GB2099131A - Controls for combustible gas - Google Patents

Abstract

A control for combustible gas comprises an electrically-operable gas-valve (1) and a flame-failure device (2) having individual housings (3 and 20) together forming a common casing. The gas-valve is controlled by a solenoid (13) and has a manually operable bypass valve (18, 19). A releasable catch can hold the bypass valve open. The flame-failure device is of conventional form, having a valve biased to its closed position and mercury-filled bellows which expands to open the valve when the mercury in a phial, communicating with the bellows, boils. The flame- failure device incorporates a bypass operative to allow some gas to flow when the valve is in its closed position. The valve operated by the solenoid may be replaced by a valve operated by a bimetal strip. <IMAGE>

Description

SPECIFICATION Controls for combustible gas This invention relates to controls for combustible gas.

The invention has been developed largely in connection with the control of the supply of gas to gas cookers for domestic use, but it must be understood that the invention can be applied to the control of combustible gas to burners in other types of apparatus such as furnaces and waterheaters.

It is often convenient and useful for a cooker to include a control embodying timing means such that the cooker can be brought into operation and/or put out of operation at a predetermined time or after a predetermined interval of time, so that the control can for example turn the cooker on or off at a predetermined time when the user is not present. Such controls are relatively common in electric cookers but are less common in gas cookers, as the controls themselves normally require electricity for their operation.

In addition to such electrically-operated controls it is usually desirable to provide other forms of control for the supply of gas; the provision of some of those controls may indeed be required by law. one well-known kind of control is the flame-failure device. As will become apparent in what follows, the present invention incorporates a flame-failure device of the kind (hereinafter referred to as the kind specified) comprising a gas-valve, which is biased towards its closed position, and a liquid-containing system comprising an expansion member and a probe interconnected by a tube, the arrangement being such that when the probe is at or near room temperature the valve is in a closed position but when the probe is heated, as by a gas flame, at least part of the liquid inthe probevapourises, forcing liquid back along the tube and causing the expansion member to expand, the expansion causing the valve to open. It is usual for the liquid in the system to be mercury. In normal use the probe is disposed adjacent to a gas-burner supplied with gas by way of the gas-valve. Then, as long as gas issuing from the burner is alight, the probe is heated and retains the valve open.

Should the flame fail, however, the probe cools and the valve moves to its closed position. There may be a bypass to the valve through which a predetermined and relatively small flow of gas continues to flow to the burner when the gasvalve is in its closed position. That flow may be sufficient to sustain a flame when the burner is relit, the flame being relatively low but nevertheless being sufficient to heat the probe so as to re-open the gas-valve. the bypass may extend through the valve itself, in which case gas is still able to pass through the valve, at a restricted rate, when the valve is in its closed position.

Other forms of controls may also be included in the gas supply line, such as manually operable on/off valve and a thermostatically controlled valve. It will thus be apparent that the control system for a gas cooker is relatively complex and that it is relatively time-consuming and costly to assemble.

An aim of the present invention is to enable such a system to be simplified.

From one aspect the present invention consists in a control unit for use in controlling combustible gas, comprising a first control element and a second control element, the first control element comprising an electrically operable gas-valve and the second control element comprising a flame-failure device of the kind specified, the elements having a common casing, and the gas-valves thereof being arranged in series between a gas inlet and a gas outlet. In passing from one valve to the other the gas preferably remains inside the casing.

It is to be understood that although it is generally preferred for the unit to be designed and used in such a manner that gas passes through the first control element and then passes through the second control element, the invention includes within its scope units designed and installed for use in the reverse manner.

Use of the control unit makes it unnecessary to provide first and second control elements separate from each other and thus avoids the need to provide a gas pipe joining those two elements.

In a preferred construction the gas-valve of the first control element has a first housing while the gas-valve of the second control element has a second housing, the two housings being secured together to form said casing. Further, the design of one of the elements or each of the elements is such that it could have closure means attached to its housing and could then be used independently of the other control.

Where the first control element has its own housing the arrangement is preferably such that when the gas-vale is open, gas can pass from an inlet in the housing, through the open gas-valve to that part of the interior of the housing opening into the housing of the second control element.

