WO2007098790A1

WO2007098790A1 - A valve unit for controlling a combustible gas supply

Info

Publication number: WO2007098790A1
Application number: PCT/EP2006/005889
Authority: WO
Inventors: Luca Peron; Stefano Zanella; Gianpiero Turrin
Original assignee: Sit La Precisa S.P.A.
Priority date: 2006-02-28
Filing date: 2006-06-20
Publication date: 2007-09-07
Also published as: ITPD20060063A1

Abstract

A valve unit for controlling the supply of a combustible gas via a supply duct (2) comprises a valve seat (3) in this duct and a first safety shutter (4) associated with this seat, electromagnetically controlled actuator means (4a) adapted to control the shutter to open or close the seat, the actuator means being associated with resilient recall means (12) acting on the shutter to urge it close the valve seat when a predetermined condition requiring the interception of this valve seat occurs. The valve unit comprises a second separate and distinct modulation shutter (5), coaxial with the first shutter and cooperating with the valve seat on the side axially opposite the first shutter, this second shutter being associated with respective actuator means (17) for a modulation control of the opening of the seat in a manner independent from the control of the first safety shutter of the seat.

Description

A valve unit for controlling a combustible gas supply Technical field

The present invention relates to a valve unit for controlling a combustible gas supply having the characteristic features set out in the preamble of the main claim. Technological background

These units are used in particular to control the supply of combustible gas to a burner or like consumer unit in order to vary its supply pressure or the flow of gas supplied in a controlled manner, preferably with continuous modulation. A typical application is in the system controlling the supply of gas to burners of boilers for domestic heating and/or heating of domestic hot water. In accordance with current technical regulations, these units normally have to comprise a dual valve device adapted to intercept the gas path in such a way that they are operationally independent and to ensure that the passage of gas is intercepted by one of the valve devices even when the other device is subject to an operating malfunction.

A typical application comprises the arrangement in cascade of a pair of electrovalves comprising respective shutters whose control rod is axially displaced by means of an electromagnet actuator in opposition to a resilient spring adapted to recall the shutter into the position intercepting the corresponding valve seat (for instance when there is no electrical supply to the electromagnet). Typically, one of the electrovalves has an exclusively on/off function, i.e. it is adapted to ensure the safe opening or closing of the respective valve seat, while the other electrovalve is adapted, in addition to the on/off function, to carry out a modulation function. It is, for instance, operationally associated with a proportional or stepped operator, i.e. it is able to assume a plurality of positions as a function of the value of the electrical supply signal supplied to the electrovalve.

An embodiment of these known valve units is disclosed in European Patent Application 1 106 923 in the name of the Applicants. The valve unit disclosed therein is provided with a motor-driven actuator adapted operationally to control a shutter which opens or closes a valve seat and which is generally adapted to carry out the function of safe interception of the gas path and the function of regulation/modulation of the supply pressure (or flow). In this respect, it comprises an actuator rod acting on the shutter and coupled kinematically to a motor, such as a step-by-step motor, the coupling being such that an actuation in rotation of the motor is followed by a displacement in axial translation of the rod from and towards the position intercepting the seat. The control of the axial displacement of the shutter therefore provides the predetermined control modulating the supply pressure or flow through the valve seat.

A further known solution is disclosed in European Patent Application 0 271 3016. In this case, the motor-driven control rod of the shutter is formed as two coaxial sections provided with portions of ferromagnetic material, capable of mutual attraction, in which the lower section, connected rigidly to the shutter, is directly urged by a resilient recall means into the position closing the valve seat.

One of the main features of these valve units is to ensure, in the valve being modulated, that the passage of gas through the valve seat is efficiently intercepted when particular conditions occur, for instance conditions in which safe closure of the valve seat has to be ensured because the electrical supply to the motor-driven actuator is discontinued. The result is that all the solutions described above have a common characteristic, i.e. the fact that the modulation function and the interception function are integrated and therefore coexist in the same shutter which carries out both functions associated with its respective valve seat.

When, in these applications, the regulated flow has to be varied over a wide range of modulation, it is necessary, however, to use different valve seat diameters and/or different geometric shapes of the shutter. This has an impact especially when, while the maximum flow supplied remains the same, it is wished to change from one type of gas to another (for instance from natural gas to liquid gas or vice versa).

