PARTIALLY-PREMIXED GAS BURNER APPLIANCE

Abstract

Partially-premixed gas burner appliance (10), comprising a combustion chamber (11), a fan (17) and a gas modulator (20). The fan (17) is configured to provide an air flow to the combustion chamber (11) and is assigned to an air inlet port (11A) of the combustion chamber or to an air duct (18) configured to provide the air to the air inlet port. An air flow restriction element (19) is assigned to the air inlet port (11A) or to the air duct (18). The air flow restriction element (19) is configured to provide a pressure drop so that the pressure downstream of the air flow restriction element (19) is lower than the pressure upstream of the same. The gas modulator (20) is configured to provide a gas flow to the combustion chamber (11), wherein a first portion of the air provided by the fan (17) is premixed with the gas flow before the gas is combusted, and wherein a second portion of the air provided by the fan (17) is mixed with the gas while the gas is combusted. The gas modulator (20) is a pneumatic gas control valve, wherein the pneumatic gas control valve has a main gas valve (22), a safety gas valve (23), a servo gas valve (24) and gas outlet pres-sure regulator (25). The gas outlet pressure regulator (25), namely a first chamber (33) of the same in which a pressure is present that influences the nominal-value of the gas outlet pressure of the pneumatic gas control valve, is connected to the air inlet port (11A) or to the air duct (18) upstream of the air flow restriction element (19) such that the gas outlet pressure provided by the pneumatic gas control valve de-pends on the air pressure upstream of the air flow restriction element (19).

Description

The invention relates to a partially-premixed gas burner appliance.

In the technical filed of gas burner appliances there are in principle two different types of gas burner appliances, namely fully-premixed gas burner appliances and partially-premixed gas burner appliances. In both types of these gas burner appliances a mixture of gas and air becomes combusted within a combustion chamber of the respective gas burner appliance. The present invention relates to a partially-premixed gas burner appliance.

EP 0 390 964 B2 and US 2009/0 197 212 A1 disclose fully-premixed gas burner appliances. In fully-premixed gas burner appliances an air flow provided by a fan is fully premixed with a gas flow provided by a gas modulator before the resulting gas/air mixture is combusted.

EP 0 103 303 A2 discloses a partially-premixed gas burner appliance comprising a combustion chamber in which gas is combusted. A fan provides an air flow to the combustion chamber. The fan is assigned to an exhaust gas outlet port of the combustion chamber. Air is sucked into the combustion chamber when the fan being assigned to the exhaust gas outlet port is running, wherein the air enters into the combustion chamber through an air inlet port. An air flow restriction element is assigned to the air inlet port of the combustion chamber. A gas modulator provides a gas flow to the combustion chamber, namely to a gas burner rod positioned within the combustion chamber. In partially-premixed gas burner appliances only a first portion of the air flow provided by a fan is premixed with the gas flow before combustion takes place. In partially-premixed gas burner appliances a second portion of the air flow provided by the fan is mixed with the gas while the combustion of the gas takes place.

DE 196 39 992 B4, DE 198 21 853 C1 and EP 2 123 979 B1 disclose other prior art.

Against this background, a novel partially-premixed gas burner appliance according to claim 1 is provided.

The novel partially-premixed gas burner appliance comprises a combustion chamber.

The novel partially-premixed gas burner appliance further comprises a fan being configured to provide air or an air flow to the combustion chamber. The fan is assigned to an air inlet port of the combustion chamber or to an air duct providing the air to the air inlet port.

The novel partially-premixed gas burner appliance further comprises an air flow restriction element assigned to the air inlet port of the combustion chamber or to the air duct. The air flow restriction element is configured to cause a pressure drop so that the air pressure downstream of the air flow restriction element is lower than the air pressure of the air flow provided by the fan upstream of the air flow restriction element.

The novel partially-premixed gas burner appliance further comprises a gas modulator being configured to provide a gas flow to the combustion chamber.

A first portion of the air or air flow provided by the fan is premixed with the gas or gas flow before the gas is combusted. A second portion of the air or air flow provided by the fan is mixed with the gas while the gas is combusted.

The gas modulator of the novel partially-premixed gas burner appliance is a pneumatic gas control valve. The pneumatic gas control valve has a main gas valve, a safety gas valve, a servo gas valve and a gas outlet pressure regulator. Such a pneumatic gas control valve is configured to be used in a fully-premixed gas burner appliance.

