Technological background The invention relates particularly to the field of systems for controlling the supply of gas to burners of heating apparatus in general, where the flames of such apparatus are intended for the direct heating of the environment or for heating an intermediate fluid circulating in a boiler installation.

Such equipment, like all installations using gas burners, is normally provided with a valve unit designed to control the supply of gas to the burner, in such a way as to adjust in a controlled way its supply pressure and/or the flow rate of gas supplied. These valve units are typically designed for multifunctional control of the flow of gas supplied to the burner, while also being required to carry out the function of shutting off the gas path for safety purposes and adjusting/modulating the supply pressure.

One of the principal components of such a valve unit is a pressure regulator device, positioned in the main gas supply pipe and typically including a valve having a diaphragm-operated obturator, the diaphragm being subjected on one side to the pressure regulated by the device and on the other side to a pressure generated by an elastic load which may be calibrated if required. By means of such a regulator device, the supply pressure is kept substantially constant and equal, with the subtraction a proportionality factor,

to the ratio between the elastic force and the surface area of the diaphragm subjected to the elastic load.

These pressure regulators can also be designed to provide amplitude- modulated pressure regulation. In such a configuration, the spring system (which generates the elastic load) of the regulator is acted on by an operating means (of the linear type for example), this term denoting any actuating means having an actuating element with controlled movement acting on the spring system to vary the elastic force generated by the spring system. Such operating devices can consist, for example, of electromagnets or controlled- shaft motors or other similar motorized means.

The components normally provided in a valve unit of the aforesaid type also include one or more solenoid valves, each comprising a obturator whose operating rod is moved axially by means of an electromagnetic actuator, in opposition to an elastic spring system for returning the obturator into the position in which it shuts off the corresponding valve seat (for example when no electric current is supplied to the electromagnet). Typically, a pair of these solenoid valves is provided (according to the technical specifications) with exclusively on-off operation, in other words for securely opening or closing the corresponding valve seats located along the supply pipe, but more complex versions can be provided, with proportional or multi-level operators, in other words versions which can assume a plurality of positions according to the value of the electrical supply signal sent to the solenoid valve.

In a known configuration of a valve unit of the aforesaid type, a first and a second on-off solenoid valve are placed in sequence along the supply pipe, together with a pressure regulator of the modulating type, controlled by

an operator, for example a proportional (or multi-level) operator. In this application, the pair of solenoid valves is required to provide the on-off control function, while the pressure regulator has the sole function modulating the pressure. A limitation which may be encountered in such applications is that three separate valve seats in series must always be provided in the main supply pipe of the valve unit, namely one seat per solenoid valve plus one for the pressure regulator downstream of these valves.

In another known configuration, there is only a pair of solenoid valves, placed in sequence in the main supply pipe, the first having an on-off function and the second having an on-off and modulation function. The latter valve can typically be associated with a proportional electromagnetic actuator. In this application, however, it is difficult to obtain a correct regulation curve for types of equipment which require different power levels or which are supplied with gas having different characteristics. This is because, in these cases where there is no pressure regulator, the supply pressure tends not to remain constant as the flow rate (power) requirement varies, or in the presence of combustible gases with different characteristics, and it is therefore difficult to identify unambiguous pressure regulation curves, although there is the advantage that only two valve seats are required in the valve unit, thus clearly making for a simpler construction.

Description of the invention The principal task and object of the invention is to provide a valve unit which is structurally and functionally designed in such a way that the limitations of the cited prior art can be overcome.

This task is fulfilled by the invention by means of a valve unit made in

accordance with the following claims.

Brief description of the drawings Further characteristics and advantages of the invention will be made clearer by the following detailed description of some preferred examples of embodiment of the invention, illustrated for guidance and without restrictive intent in the attached drawings, in which: Figure 1 is a schematic view, in longitudinal section, of a first example of a valve unit according to the invention; Figure 2 is a view, corresponding to that of Figure 1, of a second example of a valve unit according to the invention; Figure 3 is a view, corresponding that that of the preceding figures, of a further example of an embodiment of the invention; Figures 4 and 5 are diagrams of characteristic curves of operation of the valve unit according to the invention.

