GB2099128A

GB2099128A - Flame-failure devices for gas- burning appliances

Info

Publication number: GB2099128A
Application number: GB8113195A
Authority: GB
Original assignee: Concentric Controls Ltd
Current assignee: Concentric Controls Ltd
Priority date: 1981-04-29
Filing date: 1981-04-29
Publication date: 1982-12-01
Also published as: GB2099128B

Abstract

A flame-failure device for a gas- burning appliance includes a hollow, sealed body containing water or other aqueous liquid, the body consisting of a capillary tube (31), a phial (32) at one end of the tube (31) and an expansion unit (26) at the other end thereof. In use the phial is heated by a pilot flame. When the liquid in the body boils, the unit (26) expands and an abutment (27) on it engages a plate (22) at one end of a rod (21). The resulting movement of the rod opens a gas valve (15, 16, 17) in the supply line to a main burner. A heavy compression spring (23) acts on the plate (22) to resist expansion of the unit (26). Only when the temperature in the phial exceeds about 200 DEG C does the liquid boil sufficiently to open the gas valve. If the pilot flame fails, the phial cools and the expansion unit contracts thus allowing the gas valve to close. <IMAGE>

Description

SPECIFICATION Flame-failure devices for gas-burning appliances This invention relates to flame-failure devices for gas-burning appliances, that is to devices which in use are incorporated in gas-burning appliances and respond to the failure or cessation of a gas flame by the closure or restriction of a gas valve. A flame-failure device may, for example, be used to control the supply of combustible gas to a main burner and be so arranged that in use if the flame resulting from the ignition of gas from a pilot burner or subsidiary burner ceases, the device operates to close the valve through which the gas was supplied to the main burner.

A well-known type of flame-failure device comprises a hollow, sealed body containing mercury, the body having a central portion in the form of a tube with a relatively narrow Dore, a tubular phial of a larger bore at one end of the central portion and an expansion unit at the other end of the central portion, the arrangement being such that in use when the phial is heated by a gas-flame mercury in the phial boils and vapourises thus causing liquid mercury to be forced along the central portion into the expansion unit and the consequent expansion of the expansion unit, which expansion is harnessed, in use, to open a gas valve, or to maintain a gas valve open.

That type of flame-failure device operates satisfactorily and is generally reliable.

Nevertheless, the fact that it incorporates mercury has caused some anxiety. If the body containing the mercury were to leak, mercury could escape and, where the device is used in an oven, might possibly contaminate food. Liquid mercury is not particularly dangerous if ingested, but some compounds of mercury are poisonous, and there is a danger (though only a very slight danger) that mercury escaping from a flame-failure device might form a poisonous compound and be ingested. In addition mercury vapour can be injurious. Although the risks involved are very small it may nevertheless be considered desirable to avoid the use of mercury altogether. Further, mercury is relatively costly, so for this reason as well it may be desirable to avoid its use.

The present invention aims to provide a flamefailure device such that the use of mercury and the anxieties associated with its use are avoided.

According to the present invention there is provided a flame-failure device comprising a hollow, sealed body containing water or other aqueous liquid, the body having a central portion in the form of a tube with a relatively narrow bore, a phial at one end of the tubular central portion and expansion means at the other end of the central portion, the device also including a gas valve biassed towards a closed or restricted position and so arranged to open or open more fully in response to expansion of the expansion means, and pressure means operative in use to resist such expansion of the expansion means to an extent such that when the phial is heated, water or other aqueous liquid in the phial boils and causes such expansion of the expansion means only when the temperature exceeds 2000 C.

The liquid in the body preferably comprises an aqueous solution of which the freezing point is below OOC, and is preferably no greater than -50C. The solution is preferably a solution of an inorganic compound, as most organic compounds, such as glycol and others commonly used for "anti-freeze" purposes, tend to decompose or polymerise when maintained at temperatures above 2500C. Suitable compounds for depressing the freezing point are sodium chloride and potassium chloride.

The pressure means is preferably such that in use the expansion means is fully expanded only when the temperature of the gas or vapour in the phial exceeds about 2500C.

A flame-failure device embodying the present invention will now be described in more detail, by way of example with reference to the accompanying drawing which is a cross-section through the device.

The device illustrated comprises a housing 10 for a gas valve, the housing having a gas inlet 11 leading by way of an inlet chamber 13 and an outlet to a gas outlet 14. The inlet chamber 12 is of smaller diameter than the outlet chamber 13 and houses a valve member comprising a disk 1 5 and a resilient annular seal 1 6 secured to it. The valve member co-operates with a valve seat 1 7 formed as part of an insert 1 8 which is located against an annular face of the housing 1 0 formed where the outlet chamber 13 meets the inlet chamber 14. The valve member is urged towards the valve seat 1 7 by a light compression spring 19 which acts between the disk 1 5 and an end face of the inlet chamber around the gas inlet 11.