With such an arrangement it is normally necessary to provide a seal between the two housings to prevent the escape of gas between them. The seal may comprise a gasket, and the housings may be secured together in such a manner as to enable them to be repeatediy separated and secured together again.

As to the first control element this may comprise a solenoid-operated gas-valve.

Preferably the gas-valve opens in response to the solenoid being electrically powered and is biased towards a closed position so as to close or tend to close when no electricity is supplied to the solenoid. The gas valve preferably comprises a detachable and replaceable solenoid unit comprising a solenoid with an armature carrying a valve member and spring means biasing the armature and valve member towards the closed position of the gas-valve. The valve member preferably comprises a resilient element of generally conical shape mounted on one end of the armature.

Alternatively the first control element may comprise a gas-valve operated by a bi-metallic element or by bi-metallic elements heated electrically. Preferably the arrangement is such that when no electricity is supplied to the first control element, the gas-valve thereof is biased towards its closed position.

The first control unit may incorporate override means operable to enable gas to pass through the first control unit even when no electricity is supplied to the electrically operable gas-valve of the first control unit. The override means may be operative to move the electrically operable gasvalve of the first control unit to an open position; alternatively the override means may comprise a bypass valve, operative to bypass the electrically operable gas-valve of the first control unit. The bypass valve is preferably biased towards a closed position; releasable catch means may be provided to enable it to be retained in an open position. The override means is preferably adapted to be opened manually.

The provision of override means of the kind outlined in the last preceding paragraph enables the unit to be used in the event of a failure in the electricity supply.

As to the second control element, where this has its own housing the arrangement is preferably such that when the gas-valve thereof is open, gas can pass from the interior of the housing of the first control element, into the housing of the second control element through the open gas-valve and out by way of an outlet port in the housing.

Where the design of the unit is such that one of the control elements or each of the control elements can be used independently of the other control element, the housing of the control element or of each control element may be provided with a connector formation which is initially closed and which remains closed when the housing is to form part of a control unit, but which can be opened, as for example by a drilling or machining process, to provide an outlet or an inlet for gas, as the case may be, when the housing has closure means attached to it in place of the other housing.

From another aspect the present invention consists in a control system for combustible gas comprising a gas inlet leading, by way of a control unit of the kind outlined above, to a gas burner, and timing means operative to control the supply of electricity to the first control element so as to enable the gas-valve of the first element to be operated at a predetermined time or after a predetermined time interval.

An embodiment of the present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a control unit embodying the present invention, Figure 2 is an end view of the control unit shown in Figure 1, as viewed from the left of Figure 1, part of the unit being sectioned along the line 2-2 of Figure 1, and Figure 3 is a diagrammatic view of a control system embodying the present invention and incorporating a control unit of the kind shown in Figures 1 and 2.

The control unit shown in Figures 1 and 2 comprises two control elements: an electrically operable gas-valve constituting the first element 1, and a flame-failure device of the kind specified constituting the second element 2.

The electrically operable gas-valve 1 comprises a metal housing 3, formed as a casting. An inlet formation 4 is formed integrally at one side of the housing. This constitutes the gas inlet. As originally cast the inlet formation 4 comprises a generally tubular part which is directed outwards and an inner end part which is closed. During manufacture, however, the inner end part is driiled through so that the interior of the tubular part then communicates with a central chamber 5 inside the housing. The bore of the tubular part of the inlet formation 4 is tapped so as to enable it to be readily attached to gas piping in the usual manner.

The housing 3 also includes two axially aligned formations 6 and 7, each of which is of generally tubular shape. The axis of the formations 6 and 7 intersects the axis of the inlet formation 4 at right angles. In the control unit illustrated the formation 6 serves no functional purpose, and its inner end is closed. The interior of the formation 7, however, serves as to contain a bypass valve, as described in more detail below, an inner end part of the formation being drilled through so that the interior of the formation communicates with the central chamber 5.

The housing 3 has a flat face 8 parallel with the plane containing the axes of the formations 4, 6 and 7. Opening into that flat face are a main outlet 9 and a bypass outlet 10. The main outlet 9 communicates with the central chamber 5, an annular valve seat 11 being formed where the central chamber meets the main outlet. The bypass outlet 10 communicates with the interior of the formation 7.

