GB2088593A

GB2088593A - Safety devices for flued gas appliances

Info

Publication number: GB2088593A
Application number: GB8134631A
Authority: GB
Original assignee: TI Domestic Appliances Ltd
Current assignee: TI Domestic Appliances Ltd
Priority date: 1980-11-18
Filing date: 1981-11-17
Publication date: 1982-06-09
Also published as: GB2088593B

Abstract

The safety device comprises a gas control valve (2) in the gas supply line to the appliance and upstream of a gas tap (3), and a fusible plug (23) placed adjacent to an aperture communicating with the flue but not in the normal combustion product flow path of the appliance. A valve (9) is urged onto a seat (10) by a spring (16) and is attached to a diaphragm. When the gas tap (3) is closed the valve (9) is opened by gas flowing through weep passages (19 and 20) and into diaphragm chamber (13) and is held open when tap (3) is opened. If the flue becomes blocked, the combustion products are deflected over the fusible plug which will eventually melt to vent the diaphragm chamber via pipe (21) and the spring (16) will close the valve (9). Instead of weep passage (19), the control valve may have a manually operable spring loaded push rod for opening valve (9). <IMAGE>

Description

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

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.

According to the present invention, a safety device for a flued gas appliance, comprises a gas control valve for being placed in the gas supply line to the gas appliance, and a fusible plug for being placed 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, the fusible plug closing a vent pipe connected to the diaphragm chamber, the arrangement being such that if the flue becomes blocked in use, the combustion products are deflected over the fusible plug which will eventually melt to release the pressure in the diapheagm chamber and close the valve.

It is a standard requirement of gas appliance construction that in the event of temporary flue blockage such as downdraughtthe products of combustion pass through an opening in the appliance designed so that the burner can continue to operate in a satisfactory manner. Under normal flue conditions this opening allows air to be drawn from the room by the up draught caused by hot combustion gases passing up the flue. The temperature of this air stream, despite some effect by radiant and/or conducted heat, is relatively cool. Should down draught occur for any reason and the hot gases are deflected down through this opening the temperature at this position rises. Significantly, this temperature rise is sensed by the fusible plug and used to cut offthefuel supply.

Preferably, the diaphragm chamber communicates with the outlet side of the valve.

Advantageously, the control valve is provided with a manually operable valve opening arrangement for lifting the valve off of its seat to allow gas to the diaphragm chamber and hold the valve in its open position. The valve opening arrangement may comprise a push rod which can be pressed against the action of a spring to lift the valve off of its seat.

Alternatively, the control valve has a weep passage to allow a restricted flow of gas from the inlet side to the outlet side of the valve when the valve is closed.

The invention also provides a flued gas appliance having a safety device as above described and provided with a gas tap in the gas supply line to the appliance and downstream of the control valve.

In the accompanying drawings; Figure 1 shows a typical arrangement of the device fitted to a gas fire, Figure 2 shows the control valve in more detail, and Figure 3 shows a modification of the control valve of Figure 2.

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

Referring to Figure 2, the control valve 2 comprises es an inlet passage 8, a valve 9 opening and closing against seat 10, and an outlet passage 11. 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 a breather hole 18 to atmosphere. Bypassing valve 9 is a small weep hole 19 and from outlet passage 11 is another small weep hole 20. From chamber 13 a small bore pipe 21 connects to a fusible plug body 22. Inside this body 22 is secured a fusible plug 23 clamped in a gas tight manner against the end of pipe 21 by a cross pin 24.

As shown in Figure 1, the gas fire has a vent space 25 between the radiant block 5 and the flue 7. This is so that, in the event of a down draught due for example to wind, the combustion products can escape into the surrounding atmosphere without interfering with the burner. The fusible plug body 22 is placed just outside, so that in normal operation it remains relatively cool and is not exposed to the combustion products. The fusible plug 23 is so designed that if it is exposed to combustion products flowing out from the region 25, for more than a short time, the plug will melt.

The action of the control is as follows: Gas tap 3 is closed. Gas is supplied to the valve 2 at inlet 8. Valve 2 is closed. A small supply of gas passes through weep 19 and because tap 3 is closed cannot escape. This weep supply then passes through weep 20 into chamber 13 and, provided plug 23 is sealing the end of tube 21, builds up pressure over diaphragm 15 to overcome spring 16 and open valve 9. When the 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 plug 23. Should the flue 7 become blocked then the flue products are deflected down through the front vent 25 of the fire and pass upwards over the plug 23. The plug heats up and eventually melts thereby unsealing the end of pipe 21. This now releases the pressure in chamber 13 because weep 20 is insufficient to maintain the pressure and the spring 16 closes valve 9, shutting off the gas supply. The only leak past the valve is through weep 19, but this is allowable and is insignificant. Turning off the tap 3 will not restart the action until fuse 23 is replaced.

The control valve of Figure 3 is similar to that of Figure 2, but with the omission of the weep hole 19 and the addition of a manually operated push rod assembly 26.

The assembly 26 comprises a body 27 with push rod 28 of sliding fit in the body 27. The rod 28 has grooves to accept retaining washers 29 and 30. The washer 29 forms a shoulder against which presses one end of spring 31 an the other end of the spring presses against washer 32 and via this washer presses an 0 ring 33 to form a gas tight seal between push rod 28 and the internal conical face of body 27.

To put the device into operation gas tap 3 is closed. Gas is supplied to the valve 2 at inlet 8. Valve 2 is closed. The push rod 28 is pressed for a few seconds to open valve 9 and gas passes via passage 11 to tap 3. Gas also passes through weep 20 into chamber 13 and provided plug 23 is sealing the end oftube 21 builds up pressure over diaphragm 15to overcome spring 16 and keep valve 9 open. When tap 3 is opened gas passes to burner 4 and is ignited.

Should the flue become blocked and plug 23 melt, this releases the pressure in the chamber 13 as before and spring 16 closes valve 9, shutting off the gas supply with no leak past the valve.

In this case when fuse 23 is replaced, turning off tap 3 will not restart the action. The valve 9 must be opened by push rod 28.

Claims

1. A safety device for a flued gas appliance, comprising a gas control valve for being placed in the gas supply line to the gas appliance, and a fusible plug for being placed 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, the fusible plug closing a vent pipe connected to the diaphragm chamber, the arrangement being such that if the flue becomes blocked in use, the combustion products are deflected over the fusible plug which will eventually melt to release the pressure in the diaphragm chamber and close the valve.

2. The safety device of claim 1, wherein the diaphragm chamber communicates with the outlet side of the valve.

3. The safety device of claim 2, wherein the control valve is provided with a manually operable valve opening arrangement for lifting the valve off of its seat to allow gas to the diaphragm chamber and hold the valve in its open position.

4. The safety device of claim 3, wherein the valve opening arrangement comprises a push rod which can be pressed against the action of a spring to lift the valve off of its seat.

5. The safety device of claim 2, wherein the control valve has a weep passage to allow a restricted flow of gas from the inlet side to the outlet side of the valve when the valve is closed to allow a build up of pressure in the diaphragm chamber when a gas tap associated with the appliance and located between the control valve and the appliance burner is closed, so as to lift the valve off of its seat.

6. A safety device for a flued gas appliance substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.

7. Aflued gas appliance having the safety devide of any one of the preceding claims and provided with a gas tap in the gas supply line to the appliance and downstream of the control valve.