GB2526045A

GB2526045A - Valve and system for controlling a gas burner

Info

Publication number: GB2526045A
Application number: GB1402099.4A
Authority: GB
Inventors: Richard Ian Bucknall; Richard Kevin Woodward
Original assignee: Haven Ltd
Current assignee: Haven Ltd
Priority date: 2014-02-07
Filing date: 2014-02-07
Publication date: 2015-11-18
Also published as: EP3102885A1; US20160348908A1; WO2015118351A1; GB201402099D0

Abstract

A valve 104 for a gas burner gas supply comprises a valve body 202 having a gas inlet 266, a main gas outlet 278 and a bore 212. The bore 212 has an interior surface 298 a part of which defines a gas flow cavity, the gas inlet 266 and the main gas outlet 268 being in communication with the gas flow cavity. The gas valve 104 further comprises a valve spindle 206 arranged to move into and out of the gas flow cavity, an exterior portion of the valve spindle forming a flow control surface 262 and defining a gap having a volume between the flow control surface 262 and the interior surface 298 of the gas flow cavity. Relative movement of the flow control surface 262 and the gas flow cavity varies the volume of the gap and regulates a flow of gas from the gas inlet 266 to the main gas outlet 268. The spindle flow control surface is preferably frusto-conical and moves axially along the longitudinal axis of the bore. The movement of the spindle is due to a liner motor 204.

Description

VALVE AND SYSTEM FOR CONTROLLAINGA GAS BURNER

The present invention relates to a valve and a system for controlling a gas burner.

Gas control valves are used in domestic applications to control the flow rate of gas to an appliance such as a domestic gas fire so as to provide a variable size gas flame.

These valves typically incorporate means for flame ignition and a thermo-electric flame failure device for cutting off the gas supply when no flame is present.

Gas control valves typically regulate the flow of gas to the gas burner using a motor to open and close a valve seat formed in a delivery duct. The present invention provides an improved valve for controlling a gas burner.

According to a first aspect of the invention, there is provided a gas valve for controlling flow of gas to a gas burner, the valve comprising: a valve body having a gas inlet, a main gas outlet and a bore, the bore having an interior surface a part of which defines a gas flow cavity, the gas inlet and the main gas outlet being in communication with the gas flow cavity; and a valve spindle arranged to move into and out of the gas flow cavity, an exterior portion of the valve spindle forming a flow control surface and defining a gap having a volume between the flow control surface and the interior surface of the gas flow cavity, wherein relative movement of the flow control surface and the gas flow cavity varies the volume of the gap and is adapted to regulate a flow of gas from the gas inlet to the main gas outlet.

At least one of the flow control surface and the interior surface of the gas flow cavity may be tapered. The at least one of the flow control surface and the interior surface of the gas flow cavity may be frusto-conical. In particular, the flow control surface may frusto-conical and the interior surface of the gas flow cavity may have a uniform circular diameter.

The frusto-conical surface may be inclined to an axis of the valve spindle at an angle of between 2.5° and 100.

The bore may have a longitudinal axis and the relative movement of the flow control surface and the gas flow cavity may be along the axis.

The gas valve may further comprise a linear motor for propelling the valve spindle along the axis. The linear motor and the valve spindle may each be provided with cooperating threaded portions for attaching the motor to the valve spindle. The linear motor may mounted at a first end of the longitudinal bore.

The valve spindle may be provided with a first seal to prevent flow of gas to the motor.

The valve spindle may further comprise a second seal adapted to cooperate with the interior surface of the gas flow cavity to prevent flow of gas from the gas inlet to the gas outlet. ts

The valve body may further comprise a pilot gas outlet in communication with the bore.

The valve body may further comprise a low rate cross drilling bore between the gas flow cavity and the main gas outlet, for providing gas flow to provide a low rate flame.

The gas valve may further comprise means for adjusting the flow rate through the low rate cross drilling bore.