The gas outlet pressure regulator of the pneumatic gas control valve, namely a first chamber of the gas outlet pressure regulator in which a pressure is present that influences the nominal-value of the gas outlet pressure, is connected to the air inlet port of the combustion chamber or to the air duct upstream of the air flow restriction element such that the gas outlet pressure provided by the pneumatic gas control valve depends on the air pressure provided by the fan upstream of the air flow restriction element.

The present invention proposes to make use of a pneumatic gas control valve being configured to be used in a fully-premixed gas burner appliance within a partially-premixed gas burner appliance. The fan is assigned to the air inlet port of the combustion chamber or to an air duct providing the air to the air inlet port. The gas out-let pressure regulator of the pneumatic gas control valve, namely the first chamber of the same in which the pressure is present that influences the nominal-value of the gas outlet pressure, is connected to the air inlet port of the combustion chamber or to the air duct, namely upstream of the air flow restriction element. This makes it possible to provide a 1:1 ratio of the air pressure upstream of the air flow restriction element and the gas outlet pressure of the pneumatic gas control valve without the need of an electronic gas modulator. The present invention allows a very simple and reliable 1:1 gas-air control for a partially-premixed gas burner appliance.

According to a preferred embodiment, a gas burner rod having at least two segments is positioned within the combustion chamber, wherein the combustion chamber comprises for each segment of the gas burner rod an individual gas inlet port. The pneumatic gas control valve provides a gas flow to each of the individual gas inlet ports of the combustion chamber. A shut off valve may be assigned to at least one of the individual gas inlet ports to selectively open or close the respective gas inlet port thereby selectively operating the respective segment of the gas burner rod. Such a multiple segment configuration of the burner rod enables a high turn down ratio with a turn down in power input to the burner. A very effective operation of a the partially-premixed gas burner appliance can be provided.

Alternatively, the gas burner rod may not be segmented. A gas burner rod not being segmented does not require a shut off valve assigned to the gas inlet port.

According to a preferred embodiment, the first chamber of the gas outlet pressure regulator of the pneumatic gas control valve is connected to the air inlet port of the combustion chamber through a pipe or duct. This provides a very simple and reliable way to balance the air pressure drop with the gas pressure drop.

According to a preferred embodiment, the gas outlet pressure regulator of the pneumatic gas control valve comprises a diaphragm. The first chamber of the gas outlet pressure regulator of the pneumatic gas control valve is positioned on a first side of said diaphragm such that the air pressure being present within the within first chamber acts on the first side of said diaphragm. A second chamber of the gas outlet pressure regulator of the pneumatic gas control valve is positioned on a sec-and side of said diaphragm, wherein the second chamber of the gas outlet pressure regulator is connected to a gas outlet chamber of the pneumatic gas control valve such that the gas outlet pressure being present within the within second chamber acts on the second side of said diaphragm. The gas outlet pressure regulator further comprises a first spring and a second spring, wherein a spring force provided by the first spring acts on the first side of said diaphragm and a spring force provided by the second spring acts on the second side of said diaphragm. The gas outlet pressure regulator of the pneumatic gas control valve further comprises a presetting unit acting on the first spring to adapt the spring force acting on the first side of said diaphragm thereby adapting the nominal-value of the gas outlet pressure. It is possible to provide a very simple and reliable 1:1 gas-air control for a partially-premixed gas burner appliance without the need of an electronic gas modulator.

Preferred developments of the invention are provided by the dependent claims and the description of the drawings. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:

FIG. 1 shows a preferred embodiment of a partially-premixed gas burner appliance according to the invention;

FIG. 2 shows a cross section through a pneumatic gas control valve of the partially-premixed gas burner appliance of FIG. 1.

The present invention relates to a partially-premixed gas burner appliance 10.

The partially-premixed gas burner appliance 10 comprises a combustion chamber 11 in which gas G is combusted. In the shown embodiment, a gas burner rod 12 having at least two segments 12a, 12b is positioned within the combustion chamber 11. Gas G is provided to the gas burner rod 12 for combustion. The combustion of the gas G takes place under the presence of air A. The combustion of the gas G results into flames 13 and exhaust-gas E. Alternatively, the gas burner rod 12 may not be segmented in multiple segments.

In the shown embodiment, a heat exchanger 14 is positioned within the combustion chamber 11. The heat exchanger 14 is used to heat e. g. sanitary water or central heating water W for a water consumer.

The water W to be heated within the heat exchanger 14 is provided by a supply pipe 15 to the heat exchanger 14. Water W which has been heated within the heat exchanger 14 is flowing through a return pipe 16 to the respective water consumer.