A tapped bore in the housing, aligned with the main outlet 9, is engaged by a screw-threaded end portion of an axial extension 12 of a cylindrical solenoid casing 1 3. The casing 1 3 contains a solenoid coil (not shown) connected to an electric lead 14. The extension 12 includes a portion formed with parallel flats on opposite sides thereof for engagement by a spanner or similar tool.

The solenoid has an axially movable armature connected to a rod 1 5 which extends through the extension 1 2 and at its end carries a valve member in the form of a conical seal 16 of resilient material which co-operates with the valve seat 11. A spring (not shown) in the casing biases the armature towards a closed position (as illustrated) in which the seal 1 6 prevents communication between the central chamber 5 and the main outlet 9. When an appropriate electric current is passed through the solenoid coil the armature and rod move to an open position such as to permit communication between the central chamber and the main outlet.

An outer end part of the bypass formation 7 is tapped, and a cap 17 with an external screwthread of complementary shape is screwed into it.

A valve rod 1 8 extends through a central hole in the cap and at its inner end carries a valve member 1 9 which co-operates with a valve seating at the inner end of the formation. A helical compression spring around the rod 1 8 biases the valve member towards a closed position, as illustrated, in which communication is cut off between the central chamber 5 and the interior of the bypass formation 7. The outer end of the rod 1 7 can be coupled to any suitable mechanism for enabling the rod to be pulled, against the action of the spring, to open the valve, this valve constituting a bypass valve. The mechanism is preferably manually operable and preferably incorporates a releasable catch to enable the bypass valve to be retained in an open position for as long as may be desired.

The flame-failure device 2 has a die-cast metal housing 20 of which the interior is holiow. One side of the housing is open and constitutes a gas inlet. An outlet formation 21 is formed on that side of the housing opposite to the open, inlet side. Three of the four remaining sides of the housing 20 are provided with tubular formations generally similar to the blank formation 6 of the housing 3 of the gas-valve 1. Two of these formations, 22 and 23, are also blank, but could be drilled through to afford connections if desired.

The formations 6, 22 and 23 all constitute connector formations. The other formation, 24, is drilled through and provided with a tubular extension 25 which is closed by a screw at its outer end. The extension 25 can be opened to afford access for a test probe which can be used in measuring the gas pressure inside the housing 20.

The housing 20 contains a flame-failure valve of a weli-known kind. This is a flame-failure valve of the kind specified. An annular valve seat is formed around the inner end of the gas outlet formation 21. A valve member co-operates with that seat and is biased by spring means towards its closed positions. The valve member is mounted at one end of an arm pivoted to a fixed mounting at the other end. An expansion member is also mounted within the housing, this comprising a pair of metal discs, each formed with concentric corrugations and secured together at their outer edges. The central part of one disc is connected to a tube 26 which extends outside the housing. That central part of the other disc is movable relative to it and can co-operate with an intermediate part of the arm that carries the valve member. The further end of the tube is connected to a cylindrical metal phial 27.The hollow interiors of the expansion member, tube 26 and phial 27 intercommunicate with one another and are filled with mercury. At ambient temperatures the expansion member is collapsed, and the valve member engages the valve seat and is thus in its closed position. Should the phial 27 be heated in a gas flame, however, mercury in the phial boils, and the expansion member expands, engages the arm and causes the valve to open.

The housings 3 and 20 of the two elements 1 and 2 are so designed that they can be secured together with their open sides together. The two housings together form a casing for the control unit. A sealing gasket 28 is interposed between the housings. The housings are secured together by means of screws 29 which extend through holes in lugs on the housing 3 and enter complementary tapped bores in bosses in the other housing 20.

In an alternative arrangement (not shown) that part of one housing bordering the open face may enter the open face in the other housing, and the housings may be secured together by means of screws extending in holes in the overlapping parts of the housings and with their axes in a plane or planes parallel with the planes of the open faces.

The control unit may be used in a control system incorporated in a gas cooker. Such a system is illustrated diagrammatically in Figure 3.