The need therefore for different valve geometries for different ranges of flow or types of gas does not sit happily with the need to ensure constant and unchanged conditions for the safe interception of the gas path. In this case, it could not in practice be envisaged to carry out the above-mentioned adaptations in a valve unit which has already been installed and is operational because this would make it necessary to work on the member which is also adapted to carry out the function of safe closure of the gas path, with the risk of compromising or altering this function. Disclosure of the invention

The main object of the present invention is therefore structurally and operationally to improve the solutions made available up to now by the prior art, in particular to make the modulation function in the valve unit as independent as possible from the safe closure function in order advantageously to improve overall reliability, ensuring the safety function while retaining the advantages of the modulation function integrated into the valve.

These and other objects to be set out in detail in the following description are achieved by the invention by means of a valve unit for controlling the supply of a combustible gas embodied in accordance with the accompanying claims. Brief description of the drawings

The characteristic features and advantages of the invention are set out in detail in the following description of two preferred embodiments thereof, given solely by way of non-limiting example, made with reference to the accompanying drawings, in which:

Fig. 1 is a view in axial section of a first embodiment of a valve unit of the invention in a predetermined operating condition; Fig. 2 is a view in axial section of a second embodiment of a valve unit of the invention in a different operating condition with respect to Fig. 1;

Fig. 3 is a perspective view, with some parts partially dismantled, of the valve unit of Figs. 1 and 2;

Fig. 4 is a partial view of a variant of a detail of the valve unit of the preceding Figures.

Preferred embodiments of the invention

In Fig. 1, a first embodiment of a valve unit for controlling the supply of a combustible gas to a burner or like consumer unit (not shown) in accordance with the present invention is shown overall by 1. The unit 1 comprises a supply duct 2 for the transfer of gas from a supply member (not shown) to a burner apparatus (not shown) provided with a valve comprising a valve seat 3 associated with a pair of shutters 4 and 5 adapted respectively to carry out the function of opening and closing of the gas path (on/off function) and the function of modulation of the flow of gas supplied via the seat 3, as will be explained in detail below.

In compliance with current technical standards, it will be appreciated that the above-described valve device is further associated with a second safety on/off electrovalve 6 preferably disposed upstream of the valve seat 3. It comprises a valve seat 7 cooperating with a shutter 8 in order to carry out the function of safe closure of the gas path in the duct 2 if predetermined conditions occur.

Respective electromagnetic actuators, shown overall by 4a and 8a, are provided to control the shutters 4 and 8 and are functionally associated with respective solenoid means comprising corresponding electrical coils 4b, 8b.

Each of the control rods of the shutters 4, 8 is in particular formed as two coaxial sections of ferromagnetic material inserted in a respective magnetic circuit generated by the corresponding solenoid means, capable of mutual attraction, in which the lower section, connected rigidly to the shutter, is directly urged by resilient recall means into the position closing the valve seat, as will be explained in detail below.

The electromagnetic actuator 4a operationally associated with the shutter 4 will be described in detail; the other actuator associated with the shutter 8 is structurally identical and the same reference numerals followed by the apostrophe sign (^λ) will be used for corresponding components. The coaxial sections of the control rod of the shutter 4 (8) comprise a first and a second core shown respectively by 9 and 10 (9' and 10') which are structurally independent from one another and coaxial with the shutter, the upper core 9 (9') being made rigid with a stationary structure of the valve unit, and the lower core 10 (10') being coupled to the shutter and guided in a sliding manner in the body of the valve unit and thus capable of relative movement with respect to the fixed core. The cores 9, 10 (9', 10') are capable of mutual magnetic attraction by means of the excitation of the coils 4b (8b) at the location of respective surfaces 9a, 10a (9a', 10a') facing one another and forming an air gap 11 (H').

A spring forming a means resiliency recalling the shutter 4 (8) into the position intercepting the corresponding valve seat is shown by 12 (12'). An abutment member of the spring 12 (12') is shown by 13 (13') and is connected to the stationary part of the valve unit. Each spring 12, 12' therefore acts between the stationary portion of the valve body and the respective shutter 4, 8 in order to urge this shutter to close the corresponding seat 3, 7 when there is no magnetic attraction between the cores 9, 10 (9' 10') under the action of the resilient force exerted by the spring. It will be appreciated that the solenoid means comprise respective and separate electrical coils 4b, 8b, whose winding turns encompass the corresponding ferromagnetic cores of the shutters 4, 8.

Returning to the valve seat 3, in accordance with a main characteristic feature of the invention, the shutter 5 associated therewith is separate and distinct from the shutter 4, is coaxial with the latter (axis X) and cooperates with the seat 3 on the side axially opposite the shutter 4.