The central part of the insert 1 8, radially inside the valve seat 17, is formed to provide a tubular guide 20 co-axial with the seat and supported by radially extending fins such as to allow free passage of gas between them when the valve member is lifted from its seat. An operating rod 21 is mounted for axial sliding movement in the guide 20. One end of the rod co-operates with the valve member and when the valve is open, as illustrated, engages the base of a central recess in the disk 1 5. The other end of the is integrally connected to the centre of a circular plate 22. A heavy compression spring 23 around the rod 21 acts between the insert 1 8 and the plate 22, thus urging the rod 21 away from the valve member.

The outlet chamber 13 is closed by a cover 24 which is firmly secured to the housing 10 by screws 25. A sealing gasket (not shown) may be provided between the cover and the housing. The cover 24 supports an expansion unit 26 which constitutes part of a hollow body of the kind referred to above and comprises two corrugated disks of resilient metal sealed together at their peripheries. One disk carries at its centre an abutment 27 which engages the centre of the circular plate 22. The other disk is attached to an annular flange 28 at one end of a screw-threaded sleeve 29 which projects through a hole in the cover 24 and is secured by a nut 30. The interior of the expansion unit 26 communicates with the interior of a flexible metal capillary tube 31 one end of which is secured within the sleeve 29.The other end of the tube 31 is connected to one end of a tubular metal phial 32, the interior of the tube communicating with the interior of the phial. The phial 32, tube 31 and expansion unit 26 together comprise a body of the kind referred to above.

This body contains an aqueous solution of sodium chloride of which the freezing point is about -50C. When the liquid is at room temperature the expansion unit 26 is fully contracted, and the body is full of liquid. With the expansion unit contracted, the plate 22 is pushed by the spring 23 into a position such that the operating rod 21 is spaced a short way from the disk 1 5 of the valve member, whiie the light spring 1 9 presses the valve member against the valve seat 17, thereby closing the valve.

The device may be used in the following manner. The gas inlet 11 is connected to a source of combustible gas while the gas outlet 14 is connected to a main gas burner. A pilot burner is positioned adjacent to the phial 32 and is supplied with combustible gas under the control of a valve different from that incorporated in the flame-failure device. When gas from the pilot burner is first lit the phial and the liquid inside it are heated. The liquid tends to expand, but owing to the force of the heavy spring 23 applied to the expansion unit 26, expansion of that unit is initially prevented, with the result that the pressure inside the hollow body rises.This rise in pressure causes a rise in the boiling point of the liquid, and the arrangement is such that the liquid does not start to boil until the temperature of the liquid in the phial reaches at least 2000 C, and preferably about 2500 C. When the liquid starts to boil, the expansion unit starts to expand with the result that the heavy spring 23 is further compressed and the resistive force applied by the spring is increased. This in turn causes the pressure in the hollow body to rise further and the boiling point of the liquid to rise further. Thus, as the temperature of the phial increases the expansion unit progressively expands until there is no liquid remaining in the phial. The expansion unit is then fully expanded and the valve member is lifted fully off its seat, as illustrated.This may occur when the temperature of the phial is about 3000 C. By changing the force exerted by the heavy spring 23 and by changing the spring rate, the opening characteristics of the valve can be varied as desired.

While some liquid remains in the phial, the gaseous material in the phial is a saturated vapour. Once all the liquid has been boiled away, however, the gaseous material is a non-saturated or super-heated vapour. If the temperature of the phial is raised still further the vapour in the phial may expand somewhat, but the phial itself is likely to expand as well so that there is little change in the extent to which the expansion unit has expanded. Nevertheless at relatively very high temperatures the expansion of the phial often exceeds that of the vapour so that the expansion unit contracts slightly. The contraction, however, is insufficient to affect the rate of flow of gas through the open valve to any significant extent.

When the system has reached an equilibrium, at whatever temperature this occurs, there is a temperature gradient between the hottest part of the phial and the adjacent end of the capillary tube 31 such that there is a liquid/vapour interface at or adjacent to the place where the interior of the phial meets the interior of the tube, the liquid and vapour being in equilibrium at the interface. The position of the interface varies with the temperature at which equilibrium is achieved and varies with the position of the pilot flame.

In the system described above, the force exerted by the heavy spring 23 ensures that the liquid in the phial does not start to boil until a temperature of at least about 2000 C. In a modified construction (not illustrated) the plate 22 engages a stop when the phial and its contents are at room temperature, and the expansion unit is contracted to an extent such that the abutment 27 is spaced from the plate.

