GB2060832A

GB2060832A - Fluid-filled thermostats

Info

Publication number: GB2060832A
Application number: GB8031999A
Authority: GB
Original assignee: United Gas Industries Ltd
Current assignee: United Gas Industries Ltd
Priority date: 1979-10-09
Filing date: 1980-10-03
Publication date: 1981-05-07
Also published as: GB2060832B

Abstract

A thermostatically-controlled flame-failure valve for a gas-fired oven comprises a valve 13 operated by a thermostat. The thermostat has a phial 16, capillary 17 and an expansible chamber 18. The chamber 18 is located within the gas path but separated from flowing gas by a flexible barrier 21 of rubber or plastics material. This fits closely around the chamber and serves to contain any leakage from the chamber. <IMAGE>

Description

SPECIFICATION Fluid-filled thermostats This invention relates to fluid-filled thermostats of the kind where thermal expansion of the fluid operates an expansible chamber. The fluid used in such thermostats may be harmful or unpleasant, for instance mercury or eutectic mixtures of sodium and potassium.

The invention provides a fluid-filled thermostat having a sealed system comprising a phial, a capillary and an expansible chamber, said system containing said fluid, and a flexible barrier forming a seal around said expansible chamber whereby leakage from said chamber is contained.

In a preferred arrangement the expansible chamber operates a gas valve and is located in the same housing as the gas valve, but is separated from the gas stream by said barrier.

A specific embodiment of the invention is shown in the accompanying drawing, which is a side section through a thermostatically-controlled flame-failure valve, e.g., for a gas-fired oven.

The gas supply line 11 is connected with an outlet 1 2 through a valve 1 3 comprising a valve plate 14, O-ring 1 5 and guide plate 23.

Such a valve is shown in our earlier Patent No. 1,520,804 (PC346). A fluid-filled thermostat sealed system comprises a phial 1 6 which is located in a location the temperature of which is to determine the valve opening, e.g. the location of a pilot flame. The phial is connected by a capillary tube 1 7 to the interior of an expansible chamber 1 8 formed from a pair of flexible diaphragms. Expansion of the chamber by means of flexing of the diaphragms moves a push rod 20 in the sense to open the valve against spring resistance when a flame is present at the phial location and to allow the valve to close when no flame is present. The phial, capillary tube and expansible chamber are sealed and contain mercury.

This is a poisonous substance and it is essential that it should be prevented from coming into contact with food in the oven. The expansible chamber is at risk of fracturing or pinholing to allow leakage of mercury. To prevent such leakage reaching the gas stream and thereby the oven, a flexible barrier 21 is mounted surrounding the expansible chamber and separating it from the gas stream. The barrier is a cup-shaped diaphragm of a flexible material such as rubber or plastics material, with an opening surrounding a collar of the push rod 20. The open mouth of the cup is an interference fit in a recess 22 in the housing. The opening in the diaphragm surrounding the push rod is also a tight fit. The barrier is therefore sealed, but being flexible presents little resistance to the controlled movements of the push rod 20.The movements of the push rod are followed by the surrounding opening of the diaphragm, the push rod not sliding in the opening. There is also little pressure difference across the barrier to oppose its movements. In alternative embodiments the barrier diaphragm 21 may be secured to the housing by an adhesive or by spring clips.

In effect, this embodiment forms a sealed chamber in which any leaked mercury is trapped.

According to another embodiment (not shown) the barrier diaphragm is formed by coating the expansible chamber in a flexible material such as rubber or a plastics material.

This may be done by dipping the completed chamber in a solution such as that sold under the trade name "SILICOSET" and allowing it to dry. Should the underlying expansible chamber then leak, the mercury tends to form an impervious bubble or blister in the flexible coating, which again effectively forms a second sealed chamber around the expansible chamber.

While the sealed systems discussed above have referred to mercury fluid, the invention extends to sealed systems having other fluids, e.g. eutectic mixtures of sodium and potassium. The expansible chamber shown is of the kind comprising a pair of flexible diaphragms, but could equally be a bellows.

1. A fluid-filled thermostat having a sealed system comprising a phial, a capillary and an expansible chamber, said system containing said fluid, and a flexible barrier forming a seal around said expansible chamber whereby leakage from said chamber is contained.

2. A thermostat as claimed in claim 1, wherein said flexible barrier is closely adjacent one side of said expansible chamber.