The partially-premixed gas burner appliance 10 comprises a fan 17.

The fan 17 provides a flow of air A to the combustion chamber 11. The fan 17 is assigned to an air inlet port 11A of the combustion chamber 11 or to an air duct 18 providing the air A to the air inlet port 11A.

The novel partially-premixed gas burner appliance 10 further comprises an air flow restriction element 19 assigned to the air inlet port 11A of the combustion chamber 11 or to the air duct.

The air flow restriction element 19 causes a pressure drop so that the pressure downstream of the air flow restriction element 19 within the combustion chamber 11 is lower than the pressure of the air flow provided by the fan 17 upstream of the air flow restriction element 19. The air flow restriction element 19 can be provided by an orifice plate or by a venturi nozzle.

The novel partially-premixed gas burner appliance 10 further comprises a gas modulator 20 providing a flow of gas G to the combustion chamber 11, namely through at least one gas inlet port 11G of the combustion chamber 11. For each segment 12a, 12b of the gas burner rod 12 the combustion chamber 11 may have an individual gas inlet port 11G. For a gas burner rod 12 not be segmented or for each segment 12a, 12b of the gas burner rod 12 the combustion chamber 11 may have multiple gas inlet ports 11G.

A gas flow restriction element 40 is assigned to each of the gas inlet ports 11G. Such a gas flow restriction element 40 causes a pressure drop such that the gas pressure upstream of the gas flow restriction element 40 is greater than the pres-sure downstream of the gas flow restriction element 40 within the combustion chamber 11. The gas flow restriction element 40 can be provided by an orifice plate or by a venturi nozzle.

In the embodiment of FIG. 1, a shut off valve 41 is assigned to the gas inlet port 11G providing gas G to the segment 12b of the gas burner rod 12. This makes it possible to selectively open or close the gas inlet port 11G thereby selectively operating the segment 12b of the gas burner rod 12.

It would also be possible to assign such a shut off valve 41 the gas inlet port 11G providing gas G to the segment 12a of the gas burner rod 12.

The exhaust-gas E flows out of the combustion chamber 11 through an exhaust-gas outlet port 11E of the combustion chamber 11.

A first portion A1 of the air flow or air A provided by the fan 17, which enters the combustion chamber 11 through the air inlet port 11A, is premixed with the gas G provided by gas modulator 20 before the gas G is combusted.

A second portion A2 of the air A provided by the fan 17, which enters the combustion chamber 11 through the air inlet port 11A, is mixed with the gas G while the gas G is combusted.

The gas modulator 20 is provided by a pneumatic gas control valve. Said pneumatic gas control valve 20 is configured to be used in fully-premixed gas burner appliance.

The pneumatic gas control valve 20 comprises a housing 21 providing an inlet gas chamber 21a, an outlet gas chamber 21b and an intermediate gas chamber 21c coupled between the inlet gas chamber 21a, an outlet gas chamber 21b.

The pneumatic gas control valve 20 comprises further a main gas valve 22, a safety gas valve 23, a servo gas valve 24 and gas outlet pressure regulator 25.

When the safety gas valve 23 is closed, the inlet gas chamber 21a and the intermediate gas chamber 21c are fluidically separated from each other. When the safety gas valve 23 is opened, the intel gas chamber 21a and the intermediate gas chamber 21c are fluidically connected to each other.

The safety gas valve 12 is opened by an actuator 26 against a closing force provide by a spring 36. When the safety gas valve 23 is opened, also the servo gas valve 24 becomes opened. Safety gas valve 23 and servo gas valve 24 are both opened by the actuator 26.

When the main gas valve 22 is closed, the intermediate gas chamber 21c and the outlet gas chamber 21b are fluidically separated from each other.

When the main gas valve 22 is opened, the intermediate gas chamber 21c and the outlet gas chamber 21c are fluidically connected to each other.

The main gas valve 22 comprises a diaphragm 27 and a spring 28. The diaphragm 27 separates the outlet gas chamber 21b from a servo pressure chamber 29. The servo pressure chamber 29 is fluidically connected to the servo gas valve 24.

The gas outlet pressure being present in the outlet gas chamber 21b and a spring force provided by the spring 28 of the main gas valve 22 act on a first side of the diaphragm 27 of the main gas valve 22 tending to close the main gas valve 22.

