System for controlling the delivery of a fuel gas to a burner apparatus

Abstract

A system for controlling the delivery of a fuel gas to a burner apparatus includes a gas-delivery duct extending between an inlet opening and an outlet opening, a pressure-regulator device including a servo-valve in the duct, having a closure member with diaphragm control, the diaphragm being subjected, on one side, to the pressure regulated by the pressure-regulator device and, on the other side, to a calibration pressure established in a calibration chamber of the regulator device, as well as a calibration spring provided in the calibration chamber and acting on the diaphragm. The system also includes a delivery-pressure modulator unit including a modulation valve with a valve seat disposed in the duct downstream of the pressure-regulator device and cooperating with a respective closure member operatively connected to an actuator device arranged for the modulation control of the delivery pressure, as well as a flow communication device between the calibration chamber of the pressure-regulator device and the modulator unit, for bringing into the calibration chamber a pressure signal that is correlated proportionally with the gas-delivery pressure so that the pressure regulated by the pressure-regulator device is in turn correlated with the pressure signal.

Description

This application is a U.S. National Phase Application of PCT International Application PCT/IT2003/000533.

TECHNICAL FIELD

The present invention relates to a system for controlling the delivery of a fuel gas to a burner apparatus.

TECHNOLOGICAL BACKGROUND

The invention relates particularly to the field of systems for controlling the delivery of gas to burners of heating apparatus in general, the flame of which is intended for the direct heating of the environment rather than of an intermediate fluid circulating in a system with a boiler.

Apparatus of this type, like all systems using a gas burner, usually has a system for controlling the delivery of the gas-flow to the burner so as to regulate its delivery pressure and/or the flow-rate of gas delivered, in controlled manner. These systems are therefore typically directed towards a multifunctional control of the gas-flow delivered to the burner and at the same time have to ensure the functions of regulation and safety shutoff of the gas-way in addition to that of modulation of the pressure (or of the flow-rate delivered) in relation to predetermined parameters.

It is known in this field to provide systems which have a pressure regulator for keeping the pressure downstream of the regulator constant irrespective of the gas-supply pressure, and a modulator unit with a delivery-pressure modulation valve, disposed downstream of the regulator. In this case, the modulation valve operates between a pressure upstream of the modulator, which is equal to the pressure regulated by the pressure regulator, and a pressure downstream of the modulator, which is equal to the delivery pressure of the gas-flow towards the burner.

In systems of the above-mentioned type, for a preselected calibration, the pressure regulated by the pressure regulator is substantially constant as the gas-delivery pressure varies, thus defining a predetermined degree of resolution of the modulation, “resolution” being understood as the index of the so-called “discretization” (i.e. rendering discrete) of the delivery pressure that can be achieved by a modulation valve with a finite number of levels, such as the valves which are typically used in these applications.

BRIEF DESCRIPTION OF THE INVENTION

A main object of the present invention is to provide a system for controlling the delivery of a fuel gas to a burner apparatus in which, for given parameters of the system, the resolution is improved, with an amplification of the level of “discretization” of the delivery pressure such as to permit a more precise and reliable modulation of the pressure (flow-rate).

The foregoing and other objects are achieved by the invention by means of a system for controlling the delivery of a fuel gas to a burner apparatus. The system includes a gas-delivery duct extending between an inlet opening and an outlet opening, and a pressure-regulator device including a servo-valve in the duct, having a closure member with a diaphragm control. The diaphragm being subjected, on one side, to the pressure regulated by the pressure-regulator device and, on the other side, to a calibration pressure established in a calibration chamber of the pressure-regulator device. A calibration spring is provided in the calibration chamber and acts on the diaphragm. The system also includes a delivery-pressure modulator unit including a modulation valve with a valve seat disposed in the duct downstream of the pressure-regulator device and cooperating with a respective closure member operatively connected to actuator means arranged for the modulation control of the delivery pressure, and a flow communication means between the calibration chamber of the pressure-regulator device and the modulator unit, for bringing into the calibration chamber a pressure signal that is correlated proportionally with the gas-delivery pressure so that the pressure regulated by the pressure-regulator device is in turn correlated with the pressure signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and the advantages of the invention will become clearer from the following detailed description of two preferred embodiments thereof which are described by way of a non-limiting example with reference to the appended drawings, in which:

FIG. 1 is a schematic view showing a first embodiment of the control system according to the invention, in longitudinal section,

FIG. 2 is a view corresponding to FIG. 1 of a second embodiment of the system according to the invention, and

FIG. 3 is a graph representative of the system according to the invention.