In further detail, the shutter 5 is disposed downstream of the shutter 4 with respect to the direction of flow of the gas and is operationally associated with a actuator means adapted to control modulation. The section of the seat 3 cooperating with the shutter 5, shown by

14, is formed in a member 15 which is structurally independent from the stationary structure of the valve body and can be coupled to the latter in a detachable manner, so that this section 14 can be interchanged in the valve unit. The member 15 has an end of annular shape, at the location of the seat 3, whose central hole defines the amplitude of the gas supply section 14 which may be modulated by the shutter 5. A sealing system, for instance using a ring 16, may be interposed between the member 15 and the stationary structure of the valve unit.

The shutter 5 is advantageously shaped as an ogive adapted to vary the amplitude of the gas passage section 14 in the valve seat 3 in accordance with a predetermined law of variation correlated with its axial displacement.

In order to control the shutter 5, the valve unit comprises a motor- driven actuator comprising a control rod 17 coupled kinematically to a motor 18, the coupling being such that an angular rotation of the motor 18 brings about an axial translation of the rod. This coupling may for instance be embodied as a screw-nut coupling between a nut provided in the rotor of the motor and a screw obtained by external threading of part of the rod. The motor 18 is advantageously an electric motor of the step-by-step type with reversible rotation. On the side opposite the motor, the rod 17 is connected to the shutter 5 for instance by a threaded coupling.

A spring 19 is keyed on the rod 17 in a position interposed between the shutter 5 and an abutment 20 made rigid with the stationary portion of the valve unit, the function of this spring being primarily one of recovering any play in the kinematic transmission of the motor-driven actuator.

It will be appreciated that the member 15 together with the shutter 5 and the control rod 17 (including the spring 19) forms a self-contained assembly providing a unit which can be individually handled (with the components associated therewith) and therefore readily inserted and replaced in the body of the valve unit. This component unit can in practice be readily inserted and removed axially via an opening 21 in the valve body on the side axially opposite the assembly zone of the shutters 4 and 8 and their respective electromagnetically controlled actuator means. This unit can, moreover, be coupled with the motor 18 associated with the rod 17 so that the mounting of the assembly - motor, actuator rod and shutter - can be readily installed in the valve unit and readily replaced in an interchangeable manner.

A bell-shaped housing 22 is also provided to enclose the rotor 23 of the motor 18 and ensure that it is externally gas-tight. For this purpose, the bell 22, interposed between the stator and rotor members of the motor, has a cylindrical surface 22a at its open end on which a gas seal is provided by means of a sealing ring 24, for instance of the O-ring type. As an alternative, a gas seal may be provided directly on the control rod 17, for instance by sliding of O-ring sealing rings 17a (Fig. 4), so as to prevent leakages of gas into the housing area of the rotor member 23 of the motor. In this case the bell-shaped housing 22 is not required with the advantage that a conventional type of motor, which is not leak-tight, may be used.

From the point of view of the operation of the valve unit, in an initial condition intercepting the duct 2 (Fig. 1), the shutters 4 and 8 are urged by their respective recall springs into the position closing the respective valve seats. The seat 3 is in particular intercepted by the shutter 4 irrespective of the operating position of the shutter 5, as the shutters 4 and 5 are both structurally and functionally separate and distinct. When ignition of the burner is required, the shutters 4 and 8 are displaced into the position opening their respective valve seats by actuation of the respective electromagnetic controls and at the same time the rod 17 is controlled by the motor 18 to perform the predetermined modulation stroke of the shutter 5 so that the flow supplied through the section 14 of the seat 3 may be appropriately modulated. A corresponding variation of the lift of the shutter 5 with respect to the seat 3 is in practice obtained by rotation of the motor 18. As a result of the proportionality between the number of steps of the motor 18 and the lift of the shutter 5, the gas flow is modulated between the minimum and maximum rates of flow as a function of the thermal requirement. In the modulation phase, the cores 9, 10 (9', 10') continue to be anchored to one another through their reciprocal magnetic attraction. When the supply of the respective electrical coil is discontinued, the corresponding moving core 10 (10') is resiliently urged by the recall spring 12 (12') which urges the shutter to close the seat thus causing the gas path to be intercepted (Fig. 1). Whatever the operating condition of the actuator rod 17, whenever the supply to the coil associated with the shutter 4 is discontinued, there is instantaneous safe closure of the seat 3 irrespective of the operational position of modulation of the rod 17.

In order to verify the correct leak-tight operation of each of the valve seats 3, 7, independently from one another, the duct 2 is provided with a bypass duct 25 and an exhaust opening 26 adapted selectively to bring sections of the duct 2 into communication, as will be described below. The exhaust opening 26 may be intercepted by a screw 27 and is defined by a bushing 28 engaged in a leak-tight manner in a through hole 29 provided in the central section 2a of the duct 2 comprised between the valve seats 7 and 3. The opening 26 causes the central section 2a to communicate with the exterior of the valve unit and opens this section 2a to exhaust.

