GB2204939A - Gas valves - Google Patents

Abstract

A gas valve has an operating member made of or coupled to an SME brass component which expands when exposed to a heat source and thus controls a valve member 34. In one embodiment the valve includes a heat conducting member 16 which extends in use between a flame and a coil 10 made of shape memory effective brass which expands rapidly when heated through its transition point so as to displace stem 20 and hold valve 34 in an open position. If the flame fails, the heat conducting member cools, the S.M.E. brass contracts and spring 36 closes the gas valve. In another embodiment an electric resistance heater (48 Fig.2) is arranged to raise the temperature of an S.M.E. brass coil when direct current is applied. <IMAGE>

Description

GAS VALVES This invention relates to gas valves particularly of the on/off kind without any proportional flow control as required for example for flame failure devices and like.

The object of the invention is to provide a new construction of such valves.

In accordance with the invention a gas valve has an operating member made of or coupled to an S.M.E. brass component arranged to expand for valve displacement when exposed to a heat source, and thus open and close a passage for gas flow.

S.M.E. brass or shape memory effective brass is marketed by Delta Memory Metals Limited and can be tailored to give a large change in shape when the temperature of the component is raised (or lowered) through a relatively narrow transition zone, and the level or actual value of the mean temperature of the zone can be altered within certain limits.

In a first possible arrangement according to the invention the heat source is a burner flame, and the heat conducting member may be located in or near the flame to conduct heat to the S.M.E. brass which then holds the gas valve open. This is a flame failure device in that if the flame goes out the S.M.E. brass component will close the gas valve or allow it to be closed.

According to a feature of the invention, a valve according to this first arrangement can be made particularly sensitive by arranging for the heat conducting member to be carried away from the flame zone,- as the S.M.E. brass exchanges shape. Thus, if the shape change takes the member too far from the flame, the S.M.E. brass will cool and the member will be returned towards the flame: by these means the device can be made particularly sensitive and near self adjusting.

In a second possible arrangement according to the invention the heat source is an electric resistance heater which raises the temperature of the S.M.E. brass to like effect whilst the current is applied.

Two embodiments of the invention are now more particularly described with reference to the accompanying drawings: Figure 1 is a sectional elevation of a first embodiment; and Figure 2 is a similar view of a second embodiment.

Turning to the first embodiment in Figure 1, the S.M.E. brass component is in the form of a helical coil 10 trapped between a fixed end abutment 12 formed by a casing which is part of the valve body structure, and a second and moveable abutment 14 which is a flange fixed to one end of a thermal-link rod 16 which projects out of the valve and into the flame 18 position. A valve actuator 20 coaxial with the thermal-link rod 16 and has a like head 22, with possibly a thermally insulating pad 24 located between the parts 14 and 22. An optional spring 26 is trapped between the head 22 and a fixed valve part such as sealing gland 28, for the purpose of returning the parts to the illustrated position.

The valve body has an inlet 30 and an outlet 32 with a valve seat between them. The valve seat is closed by a valve head 34 carried on a stem 36 which may be urged to the closed position by spring 38. The stem 36 may project to the exterior of the valve to provide a manual override enabling the valve to be opened when required.

When the flame is present as at 18, the rod 16 heats up and transmits heat to the S.M.E. member and when the latter reaches its transition temperature the coil expands and hence displaces the coaxial rods 16 and 20 into contact with the valve member 34 so as to lift the same off its seat. At the same time, the rod 16 moves away from the flame, and by suitably positioning the rod relative to the flame position, possibly by means of an adjuster mechanism, the device may be made particularly sensitive. This may prevent overtravel of the parts 16 and 20 because of continued displacement of the S.M.E.

member on rising temperature. It may also mean that the device assumes a balanced normal working position, and if the flame fails, the S.M.E. member will rapidly cool and close the valve.

In the arrangement in Figure 2, the S.M.E. member 40 is trapped between a fixed (although possibly adjustable) end abutment 42 and flange 44 carried on rod 46. An electric resistance heater coil assembler 48 surrounds the S.M.E. member with appropriate insulation 50 externally. The operation of the arrangement in Figure 2 is generally similar to that in Figure 1.

It may be desirable to include an override switch mechanism, for example operated by the end 52 so as to disconnect the electric heater when the said end has moved a certain extent, again for the purposes of preventing overtravel. The spring 54 is particularly useful in this construction in ensuring return of the rod 46 for switch operation when the S.M.E. coil contracts, or possibly similar effects may be obtained by anchoring the ends of the S.M.E. coil to the respective flanges 42,44.

CLAIMS 1. gas valve having an operating member made of or coupled to an S.M.E. brass component arranged to expand for valve displacement when exposed to a heat source and thus open and close a passage for gas flow.

2. A gas valve as claimed in Claim 1 comprising a heat conducting member arranged to extend (in use) between a flame and the S.M.E. brass.

3. A gas valve as claimed in Claim 2 wherein the heat conducting member is arranged to be displaced by the S.M.E. brass when it expands, and in a direction which removes the heat conducting member from the flame.

4. A gas valve as claimed in Claim 1 wherein an electric resistance heater is arranged to raise the temperature of the S.M.E. brass when direct current is applied.

5. A gas valve substantially as described with reference to Figure 1 of the accompanying drawings.

Claims (5)

1. AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS

   CLAIMS 1. A gas valve arranged as a flame failure device comprising a flow path for gas supply to a burner and means for controlling said flow, said means being displaceable by an SME brass component operatively associated with a heat conducting rod which projects out of the valve and into the flame (when present) from the burner so that heat from the flame is conducted to the SME component to cause its expansion to displace said means to the open position.
2. 2. A gas valve as claimed in Claim 1 wherein the SME component is a helical coil and the rod extends through the coil.
3. 3. A gas valve as claimed in Claim 2 wherein the rod provides an end abutment for the coil and the arrangement is such that expansion of the SME displaces the rod axially in a direction which removes the rod from the flame.
4. 4. A gas valve as claimed in Claim 3 wherein the rod is urged towards the flame by a spring bearing against said abutment
5. 5. A gas valve as claimed in any of Claims 1 to 4 wherein the said means is displaceable to a closed position by a spring.