PREFERRED METHOD OF IMPLEMENTING THE INVENTION

In the above-noted drawings, a main duct for the transfer of fuel gas (hereinafter referred to simply as gas) from a delivery element to a burner apparatus (neither of which is shown) is indicated by the numeral 1. The duct 1 extends between a gas-inlet opening 2 and an opening 3 for the outlet of the gas towards the burner. The supply pressure and the delivery pressure of the gas are indicated Pi and Pu, respectively.

The body of a pressure-regulator device, generally indicated 4, is formed in the duct 1; the device 4 includes a servo-valve defining a valve seat 5 cooperating with a closure member, shown schematically at 6, the control rod 6a of which is connected rigidly to a diaphragm 7 for operating the rod 6a.

The diaphragm 7 is subjected, on one side, to the pressure which is regulated by the regulator device 4 and which is indicated Pr and, on the other side, to a pressure established in a calibration chamber 8 of the regulator. As will be described in detail below, the pressure acting on the diaphragm in the chamber is defined partly by the resilient load exerted by a calibration spring 9 housed in the chamber 8. The resilient load acting on the diaphragm 7 is adjustable by means of an adjustment screw 10. The pressure exerted on the diaphragm 7 by the spring 9 is referred to below as Pt.

The system according to the invention also has a unit, generally indicated 11, for modulating the delivery pressure Pu; the unit 11 is provided in the duct 1, downstream of the pressure regulator 4. The modulator unit comprises a modulation valve with a valve seat 12 cooperating with a closure member 13 which is operatively connected to actuator means for the modulation control of the delivery pressure Pu.

The closure member 13 has a control rod 13a the axial movement of which relative to the valve seat 12 is brought about by drive means, shown schematically and indicated as 14[,] (for example, of the stepping type), in a manner such that the regulation of the closure member 13 is of the proportional type with a finite number of modulation levels. Transmission means are provided between the drive means 14 and the rod 13a and comprise, for example, a male-and-female screw coupling arranged for converting the rotary movement of the drive means into the translational movement of the rod.

The above-mentioned modulation valve may be of the type described in the Applicant's Italian patent application No. PD 2001A000240, the description of which is therefore included herein by reference for any further characteristic not expressly mentioned.

An electronic board, schematically indicated 15, carries a respective circuit assembly arranged for controlling the actuator means and consequently for controlling the modulation function performed by the modulator unit.

It should be noted that, immediately upstream of the valve seat 12, the pressure is equal to the regulated pressure Pr, whereas in a portion, indicated 16, immediately downstream of the valve seat, the gas pressure is equal to the delivery pressure Pu.

According to the invention, the control system has a duct 17 which puts the calibration chamber 8 into flow communication with the portion 16 of the delivery duct 1 downstream of the modulation valve. The connection is such that the delivery-pressure signal Pu is brought into the calibration chamber 8 so that the pressure to which the diaphragm 7 is subjected in the chamber is the sum of the calibration pressure and of the delivery pressure Pu. As a result of the balancing of the pressures on the sides of the diaphragm 7, the pressure Pr regulated by the regulator is consequently equal to the sum of the contributions of the pressures Pt and Pu (Pr=Pt+Pu).

If the ratio between the pressures downstream and upstream of the modulator, which ratio defines the pressure gain of the system in open circuit (that is, the result that can be achieved at the output of the system without the connection of the duct 17), is indicated G (G=Pu/Pr), then according to the control system of the invention, the quantity Pu varies in accordance with the following law:
Pu=Pt(1/G−1).

As a result, as Pu decreases, the gain G decreases, permitting an increase in the resolution R, where R=1(dPu/dX), in which R is linked with the movement of the closure member 13 of the modulator unit along its own principal axis X, and is inversely proportional to Pu. In particular, if the closure member 13 of the modulator unit 11 is operated by a linear actuator of any type having levels (with a preselected number of “steps”), then R=1/(dPu/dStep).

FIG. 3 shows a graph with “Pu” on the ordinate and the levels (steps) on the abscissa, in which curve A (solid line) represents the system in open circuit, without the connection of the duct 17, and curve B (broken line) represents the system according to the invention.

With particular reference to FIG. 2, a second embodiment of the system according to the invention, in which details similar to those of the previous embodiment are indicated by the same reference numerals, provides for the modulator unit 11 to be associated with an air-gas mixer device 18 in order to obtain a combustible mixture to be transferred to the burner. More particularly, the air-flow sent into the mixer 18 is generated by a fan 19 the output of which is directed into a mixing region, for example, formed with a Venturi duct into which the gas delivered by the modulator unit 11 at the pressure Pu is injected.

