GB2189909A

GB2189909A - Gas control valves

Info

Publication number: GB2189909A
Application number: GB08708935A
Authority: GB
Inventors: Hugh Vernon Barnes; Arthur Howard Henshall
Original assignee: TI GAS SPARES Ltd
Current assignee: TI GAS SPARES Ltd
Priority date: 1986-04-16
Filing date: 1987-04-14
Publication date: 1987-11-04
Also published as: GB8708935D0

Abstract

A flued gas appliance is described having a safety device comprising a gas control valve 2 placed in the gas supply line to the gas appliance, and a self-resettable thermal valve 25 placed adjacent to an aperture communicating with the flue but not in the normal combustion product flow path of the appliance, the control valve 2 having a valve 9, a bypass passage 9a, a spring 16 for urging the valve 9 onto a seat 10, a diaphragm chamber 13 communicating with the gas flow path through the control valve 9 and a diaphragm 15 connected to the valve 9 and arranged so as to at least hold open the valve 9 against the force of the spring 16 when gas pressure builds up in the diaphragm chamber 13, the thermal valve 25 closing a vent pipe 20 connected to the diaphragm chamber 13, the arrangement being such that if the flue becomes blocked in use or if there is a prolonged downdraught, the combustion products are deflected over the thermal valve 25 which will eventually open to release the pressure in the diaphragm chamber 13 and close the valve 9, and if the flue blockage or prolonged downdraught are removed, the thermal valve is self-reset to cause the valve 9 to re-open. <IMAGE>

Description

SPECIFICATION Safety devices for flued gas appliance This invention relates to safety devices for flued gas appliances.

In the event of a blockage of the chimney or flue of a gas appliance the products of combustion have no alternative but to pass into the room in which the appliance is situated. For a short period of time this condition may not be noticed, but if it is prolonged then the room becomes stuffy and creates a drowsy effect upon the occupants which could eventually become dangerous.

In G.B. Patent No. 2,088,593 and in Co- pending Patent Application No. 85.21694 (published under No. 2 179 767A) there are described flued gas appliances which have a safety device which detects when a chimney is blocked or when there is a prolonged downdraught and which accordingly cuts off the fuel supply to the appliance. The safety devices described are based on the use of a fusible plug which is placed adjacent to an aperture communicating with the flue but not in the normal combustion flow path of the appliance.The arrangement is such that if the flue becomes blocked in use or if there is a prolonged downdraught, the combustion products are caused to be deflected over the fusible plug which eventually melts to release the pressure in a diaphragm chamber of the safety device, thereby causing the safety device to operate to cut off the fuel supply to the appliance. The fuel supply to the appliance can only be restored by a gas authority who would have to determine and if necessary correct whatever caused the fusible plug to overheat and would also have to replace the fusible plug. If the cause of overheating was only due to a downdraught or perhaps by a cold chimney which may take time to become active, then the call-out of a gas fitter becomes an expensive nuisance.

It is an object of the present invention to provide a flued gas appliance having an improved safety device whereby such call-outs may be avoided.

According to the present invention, there is provided a flued gas appliance having a safety device comprising a gas control valve placed in the gas supply line to the gas appliance, and a self-resettable thermal valve placed adjacent to an aperture communicating with the flue but not in the normal combustion product path of the appliance, the control valve having a valve, resilient means for urging the valve onto a seat, a diaphragm chamber communicating with the gas flow path through the control valve and a diaphragm connected to the valve and arranged so as to at least hold open the valve against the force of the resilient means when gas pressure builds up in the diaphragm chamber, said thermal valve closing a vent pipe connected to the diaphragm chamber, the arrangement being such that if the flue becomes blocked in use or there is a prolonged downdraught, the combustion products are deflected over said thermal valve which when it reaches a predetermined temperature is caused to open to release the pressure in the diaphragm chamber thereby to cause the valve to close, said thermal valve remaining open in the presence of said combustion products but being self-resettable in the absence of said combustion products whereby pressure in the diaphragm chamber is caused to rise to cause the valve to re-open.