The means for adjusting the flow rate through the low rate cross drilling bore may be a low rate adjuster screw which projects into the low rate cross drilling bore.

The gas valve may further comprise a flame safety device for sealing the gas flow cavity to prevent flow of gas from the gas inlet to the main gas outlet.

The flame safety device may be mounted at a second opposed end of the longitudinal bore. n j

According a second aspect of the invention there is provided a gas fire system, comprising: a gas valve as described above; a spark generator for igniting a gas flowing out of the gas valve; a microprocessor-based controller for controlling the operation of the valve spindle and the spark generator; and a user interface for providing instructions to the controHer, The user interface may be one of a wired and wireless user interface.

The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a schematic block diagram of a system for controlling a gas burner forming an embodiment of the invention; I5 Figure 2 is an exploded view of a gas valve forming an embodiment of the invention; Figure 3 is a cut-away perspective view of the gas valve of Figure 2; Figure 4a is a section view of a valve body fomiing part of the gas valve of Figure 2; Figure 4b is a cut-away perspective view of the valve body forming part of the gas valve of Figure 2; FigureS is a section view of a valve spindle forming part of the gas valve of Figure 2; Figures ôa to 6i are section views of the gas valve of Figure 2 with the valve spindle at a plurality of position to effect variable gas flow through the gas valve; and Figure 7 is a schematic representation of a remote user interface of the system of Figure 1.

Figure 1 is a schematic block diagram of a system 100 for controlling a gas burner 102 forming an embodiment of the invention. The system comprises a gas valve 104 through which the flow rate of gas is controlled. The gas valve 104 is controlled by a microprocessor-based controller/electronic control board (ECB) 106. The controller 106 also controls the operation of a spark generator 108, for generating a spark in the path 122 of the gas in order to ignite the gas as it flows through the valve 104. A local user interface t tO is disposed in close proximity to the valve 104 and is connected to the controller 106 via a wired connection. In addition, the system includes a remote user interface 112. The controller 104 is provided with a wireless receiver 114 and the remote user interface 112 is provided with a wireless transmitter 116 for providing a wireless link 118 between the remote user interface 112 and the controller 104. The system 100 further includes a power supply U0 which is connected to the controller The gas burner 102 is shown in Figure 1 within a dashed line since the gas burner does not form a part of the system 100 for controlling a gas burner of the present invention.

Figure 2 is an exploded view of the gas valve 104 forming an embodiment of the invention and Figure 3 is a cut-away view of the assembled gas valve 104. The gas valve 104 comprises a valve body 202, a linear motor 204, a valve spindle 206, an electromagnet/flame safety device 208 and an externally threaded magnet nut 210.

The valve body 202 is shown in greater detail in Figures 4a and 4b. The valve body 202 is forged in brass and has a longitudinal bore 212 extending from a first end 214 of the valve body 202 to a second end 216 thereof along a longitudinal axis of the valve body 202. The first end 214 of the valve body 202 is provided with a flange 218 having threaded fixing holes 220. The motor 204 is provided with a flange 222 having fixing holes 224. The fixing holes 224 of the motor flange 222 correspond in position to the threaded fixing holes 220 of the valve body 202 to provide for attaching the motor 204 to the valve body 202 by means of screws 226, Materials other than brass and methods other than forging may be used to form the valve body 202.

With reference to Figure 2, the flange 222 of the motor 204 divides the motor 204 into a front part 228 and a rear part 230. When the motor 204 is attached to the valve body 202 by means of the fixing screws 226 the front part 228 of the motor 204 is disposed within the longitudinal bore 212 of the valve body 202.

S

The front part 228 of the motor 204 comprises portions of reducing diameter, namely a shoulder 232, a neck 234, a motor spindle 236 and a threaded end portion 238, As stated above, the motor 204 is a linear motor such that the motor spindle 236 and threaded end portion 238 reciprocate relative to the shoulder 232 and neck 234 with a stroke of around 14mm between the frilly extended and fully retracted positions.