The system has a duct 20 for putting the calibration chamber 8 of the pressure regulator into flow communication with a casing portion 21 of the fan 19 defined in the region of the outlet of the fan 19, upstream of the air-gas mixing region, in which the output pressure of the fan, indicated Pv, is present.

As a result, the pressure Pr regulated by the regulator 4 is equal, in this case, to the sum of the contributions of the calibration pressure and of the fan output pressure (Pr=Pt+Pv). Since the pressure Pv is correlated proportionally with the gas-delivery pressure Pu, in this embodiment also, the resolution of the degree of “discretization” is consequently variable in dependence on the gas-delivery pressure Pu (or, correspondingly, on the air-output pressure Pv).

An electronic board for controlling the motor-driven actuator of the modulator unit 11 is indicated 22 and a differential pressure sensor is indicated 23; the pressure value detected by the pressure sensor 23 is sent to the electronic board 22. The pressure sensor 23 is provided with detection terminals which are arranged, respectively, in the air duct 20 and in the gas-delivery duct, in a section of the gas-delivery duct upstream of the air-gas mixing region (FIG. 2). The gas pressure is modulated by operation of the actuator 11, by means of the signal processed by the electronic board 22, in dependence on the pressure signal detected by the sensor 23, in order to keep the pressure differential at a suitable value such as to ensure that the ratio between the air flow-rate and the gas flow-rate remains constant.

For some applications, a flow sensor may be selected as the sensor 23, in particular for applications in which the pressure differential tends to adopt values close to zero.

The invention thus achieves the objects proposed, affording the advantages mentioned above over known solutions.

Claims

1. A system for controlling the delivery of a fuel gas to a burner apparatus comprising:

a gas-delivery duct extending between an inlet opening and an outlet opening,

a pressure-regulator device including a servo-valve in the duct, having a closure member with diaphragm control, the diaphragm being subjected, on one side, to the pressure regulated by the pressure-regulator device and, on the other side, to a calibration pressure established in a calibration chamber of the pressure-regulator device, a calibration spring being provided in the calibration chamber and acting on the diaphragms,

a delivery-pressure modulator unit including a modulation valve with a valve seat disposed in the duct downstream of the pressure-regulator device and cooperating with a respective closure member operatively connected to actuator means arranged for the modulation control of the delivery pressure, and a flow communication means between the calibration chamber of the pressure-regulator device and the modulator unit, for bringing into the calibration chamber a pressure signal that is correlated proportionally with the gas-delivery pressure so that the pressure regulated by the pressure-regulator device is in turn correlated with the said pressure signal.

2. The system according to claim 1 in which the calibration chamber is in flow communication with the delivery duct downstream of the modulator unit by means of a connecting duct, and the pressure signal corresponds to the gas-delivery pressure obtained by means of the modulation valve.

3. The system according to claim 1 in which the pressure signal brought to the calibration chamber of the pressure-regulator device is indicative of the air-output pressure of a fan associated with an air-gas mixer in which the output air-flow of the fan is mixed with the gas-flow delivered by means of the modulation unit at the delivery pressure.

4. The system according to claim 1 in which the modulation valve is of a proportional type with a finite number of modulation levels.

5. The system according to claim 4 in which the actuator means associated with the closure member of the modulation valve comprise a control rod the axial movement of which relative to the corresponding valve seat is controlled by drive means of the stepping type.

6. The system according to claim 5 in which the modulator unit comprises drive transmission means suitable for converting the rotary movement of the drive means into a translational movement of the operating rod of the closure member of the modulation valve.

7. A system according to claim 3 in which the flow communication means comprise a connecting duct between the calibration chamber of the pressure-regulator device and a casing portion of the fan which casing portion is defined in the region of the outlet of the fan, upstream of the air-gas mixing region of the air-gas mixer.

8. The system according to claim 3 in which the fan is of a modulating type and its output pressure can be modulated selectively between a minimum and a maximum pressure value.

9. The system according to claim 7 comprising a differential pressure sensor provided with detection terminals which are arranged, respectively, in said connecting duct and in a section of the gas-delivery duct upstream of the air-gas mixing region of the air-gas mixer.

10. The system according to claim 9 comprising electronic board control means arranged to process, in dependence on the pressure signal detected by said differential pressure sensory, a control signal for controlling said actuator means so that the delivery pressure is modulated in order to keep the pressure differential at a suitable value such as to ensure that the ratio between the air flow-rate and the gas flow-rate remains constant.

11. The system according to claim 2 in which the modulation valve is of a proportional type with a finite number of modulation levels.

12. The system according to claim 3 in which the modulation valve is of a proportional type with a finite number of modulation levels.

13. The system according to claim 7 in which the fan is of the modulating type and its output pressure can be modulated selectively between a minimum and a maximum pressure valve.