In this way, in the event of a temporary downdraught for example, the thermal valve will operate to cut off the main fuel supply to the appliance, but which when normal flue conditions are restored is resettable so that the full fuel supply is fed to the appliance. In this way unnecessary service calls are alleviated.

Some exemplary embodiments of the invention will now be described, reference being made to the accompanying drawings, in which: Fig. 1 is a schematic diagram of a gas fire in accordance with the present invention; Fig. 2 depicts in greater detail one form of safety device for use in the gas fire of Fig. 1; and Figs. 3 to 6 depict alternative forms of selfresettable thermal valve for use in the safety device of Fig. 2.

In Figure 1 the gas fire 1 comprises a safety device 2, a gas tap 3, a burner 4 placed such that flames and combustion products pass through a radiant block 5, a heat exchanger 6 and a flue 7.

Referring to Figure 2; the control valve 2 comprises an inlet passage 8, a valve 9 opening and closing against seat 10, and an outlet passage 11. The valve 9 is also provided with a bypass passage 9a between the inlet passage 8 and the outlet passage 11 which, when the valve 9 is closed, permits a restricted gas flow which is sufficient to keep the burner 4 (Fig. 1) of the gas fire 1 alight but which is low enough to prevent dangerous conditions being caused. The valve 9 is connected to a small diaphragm 12 which acts as a flexible seal between passage 11 and main diaphragm chamber 13. The valve stem 14 passes through sealing diaphragm 12 and is connected to main diaphragm 15. A spring 16 urges valve 9 onto seat 10. The diaphragm 15 is held in place by cover 17 with breather hole 18 to atmosphere.Between the inlet passage 8 and the main diaphragm chamber 13 is a small weep hole 19 and from chamber 13 is a small bore pipe 20 which connects to a self-resettable thermal valve 25.

The thermal valve 25 consists of a body 26 in which is a passage 27 which connects with the small bore pipe 20. The end of the pas sage 27 is sealed by a sealing ball 28 which is normally pressed into sealing contact with the passage 27 by a bimetallic strip 29 which is secured to the body 26 by screw 30.

When the valve is heated, the bimetallic strip 29 heats up also until a point is reached where it operates to release the sealing ball 28 from its contact with passage 27, to unseal the passage 27 and thus the pipe 20.

The setting of bimetallic strip 29 is adjustable by means of adjusting screw 31 and lock nut 32 so that the temperature at which the valve 25 operates may be adjusted.

As shown in Figure 1 the gas fire 1 has a vent space 24 between radiant block 5 and the flue 7. This is so that, in the event of a downdraught due for example to wind, the combustion products can escape into the surrounding atmosphere without interfering with the burner. The self-resettable thermal valve 25 is placed just outside, so that in normal operation it remains relatively cool and is not exposed to the combustion products.

The action of the safety device 2 is as follows:Gas tap 3 is closed. Gas is supplied to valve 2 at inlet 8. A small supply of gas passes through weep 19 into chamber 13 and, as thermal valve 25 is closed thereby sealing the end of tube 20, causes pressure to build up over diaphragm 15 to overcome spring 16 and open valve 9. When tap 3 is opened gas passes to burner 4 and is ignited.

If flue 7 is clear then the flue products pass away to atmosphere and there is no undue heating of the thermal valve 25. Should the flue become blocked or should there be a prolonged downdraught, then the flue products will be deflected down through the front vent 24 of the fire 1 and will pass upwards over the valve 25. The valve 25 heats up and eventually opens thereby unsealing the end of pipe 20. This now releases the pressure in chamber 13 because weep 19 is insufficient to maintain the pressure and the spring 1 6 closes valve 9 shutting off the main gas supply. However, a restricted gas flow still flows through bypass 9a which is sufficient to keep the burner 4 of the gas fire 1 alight but which is low enough to prevent dangerous conditions being caused.If the flue blockage or downdraught is only temporary then the valve 25 will gradually cool down until a point is reached where it resets to its normally closed condition, thereby sealing the end of the pipe 20 so that the pressure in chamber 13 once again increases until a point is reached where the valve 9 is caused to open to restore the main gas supply to the gas fire 1. By arranging that the thermal valve 25 is self-resettable, unnecessary call-outs are avoided.