The bypass duct 25 may be selectively intercepted by a screw 25a engaged in a leak-tight manner in a housing 25b of the duct 2 and is adapted to intercept or enable communication between a section upstream and a section downstream of this valve seat.

In operation, in order to verify the leak-tightness of the seat 7, the opening 26 is open to exhaust, while the bypass duct 25 remains closed. In this case, it is possible to verify the leak-tightness of the seat 7 in a functionally independent manner from the downstream valve seat 3. The dashed arrows in Fig. 1 show the direction of the gas flow in this operating condition. Vice versa, for verifying the seat 3, the opening 26 is kept closed and the bypass 25 is opened by unscrewing the screw 25a. In this way, the valve seat 7 is bypassed and the gas flows through the valve seat 3. The dot-dash arrows of Fig. 1 show the direction of the gas flow in this second operating condition.

Fig. 2 shows a second embodiment of the invention in which components similar to those of the previous embodiment bear the same reference numerals. This embodiment differs chiefly in that the solenoid means of the electromagnetic actuators comprise a single electrical coil 30 whose winding turns 30a encompass both ferromagnetic cores 10, 10' for the control of the respective shutters, in accordance with the configuration shown in detail in Fig. 3. The coil 30 is provided with an outer carcass 31 which forms the yoke structure adapted to guide the magnetic flux generated by the magnetomotive force of the coil. It will be appreciated that the ferromagnetic cores 10, 10' are disposed in a spaced relationship with one another with respective parallel and spaced directions of axial displacement.

A central median plane of axial symmetry of the coil is shown by Y and the cores 10, 10' are disposed in a symmetrical mirror position with respect to this plane.

The carcass 30a is also advantageously symmetrical with respect to the median plane Y so as to distribute the magnetic flux linked with both moving electromagnetic control cores in a balanced manner. In Fig. 2, the main direction of flow of the magnetic field generated by the coil 30 is shown by a sequence of continuous arrows. In this respect, the yoke defined by the carcass 30a and by lower plates 32 of the valve unit provides, in the vicinity of the cores 10, 10' a circuit with a substantially C- shaped cross section, the open side of this circuit being closed by each pair of cores 9, 10 (9', 10') of the respective shutter 7, 3. The choice of this arrangement, as well as the provision of a gap 33 between the plates 32, makes it possible efficiently to guide the magnetic flux linked with the cores 10, 10' thus minimising flux dispersions and increasing the overall efficiency of the electromagnetic control. In operation, the supply of the coil 30 causes the generation of the magnetic flux adapted to enable the simultaneous magnetic attraction of the two cores 10, 10' against the respective fixed cores 9, 9' against the resilient action of the springs 12, 12' with the consequent opening of the valve seats. Vice versa, when the supply of the coil 30 is discontinued, the resilient recall forces of the springs tend to urge the shutters to close against their respective valve seats, providing for the function of safe interception of the gas path through the duct 2.

The invention thus achieves the proposed objects and offers a number of advantages over known solutions.

Among the main advantages of this unit, it will be appreciated that modulation is substantially independent from the opening and closing function controlled by the electromagnetic operating means as a result of the fact that the two safety and modulation shutters cooperating with the same valve seat are separate and distinct from one another. Throughout the phase of modulation of the flow, the moving core of the magnetic circuit therefore has no influence as the modulating shutter and its respective actuator rod are structurally independent from this core. The strokes of the safety and modulation shutters cannot in particular influence one another with the result that one places no limits on the other.

Since, moreover, the safety and modulation shutters are adapted to cooperate with the same valve seat, losses of load are advantageously reduced in comparison with solutions in which a pair of separate valve seats is provided.

A further advantage lies in the simplification of the mechanical processing of the single valve seat cooperating with the safety and modulation shutters, in comparison with known solutions in which it is necessary to machine two separate valve seats.

A further advantage lies in the fact that the modulating shutter unit, including the motor and the control rod, form a self-contained individual unit which can be rapidly and readily installed and readily replaced, even in situ. Moreover, this unit may be controlled and calibrated separately prior to installation in the valve unit. This feature is particularly advantageous in applications in which it is wished to obtain a different range of modulation of the flow or when it is wished to use a different type of gas, both aspects which require modifications of the geometry of the flow section or of the shape of the shutter.

A further advantage lies in the fact that the motor of the modulation shutter does not have to oppose the resilient recall forces of the safety shutter and can therefore be chosen to have a smaller bulk and a smaller absorbed power in comparison with known solutions, thereby achieving an overall cost saving.