The system controls the supply of gas from the domestic gas mains 30 to a burner 31 in the oven, the gas passing by way of thermostatically controlled valve 32 and a control unit 33 of the kind described above. The thermostatically controlled valve 32 is of known construction and incorporates a manually operable setting knob 34, which can be rotated between an off position, in which it causes the supply of gas to the burner 31 to be cut off, and a range of on positions in which it permits gas to flow at a rate determined by the temperature of the oven. When the oven temperature exceeds a predetermined value determined by the setting of the knob 34 the thermostatically controlled valve closes; but there is a bypass inside that valve which still permits a relatively small gas flow, which is sufficient to maintain ignition at the burner.

Adjacent to the burner 31 is a spark igniter 35 operated by an electric spark generator 36 of a known kind. When the setting knob 34 of the thermostatically controlled valve 32 is turned from its off position it operates an electric switch 37 which causes the spark generator 36 to start operation (subject to the closure of a time switch described below). The spark igniter 35 then continues to operate until a flame is ignited at the burner, whereupon the flame forms a lowresistance path between the spark igniter and the burner and thus inhibits the further production of sparks.

Gas from the thermostatically operated valve 32 passes next to the electrically operated valve 38 in the control unit 33. The solenoid of that valve is connected to a suitable electricity supply 39 such as the domestic mains supply, by way of the switch 37 and of an electric time switch 40 operated by an electric clock or timer. When the switches 37 and 40 are both closed the valve opens to allow gas to flow to the burner. At the same time the spark generator 36 is brought into operation (subject to closure of the switch 37).

When the switch 40 is open the valve closes, thereby cutting off the supply of gas to the burner 31, and at the same time the spark generator is rendered inoperative.

When the electrically operated valve 38 is open, gas can pass to the flame-failure valve 41 of the unit 33. This is provided with a bypass, which may be inside or outside the housing but is preferably inside the housing alongside the valve opening or extending through the valve member itself. The bypass is of a size such as to permit gas to pass at a rate sufficient to enable a low flame to be maintained at the burner 31. Preferably the rate of flow is such that the flame generates not more than 2000 BTU per hour. The phial 42 of the flame-failure device 41 is situated adjacent to the burner so that when the gas is ignited the flamefailure device will operate to open the flamefailure valve.

In use, when the setting knob 34 is in its off position no gas can pass, and the spark generator 36 is inoperative. When the setting knob 34 is turned to any one of its on positions, while the time switch 40 is open, gas flow is still prevented due to the fact that the electrically operated valve 38 is closed. When the time switch 40 then closes, under the control of the clock, the valve 38 opens and gas can flow through the bypass of the flame-failure device 41 to the burner 31. The spark generator 36 operates to ignite that gas, but the further production of sparks is then inhibited. The valve of the flamefailure device 41 opens, allowing gas to flow freely to the burner 31. When the air in the oven reaches the predetermined temperature corresponding to the position of the setting knob, the thermostat valve 32 closes but gas still flows through the bypass to that valve.The valve 32 then opens and closes periodically so as to maintain the temperature of the oven substantially constant. Finally, when the time switch 40 opens, under the control of the clock, the electrically operated valve 38 closes and the spark generator 36 is switched off Alternatively, if the setting knob 34 is turned to its off position the valve 38 closes, cutting off the gas supply to the burner 31; the spark generator 36 is also switched off.

Should the electricity supply fail, it is still possible to use the control. The bypass valve to the valve 38 is opened manually and retained open by releasable catch means. The gas issuing from the burner is ignited with a match or a selfcontained igniter. The flame-failure device and its bypass act in the manner described above.

It is to be understood that each of the two control elements 1 and 2 is of a design such that it can be used separately from the other control element. Thus the manufacturer can make control elements which can be adapted for use either in control units of the kind described above or as separate, individual control elements. When either of the elements is to be used separately, one of the tubular formations 6,22 or 23 is drilled through and machined to form a gas outlet or gas inlet, as the case may be, while the open side of the housing 3 or 20 is blanked off by means of a closure plate.

It is to be understood that provided the valves, when closed, satisfy any appropriate requirements for sealing that may be specified for gas valves, the control unit or either of the separate control elements may be installed in such a manner that in use gas flows through it in a direction that is the reverse of that described above.

In the control unit illustrated in Figures 1 and 2, the bypass valve can be opened to enable gas to pass through the unit when the solenoid is inoperative, owing, for example, to the failure or cut-off of the electricity supply. If desired, any of a number of alternative arrangements may be employed in place of the bypass valve illustrated.

