This invention relates to a device for regulating the combustion air flow rate in a wall-mounted boiler with a sealed chamber in accordance with the introduction to the main claim.

As is well known, a boiler of the stated type comprises a sealed chamber containing a burner to which at least two ducts are connected, namely one for combustion air feed and the other for flue gas or combustion product discharge. These ducts can be coaxial (with the discharge duct within the air feed duct) or be separate depending on the duct lengths.

With particular but non-limiting reference to a boiler with said separate ducts, it is known to provide a baffle inside the feed duct to enable the combustion air flow rate to be varied and hence regulate the ratio of combustion air quantity to the gas quantity present in the burner, to limit the presence of CO₂, NO_x and CO in the flue gas leaving the boiler. By way of example, about 10³ of air to one m³ of natural gas represents an optimal air/gas ratio.

Said ratio can be regulated by means of these baffles. This however involves the following operations: measuring the flue gas "composition" (ie the content of CO, NO_x and CO₂); removing the air duct; modifying the position of the baffle or baffles within the duct; fixing the duct to the sealed chamber; again measuring the flue gas composition and if necessary repeating the duct removal, baffle adjustment and duct fixing operations. All this evidently involves considerable time and difficulty in regulating the air flow rate through the duct, with resultant high cost.

GB-A-2315323 and GB 165502 describe a device according to the preamble of the attached claim.

US 4524679 relates to a valve for directing and controlling the flow of pressurized gas comprising a socket and a spheroidal hollow shell mounted in said socket for swivel motion. The shell interiorly forms a spheroidal socket which receives an axially rotatable valve body. The shell and the valve body respectively have an alignable aperture and gas inlet. The body and shell are rotatable between a closed position and an open position wherein the aperture aligns with the inlet.

A solution alternative to baffles for modifying the air flow rate is to control the speed of the usual fan provided in the sealed chamber, this control however involving electronic devices of a certain complexity and cost.

An object of the invention is to provide an improved device for regulating the air flow rate to the sealed chamber of a boiler.

A particular object of the invention is to provide a device of the stated type which can be easily adjusted within the air feed duct without having to separate the duct from the chamber.

A further object is to provide a device of the stated type which is of simple construction and is easily mounted on a sealed chamber boiler.

These and further objects which will be apparent to an expert of the art are attained by a device in accordance with the accompanying claims.

The invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and on which:

• Figure 1 is a perspective view of a boiler to which the device of the invention is applied;
• Figure 2 is a partially broken-away perspective view of an air feed duct of the boiler of Figure 1 provided with the device of the invention; and
• Figure 3 is an exploded perspective view from below of the duct of Figure 2.

With reference to said figures, a boiler 1 comprises internally a usual sealed chamber containing a gas burner (not shown). Two separate ducts 2 and 3 are connected to this chamber, the first duct 2 being the combustion air feed duct and the other 3 being the flue gas or combustion product discharge duct.

The feed duct 2 comprises an end portion 5 directly inserted into the sealed chamber and presenting an end aperture 6 partly closed by a part 7 shaped substantially as a section of a hollow spherical cap. In this manner the aperture 6 of the portion 5 of the duct 2 lies substantially in a plane which is not perpendicular to the longitudinal axis K of the duct but lies on one side of this latter. On the end portion 5 there is mounted a member 10 having a shape such as to mate with said portion 5 preferably as a form fit. Consequently this member is also preferably shaped as a section of a spherical cap and also comprises a surface aperture 11 of dimensions preferably equal to the aperture 6 of the duct 2. This member comprises an end flange 13 which, when the member 10 has been fitted onto the duct 2, is rested on an upper part 14 of the housing 15 of the boiler 1 and is fixed to said part 14 after being suitably positioned relative to the aperture 6 of the duct 2.

By virtue of the particular shape of the member 10, the aperture 6 of the duct 2 can be varied at will depending on requirements. In this manner the correct (quantitative) combustion air feed can be chosen on the basis of the composition measurement of the flue gas leaving the boiler.

The invention is used in the following manner: with the boiler mounted and operating, an operator using known equipment measures in known manner the composition of the flue gas leaving the sealed chamber through the duct 3. If this flue gas contains a high percentage of CO₂ (and CO) the operator adjusts the flange 13 by rotating it in the direction of the arrows F of Figure 2. This movement also causes the member 10 to rotate about the duct 2 in order to change the position of the aperture 6 of this duct relative to the aperture 11 of the member 10. In the illustrated example the purpose of this change is to lessen the degree throttling of the aperture 6 by said member 10 in such a manner as to increase the useful cross-section for inflow of combustion air into the sealed chamber and hence increase the air flow rate within the burner. As a result of this there is a decrease of CO₂ within the flue gas.

Having defined the optimum position of the member 10 relative to the portion 5 of the duct 2, this member is fixed in position by usual screws (not shown) cooperating with the flange 13 and the part 14 of the housing 15 of the boiler 6.

By virtue of the invention the air flow rate to the burner can be easily regulated by means of a solution which is conceptually and constructionally simple. This regulation is achieved without removing the duct 2 from the boiler, and by acting from the outside of this duct.

A preferred embodiment of the invention has been described in which the device of the invention comprises not only the member 10 but also a particular shape for the end portion 5 of the air feed duct. The particular shape both of this duct and of the member 10 enables the air to be suitably directed into the sealed chamber.

Finally, a solution has been described applied to a combustion air feed duct separate from the flue gas discharge duct. The invention can also be applied to the case in which these ducts are coaxial and the air flow cross-section is a ring surrounding the flue gas duct.