall height of the burner whilst at the same time keeping the bunsen tube long enough for the Venturi effect to produce proper gas/air mixing for combustion.

  10. As we shall see, imprecision in terminology is carried through to the specification and claims of the patent in suit.


  11. The patent starts by explaining the disadvantages in prior burner designs which it seeks to overcome. Since much of this is relevant to the issues in this case, it is worth setting out the relevant passage:

    Various types of gas burners for cookers and hobs are known, but these have the disadvantage, among others, that they are relatively tall, for which reason they are not suitable or cannot be used for hobs which must have the most compact and flat structure possible.

    Furthermore in burners of the known type the channels for the primary air intake always lead downwards, more specifically below the hob, or towards the oven, in the case of cookers provided with an oven, or towards a chamber or in any event towards the intakes provided for the purpose below the hob.

    In addition to this the fitting and centering of burners of the known type is rather laborious and difficult, and once fitted the burners have little stability and are therefore susceptible to undue movement.

    Thus they are fitted in such a way that access to and dismantling of the needle and gas injector, when necessary, requires the removal or lifting of the top plate of the appliance or the removal of the front, with the result that the operation is never easy and convenient.

    These known burners are also rather rigid in their operating capabilities, in that they only ensure correct combustion for given pressure and gas flow conditions, a factor which means that such burners are not suited to every appliance and therefore makes it necessary to have a range of different burners to suit all requirements.

    The object of this invention is to produce a gas burner for cookers and hobs which comprises units which can be combined with ease, are conveniently accessible and are easily separable so as to eliminate the inconveniences and disadvantages of existing burners.

    Another object of the invention is to seek to provide a burner including units shaped so as to produce. the so-called Venturi effect in mixing and distribution of the gas, the said effect being obtained substantially between the support of the flame spreader and the flame spreader itself, in a radial direction and over a circular course from the centre towards the holes of the said flame spreader unit. This provides the burner with considerable versatility and flexibility in use in that correct and complete combustion is maintained at all times even in the case of extensive gas pressure variations and with all types of gas. The burner is therefore suitable for all operating requirements and can be fitted to any cooker or hob.

    A further object of the invention is to seek to provide a gas burner of very low height which can therefore be used with advantage in hobs which must be flat, or, in any event, as low as possible compatible with the installation requirements of the hob itself.

    Yet another object of the invention is to seek to provide a burner in which the primary air for mixing is drawn from the exterior directly above the cooker top or hob, eliminating the provision of a closed and isolated box or air intakes below the said level as happens when traditional gas burners are used.

    Yet another object of the invention is to seek to provide a gas burner which is easier to locate and centre and is stable when placed directly on the top of a cooker or hob or when fined to a cross-member provided below the said top, the said burner also being capable of being fitted with a flame spreader of the conventional type, which is therefore easily available.

    (Patent Application page 1 lines 5 to 78)

  12. It can be seen that the inventor identifies three alleged major disadvantages in the prior art which his invention is designed to overcome. They are that

    1. existing burner units are tall, so that they do not fit into slim hob units,

    2. the primary air which is entrained with the combustible gas comes from underneath the hob unit and

    3. existing burner units are difficult to disassemble.

    The third of these can be left to one side because, save in one very limited respect, it has not been suggested that there is anything inventive in the specific arrangement or design of parts required for the burners the subject of the patent, other than those arrangements or designs which are included to overcome the first two disadvantages. Therefore it is the first two disadvantages and the way in which they can be overcome which are significant to the issues in this case. Before turning to the rest of the specification and claims, there is one other point which should be made at this stage. In the above passage there is no suggestion that there is any interrelationship between the height of the existing burners and the feature of bringing air in from above the hob surface. As Mr Vanhegan, who appears for the claimant, agrees, neither here nor at any other place in the patent is there any suggestion that these two alleged defects in the prior art are related to one another, nor is it suggested that the inventor's solutions to these discrete problems are related to one another.

  13. The invention is described in the patent by reference to a number of drawings. For present purposes it is sufficient to refer to one only. This is set out as Figure 9 in the annex. I have added to it an indication of the flow path of the incoming primary air. Figure 10 is an exploded version of this burner which makes it easier to see its three components. Those components are a flame spreader unit (13), a removable body (12) and a support unit (2). The latter is connected by a flange (8) to the hob plate (9). The support unit has what is described as a 'sleeve' (6) which has a vertical axis, that is to say it faces vertically upwards, and a bottom wall (7) in which is located the injector (1) from which the combustible gas enters the bottom of the burner. The combination of bottom wall and sleeve creates a chamber (5). On the outside of the sleeve there are radial ribs (19). As we shall see, these define what are referred to as 'radial passages' for incoming primary air.