For example, the bypass valve may be dispensed with altogether and means may be provided to enable the solenoid-valve to be opened in such circumstances. Such means may enable the valve to be opened by the user or operator. For example a rotatable operating shaft may replace the valve rod 1 8 and extend into the central chamber 5. Its inner end carries an eccentric pin which cooperates with an abutment, such as a circlip, projecting from the rod 1 5 of the solenoid, the arrangement being such that when the shaft is rotated the pin engages the projection and moves the rod axially to its open position, against the force exerted by the spring in the solenoid.

Alternatively the valve may be opened automatically. To effect this there may be provided a solenoid-operated valve-opener largely similar to the solenoid-operated valve described above but having a wedge in place of the seal 1 6, and operating in the reverse manner, that is in a manner such that when no current passes through the solenoid the rod projects to its maximum extent but when a current passes the rod and wedge are moved to a retracted position, against the action of a relatively strong in the solenoid. The axis of the valve-opener is at right angles to that of the gas-valve. In use, the solenoid-operated valve-opener is supplied with electric current either at all times or at least throughout those periods when the themostatically controlled valve is in a position other than its off position. Thus in normal operation, whenever gas is or may be supplied to the control unit the wedge is retracted and the solenoid-operated valve is free to operate in the manner described above. Should the electricity supply fail, however, the solenoid-operated valve opener would move under the influence of its spring to a position in which its rod projected to its maximum extent. In the course of this movement the wedge would engage a projection on the rod 15 of the solenoid-operated valve and cause that valve to move to its open position or would prevent closure of the valve. Likewise, whenever the thermostatically controlled valve is in its off position the arrangement may be such that the solenoid-operated valve-opener operates to move the solenoid-operated valve to its open position.

Where there are two devices (like those described in the last preceding paragraph) such that on failure of the electricity supply both operate automatically to enable the gas supply to be maintained, means may be provided for ensuring that the devices operate in an order such that there is no break in the gas supply. For example, a capacitor may be provided in the circuit of a solenoid-operated valve to cause the solenoid to continue to retain the valve open for a short period following the cut-off of the electricity supply, while the wedge or an equivalent device comes into operation to hold the valve open mechanically.

Where (as in the system illustrated) a bypass is provided for the flame-failure device, this may permit gas to flow at a rate determined principally by the thermostatically controlled valve. In a modification, however, the bypass in the flamefailure device is such as to permit gas to flow at a rate such that the flame generates no more than a predetermined maximum, for example 2000 BTU per hour. Alternatively the arrangement may be such that the rate of flow is such as to maintain the oven at a predetermined temperature such as 850C. A control unit containing a flame-failure device of either kind can be used in a system enabling slow cooking to be effected when the flame-failure valve is closed.

In an alternative arrangement the first element incorporates a bypass valve, but unlike the bypass valve illustrated, which is manually operated, the bypass valve is electrically operated. The bypass valve is automatically opened when the electricity supply to it is cut off. This valve may be operated by an electrically heated bi-metal element but is preferably operated by a solenoid in such a manner that the passage of electricity holds the bypass valve closed, but spring means causes the valve to open when the supply of electricity is cut off.

In another modification of the control unit, the gas-valve is operated by an electrically heated bimetal strip, rather than by a solenoid. The gasvalve comprises a metal housing formed as a casting. The overall shape of the housing is generally rectangular, and the housing is open on one side. An inlet formation is formed integrally with one of the other sides of the housing. As originally cast the inlet formation comprises a generally tubular part extending outwards from the side with which it is formed, the inner end of the part being closed. During manufacture, however, the inner end is drilled through so that the interior of the tubular part then communicates with the interior of the housing. The tubular part is also tapped to enable it to be readily attached to gas piping in the usual manner.At least one other side of the housing is formed with a connector formation, similar in overall shape to the inlet formation in that it comprises a generally tubular part extending outwards and closed at its inner end. The connector formation (or each of the connector formations, where there are more than one) is not drilled through and machined when the housing is to be incorporated in a control unit embodying the invention.