A further advantage is that the modulation shutter may be dimensioned with respect to its valve seat with a very small coupling play as a result of the fact that, as it has no safety function, any wear which may occur during operation does not compromise the safety function as it cannot affect the closure force of the safety shutter. These reductions of the coupling play also enable constructional simplifications and reduced costs in the production of the modulation unit.

The possibility of providing a modulation shutter separate and distinct from the safety shutter also enables, in accordance with the invention, high precision in the control of the modulation resulting in a unequivocal correspondence between the control signal and the modulated flow value. This aspect is very relevant in those applications in which it is wished also to control combustion through the use of sensors adapted to detect the presence of carbon monoxide or other combustion residues contained in the combusted vapours.

In particular, when use is made of calibration systems with predetermined curves, in which the CO values are correlated with combustion characteristics, the feature of high precision in the flow modulation means that these calibration systems can be applied in a reliable and precise manner.

Claims

C L A I M S

1. A valve unit for controlling the supply of a combustible gas via a supply duct (2), comprising: a valve seat (3) in this duct (2) and a first safety shutter (4) associated with this seat, electromagnetically controlled actuator means (4a) adapted to control the shutter (4) to open or close the seat (3), - the actuator means (4a) being associated with resilient recall means (12) acting on the shutter (4) to urge it close the valve seat (3) when a predetermined condition requiring the interception of this valve seat occurs, characterised in that it comprises a second separate and distinct modulation shutter (5), coaxial with the first shutter (4) and cooperating with the valve seat (3) on the side axially opposite the first shutter (4), and in that this second shutter (5) is associated with respective actuator means (17) for a modulation control of the opening of the seat (3) in a manner independent from the control of the first safety shutter (4) of the seat.

2. A valve unit according to claim 1, wherein the valve seat (3) comprises a gas supply section (14) associated with the second shutter (5), this section being defined in a member (15) which may be removed and which may be made rigid with the stationary structure of the valve unit, so that the section (14) is interchangeable in this unit.

3. A valve unit according to claim 1 or 2, wherein this member (15), together with the second shutter (5) and the actuator means (17) of the second shutter form a self-contained unit, which may be individually handled, and can be made rigid in a detachable manner with the stationary structure of the valve unit.

4. A valve unit according to claim 3, wherein this unit may also be made rigid with a motor means (18) operationally associated with the actuator means (17) of the second shutter (5), so that it can be interchangeably replaced, together with the motor means (18), in the valve unit.

5. A valve unit according to claim 4, wherein the actuator means of the second shutter comprise a control rod (17) operationally associated with the motor means (18) for the modulation control, kinematic coupling means being interposed between the control rod and the motor means in order to convert a movement of rotation of the motor means into a movement of translation of the control rod (17) of the shutter (5).

6. A valve unit according to claim 5, wherein the motor means comprise a reversible electric motor (18) of the step-by-step type.

7. A valve unit according to one or more of the preceding claims, comprising a second valve seat (7) in the duct (2) and solenoid means operationally associated with the valve seats (3, 7) in order to control the respective shutters (4, 8) between a first operating condition in which the solenoid means are electrically supplied and a second operating condition in which the solenoid means are not supplied, each valve seat (3, 7) being provided with a respective ferromagnetic core (10, 10') associated with the magnetic circuit of the solenoid means in order to control the respective shutter between the operating conditions, wherein the solenoid means comprise a single coil (30) whose winding turns (30a) encompass both the ferromagnetic cores (10, 10') for the electromagnetic control of the respective shutters and the cores are disposed in a mutual spaced relationship with their respective directions of operational displacement mutually spaced from one another.

8. A valve unit according to claim 8, wherein the directions of operational displacement of the electromagnetic control cores (10, 10') are oriented parallel to one another.

9. A valve unit according to one or more of the preceding claims, comprising, in the supply duct (2), at least one exhaust opening (26) and bypass duct (25) adapted to bring duct sections into reciprocal communication or to open to exhaust one or a plurality of these sections so as to make the functions of sealing of the valve seat (3) and of a second valve seat (7) disposed in cascade along the supply duct independent from one another.

10. A valve unit according to claim 9, wherein the exhaust opening (26) is provided in the duct section comprised between the valve seats (3, 7) in order selectively to open this section to exhaust, the bypass duct

(25) being provided in order selectively to bring into communication a duct section upstream and a section downstream with respect to the valve seat (7) disposed upstream of this exhaust opening (26), this bypass duct (25) enabling a bypass of the corresponding valve seat (7) between the sections upstream and downstream thereof.