  14. Mounted over, and centred on, the support unit is the removable body (12). This has an outer skirt ending in an edge (17), which is located a short distance above the hob plate, thereby creating a circumferential passage (18), through which primary air can be drawn. The removable body contains what is described as a "central tubular portion" (14). As shown in this drawing, this incorporates an internal circular sleeve which can be moved up and down, to adjust the gas-flow characteristics of the burner so as to ensure that the burner will work with different types of gas. This feature has little relevance to the issues in this case. The flue within the central tubular portion includes a through opening (15), which leads to the underside of the flame spreader (13). The removable body also has radial centering fins (16), only one of which is shown in the drawing, which make sure that the body fits snugly into the open mouth of the chamber in the support. Finally, mounted over the other components, is the flame spreader. This includes a row of holes or outlet ports (21), from which the gas/air mixture can exit the burner.

  15. In operation, combustible gas exits under pressure from the injector at the bottom of the chamber in the support. It passes upwards, drawing in surrounding air. This creates the air flow pattern which is depicted in Figure 9. The primary air is sucked in from just above the hob unit, passes into the burner by way of the circumferential passage (18), up through the radial passages defined by the radial ribs (19) on the outside of the sleeve (6) of the support unit. It then descends in the vertical passages (16) between the sleeve and the central tubular portion (14) of the removable body. At the bottom of the chamber (5) it becomes entrained with the combustible gas and begins to mix at that location. The gas/air mixture passes up through the lumen in the central tubular portion, including the through opening (15) and into the disc-shaped space between the top surface (12) of the removable body and the under surface (13) of the flame spreader. It passes laterally and exits the burner through the outlet ports 21, where it burns in the secondary air surrounding the burner unit.

  16. Of particular importance to this case and the patent is the shape and function of the disc-like space under the flame spreader. The patent describes this as follows:

    The upper surface 12' of the body 12 and the internal surface 13 of the flame spreader 13 which are opposite each other may, depending on requirements, e.g. the pressure of the gas which is to be burnt, the type of gas. etc., be divergent, parallel, or convergent, from the centre towards the periphery or towards the series of holes 21 in the flame spreader 13. In any case, the said opposing surfaces 12 and 13 define a radial passage of circular extent 22 through which the gas-air mixture, which is produced in the central opening 15, is passed to the holes 21 of the flame spreader 13, where combustion occurs. In accordance with the Venturi effect, the velocity decreases and the pressure recovers, either as the result of the shape of passage 22 when this is given a particular divergent shape, or because the cross-section of the passage increases as a function of radius from the centre of the periphery. In this way the mixture is supplied and its combustion is correct and complete even in the case of major variations in the pressure and type of gas used.

    (emphasis added)

  17. Notwithstanding the emphasis of the arguments advanced during the hearing, the first italicised passage makes clear that there is no requirement for the passage between the underside of the flame spreader and the upper side of the support to be divergent. This is reinforced by the second, which makes it clear that the effect with which this patent is concerned which it calls the "Venturi effect" can be achieved either by the passage being divergent or because of lengthening of the front over which the gas is passing as it gets further away from the centre. This is the point illustrated in Figure 8 and explained in paragraph 8 above.


  18. The parties agreed that all the issues of validity and infringement can be determined in relation to claim 1 alone. I have set this out below, split into sections which may make comprehension somewhat easier:

    A burner for gas cookers and hobs, comprising


    a support bearing a gas supply injector or needle,


    a body associated with this support defining a chamber in which the gas is mixed with primary air drawn from the outside, and


    a flame spreader unit mounted on the said body defining therewith a passage for promoting complete mixing of the gas and primary air and for the supply of the gas-air mixture for burning through the holes of the said flame spreader,


    wherein the said support has a sleeve portion having a vertical axis and defining a chamber which is open at the top and closed at the bottom and contains the said injector or needle, the said sleeve portion having a peripheral flange by which it is securable to the plate of a cooker or hob, and the said sleeve portion being associated with


    a body having a tubular central portion defining a through opening which is concentric with the said chamber, and a peripheral portion with an edge which extends downwards to lie proximate to the said plate, in use, defining therewith a circumferential passage for the intake of primary air above the said plate, the said body having radial passages for passing the primary air into the said chamber in order to form the gas-air mixture,


    and the flame spreader unit being supported on the said body overlying the hole in the tubular portion of the body itself,


    the upper surface of the said body and the internal surface of the said flame spreader unit, which are opposite to each other, define a radial passage of circular shape through which the gas-air mixture passes from the said through hole to the holes in the flame spreader with a suitable reduction in velocity and a recovery of pressure, the radial mixing passage being shaped to produce a Venturi effect to promote complete mixing and distribution of the gas and the primary air.