The gas inlet leads to a valve seating. A valve member is mounted to co-operate with the seating so as to be movable between open and closed positions. The valve member is preferably mounted at one end of an arm pivotally supported at its other end. Spring means biases the valve member towards its closed position. A bi-metal strip is cantilevered from a fixed mounting at one end. An electrical heating element is wound round the strip. When the strip is heated by the element it bends, and the movement of its free end engages the arm or otherwise causes the valve member to move to its open position, overcoming the force exerted by the spring means. When the strip is at ambient temperature it permits the spring means to close the valve. A manually operable button projects from the housing. When depressed it overcomes the force exerted by the spring means and causes the valve to open.

Releasable catch means may be provided to enable the button to be held reieasably in its depressed condition, thus enabling the valve to remain open until the catch means is manipulated to release the button. The arrangement is such that when the valve is open, gas entering the element through the gas inlet can pass to that part of the interior of the housing having the open side. In addition, the outlet formation or each of the outlet formations is so disposed that if its inner end were drilled through it would communicate with the same part of the interior of the housing.

The housing of the gas-valve is secured to the housing of the flame-failure device, to form a casing for the control unit. The housings may be secured together in any of the ways described above.

Claims (21)

Claims

1. A control unit for use in controlling combustible gas, comprising a first control element and a second control element, the first control element comprising an electrically operable gas-valve and the second control element comprising a flame-failure device of the kind specified, the elements having a common casing, and the gas-valves thereof being arranged in series between the gas inlet and a gas outlet.

2. A control unit according to claim 1 in which the arrangement is such that in passing from one valve to the other the gas remains within the casing.

3. A control unit according to either of claims 1 and 2 in which the gas-valve of the first control element has a first housing while the gas-valve of the second control element has a second housing, the two housings being secured together to form said casing.

4. A control unit according to claim 3 in which the arrangement is such that when the gas-valve is open, gas can pass from an inlet in the housing of the first control element, through the open gasvalve to that part of the interior of the housing opening into the housing of the second element.

5. A control unit according to claim 4 in which there is a seal in the form of a gasket between the two housings to prevent the escape of gas between them.

6. A control unit according to any of claims 3 to 5 in which the housings are secured together in such a manner as to enable them to be repeatedly separated and secured together again.

7. A control unit according to any one of the preceding claims in which the first control element comprises a solenoid-operated gasvalve.

8. A control unit according to claim 7 in which the gas-valve opens in response to the solenoid being electrically powered and is biased towards a closed position so as to close or tend to close when no electricity is supplied to the solenoid.

9. A control unit according to claim 8 in which the solenoid-operated gas-valve comprises a detachable and replaceable solenoid unit comprising a solenoid with an armature carrying a valve member and spring means biasing the armature and valve-member towards the closed position of the gas-valve.

10. A control unit according to claim 9 in which the valve member comprises a resilient element of generally conical shape mounted on one end of the armature.

11. A control unit according to any one of claims 1 to 6 in which the first control element comprises a gas-valve operated by a bimetallic element or by bi-metallic elements heated electrically.

12. A control unit according to claim 11 in which the arrangement is such that when no electricity is supplied to the first control element, the gas-valve thereof is biased towards its closed position.

13. A control unit according to any of the preceding claims in which the first control unit incorporates override means operable to enable gas to pass through the first control unit even when no electricity is supplied to the electrically operable gas-valve of the first control unit.

14. A control unit according to claim 1 3 in which the override means is operative to move the electrically operable gas-valve of the first control unit to an open position.

1 5. A control unit according to claim 13 in which the override means comprises a bypass valve, operative to bypass the electrically operable gas-vaive of the first control unit.

16. A control unit according to claim 1 5 in which the bypass valve is biased towards a closed position.

1 7. A control unit according to claim 1 6 in which releasable catch means is provided to enable the bypass to be retained in an open position.

1 8. A control unit according to any one of claims 14 to 17 in which the override means is adapted to be opened manually.

1 9. A control unit substantially as hereinbefore described with reference to the accompanying drawings.

20. A control system for combustible gas comprising a gas inlet leading, by way of a control unit according to any one of the preceding claims, to a gas burner, and timing means operative to control the supply of electricity to the first control element so as to enable the gas-valve of the first element to be operated at a prede,ermined time or after a predetermined time interval.

21. A control system according to claim 20 which also includes a thermostat operative to vary the flow of gas to the burner in response to changes in temperature of air heated by the burner.