When the motor 204 is fully contracted, as is described below with reference to Figure 6i, the motor spindle 236 is withdrawn into the neck 234, The valve spindle 206 is shown in greater detail in Figure 5. The valve spindle 206 has a circular cross section of varying diameter along its axial length, giving the valve spindle full rotational symmetry. The valve spindle 206 has a bore 240 for receiving a portion of the front part 228 of the motor 204. The bore 240 has a mouth 242 and a root 244, the mouth 242 having a diameter which is greater than the diameter of the root 244. The root 244 is threaded for connection to the threaded end portion 238 of the front part 228 of the motor 204, The mouth 242 of the bore 240 receives the shoulder 232 of the front part 228 of the motor 204 when the front part 228 of the motor 204 is fully contracted, The valve spindle 206 has two circumferential grooves in its outer surface. A main seal circumferential groove 246 is disposed towards the open end 248 of the valve spindle 206. This circumferential groove 246 receives a main seal 250, shown in Figures 2 and 3. A cross port seal circumferential groove 252 is disposed towards the opposed end 254 of the valve spindle 206. This second circumferential groove 252 receives a cross port seal 256, as shown in Figures 2 and 3, Returning to Figure 5, the portion 258 of the valve spindle 206 beyond the cross port seal circumferential groove 252 is comprised of two sub-portions. The sub-portion 260 proximal to the cross port seal circumferential groove 252 has a tapering diameter such that it is frusto-conical and forms a flow control surface 262. The sub-portion 264 distal to the cross port seal circumferential groove 252, i.e., the portion of the valve spindle 206 distal to the bore 240 thereof, has a diameter which is smaller than the diameter of the proximal sub-portion 260. The end 254 of this sub-portion 264 serves as a flame safety device (FSD) actuation face, as is described below.

The dimensions arid shape of the frusto-conical flow control surface 262 depend on the type of gas used in the gas valve 04. For example, where the gas valve 104 is to be used with natural gas the angle e at which the flow control surface 262 is inclined relative to an axis of the valve spindle 206 is 5°. Where the gas valve 104 is to be used with liquefied petroleum gas (LPG) the angle 0 is set to 2.50. As is described below, the shape of the flow control surface 262 is set so as to regulate the gap between the flow control surface 262 and an inner circumferential surface 298 of the longitudinal bore 202 in a portion C of the valve body 202. By moving the flow control surface 262 in and out of this portion C of the longitudinal bore 212 the volume of the gap is varied to control the flow rate of gas through this gap.

It will be understood by a person skilled in the art that the inclination angle 0 can be set at angles other than 2,5° arid 50 as described above, since the flow rate of gas between the flow control surface 262 and the inner wall 298 of the longitudinal bore 212 of the section C can be controlled by adjusting the length and shape of the flow control surface 262 arid the inner surface 298 of the longitudinal bore 212. The tapered circular exterior of the flow rate surface 262 arid the corresponding circular bore inner surface 298 provide the advantage that the orientation of the valve spindle 206 relative to the valve body 202 does not affect the performance of the flow control surface 262. This is particular useful since the valve spindle 206 is screwed to the motor spindle end portion 238 of the linear motor 204, hence the final rotational orientation of the valve spindle 204 is immaterial to its performance.

Whereas the flow control surface 262 of the valve spindle 206 described above has a circular exterior of varying diameter along its longitudinal axis, having ifill rotational symmetry around its axis, in other embodiments the valve spindle may have a non-round exterior shape. Rather, the exterior surface of the valve spindle can be shaped to cooperate with the interior surface of the longitudinal bore so as to vary the volume of the gap between the flow control surface and the bore interior surface in a suitable manner to vary gas flow through this volume as the flow control surface reciprocates within the cavity defined by the interior surface of the longitudinal bore. Hence, in other embodiments the flow control surface and the inner bore surface may be shaped other than round, for example oval, triangular, rectangular, pentagonal, hexagonal or other regular or irregular polygonal shape, as long as the reciprocating movement of the flow control surface into the longitudinal bore varies the volume of the gap between these portions and consequently the flow rate of gas over these portions.