The pressure in the body is therefore equal to or only a little above atmospheric pressure. When the phial is heated the liquid inside it boils at about 100 C or a little greater temperature so that there is some initial expansion of the expansion unit. As soon as the abutment 27 engages the plate, however, further expansion is strongly resisted, and the pressure in the body rises as the temperature of the phial rises, until the temperature rises above at least about 2000 C. Thus, as before, the valve is not opened until the temperature of the liquid in the phial exceeds about 2000 C.

For the boiling point of the aqueous solution to be raised to between 2500C and 300 C it is necessary for the pressure within the hollow body to be between about 500 and 700 p.s.i. (pounds per square inch). The spring 23 must be designed to exert an appropriately large force. In a typical embodiment of the present invention the total volume of the hollow body, when the expansion unit 26 is contracted, is about 1 ml, the internal diameter of the capillary tube 31 being about 0.015 inches.

If desired the expansion unit 26 may be encapsulated in a block of rubber or other resilient material to improve load distribution over the outside surface of the unit and to prevent unwanted or permanent distortion of the diaphragm or to reduce the likelihood of such distortion occuring.

Whichever of the arrangements outlined above is used, it will be appreciated that if the flame at the pilot burner goes out, as for example by being blown out or by the failure of the gas supply or by the gas supply to the pilot burner being turned off, the phial will quickly cool, its contents will liquefy again, and the valve will close.

Claims (Filed 29.4.82) 1. A flame-failure device comprising a hollow, sealed body containing water or other aqueous liquid, the body having a central portion in the form of a tube with a relatively narrow bore, a phial at one end of the tubular central portion and expansion means at the other end of the central portion, the device also including a gas valve biased towards a closed or restricted position and so arranged as to open or open more fully in response to expansion of the expansion means, and pressure means operative in use to resist such expansion of the expansion means to an extent such that when the phial is heated, water or other aqueous liquid in the phial boils and causes such expansion of the expansion means only when the temperature exceeds 2000C.

2. A device as claimed in claim 1 in which the liquid in the phial boils and causes expansion of the expansion means only when the temperature exceeds 2500 C.

3. A device according to claim 1 or claim 2 in which the liquid in the body comprises an aqueous solution which has a freezing point below OOC.

4. A device according to claim 3 in which the freezing point of the aqueous solution is no higher than -50C.

5. A device according to any one of the preceding claims in which the liquid in the body comprises an aqueous solution of an inorganic compound.

6. A device according to claim 5 in which the inorganic compound comprises sodium chloride.

7. A device according to claim 5 in which the inorganic compound comprises potasium chloride.

8. A device according to any one of the preceding claims in which the pressure means is arranged in use to resist expansion of the expansion means to an extent such that the expansion means is fully expanded only when the temperature of the gas or vapour in the phial exceeds 2500C.

9. A device according to claim 8 in which the expansion means is fully expanded only when the temperature of the gas or vapour in the phial reaches about 3000 C.

1 0. A device according to any one of the preceding claims in which there is an operating member operative to transmit motion caused by expansion of the expansion means to the gas valve to open or more fully open the gas valve.

11. A device according to claim 10 in which the pressure means acts on said operating member to oppose said motion.

12. A device according to claim 11 in which there is a stop so positioned that when the aqueous liquid is at room temperature force exerted by the pressure means is borne by the stop means rather than by the expansion means.

13. A device according to any one of the preceding claims in which the gas valve comprises a valve member which co-operates with a valve seat, and there is a spring urging the valve member towards the valve seat, the arrangement being such that the pressure means exerts no force on the valve member.

14. A device according to any one of the preceding claims in which the expansion means comprises two corrugated disks of resilient metal sealed together at their peripheries.

1 5. A device according to claim 14 in which the corrugated disks are encapsulated in a block of resilient material to improve load distribution over the outside surface of the disks.

16. A flame-failure device substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the phial will quickly cool, its contents will liquefy again, and the valve will close. Claims (Filed 29.4.82)

1. A flame-failure device comprising a hollow, sealed body containing water or other aqueous liquid, the body having a central portion in the form of a tube with a relatively narrow bore, a phial at one end of the tubular central portion and expansion means at the other end of the central portion, the device also including a gas valve biased towards a closed or restricted position and so arranged as to open or open more fully in response to expansion of the expansion means, and pressure means operative in use to resist such expansion of the expansion means to an extent such that when the phial is heated, water or other aqueous liquid in the phial boils and causes such expansion of the expansion means only when the temperature exceeds 2000C.