1 AUSTRALIA Patents Act 1990 SIT LA PRECISA S.P.A. CON SOCIO UNICO COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A device for controlling the supply of fuel gas to a burner, in particular for water heater appliances The following statement is a full description of this invention including the best method of performing it known to us:- A device for controlling the supply of fuel gas to a burner, in particular for water heater appliances SPECIFICATION The present invention relates to a device for controlling the supply of fuel gas to 5 a burner in accordance with the features set out in the preamble of claim 1. The invention is applied in particular, although not exclusively, in the sector of devices for the multi-function control of the supply of fuel gases to valve units designed for uses in heating appliances, in particular domestic water heater appliances. 1o In a typical known solution with respect to these devices, a magnetic safety unit with a pilot and a thermocouple is associated with a relative manual arming system and with at least one valve having a mechanical or electrical operator for controlling a gas supply to a main burner directly or indirectly (servo-assisted system). 15 In these applications, it is also known to provide a pilot duct through which a predetermined flow of gas, correlated with the pressure regulated by a pressure regulator disposed in the pilot duct, is supplied in order to supply the pilot burner flame. As a result, the flow supplied to the pilot burner is the same during both 20 operation of the pilot burner alone, when the main gas throughput is intercepted, and during operation of the main burner. It would be preferable, however, to reduce the rate of flow in the rest phases of the pilot burner, when only the pilot flame is ignited, with a view to efficient saving of fuel gas (with the pilot introducing less energy into the system), while 25 at the same time ensuring a higher flow of gas to the pilot to facilitate ignition 1 At of the main burner. The object of the present invention is to provide a device for controlling the supply of fuel gas to a main burner, in particular for water heater appliances, which is structurally and functionally designed to ensure levels of flow to the 5 pilot burner which are appropriate for the various operating stages, with more efficient fuel consumption when only the pilot burner is ignited. This object is achieved by a device for controlling the supply of fuel gas to a burner embodied in accordance with the appended claims. Other advantages and features of the present invention will become clear from 10 the following detailed description of preferred embodiments thereof, given with reference to the appended drawings which are provided purely by way of non limiting example and in which: - Fig. 1 is a diagrammatic view in longitudinal section of a first embodiment of the control device of the invention; 1s - Fig. 2 is a similar view to Fig. 1 of a second embodiment of the control device of the invention; - Fig. 3 is a similar view to the preceding Figures of a third embodiment of the control device of the invention; - Fig. 4 is a similar view to the preceding Figures of a fourth embodiment 20 of the control device of the invention. With reference, first, to Fig. 1, a device for controlling the supply of fuel gas to a burner of a domestic water heater embodied in accordance with the present invention, is shown overall by 1. The device 1 comprises a valve unit disposed in a main gas supply duct 2 25 between a gas inlet section 3 and an outlet section 4 where the gas is supplied 2 to a main burner 4a. A main valve, shown overall by 5, is disposed along the main duct 2. The valve 5 comprises a valve seat 5a associated with a respective shutter 5b, for instance with membrane control 5c for the opening of the seat 5a in opposition 5 to a respective resilient recall means such as a respective spring 5d. The valve 5 acts as an on/off valve for the safe closure of the main gas channel, as will be described in detail below. The valve 5 may be associated with an electrovalve for controlling the servo assisted circuit, shown by 7, disposed to open and close an auxiliary duct 8 for 10 driving the servo- circuit, which forms the take-up duct for the pressure signal to be transferred to the drive chamber of the servo-circuit. The membrane 5c acts directly on a control stem Se of the shutter 5b which is in turn urged to close the seat by the spring 5d. One side of the membrane 5c defines a drive chamber 10 which communicates is with the main duct 2, upstream of the valve 5, via the duct 8. More particularly, the duct 8 has a first portion 8a, extending upstream of the electrovalve 7, and a second portion 8b, prolonging the first, extending downstream of the electrovalve 7 and communicating with the chamber 10. A throttle 30 is provided in the duct