GB2105888A

GB2105888A - Detecting flue blockage

Info

Publication number: GB2105888A
Application number: GB08127764A
Authority: GB
Inventors: Cecil Duckworth; David Edwin Steade
Original assignee: WORCESTER ENGINEERING Co
Current assignee: WORCESTER ENGINEERING Co
Priority date: 1981-09-15
Filing date: 1981-09-15
Publication date: 1983-03-30

Abstract

A device for detecting flue blockage or failure in a combustion heating appliance comprises a switch 18 and a sensor 19 adapted to operate the switch upon a rise in pressure of the flue draught above a predetermined value; operation of the switch being arranged to actuate a warning device and/or an operating control for the appliance. The sensor may detect a rise in pressure of the flue draught by sensing a rise in temperature in a location to which flue gases are delivered only upon a rise in pressure of the flue draught. <IMAGE>

Description

SPECIFICATION Method and device for detecting flue blockage or failure in a combustion heating appliance The invention relates to a method and device for detecting flue blockage or failure in a combustion appliance. When a combustion heating appliance, such as a gas, oil or solid fuel boiler, is operating correctly the flue, or chimney, carries the combustion gases safely away into the ambient atmosphere. However, should the flue become blocked, for example because of a fall of soot or a foreign body becoming lodged in it, or fail to operate properly for any other reason, combustion gases may leak from the appliance with a consequent risk of poisoning of persons in the vincinty. The risk is particularly high with solid fuel boilers where the carbon monoxide content of the flue gases is high.The present invention sets out to provide a method and device for detecting flue blockage or failure so that such leakage of flue gases can be avoided.

The invention makes use of the fact that when a flue is operating correctly the flue draught normally produces at the exit of the appliance a pressure which is slightly negative in relation to atmospheric pressure. Should the flue fail, for example by becoming blocked, this flue draught pressure rises above atmospheric pressure and this rise in pressure may thus be used to indicate that a flue failure has occured.

According to the invention, therefore, a method of detecting flue blockage or failure in a combustion heating appliance comprises providing switch means and a sensor adapted to operate the switch means upon a rise in pressure of the flue draught above a predetermined value, operation of the switch means being arranged to actuate a warning device and/or an operating control for the appliance.

The invention also provides a combustion heating appliance including switch means and a sensor adapted to operate the switch means upon a rise in pressure of the flue draught above a predetermined value, operation of the switch means being arranged to actuate a warning device and/or an operating control for the appliance.

The sensor may be a pressure-sensitive device which senses a rise in the pressure of the flue draught directly. Alternatively, and preferably, the sensor is a device responsive to the presence of flue gases and disposed in a location to which flue gases are delivered only upon rise in the pressure thereof above said predetermined value. For example, the sensor may be located in a passage communicating between the ambient atmosphere and a zone of the appliance through which flue gases normally pass. Thus, when the appliance is operating normally and the flue gases are at a negative pressure, ambient air will flow through said passage into said zone of the appliance. However, if the pressure of the flue gases rises above ambient air pressure, due to flue blockage or failure, flue gases will flow along the passage from said zone to atmosphere and will thus pass over the sensor.

In this case, the sensor is preferably a temperature responsive device which detects the presence of flue gases by responding to the temperature thereof.

The sensor may be disposed at any suitable location and may, for example, be located so as to be responsive to flue draught pressure below the flue hood. The aforesaid switch means are preferably manually resettable. Alternatively, the switch means may be arranged to reset automatically upon flue draught pressure falling below said predetermined value again, although in this case there may be no indication to the user that tempo- rary flue blockage or failure has occurred.

In the case where the switch means operate a warning device, the device may give a visual warning, an audible warning or both.

Where the switch means actuate an operating control for the appliance, the operating control is preferably arranged to close down the appliance. Thus, in the case of a gas- or oil-fired appliance, the switch may operate to shut off the fuel supply. In the case of a solid fuel appliance the switch may be arranged, when operated, to switch off the fan which delivers combustion air to the appliance, or to close off the air inlet flap should the appliance be of the kind which works under natural draught conditions.

The invention includes within its scope a device comprising switch means and a sensor for use in a combustion heating appliance as hereinbefore referred to.

The following is a detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawing which is a diagrammatic vertical section through a detection device fitted to a solid fuel boiler.

The solid fuel boiler 10 is of conventional form and comprises a plurality of heat exchange tubes 11 extending upwardly from the combustion chamber (not shown) to a chamber 1 2 which communicates with the flue through a flue hood.

As previously mentioned, during normal operation of the boiler the flue draught will cause a slight negative pressure in the chamber 12.

