GB2103352A - Safety devices for gas-fired appliances - Google Patents

Abstract

A gas fire (11) with radiants (12) has a front surface (13) which with an open flue in use does not rise above a known temperature. A fusible link (16) is secured to the surface (13) and holds a lever system (17) against the tension of a spring (18). When excessive temperatures are encountered link (16) melts and the linkage (17) is released operating a link (19) which operates a ratchet mechanism (21) returning a gas valve (not shown) to a closed position. Thus the gas fire cannot be used. Alternatively, a warning device may be operated. Excessive temperatures of the surface (13) are likely to be due to blockage of an exhaust flue, when hot exhaust gases are being forced back through the radiants. Other means for detecting the blockage of a flue are also described, for example, by detecting a drop in the exhaust gas temperature or by monitoring gas movement in the flue. <IMAGE>

Description

SPECIFICATION Gas-fired appliances This invention relates to gas-fired appliances of the kind which direct their exhausts into flues. A problem with such appliances is that there is a tendency for the internal surface of the flue to deteriorate and fall as rubble and block the flue. When this happens the exhaust is forced back into the room being heated. Because of tha reduced through-pull of combustion air, there may be incomplete combustion of the gas and poisonous carbon monoxide may be produced. The exhaust gases in the room may therefore be lethal.

This invention provides means for detecting the blockage of a flue indirectly by the detection of an ancillary condition, i.e. temperature, either in the flue or in the appliance, or the amount of draught in the flue.

One embodiment of the invention uses the temperature change at the front of the appliance which rises when exhaust gases are discharged into the room. This embodiment may have a fusible link which when melted allows operation of a mechanism shutting off the fire. Alternatively, or additionally, a warning device may be operated.

Another embodiment of the invention for use with an appliance having a heat exchanger uses the drop in temperature in the heat exchanger when no exhaust gases are drawn through to operate a warning device or to shut off the fire.

Afurther arrangement combines the temperature increase at the front of the appliance and the temperature drop in the heat exchanger to operate a shut-off. This may be a back-to-back arrangement of thermal detectors, e.g. thermocouples.

Another arrangement uses a vane or spinner to detect gas movement in the flue or passages adjacent thereto to detect movement and operate warning devices. One such arrangement provides an ancillary air stream drawn into the flue below the exhaust poisiton, so giving a warning before the exhaust itself is blocked.

Some specific embodiments of the invention are shown in the accompanying drawings, in which: Figure 1 is a perspective view of a gas fire with parts cut away to show a blocked flue safety device accordiríg to the invention, Figure2 is a view of a blocked flue indicator, Figure 3 is a diagrammatic side section through a gas fire with heat exchanger showing another form of blocked flue safety device, Figure 4 is a diagrammatic side section through a gas fire with heat exchanger showing a blocked flue indicator, Figure 5 is a diagrammatic side section through a gas fire showing another form of blocked flue indicator, Figure 6 is another diagrammatic side section through a gas fire showing yet another form of blocked flue indicator, Figure 7 is another diagrammatic side section through a gas fire showing a blocked flue detector, and Figure 8 is a diagrammatic representation of a latching mechanism for a gas fire.

Referring to Figure 1, a gas fire 11 with radiants 12 has a front surface 13 above the radiants which in normal running gets warm but does not go above a known temperature. If the flue (not shown) is blocked the hot exhaust gases are forced back through the front grill 15 in front of the radiants so that the surface 13 becomes excessively hot. By sensing this increased temperature, the blocking of the flue is detected. In this embodiment a fusible link 16 is secured to the front surface 13 and holds a lever system in an inoperative position againstthetension of spring 18. The fusible link is chosen to melt at an abnormally high temperature for the front surface, so indicating a blocked flue. When the link gives way, spring 18 pulls the lever system down, operating a link 19.The link is connected into the linkage by which the gas control knob 20 opens the gas valve in a manner such as to prevent opening of the valve. It may for instance operate a clutch mechanism to disconnect the gas tap and return the valve to a closed position. Alternatively it may operate a ratchet mechanism 21, again returning the valve to closed position and thereafter locking the control knob against operation.