With reference to Figures 4a and 4b, the valve body 202 has a gas inlet 266, a main gas outlet 268 and a pilot gas outlet 270. Each of these passages/apertures 266, 268, 270 is in direct communication with the longitudinal bore 212 of the valve body 202.

The longitudinal bore 212 is divided into four sections as shown in Figure 4a, each section have a generally circular cross-section. Starting from the flanged end 214 of the valve body 202, the first section A has the largest diameter and is adapted to receive the shoulder 232 of the front part 228 of the motor 204.

The second section B has a reduced diameter of around 15mm and is dimensioned to accommodate the main seal 250 of the valve spindle 206, which is arranged to reciprocate within the second section B. As can be seen in Figure 4b, the second section B is in communication with the main gas outlet 268 and acts as a main flow bore.

The third section C has a further reduced diameter of around 7mm and is in communication with a low rate cross-drilling bore 269 and the pilot gas outlet 270.

The low rate cross-drilling bore 269 is in communication with a low rate adjuster screw receiving bore 286 and the main gas outlet 268. The low rate adjuster screw receiving bore 286 is threaded, This third section C acts as a flow control bore, A front portion 272 of the valve spindle, which includes the cross port seal 256, is arranged to reciprocate within the third section C so as to control a flow of gas to the main gas outlet 268, the low rate cross-drilling bore 269 and the pilot gas outlet 270.

The fourth section D, which runs from and has a larger diameter than the third section C to the end 216 of the valve body 202 is dimensioned to receive the electromagnet 208 and the magnet nut 210. The fourth section D is in communication with the gas inlet 266 and receives the electromagnet 208 and the magnet nut 210. The distal portion 271 of the fourth section D is internally threaded to cooperate with the external thread of the magnet nut 210, This fourth section D acts as a flame safety device bore.

The electromagnet 208 serves as a flame safety device (FSD). The FSD comprises a body 274 and a piston 276. The piston 276 comprises a reciprocating shaft 278. A return spring 280 is disposed around the shaft 278 and a rubber seal 282 is disposed at a distal end of the shaft 278. When current is supplied to the FSD 208 to energise an electromagnet (not shown) within the body 274, the piston 276 is latched in position.

The current is typically provided to the FSD from a thermocouple, as is described below, When the piston 276 is pushed into the body 274 against the force of the spring 280 the application of current to the electromagnet holds the piston 276 stationary against the biasing force of the spring 280. In this contracted position the seal 282 is spaced from an end 284 of the longitudinal bore 212 in the third section C of the valve body 202, to allow unrestricted flow of gas from the fourth section D to the third section C (the flow control bore) of the longitudinal bore 212. When the flow of current is removed from the FSD 208 the spring 280 urges the FSD piston 276 and seal 282 away from the piston body 274 so as to abut the end 284 of the longitudinal bore 212 in the third section C of the valve body 202, which acts as a seat 284 for the seal 282, When the seal 282 abuts the seat 284, the longitudinal bore 212 in the third section C (the flow control bore) of the valve body 202 is sealed to prevent flow of gas out of the valve body 202.

The FSD 208 is held in place within the valve body 202 by means of the magnet nut 210, which is screwed into the end 216 of the valve body 202. An aperture 285 is provided in the magnet nut 210 to provide access to the electromagnet 208, for example by a thermocouple connector.

The gas valve 104 shown in Figure 2 further comprises a low rate adjuster screw 288 which has a partially threaded exterior so that it can be screwed into the low rate adjuster screw receiving bore 286. With reference to Figure 3, the low rate adjuster screw 288 has a conical end 290. As the low rate adjuster screw 288 is screwed in and out of the low rate adjuster screw receiving bore 286 the conical end 290 of the low rate adjuster screw 288 regulates the flow of gas from the low rate cross-drilling bore 269 to the main gas outlet 268. The low rate adjuster screw 288 carries an 0-ring 292 in a groove to prevent flow of gas out of the low rate adjuster screw receiving bore 286.