  19. The first task is to decide what this language means. The meaning should be the same, whatever the nature of the alleged infringement, and it is therefore better to consider this issue first and without regard to the detailed construction of the Meneghetti products in suit. The support referred to in (i) and (iv) of the claim is the "support with chamber" illustrated at the bottom of Figure 10. The body referred to in (ii) and (v) is the "body with radial passages and central tube" illustrated in the middle of Figure 10. The flame spreader of (iii) and referred to in (vii) is the part so identified at the top of Figure 10. The parties disagree on the meaning of some of the other wording in this claim.

    The burner holes

  20. Feature (iii) refers to "the holes of the said flame spreader" and feature (vii) refers to "holes in the flame spreader". It has not been suggested that anything turns on the difference between "of" and "in". In my view there is little doubt that what is referred to is holes which are located within the flame spreader, such as those illustrated in Figure 10. The claim does not refer to burner holes in any other location.

    "A sleeve portion having a vertical axis and defining a chamber"

  21. This is a reference to the part of the burner which is made up of those parts which, in Figure 9, are identified as the sleeve (6) and the bottom wall (7). Together they make a generally cup-shaped chamber (5). Based largely on this illustration, Mr Wilson, who appears for Meneghetti, argues that the sleeve must have essentially vertical walls. There is nothing in the claim or the specification which requires such a limitation. However Mr Wilson says that without such a vertical wall, the burner would be susceptible to side draughts because the wall, as illustrated, is a hurdle over which the incoming primary air has to pass and would also be likely to collect water which might be spilled on the hob surface once again, the vertical wall represents a barrier between spilt fluid and the base of the chamber in which the gas injector (1) is located. For these reasons, the claim should be read as if there is a requirement for essentially vertical walls.

  22. I am not persuaded by this argument for three reasons.

    • First, there is nothing in the specification which says that the sleeve walls are designed to prevent cross-draughts or hinder spilt fluid reaching the gas injector. This may be an unheralded benefit of the design in Figure 9, but there is nothing to suggest that it was recognised by the inventor or played any part in his decision as to the precise shape of the burner.

    • Second, the Figures to the patent are by way of illustration only. There is nothing to suggest that they were meant to define or limit design characteristics which are not the subject of specific consideration by the inventor.

    • Third, implicit in Mr Wilson's argument is the assertion that the use of an essentially vertical sleeve achieves the benefits which he has identified. In fact, it is easy to see that they do no such thing. Figure 11 illustrates a modified sleeve arrangement which shows that an essentially vertical sleeve can be used without achieving the benefits which he promotes.

    The "body having radial passages"

  23. These are the radial passages defined by the radial ribs (19) in Figure 9. The primary air is drawn through a circumferential passage (18) and into the chamber (5) by way of the vertical passages (16). The presence of the radial ribs (19) splits this incoming air into a number of 'radial passages', the number and length of those passages being the same as the number and vertical depth of the ribs. As I understand Mr Wilson's argument, these radial passages have to be of substantial length. I am not sure where he says this restriction comes from, but I can see no justification for it. There is nothing in the specification or the claims which suggests that these radial passages have any particular dimensions. Indeed, there is nothing in the specification or claims which indicate that these passages have any function at all. The passages are merely a reflection of the fact that the incoming primary air has to bypass the radial ribs. In the result, the incoming air is divided in these locations into separate streams. The patentee has described this as occurring in radial passages.

    "the radial mixing passage being shaped to produce a Venturi effect to promote complete mixing and distribution of the gas and the primary air"

  24. These are the words in the claim which have given rise to the major dispute in this action. Mr Wilson's argument is that these words mean that complete mixing has to occur in the radial mixing passage rather than in the vertical tube. If that is so,

    1. it is not proved that this is the case with the alleged infringement,

    2. it is difficult to see how it could ever be proved, the specification giving no help as to how to measure such complete mixing and

    3. the claim would be bad for added matter.

    Furthermore, he says that there is no indication of what "complete mixing" means. How complete is complete?

  25. Mr Wilson is correct when he says that there is nothing in the specification which indicates, at least directly, how complete the mixing must be nor how it is to be measured in the narrow radial passage under the flame spreader. This is not a trivial matter. Measurement of the degree of mixing would need to be carried out in the outlet ports of the flame spreader. This is because, whatever 'complete mixing' may mean, it has to happen by the point at which the gas/air mixture is ignited. Measuring in that location on a burner is likely to prove very difficult, not least because it would be necessary to ensure that the method of measuring the mixture did not itself interfere with the passage of the gas/air mixture. Any such interference would alter the fluid flows in the burner, change the mixing and, therefore, might invalidate the measurements.