Preferred embodiments of the invention In the cited figures, the number 1 indicates the whole of a multi- function valve unit for controlling the supply of a combustible gas (referred to below simply as"gas"), made in accordance with the present invention.

The valve unit 1 comprises a supply pipe 2 for transferring gas from a supply element to a burner apparatus (neither of which are illustrated), this pipe extending from a gas inlet aperture 3 to an aperture 4 for the outlet of the gas to the burner. At the outlet 4, the pipe has a restricted cross section, being shaped for example in the form of a nozzle 4a.

The pipe 2 houses a solenoid valve 5 for permitting the flow of gas in the pipe 1 or safely shutting it off, by the on-off operation of its obturator on

the corresponding valve seat. The valve is, for example, of the normally closed type, and comprises an electromagnetic actuator of a conventional type with an elastic return mechanism designed to move the obturator to close the valve seat when no power is supplied to the electromagnet.

Downstream of the solenoid valve 5, the valve unit 1 comprises a pressure regulator device, indicated as a whole by 6, including a valve seat 7, formed in the pipe 2, interacting with a obturator 8, whose operating rod 9 is connected rigidly to a diaphragm 10 which operates it.

The diaphragm 10 is subjected on one side to the supply pressure regulated by the regulator device 6, indicated by Pu, and on the other side to an elastic load generated by a spring system 11 whose axial ends lla, lib are connected, respectively, to the diaphragm 10 and to a wall 12 of a fixed structure of the valve unit. The face of the diaphragm 10 on which the spring system 11 acts is also made subject to atmospheric pressure by the provision of an orifice 13 through which the spring housing chamber 11, partially delimited by the diaphragm 10 and by the wall 12, communicates with the exterior.

The pressure regulator device 6 additionally comprises an operating means, indicated as a whole by 14, directly associated with the obturator 8 to drive the latter with a controlled movement with respect to the valve seat 7, as described more fully below.

The operating means 14 comprises a rodlike member 15 which can be translated coaxially with the rod 9 of the obturator 8, in a direction indicated by X in the figures. The member 15 has at its free end a disc 16 extending transversely to the axis X and positioned to face the obturator 8, on the

opposite side from the rod 9. The number 17 indicates a spring system acting between the disc 16 and the obturator 8.

The operating means 14 is of the proportional or multi-level type, and therefore the actuating member 15 can assume a plurality of positions along the direction X, in a controlled translatory movement. This member 15 can be made, for example, as the moving element of a proportional electromagnet, in which the spatial positions of this element along the axis X are correlated proportionally with the intensity of the electrical signal (with the strength of the current, for example) sent to the operating electromagnet.

Alternatively, the operating means 14 can conveniently be made in the form of a reversible electric motor of the stepping type with means (such as male and female thread couplings or the like) for converting the rotation of the rotor to a translatory movement of the member 15, in which the positions reached by this member along the direction X are correlated with the number of revolutions which the motor is made to perform.

In all the possible embodiments of the operating means 14, the rodlike member 15 is made to be returned to a predetermined safety position whenever the command signal ceases to be supplied to the operating means.

This safety device can be made in the form of electromagnetic release means or elastic return means, according to the chosen embodiment. In all cases, the safety device is such that the member 15 is returned to a predetermined position independently of the operating condition reached by the operating means, whenever the command signal to the latter is interrupted or is, for example, below a predetermined threshold value which has been set.

With particular reference to Figure 1, the valve seat 7 is shut off, in the

absence of a command signal to the operating means 14, by the elastic action of the spring system 17, which, in opposition to the elastic load of the spring system 11, pushes the obturator 8 to close the seat 7. The spring systems 11 and 17 are therefore designed in such a way that, in this condition, the elastic action of the spring system 17 is stronger than the elastic action of the spring system 11, to ensure the closing action of the obturator 8.