The gas valve 104 further comprises two ball seals 320 which are used to seal cross-drilled holes. The valve body 202 further comprises two mounting feet 294.

The operation of the gas valve 104 is now described with reference to Figures 6a to 6i, which show the valve spindle 206 at a number of positions within the longitudinal bore 212 of the valve body 202.

In Figure 6a, the flame safety device (FSD) 208 has been released so that the seal 282 at the end of the piston 276 is urged against the end 284 of the longitudinal bore 212 in the third section C of the valve body 202, to seal the third section C, thereby preventing gas flow from the gas inlet 266 to the main gas outlet 268, the low rate cross-drilling bore 269 and the pilot gas outlet 270.

In order to operate the gas burner 102 the seal 282 must be moved away from the end 284 of the third section C (the flow control bore) of the longitudinal bore 212, This is performed by fully extending the linear motor 204, so that the valve spindle 206 and the motor spindle 236 are at their rightmost position. This is shown in Figure 6b, where the motor spindle 236 is extended by around 14 mm from the neck 234 of the linear motor 204. In this position, the end 254 of the valve spindle 206 pushes the seal 282 of the flame safety device 208 against the force of the spring 280 so that there is a clearance 296 between the seal 282 and the end 284 of the longitudinal bore 212 in the third section C (the flow control bore).

Once the flame safety device 208 has been latched open the motor spindle 236 is partially retracted into the neck 234 of the linear motor 204 so that the motor spindle 236 protrudes from the neck 234 by around 11 mm, as shown in Fignre 6c. In this position, the cross port seal 256 on the valve spindle 206 is positioned between the pilot gas outlet 270 and the low rate cross-drilling bore 269. Since the cross port seal 256 prevents flow of gas along the longitudinal bore 212 beyond the cross port seal 256, gas which enters into the longitudinal bore 212 via the gas inlet 266 is only able to leave the longitudinal bore 212 via the pilot gas outlet 270. Hence, the position of the valve spindle 206 as shown in Figure 6c represents a safe position where the flow of gas is restricted to the amount to burn as the pilot light.

In order to increase the size of the flame beyond a pilot light, the valve spindle 206 is moved further to the left, towards the linear motor 204, so that the cross port seal 256 moves beyond the low rate cross-drilling bore 269, as shown in Figure 6d. In this position, gas is able to travel into the low rate cross-drilling bore 269 to subsequently flow out of the main gas outlet 268. As described above, the flow rate through the low rate cross-drilling bore 269 is set by adjusting the low rate adjuster screw 288 in the low rate adjuster screw receiving bore 286.

To increase the size of the flame further, the valve spindle 206 is moved closer to the linear motor rear part 230, as shown in Figures 6e-6i. In Figure 6e, the separation between the valve spindle 206 and the shoulder 232 of the linear motor 204 is around 3.7 mm. In this position, the cross port seal 256 is withdrawn from the third section C (the flow control bore) of the longitudinal bore 212, such that the cross port seal 256 is not in contact with an interior circumferential wall 298 of the longitudinal bore 212.

Consequently, gas can pass over the flow control surface 262 of the valve spindle 206 and flow directly into the main gas outlet 268 via the main flow bore. The main seal 250 on the valve spindle 206 prevents gas from escaping through the linear motor 204 and between the motor 204 and the first end 214 of the valve body 202.

Since the cross port seal 256 is no longer within the third section C of the longitudinal bore 212, gas is able to flow from the third section C of the longitudinal bore 212 into the second section B thereof (the main flow bore). The gas flow rate from the third ii section C to the second section B is regulated by the position of the flow control surface 262 within the third section C. In particular, the interior walls 298 of the third section C define a main gas flow cavity through which gas is able to pass and the flow control surface 262 of the valve spindle 206 partially fills this cavity to restrict gas flow from the third section C to the second section B so as to force the gas to flow between the flow control surface 262 and the interior wall 298 of bore 212. By varying the extent to which the flow control surface 262 is disposed within the cavity the gas flow rate is varied.