portion 8b. 20 The drive chamber 10 is connected to the main duct 2, downstream of the valve seat 5a of the valve 5, by a respective discharge duct 28 in which a pressure regulator, shown overall by 32, is provided. The regulator is a membrane pressure regulator, known per se, in which one side of the membrane defines a drive chamber 33 communicating, by means of a portion 25 28a of the duct 28, with the main duct 2 (downstream of the valve 5) and is 3 also able to intercept the output section of the other portion 28b of the duct 28 communicating with the drive chamber 10. The opposite side of the membrane is urged by a calibration spring 35 disposed in a chamber open to atmosphere via an opening 36. The pressure regulator 32 is designed to react to the supply 5 pressure variations and to compensate them and return the pressure to a calibration value predetermined by regulation of the spring 35. The pressure regulator 32 may also be designed with a pressure modulation function, for instance as a modulating regulator of electromagnetic type (by means of a motor, linear actuator) or of pneumatic (membrane) type. 10 At the location of the electrovalve 7, the relative portion of the duct 8 may be opened and closed at will by an electromagnet 11, of on/off type with resilient recall, acting on a shutter member 12 associated with the throughput section of the duct 8 which may be displaced to and from a position intercepting the throughput section. 15 The valve unit of the device of the invention comprises an auxiliary gas line, branching from the main line, via which a pilot burner 16 is supplied. The auxiliary line has a pilot duct 16a which branches from the main duct 2 in order to supply the pilot burner 16. Starting from the inlet section, in the main duct 2, there is a first section 18' 20 prolonged by a second section 18" via an interposed valve seat 18, on which a magnetic thermoelectric safety unit with manual arming 20 (or, as an alternative, with an automatic arming system) acts, this unit including a shutter 18a which is held in the position opening the seat 18 by the excitation of the magnetic unit generated by the voltage of a thermocouple (not shown) when 25 there is a flame at the pilot burner 16. 4 The section 18" communicates with the main duct 2, downstream of the seat 18, and with the drive duct 8. The section 18", extending downstream of the seat 18, is also connected with the pilot duct 16a via an interposed valve seat 20a. 5 A shutter 20b rigid with the control stem 20c of a knob member 20d of the magnetic unit acts on the valve seat 20a. The drawing shows a top view of the knob 20d illustrating the operating positions which may be selected (OFF, PILOT, ON). The knob member 20d is connected to the actuator stem 20c to carry out the 10 manual arming of the safety unit, in a manner known per se, in which, in the arming position (PILOT), the ignition of an ignition member (not shown, for instance of piezoelectric type) associated with the pilot burner 16, is simultaneously controlled. The knob 20d may also be switched to the closed position (OFF) in which the valve seats 18 and 20a are intercepted by the 15 corresponding shutters of the magnetic safety unit. A pressure regulator 40, with membrane control, designed to regulate the pressure of the gas and therefore the flow supplied to the pilot burner 16 operates in the pilot duct 16a. The pressure regulator 40 includes a servovalve forming a valve seat 40a 20 cooperating with a shutter shown diagrammatically at 40b, whose control stem 40c is rigidly connected to a control membrane 41 for its control. The membrane 41 is subject on one hand to the pressure regulated by the regulator device and on the other hand to a pressure established in a calibration chamber 42 of the regulator and to the resilient force of a spring 43. 25 According to the invention, a connection duct 45 is provided and brings the 5 calibration chamber 42 into fluid communication with a section of the main duct 2 downstream of the valve 5, i.e. in a valve portion subject to a gas pressure when the shutters 12 and 5 are in the open position. As an alternative, it is possible for the connection duct 45 to bring the chamber 5 42 into fluid communication with a section of the portion 8b of the duct 8 disposed downstream of the electrovalve 7. The pressure signal downstream of the valve 5 (or in the above-mentioned alternative version, in the section 8b of the drive duct), is supplied to the calibration chamber 42 via the duct 45. 10 It is possible, as a result of the provision of the connection duct 45, to obtain two separate pressure (and therefore flow) levels in the gas supplied via the pilot duct. A first pressure level is generated in the pilot duct when the valve 5 is in the closed condition (with the valve 7 closed). 