Starting from this condition (not shown in the figure), when a command signal has been sent to the operating means 14, the member 15 is moved away from the obturator 8, and therefore the elastic load generated by the spring system 17 is progressively reduced (Figure 1) and the pressure is consequently modulated proportionally in correlation with the ratio between the resultant of the elastic forces (spring systems 11 and 17) and the surface of the diaphragm on which this resultant of forces acts.

In the absence of a command signal to the operating means 14, the member 15 is returned to an outer safe position in which the elastic return of the spring system 17 pushes the obturator 8, as indicated previously, to close the valve seat 7.

Figure 2 shows schematically a second example of embodiment of the valve unit according to the invention, in which components similar to those of the preceding example are identified with the same numerical references.

The valve unit differs from the preceding example primarily in that the spring system 11 acts between the diaphragm 10 and the disc 16 of the operating means 14, which is positioned on the opposite side of the said diaphragm from the obturator 8, and the spring system 17 acts between the obturator and a fixed part of the pipe 2.

In this embodiment, when the operator 14 has been inactivated, the elastic load of the spring system 17 is greater than the elastic load of the spring system 11, so that the obturator 8 is pushed to close the valve seat 7.

As a result of the activation of the operator 14, the disc 16 is moved so that it compresses the spring system 11, consequently increasing the corresponding elastic load which is exerted. When this load is sufficient to overcome the elastic load of the spring system 17, the valve seat is opened and the pressure is regulated proportionally to the ratio between the resultant of the elastic forces (exerted by the corresponding spring systems 11 and 17) and the surface of the diaphragm 10 on which this resultant of forces acts.

In the described examples, the valve unit is also designed so that it can be provided with means of adjusting the spring systems 11 or 17, comprising for example bearing discs of the corresponding spring systems which are adjustable by means of regulating screws having a conventional structure.

These adjusting means advantageously ensure that the valves are interchangeable, regardless of the pressure regulation characteristic.

In addition to the possible configurations of the operating means 14 described above, this means can be of what is called the moving-coil type, as described in detail below with reference to Figure 3.

This operator comprises a permanent magnet 20 in which a ring-shaped air gap 21 is formed. A circular coil 22, having a predetermined current flowing through its turns, is axially movable in the air gap 21. The magnetic induction field into which the coil 22 carrying electrical current is inserted has the effect of generating a force which can move the coil axially, in the direction X. This force is also substantially constant along the predetermined path and is known

to be proportionally correlated with the strength of the current flowing through the coil. As shown schematically in Figure 4, the coil 22 can conveniently be fixed to an end of a bar-shaped stem 23, whose opposite axial end is connected to the obturator 8. An intermediate portion of the said stem 23 is also fixed to the diaphragm 10. A closing spring system 24 acts between the obturator 8 and a wall of the pipe 2.

If no current is flowing in the coil 22, the elastic load of the spring system 24 pushes the obturator 8 to close the valve seat 7. When current is passed through the coil 22, the obturator 8 is subjected to the resultant of the elastic forces (spring system 24) and magnetic induction forces (coil 22), and the opening of the valve seat 7 can therefore be regulated, thus regulating the gas supply pressure. It should also be noted that the supply pressure can be controlled electrically with on-off or modulating operating characteristics, as shown in the diagrams of Figure 4 and 5 respectively.

Advantageously, this moving-coil operator also has extremely low friction, making the control of the system more precise. It is also possible to introduce into the current signal alternating and continuous components, superimposed on each other and of predetermined amplitude, to further reduce any friction and hysteresis and thus provide greater overall precision of operation.

The electrical control of the pressure regulator can also make it possible to detect any instability (by measuring the coil impedance or by using suitable sensor means for example) and to rectify it electronically (by introducing suitable damping signals, for example).

The invention thus performs the task and achieves the objects which were proposed, while also yielding the cited advantages with respect to the known solutions.