A servo gas pressure being present within the servo gas chamber 29 acts on the second side of the diaphragm 27 of the main gas valve 22 tending to open the main gas valve 22.

The servo gas chamber 29 is further fluidically connected to the the gas outlet pressure regulator 25 of the pneumatic gas control valve 20 through a pressure relief valve 38.

The gas outlet pressure regulator 25 of the pneumatic gas control valve 20 comprises a diaphragm 30 and two springs 31, 32. The diaphragm 30 of the gas outlet pressure regulator 25 separates a first chamber 33 of the gas outlet pressure regulator 25 from a second chamber 34 of the same.

The pressure being present within the first chamber 33 of the gas outlet pressure regulator 25 influences the nominal-value of the gas outlet pressure within the out-let gas chamber 21b of the pneumatic gas control valve 20. The pressure being present within the first chamber 33 of the gas outlet pressure regulator 25 acts on a first side of the diaphragm 30 of the gas outlet pressure regulator 25. Further on, a spring force provided by the spring 31 acts on a first side of the diaphragm 30.

The second chamber 34 of the gas outlet pressure regulator 25 is positioned on a second side of said diaphragm 30, wherein the second chamber 34 of the gas out-let pressure regulator 25 is fluidically connected to the gas outlet chamber 11b of the pneumatic gas control valve 20 such that the gas outlet pressure being present within the gas outlet chamber 21b and within the second chamber 34 of the gas outlet pressure regulator 25 acts on the second side of the diaphragm 30 of the gas outlet pressure regulator 25. Further on, a spring force provided by the spring 32 acts on a second side of the diaphragm 30.

The gas outlet pressure regulator 25 of the pneumatic gas control valve 20 further comprises presetting unit 35 acting on the first spring 31 to adapt the spring force acting on the first side of said diaphragm 30. With the presetting unit 35 the nomi-nal-value of the gas outlet pressure of the pneumatic gas control valve 20 can be adapted. The presetting unit 35 can be used to provide an offset or a delta between the pressure on either side of the diaphragm 30 of the gas outlet pressure regulator and as a result an offset or a delta between the generated air pressure and the gas outlet pressure.

The pressure relief valve 38 through which the servo gas chamber 29 is fluidically connected to the gas outlet pressure regulator 25 of the pneumatic gas control valve 20 is integrated into the diaphragm 30 of the gas outlet pressure regulator 25.

According to the present invention, the gas outlet pressure regulator 25 of the pneumatic gas control valve 20, namely the first chamber 33 of the gas outlet pres-sure regulator 25 in which the pressure is present that influences the nominal-value of the gas outlet pressure, is permanently fluidically connected to the air inlet port 11A of the combustion chamber 11 or to the air duct providing the air A to the air inlet port 11A upstream of the air flow restriction element 18 such that the gas out-let pressure provided by pneumatic gas control valve 20 depends on to the air pressure provided by the fan 17 upstream of the air flow restriction element 18.

As shown in the Figures, the first chamber 33 of the gas outlet pressure regulator of the pneumatic gas control valve is connected to the air inlet port 11A of the combustion chamber 11 or to the air duct 18 through a pipe or duct 37.

The pneumatic gas control valve 20 features a positive servo system. The main gas valve 22 is closed by the spring 28 in the normal shut down position and can only be opened when pressure within the servo gas chamber 29 is sufficient to over-come the spring force of the spring 28. This ensures the main gas valve 22 will au-tomatically close in the event of power or gas supply failure.

An element of the pneumatic gas control valve 20 is the gas outlet pressure regulator 25 which comprises the pressure relief valve 38 integrated in the diaphragm 30 which controls the main gas valve 22.

When the safety gas valve 22 and the servo gas valve 24 are both opened by the actuator 26, then gas flows through the servo gas valve 24 into the servo pressure chamber 29 and to the pressure relief valve 38. This gas pressure within the servo pressure chamber 29 moves the main valve diaphragm 27 upwards enough to open the main gas valve 22. As soon as the main gas valve 22 has opened, the outlet gas pressure will be sensed by the regulator diaphragm 20 via a feedback channel 39 connecting the second chamber 34 of the gas outlet pressure regulator to the gas outlet chamber 21b pneumatic gas control valve 20.

