GB2270563A - Flame-failure device - Google Patents

Abstract

Flame-failure devices having a phial (36)/capillary (34)/expansible chamber system controlling a fuel flow valve for controlling fuel to a burner have a gas-filled system and a gas-adsorbent material (40) such as charcoal in the phial (36). The use of the adsorbent material enables the sensitivity of the system to be as good as or better than conventional water or mercury filled systems, while enabling the phial to be still as compact as those used for such systems. The devices are of particular value in gas cookers for mounting under work surfaces or with double ovens, where their small size and high sensitivity are advantageous. The gas used in the device may be argon. <IMAGE>

Description

FLAME-FAILURE DEVICE This invention relates to a flame-failure device, by which is meant a device associated with a valve supplying fuel to a burner producing heat by combustion of the fuel, the device including a phial positioned to be heated by the flame and designed to keep the valve open only while the phial is being heated.

Such devices find major application in gas burners forming part of domestic cookers. It is important to close off the supply of gas to a burner if the flame is extinguished (e.g. by a pan boiling over, a gust of wind or the rapid opening or closure of an oven door) so that the danger of a build up of escaped gas, which may then ignite explosively and start a fire, is avoided.

The phial of such flame failure devices is usually connected to a valve-control device, e.g. a chamber having at least one wall in the form of a diaphragm, or a bellows, through a length of small-bore (capillary) conduit so as to keep as low as possible that proportion of the internal volume of the phial, capillary and chamber which is not heated by the flame. In addition, the internal volume is conventionally partly filled with a liquid, originally usually mercury, but in more recent years water. In use this pressurises the internal volume by vaporisation of part of the liquid. When the flame goes out, the vapour is condensed to lead to a quick and steep reduction in the internal pressure, intended to lead to the fuel valve shutting rapidly.

Theoretically, filling the internal volume with a gas can provide a workable system, but in order to achieve adequate sensitivity the phial volume must be large (on cooker applications usually implying a phial diameter of at least 6 mm, and a length of at least 15 mm) and the fuel valve also of large diameter to give satisfactory operation. This is undesirable, as requiring more raw material to make the unit, and taking up more space. The use of mercury or water filled devices has thus become practically universal in domestic cookers.

However, changes in cooker design in recent years have led to difficulties in practice, most notably in the case of cookers installed under worktops and those with a second oven. In such situations, the ambient temperature around the phial tends to fall relatively slowly when the flame goes out, so that the temperature adjacent to the burner remains above the temperature at which closure of the fuel valve is effected for some time, leading to unacceptably-prolonged delays between flame extinction and valve closure.

The present invention aims at providing a flame-failure device which uses detector phials of small diameter and volume which are gas-charged and yet which respond quickly to flame extinction and establishment.

Accordingly the present invention provides a temperatureresponsive flame-failure device comprising a rigid hollow phial connected by a small-bore conduit to an expansible chamber at least one wall of which is formed by a resilient diaphragm or which includes a bellows or like device, and a fuel control valve responsive to movement of part of the chamber to control the flow of fuel to a burner situated adjacent the phial, the arrangement being such that extinction of the flame at the burner causes the valve to close within a short period, characterised in that the phial contains a body of gas adsorbent material with the remainder of the closed volume bounded by the phial, conduit and chamber being filled with a gas adsorbable by the adsorbent material.The adsorbent material may be charcoal or other high surface area material such as a molecular sieve material which can adsorb a large volume of gas relative to its own volume.

In a method of making the flame-failure device of the present invention, a length of tubing which is to form a phial has a quantity of adsorbent placed within it the tubing being connected to or integral with a length of small-bore conduit in fluid communication with a chamber, preferably a double walled chamber of which both walls are formed by diaphragms. At least the wider-bore part of the tubing containing the adsorbent is then heated while the internal volume of the tubing, conduit and chamber is evacuated by means of a vacuum pump. The internal volume is then filled with a suitable gas, such as argon, when the tubing is cool. The tubing may have the diameter of only part of its length reduced to that of, or to form, the small-bore conduit by means of a swaging or like process. The internal volume can be sealed off from the vacuum pump before or after the charging process.The tubing and at least some of the conduit may be subjected thereafter to an annealing process in known fashion.

The volume of adsorbent relative to volume of system may be varied as may the gas pressure to give require temperature/deflection characteristics to the thermal system. Because of the presence of the adsorbent, the change in the pressure within the system may vary strongly depending on the temperature of the phial, but the phial does not have to be very large. A major advantage of the invention resides in the ability to use a narrow diameter phial, easily formed integrally from the capillary conduit by a simple forming process, and sufficiently small to be compatible with existing mercury - and water-filled types, i.e. to be no larger in terms of phial diameter, typically 3 mm.