  26. However, it seems to me that this lack of indication of how to measure the mixture inside the burner and any discussion of how complete the mixing has to be, is not an accident. The patent is concerned with burners which work. That is to say it is concerned with a burner which is designed in such a way that it will produce and support a good flame when used on a hob, even when there is a cooking utensil in position over it. Neither of the experts called to give evidence appeared to have any difficulty in identifying a 'good' flame. A gas which contains insufficient primary air or in which there is insufficient mixing will burn with a luminous, sooty flame. The patented burners, like all other burners for hobs, must achieve sufficient mixing to give complete burning, in the sense of a good flame. There is nothing in the claims or the specification which indicates that the inventor was trying to achieve either perfect mixing, which might be the acontextual meaning of "complete mixing", or even any numerically defined degree of mixing. When the claims and the specification refer to complete mixing of the gas, they mean no more than such mixing as will give rise to a good flame in use, that is to say, a flame which those in the art would recognise as satisfactory. Mathematical precision is not required.

  27. However, this does not deal with Mr Wilson's major point, namely that the mixing must be achieved in the radial section under the flame spreader. If sufficiently good mixing is achieved in the vertical tube immediately under the flame spreader, then the radial passage serves no function. The relevant words in the claim are:


    a flame spreader unit mounted on the said body defining therewith a passage for promoting complete mixing of the gas and primary air and for the supply of the gas-air mixture for burning through the holes of the said flame spreader ....


    .... the radial mixing passage being shaped to produce a Venturi effect to promote complete mixing and distribution of the gas and the primary air ....

  28. Attractive as Mr Wilson's argument is, I am not persuaded by it. Claim 1 does not say that the radial passage achieves complete mixing nor does it say that complete mixing takes place in the radial passage. The passage must 'promote' mixing and distribution of the gas. However the achievement of mixing and distribution is not restricted, and could not be restricted, to the radial passage alone. It is inevitable that some mixing will take place in the vertical tube and that the latter will contribute to the distribution of the gas. It seems to me that the inventor is not trying to limit his claim to burners in which complete mixing occurs in the radial passage. There is no reason why he should. A burner which achieves sufficient mixing in the vertical tube so as to produce a good flame at the outlet ports is a worthwhile device. The part of the device, identified as being where a Venturi process must take place, would still achieve what the specification teaches, namely the essential pressure recovery which enables sufficient gas/air mixture to be pumped out of the outlet ports. I have come to the conclusion that when the claim refers to the radial passage 'promoting' it means no more than that the passage facilitates or plays a part in complete mixing and distribution.

    A "tubular central portion defining a through opening"

  29. As explained above, in Figure 9 the tubular central portion is identified as (14) and it includes the through opening (15). Mr Vanhegan argues that this feature must be essentially cylindrical. In some senses, this mirrors Mr Wilson's argument that the sleeve portion should be cylindrical. It also fails. There is nothing in the specification which indicates that this portion should be cylindrical nor is there any technical reason why it should, or a reader would assume it should. This part of the device is the location where mixing of combustible gas and primary air commences. It only has to perform the functions of allowing initial mixing to occur and allowing the gas to reach the underside of the flame spreader. There is no reason why it should not be divergent or convergent, a mixture of the two or cylindrical. In all four of these possibilities it would be expected to, and would in fact, perform its functions.

  30. Finally, before leaving the issue of construction, it should be noted that there is nothing in this claim which relates the location of the circumferential passage, through which the primary air is sucked from above the hob unit, to the location, design or output of the burner holes or, of course, to any of the internal features within the burner and under the flame spreader which secure the Venturi effect. In other words, as mentioned above, there is nothing which relates the pressure recovery features of the invention or features which related to the patented burners' overall height, to the way in which the primary air is introduced into the burner. As the witnesses agree, one of the potential problems which can be expected if primary air is taken from above the hob is that it may be too close to the burning flame, so that products of combustion become entrained in the primary air, thereby interfering with performance of the burner. This phenomenon is referred to as 'vitiation'. There is nothing in the claim, or the body of the specification, which prevents vitiation being a problem with the patented design of burner, nor is any solution to this problem suggested.


  31. The Meneghetti products which are complained of in these proceedings are similar in overall appearance and principles of construction to those put on the market by SABAF. Whole and sectioned samples of the SABAF and Meneghetti commercial products were supplied to me for use in the trial. The design of the alleged infringement is illustrated in Figures 12 to 14 in the Annex. Figure 12 consists of an exploded perspective view of the product. Figure 13 is a cross section which is the equivalent to Figure 9 relating to the patented burner. Figure 14 is an exploded cross section drawing of the Meneghetti product which is the equivalent to Figure 10 relating to the patented burner.

  32. As will be seen from the Figures there are many respects in which the design and the mode of operation of the Meneghetti burner is similar to the burner disclosed in the patent. As shown in Figure 12, the Meneghetti burner is made up essentially of three parts: a flame spreader (25), a removable body (22) and a support unit (1) which includes a gas injector (7). The removable body includes a central vertical tubular chamber (13 in Figure 13) which will allow a mixture of combustible gas and primary air to rise and pass into the gap between the underside of the flame spreader and the top of the removable body and laterally to exit from a series of holes in the periphery of the top of the burner just below the flame spreader.