To increase the size of the flame further, the valve spindle 206 is moved closer to the motor rear part 230 with a separation of around 2.8 mm, to increase a volume of the gap between the flow control surface 262 and the inner circumferential wall 298 of the longitudinal bore 212 in the third section C (the flow control bore) of the bore 212, as shown in Figure of In Figure 6g, the gap between the valve spindle 206 and the neck 234 is reduced to around 1.9 mm, thereby increasing the volume of the gas flow path between the flow control surface 262 and the inner circumferential wali 298 of the longitudinal bore 212 in the third section C of the bore 212. This gap is increased further in Figure 6h, where the gap between the valve spindle 206 and the neck 234 is reduced to around 1 mm, Finally, in Figure 6i, the motor spindle 236 is retracted to its full extent into the neck 234 so that the valve spindle 206 is flush with the neck 234. In this position, the flow control surface 262 is frilly retracted from the third section C of the longitudinal bore 212 so that the volume of the gap between the flow control surface 262 and the inner circumferential wall 298 of the longitudinal bore 212 in the third section C is at its maximum, thereby providing the maximum gas flow between the gas inlet 266 and the main gas outlet 268. It is to be noted that in each of Figures 6e-6i, as well as there being gas flow from the second section B of the longitudinal bore 212 directly into the main gas outlet 268, gas continues to flow through the low rate cross-drilling bore 269.

An advantage of the present invention is that due to the frusto-conical shape of the flow control surface 262, the linear reciprocating motion of the valve spindle 206 accurately controls the flow of gas to the main gas outlet 268 and consequently the size of the gas flame. The accurate positioning of the valve spindle 206 and its flow control surface 262 is controlled by the micro-processor based controller 06, as is described below, The microprocessor-based controller/electronic control board (ECB) 106 controls the operation of the gas valve 104 based on inputs received from one or both of the user interfaces 110, 112. The ECB 106 also controls the spark generator 108. Since a mains power supply is not always found near to a domestic gas fire, the ECB is powered by a battery pack 20 comprising commonly available cells, such as a 9V PP3 battery. The power source 120 provides power for ECB thnctionality, spark generation and motor operation.

In particular, the ECB 106 provides positional instructions to the linear motor 204 in order to propel the valve spindle 206 to vary the gas output conditions. The ECB 106 further provides operational output sequences providing safety lockouts, audible warning tones and monitoring of current and voltage levels from the power source 120 and thermocouple inputs.

The ECB 106 also monitors the power source 120 for a ciitical level. If the voltage and/or current falls below this predetermined level a low power lock out' occurs, This initiates preventing further operation and unsafe operation of the gas valve 104.

Similarly, disconnection of the power source 120 during operation of the gas valve 104 results in shut down of the system 100 into a safe condition, by releasing the flame safety device 208.

The ECB 106 is provided with an earth lead (not shown). This earthed connection helps prevent anomalies occurring during system 100 usage. The earth lead connects to a terminal on the ECB 106 and to the chassis of the appliance th2 to which the system 100 is to be installed.

Since the electrical components of the system 100 are battery powered, it is important to efficiently use the available electrical power. The ECB 106 has a power saving sleep' mode, which limits the activity of the ECB to a minimum ensuring maximum energy efficiency.

A cold start' initiation sequence has been incorporated to overcome problems with control valve operation at low ambient temperature conditions, e.g., early in the morning. An additional allocation of power is provided to the control valve motor 204 to ensure operation and to increase system efficiency. Once the ambient temperature increase, generally, less power is required for the start-up initiation sequences.