When the force provided by the pressure within the second chamber 34 of the gas outlet pressure regulator 25 is greater than the force provided by the pressure within the first chamber 33 and by the presetting unit 35, the pressure relief valve 38 opens relieving some of the working pressure within the servo pressure chamber 29. This reduces the force against the main valve spring 28 allowing the main gas valve 22 to close proportionally. Thus, the main gas valve 22 limits the gas outlet pressure. As a result, the gas outlet pressure is continuously maintained by com-paring the gas outlet pressure being present in the second chamber 34 of the gas outlet pressure regulator 25 with the pressure being present in the first chamber 33 of the gas outlet pressure regulator 25 and adjusting the position of the main gas valve 22 accordingly.

The fan 17 is located at the air inlet of the combustion chamber 11. The air pres-ssure which is generated by the fan 17 is transferred to first chamber 33 of the gas outlet pressure regulator 25 to generate the outlet gas pressure. This allows to provide a very simple and reliable 1:1 gas-air control for a partially-premixed gas burner appliance.

The gas outlet pressure and thereby the gas flow provided by the pneumatic gas control valve 20 is a function of air pressure generated by the fan 17. An offset or a delta between the pressure on either side of the diaphragm 30 of the gas outlet pressure regulator 25 may be provided by the presetting unit 35. At any speed of the fan 17 the pressure drop over air flow restriction 19 equals the pressure drop over the or each gas flow restriction 40. So, the air flow and the gas flow are con-trolled proportionally. With presetting unit 35 the gas flow can be influenced to ad-just to desired gas and air ratio setting.

LIST OF REFERENCE SIGNS

• • 10 partially-premixed gas burner appliance
  • 11 combustion chamber
  • 11A air inlet port
  • 11G gas intel port
  • 11E exhaust-gas outlet port
  • 12 gas burner rod
  • 12a segment
  • 12b segment
  • 13 flame
  • 14 heat exchanger
  • 15 supply pipe
  • 16 return pipe
  • 17 fan
  • 18 air duct
  • 19 air flow restriction element
  • 20 gas modulator/pneumatic gas control valve
  • 21 housing
  • 21a intel gas chamber
  • 21b outlet gas chamber
  • 21c intermediate gas chamber
  • 22 main gas valve
  • 23 safety gas valve
  • 24 servo gas valve
  • 25 gas outlet pressure regulator
  • 26 actuator
  • 27 diaphragm
  • 28 spring
  • 29 servo pressure chamber
  • 30 diaphragm
  • 31 spring
  • 32 spring
  • 33 chamber
  • 34 chamber
  • 35 presetting unit
  • 36 spring
  • 37 duct
  • 38 pressure relief valve
  • 39 feedback channel
  • 40 gas flow restriction element
  • 41 shut off valve

Claims

1. A partially-premixed gas burner appliance, comprising:

a combustion chamber,

a fan configured to provide an air flow to the combustion chamber, wherein the fan is assigned to an air inlet port of the combustion chamber or to an air duct configured to provide the air to the air inlet port,

an air flow restriction element assigned to the air inlet port of the combustion chamber or to the air duct and configured to provide a pressure drop so that the pressure downstream of the air flow restriction element is lower than the pressure upstream of the air flow restriction element,

a gas modulator being configured to provide a gas flow to the combustion chamber, wherein a first portion of the air provided by the fan is premixed with the gas flow before the gas is combusted, wherein a second portion of the air provided by the fan is mixed with the gas while the gas is combusted, wherein the gas modulator is a pneumatic gas control valve having a main gas valve, a safety gas valve, a servo gas valve, and a gas outlet pressure regulator, wherein the gas outlet pressure regulator, namely a first chamber of the gas outlet pressure regulator in which a pressure is present that influences the nominal-value of the gas outlet pressure of the pneumatic gas control valve, is connected to the air inlet port or to the air duct upstream of the air flow restriction element such that the gas outlet pressure provided by the pneumatic gas control valve depends on the air pressure provided by the fan upstream of the air flow restriction element.

2. The partially-premixed gas burner appliance as claimed in claim 1, wherein the first chamber of the gas outlet pressure regulator of the pneumatic gas control valve is connected to the air inlet port of the combustion chamber or to the air duct through a pipe or duct.

3. The partially-premixed gas burner appliance as claimed in claim 1,

wherein the gas outlet pressure regulator of the pneumatic gas control valve comprises a diaphragm,

wherein the first chamber of the gas outlet pressure regulator is positioned on a first side of the diaphragm such that the pressure present within the first chamber acts on the first side of the diaphragm,

wherein a second chamber of the gas outlet pressure regulator is positioned on a second side of the diaphragm, wherein the second chamber of the gas outlet pressure regulator is connected to a gas outlet chamber of the pneumatic gas control valve such that the gas outlet pressure present within the second chamber acts on the second side of the diaphragm.