One wall 1 3 of the chamber 1 2 is formed with a number of holes 14, (for example, three holes may be provided). Secured to the outer surface of the wall 1 3 so as to cover the holes 14 is a duct 15. The duct 15 is open at the bottom so that any dust or dirt particles will not block the duct and prevent the pas sage of air therethrough. A cover 1 6 is mounted on the outer wall of the duct 1 5 by screws 1 7 and contains a thermostatic switch 18, the temperature-sensitive part 1 9 of which projects into the duct 1 5 through an aperture in the outer wall thereof.The switch is provided with a manual reset button 20 and is connected by an electric lead 21 to a warning device and/or an operating control for the boiler.

In normal operation of the boiler the slight negative pressure in the chamber 1 2 causes cool ambient air to flow through the duct 1 5 and into the chamber 1 2 through the holes 1 4. The sensor 1 9 is therefore only subjected to ambient air temperature, say about 20"C, and the switch remains inoperative. If the flue becomes blocked or otherwise fails, the pressure in the chamber 1 2 rises above ambient air pressure and consequently the flow through the duct 1 5 is reversed, flue gases flowing out of the chamber 1 2 and past the sensor 19.The temperature of the flue gases is likely to be above 200"C and this rise in temperature causes operation of the switch 18.

The switch may be arranged, when operated, to actuate a visual and/or audible warning device mounted adjacent the boiler or at a remote monitoring location. Preferably also, operation of the swich is arranged to turn off the air delivery fan which is delivering combustion air to the boiler, or to operate a solenoid or similar device to close the air inlet flap should the boiler be of the kind which works under natural draught conditions. This cutting off of the combustion air will almost immediately reduce the emission of flue gases from the boiler and eventually the boiler will go out completely. Such a shut-down arrangement is preferred since it reduces and eventu ally stops the emission of poisonous flue gases should the warning signals be unheeded.

The manual reset button 20 enables the device to be reset once the cause of the flue blockage or failure has been removed.

The sensing device may be located in any area where it will respond to the change in pressure of the flue draught, and in some boilers it may be preferable to mount the device nearer to the combustion chamber or actually in parrt of the heat exchanger system.

Although the invention has described in relation to a solid fuel boiler it is equally applicable, as previously mentioned, to gas- or oil-fired boilers and indeed to any combustion heating appliance.

With some installations the flue may fail to operate correctly, causing flue gas leakage, due to wind being in such a direction as to force a draught back down the flue, and it will be appreciated that the invention will respond to this situation also.

Claims

1. A method of detecting flue blockage or failure in a combustion heating appliance comprising providing switch means and a sensor adapted to operate the switch means upon a rise in pressure of the flue draught above a predetermined value, operation of the, switch means being arranged to actuate a warning device and/or an operating control for the appliance.

2. A combustion heating appliance including switch means and a sensor adapted to operate the switch means upon a rise in pressure of the flue draught above a predetermined value, operation of the switch means being arranged to actuate a warning device and/or an operating control for the appliance.

3. An appliance according to claim 2, wherein the sensor is a pressure-sensitive device which senses a rise in the pressure of the flue draught directly.

4. An appliance according to claim 2, wherein the sensor is a device responsive to the presence of flue gases and disposed in a location to which flue gases are delivered only upon rise in the pressure thereof above said predetermined value.

5. An appliance according to claim 4, wherein the sensor is located in a passage communicating between the ambient atmosphere and a zone of the appliance through which flue gases normally pass.

6. An appliance according to claim 4 or claim 5, wherein the sensor is a temperature responsive device which detects the presence of flue gases by responding to the temperature thereof.

7. An appliance according to any of claims 2 to 4, wherein the sensor is located so as to be responsive to flue draught pressure below the flue hood.

8. An appliance according to any of claims 2 to 7, wherein the switch means are manually resettable.

9. An appliance according to any of claims 2 to 7, wherein the switch means are arranged to reset automatically upon flue draught pressure falling below said predetermined value again.

10. An appliance according to any of claims 2 to 9, wherein the switch means operate a warning device and the device gives a visual warning, an audible warning or both, when operated.

11. An appliance according to any of claims 2 to 10, wherein the switch means actuate an operating control for the appliance, the operating control being arranged to close down the appliance.

12. An appliance according to claim 11, wherein the switch means operate to shut off the fuel supply.

1 3. A solid fuel appliance according to claim 11, wherein the switch means are ar ranged, when operated, to switch off a fan which delivers combustion air to the appliance, or to close off an air inlet flap.

14 A device comprisng switch means and a sensor suitable for use in a combustion heating appliance according to any of claims 2to 13.

15. A device according to claim 14 and substantially as hereinbefore described with reference to the accompanying drawings.

1 6. A combustion heating appliance including a device according to claim 14 and substantially as hereinbefore described with reference to the accompanying drawings.