  33. The fluid flows in the burner are also similar to those in the SABAF design. This is depicted (27) in Figure 13. Primary air is drawn in under the skirt of the removable body (17, 18), passes towards the centre of the device where it becomes entrained with combustible gas moving in a vertical direction out of the gas injector (7). The gas/primary air mix moves up the tubular passage (13) in the removable body, passes laterally in the diverging passage between the flame spreader (25) and the top surface of the removable body and then out of ports just under the flame spreader. However there are a number of detailed differences which have been the subject of discussion during the trial.

  34. First, the burner holes are not 'in' the flame spreader. This is shown particularly clearly in Figures 12 and 14. The removable body has a castellated top. The flame spreader, which is essentially flat on its underside, sits on top, thereby closing the open mouths of the castellations. The holes through which the gas/primary air mixture leaves the burner are thus created by the interaction between the underside of the flame spreader and the upper surface of the castellated portion of the removable body. It can be said that the opening in each hole is made, in the top part, by the flame spreader and, in the bottom part, by the removable body. Mr Wilson says that the holes are not 'of' the flame spreader nor are they 'in' the flame spreader, as specified in Claim 1. Accordingly there is no infringement.

  35. I do not accept this argument. It is clear from the specification that the detailed design of the flame spreader is not a matter with which this patent is concerned. Indeed, the design of the flame spreader is described in the specification as 'conventional'. The inventive concepts asserted by the patentee relate to the intake of primary air and Venturi mixing. They have nothing to do with the detailed design of the outlet ports. In my view this is just the type of trivial mechanical detail which would be ignored by any reader in the art. Neither Mr Wilson nor Mr Vanhegan placed particular emphasis on the structured approach to deciding the scope of a claim as set out in Improver Corp. v. Remington Consumer Products Ltd [1990] FSR 181. However whether one uses that approach or simply applies the words in the Protocol, the absence of this feature in the Meneghetti burner does not avoid infringement. The difference between the holes being in the flame spreader, as opposed to being just under it, would have no effect on the way the burner works and would be recognised as such. A man in the art would consider this an obvious and trivial modification of no operational significance.

  36. Second, it will be seen from Figure 14 that the support unit (1) has a much more splayed-out appearance, so that the depression surrounding the gas injector is more in the shape of a shallow bowl rather than a cup with vertical sides as depicted in the patent (see Figure 9). It is because of this difference that Mr Wilson argues that the "sleeve portion having a vertical axis and defining a chamber" referred to in the claim must refer to a sleeve with essentially vertical walls, as opposed to a vertical axis. For reasons set out above, I do not accept this construction. Even with its splayed-out design, the Meneghetti product incorporates a sleeve portion having a vertical axis defining a chamber. This feature does not avoid infringement either.

  37. Third, Mr Wilson says that in the Meneghetti device there are no 'radial passages' as required by the claim. All that exist are three legs depending from the underside of the removable body which are in the flow path of the incoming primary air. These cannot create radial passages. I disagree. Once again, the radial passages in the device depicted in the SABAF patent are not put forward as having any special function. The passages are an inevitable corollary of there being obstructions in the primary air pathway. They are not said to do anything. Their shape and dimensions are irrelevant, as long as they do not prevent the primary air from reaching the centre of the burner. It seems to me that the depending legs (19) as shown in Figures 13 and 14 split the incoming air path into three short radial passages which are in all material respects the same as the equivalent passages in the SABAF design. This argument of non-infringement fails also.

  38. Fourth, there is an issue between the parties as to whether the Meneghetti burner has a 'radial mixing passage' under the flame spreader "being shaped to produce a Venturi effect to promote complete mixing and distribution of the gas and the primary air". The meaning of these words in the claim has been considered at paragraphs 24 to 28 above. It is not suggested that the relevant passage in the Meneghetti burner is not of Venturi shape, within the very wide meaning of those words when used in the specification. Nor is it denied that there will be pressure recovery so that the gas/air mixture is at sufficient pressure at the burner holes to ensure that sufficient of the mixture passes through the holes to support a good flame. The difference between the parties concentrates on the issue of whether there is complete mixing in the passage under the flame spreader. As indicated above, I do not accept Mr Wilson's construction of these words in the claim. There is no dispute that there is a Venturi effect generated in the passageways in the Meneghetti burner and that the space under the flame spreader and above the movable body facilitates or plays a part in mixing and distribution of a gas/air mixture which is suitable for producing complete combustion. It follows that this argument of non-infringement fails also.

  39. In the result, I have come to the conclusion that the Meneghetti burner falls within the scope of the claim and infringes.