4. The partially-premixed gas burner appliance as claimed in claim 3,

wherein the gas outlet pressure regulator comprises a first spring, wherein a spring force provided by the first spring acts on the first side of the diaphragm

wherein the gas outlet pressure regulator comprises a second spring, wherein a spring force provided by the second spring acts on the second side of staid the diaphragm,

wherein the gas outlet pressure regulator comprises a presetting unit being configured to act on the first spring and to adapt the respective spring force acting on the first side of the diaphragm.

5. The partially-premixed gas burner appliance as claimed in claim 4, wherein the presetting unit is configured to adapt the nominal-value of the gas outlet pressure of the pneumatic gas control valve.

6. The partially-premixed gas burner appliance as claimed in claim 3,

wherein the main gas valve of the pneumatic gas control valve comprises a diaphragm and a springer, wherein the gas outlet pressure provided by the pneumatic gas control valve and a spring force provided by the spring of the main gas valve act on a first side of the diaphragm of the main gas valve to close the main gas valve, wherein a servo gas chamber is positioned on a second side of the diaphragm of the main gas valve, wherein a servo gas pressure being present within the servo gas chamber acts on the second side of the diaphragm of the main gas valve to open the main gas valve, wherein the servo gas chamber is connected to the servo gas valve of the pneumatic gas control valve and to the gas out-let pressure regulator of the pneumatic gas control valve.

7. The partially-premixed gas burner appliance as claimed in claim 6, wherein the servo gas chamber is connected to the gas outlet pressure regulator through a pressure relief valve integrated in the diaphragm of the gas outlet pressure regulator.

8. The partially-premixed gas burner appliance as claimed in claim 1,

wherein a gas burner rod having at least two segments is positioned within the combustion chamber,

wherein the combustion chamber comprises for each segment of the gas burner rod at least one individual gas inlet port,

wherein the pneumatic gas control valve provides a gas flow to each of the individual gas inlet ports of the combustion chamber.

9. The partially-premixed gas burner appliance as claimed in claim 8, wherein a shut off valve is assigned to at least one of the individual gas inlet ports to selectively open or close the respective gas inlet port thereby selectively operating the respective segment of the gas burner rod.

10. The partially-premixed gas burner appliance as claimed in claim 1, wherein the pneumatic gas control valve is configured to be used in a fully-premixed gas burner appliance.

11. The partially-premixed gas burner appliance as claimed in claim, wherein the gas outlet pressure regulator of the pneumatic gas control valve comprises a diaphragm,

the first chamber of the gas outlet pressure regulator is positioned on a first side of the diaphragm such that the pressure present within the first chamber acts on the first side of the diaphragm,

a second chamber of the gas outlet pressure regulator is positioned on a second side of the diaphragm, wherein the second chamber of the gas outlet pressure regulator is connected to a gas outlet chamber of the pneumatic gas control valve such that the gas outlet pressure present within the second chamber acts on the second side of the diaphragm.

12. The partially-premixed gas burner appliance as claimed in claim 4, wherein

the main gas valve of the pneumatic gas control valve comprises a diaphragm and a spring, wherein the gas outlet pressure provided by the pneumatic gas control valve and a spring force provided by the spring of the main gas valve act on a first side of the diaphragm of the main gas valve to close the main gas valve, wherein a servo gas chamber is positioned on a second side of the diaphragm of the main gas valve, wherein a servo gas pressure being present within the servo gas chamber acts on the second side of the diaphragm of the main gas valve to open the main gas valve, wherein the servo gas chamber is connected to the servo gas valve of the pneumatic gas control valve and to the gas out-let pressure regulator of the pneumatic gas control valve.

13. The partially-premixed gas burner appliance as claimed in claim 5, wherein

the main gas valve of the pneumatic gas control valve comprises a diaphragm and a spring, wherein the gas outlet pressure provided by the pneumatic gas control valve and a spring force provided by the spring of the main gas valve act on a first side of the diaphragm of the main gas valve to close the main gas valve, wherein a servo gas chamber is positioned on a second side of the diaphragm of the main gas valve, wherein a servo gas pressure being present within the servo gas chamber acts on the second side of the diaphragm of the main gas valve to open the main gas valve, wherein the servo gas chamber is connected to the servo gas valve of the pneumatic gas control valve and to the gas out-let pressure regulator of the pneumatic gas control valve.