The ECB 106 has an on-board spark generator 108 that provides the capability to ignite the gas. The spark generator 108 is utilised on the ignition stage of the start-up t5 sequence. Once the ECB 106 has detected that the gas is lit the spark generator t08 ceases to operate, further improving the energy efficiency of the system 100. This is performed by using a thermocouple in the gas flame. Once the gas is lit the temperature of thermocouple rises and a current is generated in the thermocouple. If the flame is extinguished or fails to ignite, the current monitoring of the ECB t06 will detect this and trip the FSD 208 causing it to drop out and close seal 282 against the end 284 of the longitudinal bore 286 in the third section C of the valve body 202, as shown in Figure 6a.

Two user interface are provided, namely a local user interface 110 which is wiredly connected to the ECB 106 and a remote user interface 112 which is wirelessly connected to the ECB 106, the latter being the primary interface. The method of wireless transmission is infra-red (IR) for which a corresponding receiver 114 connected to the ECB 106 is required. Alternate transmission technology, including radio frequency, may be used. The skilled person will understand that wireless technologies other than IR and RF technologies may be used.

Figure 7 is a schematic view of the buttons of the remote user interface 112. The remote user interface 112 has four buttons, marked Max' 702, Mm' 704, Up' 706 and Down' 708. Single button presses or combinations of buttons 702, 704, 706, 708 are required to convey the required command to the ECB and control valve. For example, to start the system 100 a combination of the Max' 702 and Mm' 704 buttons are pressed for three seconds or a similar predetermined period of time. This dual button requirement also provides a child lock safety feature incorporated into the handset design to prevent accidental start up. The local user interface 110 may have the same buttons.

The operation of the system 100 is described below. The flame of the gas burner 102 is ignited as follows. One or more buttons 702, 704 on the remote 112 or local 100 user interface are pressed to send a signal to the ECB 106. The ECB 106 then sends a signal to the linear motor 204 to drive the end 254 of the valve spindle 206 forward against the FSD piston 276 as shown in Figure 6b. In this position gas can flow out of the valve body 202 to the pilot gas outlet 270 alone. The spark generator 108 is used to ignite the gas. Once the gas is ignited the thermocouple is heated and a current is generated. Once sufficient heat is generated to latch open the FSD 208 the spark generator 108 no longer generates a spark.

Once the flame in the gas burner has been established the user controls the flame height by pressing buttons 702, 704, 706, 708 on the user interface 110, 112 to move the valve spindle 206 as shown in Figures 6c-6i. By using a linear motor 204 to propel the flow control surface 262 towards and away from the inner circumferential wall 298 of the third section C of the longitudinal bore 212 the invention provides a compact gas valve 104 which can accurately control the size of the flame over an infinitely variable range, If the Max' button 702 is pressed the valve spindle 206 is moved all the way to the left as shown in Figure 6i. If the Mm' button 704 is pressed the valve spindle 206 is moved to the position shown in Figure 6d where gas flows to the burner 102 via the pilot gas outlet 270 and the low rate cross-drilling bore 269. It is also possible to switch the appliance to pilot only. is

When the user has finished using the system 100, the off' function can be activated whereby the system 100 will stop gas flow into the appliance and leave the appliance in a safe condition as shown in Figure 6a. The system 100 is now ready for the start-up sequence to be re-activated.

Various modifications will be apparent to those in the art and it is desired to include all such modifications as fall within the scope of the accompanying claims, For example, in the embodiment described above the flow control surface 262 is frusto-conical and the gas flow cavity defined by the interior wall 298 of the longitudinal bore 212 in the third section C has a uniform diameter. In other embodiments the flow control surface may have a uniform diameter and the wall of the gas flow cavity may be tapered, having a frusto-conical shape. Alternatively, both of the flow control surface and the interior wall of the bore 212 may have a fmsto-conical shape. Similarly where the flow control surface has a non-round exterior surface and the interior surface of the bore has a corresponding non-round surface, the flow control surface may have a uniform diameter and the interior surface of the bore may have a tapered diameter or both of the flow control surface and the interior surface of the bore may be tapered. In all cases the skilled person will understand that the corresponding surfaces of the flow control surface and the interior of the bore should be shaped so that relative motion of the flow control surface and the interior of the flow control bore varies the volume of the gap between these surfaces and regulates the flow of gas through the gap.