The present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a sectional view of one form of fuel control valve operated by flexure of a diaphragm in fluid communication with a small-diameter phial of the present invention, and Figure 2 is an axial cross-section through phial of the present invention connected to a length of conduit.

In the following description, those parts which are common to the two figures are given the same reference.

The device shown in Figure 1 comprises a valve control body 2 having in it an inlet 4 for a supply of fuel gas.

The initial passage of gas from port 4 into an internal chamber 6 is controlled by a valve member 8 controlled by an electric solenoid 10. Other forms of the device may be envisaged which do not include an electric solenoid and where the gas goes directly into chamber 6. Gas admitted under pressure into chamber 6 is intended to flow through an annular gap between a valve plate 12 and an O-ring 14. Gas flowing through this gap passes into an operating chamber 16 from whence it flows to an outlet port 18 in communication with an appropriate burner intended to heat the oven or like device fitted with the flame-failure detector of the present invention.

The valve plate 12 is biased into the valve-closed position by means of a compression spring 20 bearing on the back of the valve plate. Projecting from the centre of the other face of the valve plate is a follower 22 in contact with the centre of an annular diaphragm 24 welded or otherwise secured to one end face of a pressure chamber 26 formed in the interior of a fixed cylinder 28 of which the axial position relative to body 2 is controlled by a screw-threaded sleeve 30 in engagement with body 2. When the exact position of the centre of diaphragm 24 has been fixed relative to body 2 and to the end of follower 22, the sleeve is locked in place by means of a nut 32. Sealed into the cylinder 28 are the ends of two small-bore conduits 34 of which one leads to a phial 36 as shown in Figure 2, and the other is used for charging the system with gas. This charging tube may be omitted and charging carried out from the end of the phial. Although not shown in the drawing, a ferrule may be fitted onto the capillary and crimped onto the reduced diameter of the phial to enable the phial to be clipped in place so that one end projects into the space intended to be filled with flame when the burner is working. The phial 36 and conduit 34 may be integral with each other, in that both are formed from a length of tubing which is initially of the same diameter as the desired outside diameter of phial 36.

After the interior of at least that length of tubing which is to form phial 36, i.e. up to the tapering section 38, has been filled with adsorbent material 40, for example charcoal and the tube sealed, the length of filled tubing is heated while the interior thereof is connected to a vacuum pump to remove the gases and vapours driven off from the adsorbent. When substantially all the moisture and occluded gases have been driven off the adsorbent, and removed from the interior of the tubing, a suitable gas such as argon is caused to flow into the interior of the tubing to be taken up preferentially by the adsorbent, which adsorbs several times its own volume of argon. The system is then sealed.

Installed in a cooker and in use, with the phial 36, conduit 34 and chamber 26 being a closed system, any deadsorbtion of the argon arising from the temperature to which the phial is raised by its exposure to a flame being monitored causes the internal pressure to rise to a value at which a centre portion of diaphragm 24 is flexed outwardly to an extent which is a function of the said internal pressure. This keeps the valve open and gas flowing to the burner.

When the flame being monitored is extinguished, the small thermal capacity of the phial 36 and its body of adsorbent 40 causes the phial to lose temperature rapidly. This causes the charcoal to readsorb at least some of the deadsorbed gas, leading to a relatively-rapid decrease in the said internal pressure. This leads to a reduction in the flexure of diaphragm 24, which in turn reduces its thrust on follower 22, allowing the spring 20 to move the valve plate 12 to its closed position, thus cutting off the further supply of fuel to outlet port 18 and from these to the associated burner.

The device of the present invention shown in the drawings constitutes a flame failure device with a flame-detector phial of such narrow dimensions that it is able to be substituted for known water-filled or mercury-charged flame-failure detectors without any loss of the rapid response time desired in such detectors. Indeed, because of the sensitivity of the relationship of the amount of absorbed argon to the temperature of the adsorbent 40, the device of the present invention is able to operate in environments in which water-charged detectors are unable to act sufficiently quickly.

Claims (3)

CLAIM

1. A temperature-responsive flame-failure device comprising a rigid hollow phial connected by a small-bore conduit to a chamber having at least one movable wall and a fuel control valve responsive to movement of the chamber wall to control the flow of fuel to a burner situated adjacent to the phial, the arrangement being such that extinction of the flame at the burner causes the valve to close within a short period, characterised in that the phial contains a body of adsorbent material, with the remainder of the closed volume within the phial, conduit and chamber being filled with a gas adsorbable by the adsorbent material.

2. A flame-failure device according to Claim 1, wherein the adsorbent material is charcoal and the gas is argon.

3. A flame-failure device according to Claim 1 or 2 wherein the outer diameter of the phial is less than 4 mm.