The self-resettable thermal valve 25 of Fig.

2 relies to some extent on the gas pressure in the passage 27 to unseat the sealing ball 28 and it has been found that there is sometimes a tendency for the sealing ball 28 to "stick" so that the passage 27 remains sealed even though the bimetallic strip 29 has operated.

In Figs. 3 to 5 of the drawings, there are shown modifications of the thermal valve 25 of Fig. 2 in which this problem is overcome.

In the thermal valve 25 of Fig. 3, the problem of the sealing ball 28 "sticking" when the bimetallic strip 29 operates to release it, is overcome by providing a compression spring 33 in the passage 27 and arranged to bias the sealing ball 28 out of sealing contact with the passage 27, the spring bias normally being overcome by the bimetallic strip 29 but becoming effective when the bimetallic strip operates to force the sealing ball 28 out of contact with the passage 27.

In Fig. 4 of the drawings there is shown a thermal valve 25 similar to that of Fig. 3 except that the passage 27 is extended forwards to include within it the sealing ball 28 as well as the compression spring 33, the passage 27 being provided with an inwards restriction 34 which forms a seat for the sealing ball 28, the compression spring 33, in the normal position of the thermal valve 25, urging the sealing ball 28 into sealing contact with the restriction 34 to seal the passage 27. In this normal position of the thermal valve 25, the bimetallic strip 29 is arranged so that it is clear i.e. does not contact the sealing ball 28. When the thermal valve 25 operates, it is arranged that the bimetallic strip 29 deflects towards the sealing ball 28, so moving it out of contact with the restriction 34 thereby unsealing the passage 27.

In the thermal valve 25 shown in Fig. 5 of the drawings, the use of a sealing ball 28 and spring 33 as used in the valves of Figs. 4 & BR< 5, are obviated by arranging that the passage 27 is provided with an exit nozzle 35 which projects from the body 26 of valve 25 adjacent to the end of the bimetallic strip 29, and by providing the bimetallic strip 29 with a pad 36 of a material such as synthetic rubber. In the normal position of the thermal valve 25, the pad 36 is pressed into contact with the nozzle 35 by the bimetallic strip 29 to seal the passage 27. However, when the thermal valve 25 operates, the bimetallic strip 29 is caused to operate to move the pad 36 away from the nozzle 35 thereby unsealing the passage 27.

In Fig. 6 of the drawings there is shown an alternative form of construction of the thermal valve 25 of Fig. 2. The thermal valve 25 shown in Fig. 6 comprises a body member 40 into one end 41 of which is secured the small bore pipe 20 (Figs. 1 and 2). The other end 42 of the body member 40 is externally threaded and has in screw threaded engagement with it a valve housing 43 of generally hollow construction. The housing 43 is provided with an internal valve seat 44 against which is urged a sealing ball 45 by means of a compression spring 46.

The free end 47 of the housing 43 is provided with an internally threaded axial hole 48 into which is screwed one end of a tube 49 of low-expansion material e.g. stainless steel the other end 50 of which is partially closed by flattening to form a stop for a ball 51 located inside the tube 49. Also located inside the tube 49 is a loose-fitting rod 52 of a highexpansion material e.g. brass.