1s At this stage, as no gas is passing through the electrovalve 7, no pressure correlated with the supply pressure is determined in the main duct downstream of the valve 5 (or, in the above-mentioned alternative version, in the portion 8b of the duct 8) and the regulator therefore determines a pressure correlated solely with the resilient force of the spring 43 which causes a first level of 20 supply flow to the pilot burner to maintain the pilot flame (the main burner is not activated). The subsequent opening of the valve seat 5, by excitation of the electrovalve 7, causes, in the main duct downstream of the valve 5 (or, in the above mentioned alternative version, in the portion 8b of the duct 8), a pressure 25 signal equal to or correlated with the supply pressure in the main duct, which 6 signal, transferred by means of the duct 45 to the calibration chamber 42, determines a second pressure level regulated by the regulator, greater than the first level, and such as to enable the ignition of the main burner to which the gas flow is supplied after opening of the main duct 2. 5 It is thus possible to obtain a so-called 'two-stage' pilot burner 16, with a first reduced flow level designed solely to maintain the pilot burner flame, and a second higher flow level designed to ignite the main burner. Fig. 2 shows a second embodiment of the device of the invention, in which details similar to those of the previous embodiment bear the same reference io numerals. In this embodiment, the control device is applied to a valve of thermostat type, of the so-called 'thermo-mechanical thermostat' type, in which the valve seat 5a obtained in the main duct 2 is associated with a corresponding shutter 5b controlled by a thermo-mechanical actuator 50. A valve unit of this type is is disclosed in Italian Patent Application PD2000A000138, in the name of the Applicants, whose specification is understood to be fully included here for any detail which is not described in detail below. The above-mentioned actuator comprises a member 51 sensitive to water temperature variations which is disposed in contact with the water to be heated 20 and is connected in operation to the shutter 5b of the valve. As a result of the thermal expansion of this member, a displacement correlated with the variation of the water temperature is generated, by a bi-stable elastic device 52, with respect to the control stem 5c of the shutter, as a result of which the shutter is caused to close the corresponding valve seat to intercept the flow of gas when 25 a predetermined temperature value is exceeded. 7 In this embodiment, the device of the invention connects the calibration chamber 42, by means of the duct 45, with a section of the main duct 2 disposed downstream of the valve seat 5 with respect to the direction of the flow of gas, thus obtaining the two-stage pilot function described above. s Fig. 3 shows a third embodiment of the device of the invention, in which details similar to those of the previous embodiments bear the same reference numerals. In this embodiment, the control device is applied to a valve unit in which a pair of main servo-valves 5, 6 are provided in cascade with one another and a 1o draught switch 55 of pneumatic type is disposed in the combustion fume discharge duct 56. A valve unit of this type is disclosed in Italian Patent Application PD2010A000385, in the name of the Applicants, whose specification is understood to be fully included here for any detail which is not described in detail below. is Similarly to the previous embodiment, the device of the invention connects the calibration chamber 42, by means of the duct 45, with the section of the main duct 2 disposed downstream of the valve seat 6a of the servo-valve 6 with respect to the direction of the flow of gas, thus obtaining the two-stage pilot function described above. 20 Fig. 4 shows a fourth embodiment of the device of the invention, in which details similar to those of the previous embodiments bear the same reference numerals. This embodiment differs from the preceding embodiment chiefly in that it includes a draught switch 55 with a motor-driven actuator 60, as shown 25 diagrammatically in the corresponding Figure. Similarly to the previous 8 embodiment, the calibration chamber 42 of the regulator is connected, via the duct 45, with the section of the main duct 2 disposed downstream of the valve seat 6a of the servo-valve 6 with respect to the direction of the flow of gas, thus obtaining the two-stage pilot function described above. 5 The invention thus achieves the above-mentioned objects and also achieves the advantages listed with respect to known solutions. It should in particular be noted that it is possible, as a result of the invention, substantially to reduce the energy introduced into the system by the pilot burner during the "rest" stage in which no gas passes through the main duct in the direction of the main burner. 9