Claims

CLAIMSI. A gas valve for controlling flow of gas to a gas burner, the valve comprising: a valve body having a gas inlet, a main gas outlet and a bore, the bore having an interior surface a part of which defines a gas flow cavity, the gas inlet and the main gas outlet being in communication with the gas flow cavity; and a valve spindle arranged to move into and out of the gas flow cavity, an exterior portion of the valve spindle forming a flow control surface and defining a gap having a volume between the flow control surface and the interior surface of the gas flow cavity, wherein relative movement of the flow control surface and the gas flow cavity varies the volume of the gap and is adapted to regulate a flow of gas from the gas inlet to the main gas outlet.
2. A gas valve as claimed in claim 1, wherein at least one of the flow control tS surface arid the interior surface of the gas flow cavity are tapered.
3. A gas valve as claimed in claim 2, wherein the at least one of the flow control surface and the interior surface of the gas flow cavity are fmsto-conical.
4. A gas valve as claimed in claim 3, wherein the flow control surface is fmsto-conical and the interior surface of the gas flow cavity has a uniform circular diameter.
5. A gas valve as claimed in claim 3 or 4, wherein the frusto-conical surface is inclined to an axis of the valve spindle at an angle of between 2.5° and 10°.
6. A gas valve as claimed in any one of the preceding claims, wherein the bore has a longitudinal axis and the relative movement of the flow control surfhce and the gas flow cavity is along the axis.
7. A gas valve as claimed in claim 6, further comprising a linear motor for propelling the valve spindle along the axis.
8. A gas valve as claimed in claim 7, wherein the linear motor and the valve spindle are each provided with cooperating threaded portions for attaching the motor to the valve spindle.
9. A gas valve as claimed in claim 7 or 8, wherein the linear motor is mounted at a first end of the longitudinal bore.
10. A gas valve as claimed in claim 7, 8 or 9, wherein the valve spindle is provided with a first seal to prevent flow of gas to the motor.1. A gas valve as claimed in any one of the preceding claims, wherein the valve spindle ifirther comprises a second seal adapted to cooperate with the interior surface of the gas flow cavity to prevent flow of gas from the gas inlet to the gas outlet.tS t2. A gas valve as claimed in any one of the preceding claims, wherein the valve body further compiises a pilot gas outlet in communication with the bore.13. A gas valve as claimed in any one of the preceding claims, wherein the valve body further comprises a low rate cross drilling bore between the gas flow cavity and the main gas outlet, for providing gas flow to provide a low rate flame.t4. A gas valve as claimed in claim 13, further comprising means for adjusting the flow rate through the low rate cross drilling bore.t5. A gas valve as claimed in claim 14, wherein the means for adjusting the flow rate through the low rate cross drilling bore is a low rate adjuster screw which projects into the low rate cross drilling bore.16. A gas valve as claimed in any one of the preceding claims and further comprising a flame safety device for sealing the gas flow cavity to prevent flow of gas from the gas inlet to the main gas outlet.17. A gas valve as claimed in claim 16, wherein the flame safety device is mounted at a second opposed end of the longitudinal bore.18. A gas fire system, comprising: a gas valve as defined in any one of the preceding claims; a spark generator for igniting a gas flowing out of the gas valve; a microprocessor-based controller for controlling the operation of the valve spindle and the spark generator; and a user interface for providing instructions to the controller.19. A gas fire system as claimed in claims 18, wherein the user interface is one of a wired and wireless user interface.20. A gas valve substantially as hereinbefore described with reference to the Figures2toó.21. A gas fire system substantially as hereinbefore described with reference to the accompanying drawings.