The tube 49 is adjusted in the housing 43 so that in the ambient temperature condition the sealing ball 45 seats on the seat 44 to close the valve 25. However, if the thermal valve 25 is subjected to increased temperature such as would happen due to a flue blockage deflecting hot flue gases over it then the difference in expansion between tube 49 and rod 52 causes the latter to push against ball 51 and sealing ball 45, thereby causing the sealing ball to be un-seated so as to allow gas to escape via venting holes 53 provided in the wall of tube 49. Thus the pipe 20 is unsealed which causes the valve 9 (Fig. 2) to close so as to shut-off the main gas supply.

When the flue blockage is removed, the tube 49 and rod 52 of the thermal valve 21 cool down and resume the condition where sealing ball 45 locates on seat 44 and effectively seals pipe 20, thereby allowing the valve 9 to open to restore the main gas supply to the gas fire 1.

In Fig. 2, the valve 2 is depicted with the main diaphragm chamber 13 communicating with the inlet 8 via the weep hole 19. However, it should be appreciated that whilst this is the preferred implementation, it is possible for the diaphragm chamber to communicate with the outlet 11 via a suitable weep hole as is shown in Patent No. 2,088,593 already referred to. Also, although in the valve 2 of Fig.

2 a bypass passage 9a is provided between the inlet 8 and outlet 11, the provision of such a passage is not essential.

Claims

1. A flued gas appliance having a safety device comprising a gas control valve placed in the gas supply line to the gas appliance, and a self-resettable thermal valve positioned adjacent to an aperture communicating with the flue but not in the normal combustion product flow path of the appliance, the control valve having a valve, resilient means for urging the valve onto a seat, a diaphragm chamber communicating with the gas flow path through the control valve and a diaphragm connected to the valve and arranged so as to at least hold open the valve against the force of the resilient means when gas pressure builds up in the diaphragm chamber, said thermal valve closing a vent pipe connected to the diaphragm chamber, the arrangement being such that if the flue becomes blocked in use or there is a prolonged downdraught, the combustion products are deflected over said thermal valve which when it reaches a predetermined temperature is caused to open to release the pressure in the diaphragm chamber thereby to cause the valve to close, said thermal valve remaining open in the presence of said combustion products but being self-resettable in the absence of said combustion products whereby pressure in the diaphragm chamber is caused to rise to cause the valve to re-open.

2. An appliance as claimed in claim 1, in which the control valve comprises means for providing a restricted gas flow to bypass said valve.

3. An appliance as claimed in claim 1 or claim 2, in which the self-resettable thermal valve of the safety device comprises a ball valve operable in conjunction with a bimetallic strip whereby the valve is normally closed and opens when the temperature thereof exceeds a predetermined level.

4. An appliance as claimed in claim 3, in which the bimetallic strip is normally effective for biassing the ball valve into a valve closed position and which when the thermal valve reaches said predetermined temperature releases said ball valve to permit said thermal valve to open.

5. An appliance as claimed in claim 4, comprising spring means operable on said ball valve for biassing it into a valve open position.

6. An appliance as claimed in claim 3, comprising spring means for biassing said ball valve into a valve closed position and in which the bimetallic strip when the thermal valve reaches said predetermined temperature operates on said ball valve to cause said thermal valve to open.

7. An appliance as claimed in claim 1 or claim 2, in which the self-resettable thermal valve of the safety device comprises a bimetallic strip operable in conjunction with a sealing pad for causing said thermal valve to be normally closed and opens when the thermal valve reaches said predetermined temperature.

8. An appliance as claimed in any of claims 3 to 7, in which the bimetallic strip is adjustably set whereby the temperature at which the thermal valve operates may be adjusted.

9. An appliance as claimed in claim 1 or claim 2, in which the self-resettable thermal valve of the safety device comprises a ball valve operable in conjunction with a differentially expansible tube and rod arrangement whereby said ball valve is normally closed and opens when the temperature of said arrangement exceeds a predetermined level.

10. An appliance as claimed in claim 9, in which said rod is of high-expansion material and is located inside said tube which is of low-expansion material.

11. A gas fired appliance substantially as hereinbefore described with reference to the accompanying drawings.