  40. Mr Wilson argues that, even if the Meneghetti product falls within the scope of claim 1, his client does not infringe because it carried out no relevant act in the jurisdiction. Mr Vanhegan answers this in two ways; Meneghetti is liable,

    • first as an importer,

    • second as a joint tortfeasor with MFI.

  41. The relevant facts are as follows. Meneghetti has a British sales agent who participated in discussions with MFI which led to them buying Meneghetti burners for their hobs. It is not suggested that the activities of the agent, per se, renders Meneghetti liable for infringement. The burners bought by MFI were from Meneghetti's standard range but they were installed in hob units to which an MFI trade mark was applied. The hobs were clearly destined for MFI's British market. The hob units were supplied with English language instruction booklets. These were drafted by MFI, but Meneghetti arranged for them to be printed. The hobs were also supplied with English style electric wiring instructions. There is no dispute that title to the hobs, including the burners, passed to MFI in Italy. Originally, MFI arranged for the hobs to be collected by its lorries from Meneghetti's plant in Italy. From November 1998 onwards, delivery of the goods was by independent haulier. The haulier was chosen, paid and instructed by Meneghetti. The costs of doing this were subsequently recovered from MFI. SABAF did not plead, and did not ask leave to amend to plead, that Meneghetti or its agent offered to supply the burners in England.

  42. First I shall consider the allegation that Meneghetti is liable as an importer as and from November 1998. In my view this allegation succeeds. The independent haulier was instructed by and carried out the transportation on behalf of Meneghetti. If there was a breakdown in delivery, Meneghetti would be responsible for taking the matter up with the haulier. Similarly, if, for example, a cheque paid to the haulier was not honoured by the bank, it was to Meneghetti that the haulier would look. MFI was isolated from this part of the logistics. I think it would be fair to say that Meneghetti was arranging importation into England as part of its service to its customer. The fact that it was subsequently reimbursed for this service, does not alter the fact that it was Meneghetti which was importing the goods for commercial purposes.

  43. On the other hand, I do not accept Mr Vanhegan's arguments on joint tortfeasorship. He says that the facts here demonstrate a common design between MFI and Meneghetti to sell burners in England. I disagree. It is apparent that Meneghetti was content that its burners were used and sold by MFI in England, just as, no doubt, it was content that its products were sold in a very large number of other countries in the world. It is also apparent that it was prepared to help its customers, for example by supplying them with instruction booklets in the language of the market in which the customer traded. But this does not demonstrate a common design. Meneghetti assisted its customer and facilitated the latter's business, but at all times the sale and use of the burners in the English market was solely the commercial venture of MFI. I think Mr Wilson is right to say that Meneghetti had no interest in whether MFI actually sold the hobs with burners in England. As far as it was concerned, MFI could have decided to store or destroy the complete stock, or send them to a market where there were no SABAF patents. Meneghetti's actions were those of a company making its standard products available to customers, like MFI, from all over the world. It did not have a common design with MFI to market in England.



  44. Undoubtedly the major issue on validity is obviousness. Before considering the prior art in issue, there is one point of principle to consider. As I have mentioned already, the two important features of the SABAF burners which are said to constitute an invention are

    1. drawing primary air in from above the hob unit and

    2. the use of a flow path under the flame spreader in which the Venturi effect will be present.

    As I have also mentioned, there is nothing in the specification to suggest, nor has it been seriously argued, that these two features interact with each other.

  45. Mr Wilson says that SABAF's claimed invention is a collocation of two known or obvious integers. Under pre-1977 law, it was well accepted that there was no invention in putting together such integers. Mr Wilson says that the same law applies now, even if it is difficult to fit into the structured approach to obviousness as described in Windsurfer. Examples of it in practice are to be found in a number of EPO decisions including Kommerling [1992] EPOR 98 and Sedlbauer [1993] EPOR 147. A particularly convenient statement of the principle is set out in the Guidelines for Substantive Examination at 56:C-IV (B1):

    Obvious and consequently non-inventive combination of features:

    The invention consists merely in the juxtaposition or association of known devices or processes functioning in their normal way and not producing any non-obvious working inter-relationship.

    Example: Machine for producing sausages consists of a known mincing machine and a known filling machine disposed side by side.

    The sausage machine example will be familiar to any British patent practitioner.

  46. Based on this, Mr Wilson says that SABAF's alleged invention consists of nothing more than the juxtaposition of two known or obvious expedients. The result is not greater than the sum of its parts.