3. A thermostat as claimed in claim 2, wherein said flexible barrier is a cup-shaped diaphragm of rubber or plastics material.

4. A thermostat as claimed in claim 2, wherein said flexible barrier comprises a coating of rubber or plastics material, substantially covering the expansible chamber.

5. A thermostat substantially as described hereinbefore with reference to the accompanying drawing.

6. A flame-failure gas valve having a thermostat, as claimed in any of claims 1 to 5, the expansible chamber being located within a gas path of the gas valve but separated from the gas by said flexible barrier.

7. A gas valve as claimed in claim 6, wherein said flexible barrier is secured to a housing of the valve to surround the expansible chamber.

8. A gas valve as claimed in claim 7, wherein said expansible chamber operates a push rod which contacts a valve plate of said valve, said push rod passing through an opening in the flexible barrier which fits tightly

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Fluid-filled thermostats This invention relates to fluid-filled thermostats of the kind where thermal expansion of the fluid operates an expansible chamber. The fluid used in such thermostats may be harmful or unpleasant, for instance mercury or eutectic mixtures of sodium and potassium. The invention provides a fluid-filled thermostat having a sealed system comprising a phial, a capillary and an expansible chamber, said system containing said fluid, and a flexible barrier forming a seal around said expansible chamber whereby leakage from said chamber is contained. In a preferred arrangement the expansible chamber operates a gas valve and is located in the same housing as the gas valve, but is separated from the gas stream by said barrier. A specific embodiment of the invention is shown in the accompanying drawing, which is a side section through a thermostatically-controlled flame-failure valve, e.g., for a gas-fired oven. The gas supply line 11 is connected with an outlet 1 2 through a valve 1 3 comprising a valve plate 14, O-ring 1 5 and guide plate 23. Such a valve is shown in our earlier Patent No. 1,520,804 (PC346). A fluid-filled thermostat sealed system comprises a phial 1 6 which is located in a location the temperature of which is to determine the valve opening, e.g. the location of a pilot flame. The phial is connected by a capillary tube 1 7 to the interior of an expansible chamber 1 8 formed from a pair of flexible diaphragms. Expansion of the chamber by means of flexing of the diaphragms moves a push rod 20 in the sense to open the valve against spring resistance when a flame is present at the phial location and to allow the valve to close when no flame is present. The phial, capillary tube and expansible chamber are sealed and contain mercury. This is a poisonous substance and it is essential that it should be prevented from coming into contact with food in the oven. The expansible chamber is at risk of fracturing or pinholing to allow leakage of mercury. To prevent such leakage reaching the gas stream and thereby the oven, a flexible barrier 21 is mounted surrounding the expansible chamber and separating it from the gas stream. The barrier is a cup-shaped diaphragm of a flexible material such as rubber or plastics material, with an opening surrounding a collar of the push rod 20. The open mouth of the cup is an interference fit in a recess 22 in the housing. The opening in the diaphragm surrounding the push rod is also a tight fit. The barrier is therefore sealed, but being flexible presents little resistance to the controlled movements of the push rod 20.The movements of the push rod are followed by the surrounding opening of the diaphragm, the push rod not sliding in the opening. There is also little pressure difference across the barrier to oppose its movements. In alternative embodiments the barrier diaphragm 21 may be secured to the housing by an adhesive or by spring clips. In effect, this embodiment forms a sealed chamber in which any leaked mercury is trapped. According to another embodiment (not shown) the barrier diaphragm is formed by coating the expansible chamber in a flexible material such as rubber or a plastics material. This may be done by dipping the completed chamber in a solution such as that sold under the trade name "SILICOSET" and allowing it to dry. Should the underlying expansible chamber then leak, the mercury tends to form an impervious bubble or blister in the flexible coating, which again effectively forms a second sealed chamber around the expansible chamber. While the sealed systems discussed above have referred to mercury fluid, the invention extends to sealed systems having other fluids, e.g. eutectic mixtures of sodium and potassium. The expansible chamber shown is of the kind comprising a pair of flexible diaphragms, but could equally be a bellows. CLAIMS

8. A gas valve as claimed in claim 7, wherein said expansible chamber operates a push rod which contacts a valve plate of said valve, said push rod passing through an opening in the flexible barrier which fits tightly around the push rod.

9. A flame-failure gas valve as claimed in any of claims 6 to 8, wherein said sealed system contains mercury.

1 0. A flame4ailure gas valve substantially as described hereinbefore with reference to the accompanying drawing.