In an alternative arrangement (not shown) the linkage 17 operates an indicator, either additionally or alternatively to the locking of the gas valve.

The arrangement of Figure 2 is for mounting on a front surface of a gas fire similar to surface 13 of Figure 1. It comprises a bimetallic strip 22 secured at end 23 and carrying at its free end a two-coloured flag 24. When excess temperatures are sensed the strip bends to bring a red coloured part 25 of the flag into a viewing window 26. Normally a green coloured part 27 is viewed showing safe conditions.

The strip 22 may be replaced by a bimetallic coil (not shown) operating a similar flag warning system.

In a further arrangement (not shown) the bimetallic strip operates directly or indirectly to close a gas supply valve. It may for instance release a catch on a spring-loaded pawl which causes the gas valve to close.

Another sensing arrangement is shown in Figure 3 for use in a gas fire having heat exchangers 30 through which hot exhaust gas passes on path A two enter the flue 31. Room air passes over the heat exchangers to supply warm air to the room. In such a fire the temperature at point 32 on the front surface should be at a warm but not hot temperature, while the temperature in the heat exchangers, e.g. at point 33 should be hot. Thermocouples are mounted at these points to detect these temperatures and are connected in an electrical circuit in a back-to-back configuration, i.e. the EMF generated by the thermocouple at 32 cancels out the EMF generated by the thermocouple at 33 when these points are both at normal operating temperatures. A solenoid 34 is also connected into this circuit and operates a safety valve 35 in the gas supply to the fire.When the flue 31 is blocked, i.e. when the rubble 36 reaches a level at which the outlet from the fire is blocked, the temperatures at 32 and 33 are reversed. The exhaust gases now no longer take the path A, but follow path B, so point 32 becomes very hot while point 33 cools.

This reversal of the temperatures allows an overall EMF to occur in the circuit and operate solenoid 34 to close the valve 35. This will happen every time the householder attempts to light the fire.

An alternative to the valve closure method of Figure 3 is shown in Figure 4, where a bimetallic coil 40 situated in the heat exchanger 41 operates through a lever 42 a flag 43. The flag is viewed through a window 44 and is in two parts, a "safe" indication 45 coloured green and a "danger" indication 46 coloured red. Accordingly when a high temperature is sensed in the heat exchanger, the flag will indicate "safe" and when a low temperature is sensed the flag will indicate "danger". These indications will only be valid when the system has warmed up.

This system has the advantage that it will accommodate both high and low rate fire operation. The coil/lever arrangement gives a potentially large movement for a small temperature change but excess movement at high fire rates may be prevented by stops.

A further method of detecting a blocked flue is to sense the draught in the flue. In Figure 5 an air channel 50 is provided low down in the flue 51 so that room air is sucked into the flue when the flue is operating properly. The air channel 50 passes through the fire 52 and has a vane spinner 53 positioned to be rotated by the flowing air. When the spinner is rotating therefore it is an indication that the rubble 54 has not reached a level to block the exhaust 55. The rotation may be checked by manual inspection from time to time or may be arranged to operate a flag warning. This arrangement has the advantage of giving advance warning, because the air channel is below the exhaust 55. Warning will therefore be given before actual danger is present.

The same principle of direct detection of air or gas movement in the flue may be used in alternative arrangements, as shown in Figure 6. A vane 60 is placed adjacent or in the exhaust passage and operates a flag 61 through a lever system.

Alternatively, the temperature in or adjacent the air passage 50 of Figure 5 may be sensed. While air is flowing the temperature will remain low, rises being due to blockage of the flue.

One example of this last arrangement is shown in Figure 7. Here a thermocouple 62 and a heating element 63 are placed close together in or adjacent the air passage. With the heating element energized, the draught in the flue reduces the temperature sensed by the thermocouple. When the flue is blocked there is no draught, the temperature rises and the thermocouple causes solenoid-operated gas valve 64 to close. This system using a heating element could also be incorporated in the arrangement of Figure 3. Thermistors or thermopiles may also be used in this type of device.