  47. Mr Vanhegan concedes that the law of collocation applies under the 1977 Act just as it did before. He accepts that the extract from the Guidelines for Substantive Examination set out above is a fair statement of that principle, although he also concedes that it may be expressed a bit narrowly, because the objection of mere collocation would apply as much to the putting together of obvious, but non-interrelating, devices and process as to the putting together of known such devices and processes. However he says that it is not enough to ask whether the two (or more) devices or processes are individually known and obvious and do not interact. He says that Meneghetti must also show that there is a reason why the devices should be put together. In other words before a collocation of known or obvious parts can be invalid it must be obvious to put them together. In my view this would turn the law of collocation on its head. Since, by definition, the devices or processes do not relate to each other and do not affect each other's function or performance, there is little technical incentive for the worker in the field to put them together. Thus the lack of interrelationship would render the collocation non-obvious. As a result, virtually all collocations would become patentable.

  48. I accept Mr Wilson's approach on this issue. The law of patents is set on a public policy foundation that a man in the art cannot be stopped by a subsequent patent from using one or more known or obvious devices. He is not to be regarded as having been issued with a ration card allowing him to use only one such device. If there is no inventive step in using one and there is no inventive step in using another, there is no inventive step in using the two together. Where the devices or features interact, different considerations may apply.

  49. In the light of these considerations, I can turn to the two features which are put forward as the inventive heart of the patent.

    Taking primary air from above the hog surface

  50. It is not in dispute that this was known and practised before the priority date. The problem of vitiation, referred to in paragraph 30 above, was known in the prior art. The obvious solution to it was to keep the flames a sufficient distance away from the air inlet. There is nothing in the patent which addresses vitiation and there is nothing to suggest that the patented device is more or less prone to vitiation.

  51. In relation to this feature Meneghetti relied on two pieces of prior art. For present purposes it is sufficient to refer to one only, the Alpes-Inox SpA hob. This was a commercially available hob unit which was sold before the priority date. Apparently it was regarded as being at the 'Rolls Royce' end of the market. An illustration of its design is set out in Figure 15 in the Annex. This shows primary air ("aria primaria") being taken in above the hob surface. The flow path in the burner is similar to that of the burner in the SABAF patent. It passes down to a chamber surrounding the gas injector. The primary air and gas mix in a vertical tubular chamber ("miscela combustibile"). It was argued on behalf of Meneghetti that there must be some Venturi effect as the gas/air mix passes radially under the flamespreader. In my view that was not proved.

    A radial mixing passage being shaped to produce a venturi effect to promote complete mixing and distribution of the gas and the primary air

  52. Meneghetti relied on a number of pieces of prior art to demonstrate that this feature was known in the prior art. By the time he came to address me, Mr Wilson was content to rely on two pieces of prior art which he says clearly demonstrate that having a Venturi in the radial passage was known. The first of these is Italian Patent Specification No. 696,101 in the name of Zanussi. The patent describes three versions of its burner and these designs are illustrated by three drawings which are reproduced as Figures 16 to 18 in the Annex. There is no doubt as to the nature and purpose of the designs illustrated. Zanussi describes its invention as follows:

    It is well known that normal gas burners for cooking appliances for domestic use are mainly composed of a mixing or Venturi tube, which may be vertical or horizontal, and a head comprising the expansion or turbulence chamber around which the gas outlet holes are appropriately arranged.

    The Venturi or mixing tube generally consists of a convergent opening ending in the smallest section calculated to suit the specific thermal power of the burner, beyond which begins the divergent section, which together with the axis of the Venturi tube forms an angle of 3 or 4, the minimum length of which is generally determined in function of a multiple of the diameter of the smallest section of the actual Venturi tube. This multiple may vary according to the characteristics of the burner which it is intended to produce and the type of gas which it is intended to burn.

    Therefore, burners built in the traditional way, that is, with the divergence lying along a linear, rectilinear or curved axis, have the disadvantage of being particularly cumbersome because of the length of their mixing or Venturi tube, thereby preventing a more rational design of the appliance for which they are intended, in addition to being more costly due to the greater weight of the material used.

    The purpose of this invention is a horizontal or vertical gas burner whose mixing or Venturi-tube divergence, in addition to developing along a linear axis, whether vertical, horizontal, rectilinear or curved, also continues radially in the circular space comprised between the pan and an appropriately shaped surface which may be made up of a special diaphragm or by the internal surface of the flame distributor; the invention achieves the aim of substantially reducing the length of the Venturi tube in the initial section, whether it is vertical or fairly horizontal.

  53. The only difference between the Venturi arrangement shown and described in Zanussi and that illustrated in the SABAF patent is that in the former the divergence starts in the vertical tubular section whereas in the latter it commences in the radial section. It is for this reason that it was important for SABAF to argue that the "tubular central portion defining a through opening" in the claim must be essentially cylindrical. As explained above, I reject that construction. It follows that the Venturi arrangements described and illustrated in the Zanussi patent are of the same type as those covered by the claim of the patent. The passage from the Zanussi patent set out above also indicates that the inventor of the prior art decided to put part of the Venturi in the radial section under the flame spreader for the same reason as SABAF, namely to reduce the overall height of the burner.

  54. I should also refer to the other piece of prior art relied on by Mr Wilson in his oral argument, namely French Patent Specification No. 1,197,178 in the name of Hourdry. The patent is directed to the manufacture of gas burners for hobs which are not as tall as the prior art, that is to say Hourdry was seeking to achieve the same objective as SABAF. The description of the Hourdry burner in the specification is supported by a number of drawings, two of which are reproduced as Figures 19 and 20 in the Annex. Hourdry describes his solution to the height problem as follows:

    The object of the invention is a gas burner of the type entraining primary air in a Venturi tube through a gas injection nozzle characterised in that the Venturi effect is produced perpendicularly to the axis of the injection nozzle and circularly to the upper portion of a burner which is low in terms of height between the cover plate of the burner and an adjacent inner tray with a central opening of suitable profile above the gas injection nozzle.

  55. SABAF criticize this piece of prior art on two bases.

    • First it is said that there is no vertical tubular passage leading to the radial Venturi section.

    • Second it is said that the Hourdry specification describes his burner as being made of steel parts which are press-fitted together.

    This is said to be an unsatisfactory way of assembling a burner and would make it difficult to disassemble.

  56. The first of these points is of little significance. It is not suggested that there is anything inventive in having a vertical tubular passage. The inventive step, if there is one, is having the Venturi arrangement in the radial passage under the flame spreader. The latter feature is illustrated and described in Hourdry. As far as the vertical tubular passage is concerned, there is nothing in the SABAF patent which requires it to be of any particular length. It could be very short indeed if the radial Venturi arrangement is sufficient to give adequate mixing and pressure recovery.

  57. The second point is also of little weight. Although one of the objectives of the patent is to make burner assemblies which are easy to disassemble (see paragraph 12 above), there is nothing in the SABAF patent which excludes press-fitted constructions. Indeed, there is no feature of the claim which is essential to or necessarily delivers easy disassembly. In addition there is nothing in Hourdry which suggests that his invention is limited to burners made by press-fitting. On the contrary, Hourdry describes his inventive step quite generally in terms of using a radial Venturi passage.

  58. It follows that both of the features which are put forward as the inventive heart of the SABAF claim are known and their use together is a mere collocation. Accordingly the patent is invalid for obviousness.

  59. Before ending, there are two other matters I should mention.

    • First, Mr Vanhegan argues that his client's case of non-obviousness is supported by the commercial success of devices made in accordance with the patent. The issue of commercial success was considered at some length in Haberman v Jackel [1999] FSR 683. No purpose would be served by repeating what was said in that case. In my view SABAF has failed to show that there was relevant commercial success here. It is true that a large number of companies now make burners or use burners which SABAF asserts falls within the scope of the claims of its patents and that, in the early days, a significant number of large manufacturers took licences under the patent. However the royalties charged were very small indeed. They were pitched at such a low level that it would have made little sense for anyone to refuse the offer of a licence and to have litigated instead.

    • Second, I am not persuaded that there was a long felt want either for an air intake above the hob surface or for the shorter burner which is provided by the SABAF design. As to the former, as I have said, it was available anyway. As to the latter, the height of burners had already been reduced by the use of bent supply tubes which ran horizontally under the hob. Furthermore I accept the evidence given by Mr Sutton during the trial that what held up the development and deployment of burners like the SABAF one was attributable to the natural reluctance of those in the art to change from existing designs which worked well and for which expensive tooling already existed. In any event, even if there had been commercial success, that would not have persuaded me that there was an invention here. If SABAF's patent had been restricted either to the radial Venturi or the above-hob air intake alone, it would clearly have been invalid. It is the joining together of these two features which is said to constitute the invention but, for reasons already given, that is a mere collocation and does not qualify as an inventive step.

  60. The other point is that Meneghetti also argue that the patent is invalid because an impermissible amendment was made to it in the Patent Office. This allegation is dependent upon Mr Wilson being right on his construction of the words "the radial mixing passage being shaped to produce a Venturi effect to promote complete mixing and distribution of the gas and the primary air" in claim 1. Even if it was a good argument on the basis of his construction, which I doubt, it is not arguable on the construction of the claim at which I have arrived.

  61. For these reasons, this action fails.


Improver Corp. v. Remington Consumer Products Ltd [1990] FSR 181

Kommerling [1992] EPOR 98

Sedlbauer [1993] EPOR 147

Haberman v Jackel [1999] FSR 683


Mr Mark Vanhegan for the Claimant (instructed by Field Fisher Waterhouse)

Mr Alastair Wilson QC and Mr Peter Colley for the Second Defendants (instructed by Middleton Potts)

[a] a company incorporated under the laws of Italy

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