Figure 1 shows a lever system which closes a gas valve when a blocked flue is detected. A simplified mechanism for preventing further opening of the gas valve is shown in Figure 8. A shaft 65, which may be the shaft by which the gas valve is manually opened or a shaft moveable therewith, carries a disc 66 fixed to rotate therewith. A radial slot 67 extends from the circumference of the disc. Above the disc a blade 68 is pivoted at 71, the blade being of a thickness to enter easily into the slot 67. A bimetallic strip 69 is secured at 70 to the front surface of the fire so that the strip bends in the direction of arrow C when the strip is heated. The blade 68 has one end adjacent the disc 66 heavier than its end adjacent the strip so that when free it tends to pivot in the sense to dip its heavy end.The strip 69 at normal operating temperatures overlies the light end of blade 68 so preventing this dipping movement.

When abnormally high temperature are encountered, however, the strip 69 bends out of the path of the blade 68. The heavy end of the blade 68 therefore drops onto the rim of disc 66. While the gas valve is open the shaft 65 and disc 66 are in positions similar to that shown in the drawing, the slot 67 not being in line with the blade. In the OFF position of the gas valve, the shaft and disc 66 are moved so that the slot 67 is vertical at the top of the disc, whereby if the blade 68 has dropped onto the rim during the previous use of the fire, it will then drop further into the slot 67. The valve is then locked against any opening movement. Although this does not stop the fire immediately a blockage occurs, it does prevent any further use after the fire has been turned off.

To increase the downward pull on the heavy end of blade 68, a spring 72 may be provided. The bimetallic strip 69 may be replaced by othertemperature sensitive means, e.g. a fusible link or a coil of memory metal which changes its configuration when an excessive temperature is sensed. The latch described may be used with any of the temperature or air-movement detecting devices described above.

Claims (14)

1. .1 Agas-firedappliance having means for detecting the blockage of a flue indirectly by the detection of change in an ancillary condition in the flue or in the appliance caused by reduced exhaust gas flow.
2. 2. An appliance as claimed in claim 1, wherein said ancillary condition is the temperature of parts of the appliance normally cooled by the gas flow, and said means comprises a temperature sensitive device.
3. 3. An appliance as claimed in claim 2, wherein said temperature sensitive device comprises a fusible link or a bimetallic means located on or adjacent a front casing member of the appliance.
4. 4. An appliance as claimed in claim 2, wherein said temperature sensitive device comprises a bimetallic means located in or adjacent a heat exchanger of the appliance.
5. 5. An appliance as claimed in claim 2, wherein said temperature sensitive device comprises a pair of thermocouples, one located at or adjacent the front of the appliance, the other located in or adjacent a heat exchanger of the appliance, the two thermocouples being connected back-to-back in an electrical circuit.
6. 6. An appliance as claimed in claim 1, wherein said ancillary condition comprises air flow through an air channel located beneath an exhaust outlet of the appliance, and said means comprises either a temperature sensitive device or an air flow detecting device.
7. 7. An appliance as claimed in claim 6, wherein said air flow detecting device comprises either a vane or a spinner moved by gas movement or a thermocouple and heater cooied by the gas movement.
8. 8. An appliance as claimed in claim 1, wherein said ancillary condition comprises exhaust gas flow in or adjacent an exhaust pipe of the appliance and said means comprises an air flow detecting device.
9. 9. An appliance as claimed in claim 8, wherein said air flow detecting device comprises a rotatable spinner.
10. 10. An appliance as claimed in any of claims 1 to 9, including a warning device operable on detection of a change consistent with the flue being blocked.
11. 11. An appliance as claimed in any of claims 1 to 10, including means for closing or preventing the opening of a gas valve of the appliance.
12. 12. An appliance as claimed in claim 11, wherein said means for preventing the opening of a gas valve of the appliance comprises a latch member engageable in another member which moves with said gas valve, said latch member being held out of said engagement by means detecting said change of ancillary condition.
13. 13. An appliance as claimed in claim 12, wherein said latch member comprises a blade, said other member comprises a disc with a slot in which said blade may engage, and a bimetal or memory metal means holds said blade out of said engagement when it experiences normal temperatures.
14. 14. A gas-fired appliance substantially as described hereinbefore with reference to any of the accompanying drawings.