GB2403530A

GB2403530A - Gas burner control

Info

Publication number: GB2403530A
Application number: GB0410218A
Authority: GB
Inventors: Paul Harrison
Original assignee: NATURAL GAS SERVICES Ltd
Current assignee: NATURAL GAS SERVICES Ltd
Priority date: 2003-05-07
Filing date: 2004-05-07
Publication date: 2005-01-05
Anticipated expiration: 2024-05-07
Also published as: GB0310576D0; GB0410218D0; GB2403530B

Abstract

An installation includes air extraction means 7 and comprises at least one main gas burner and a pilot burner associated with the or each main gas burner. The main burner and the respective pilot burner is supplied with gas from a common supply controlled by a main gas control valve 2. The burner installation also includes a controller 3 arranged to allow the main control valve to open only when the air extraction means is operating, and a bypass pipe 4 around the main valve and including a pilot valve 6. The valves may be solenoid operated and connected to the controller, which is linked to gas pressure sensors 9,10 to cause the pilot valve to close in response to a pre-determined drop in pressure at the burner or the loss of gas pressure between the main valve and the burner. The bypass is dimensioned to supply sufficient gas only for the pilot burner or burners, and the pilot valve may remain open to permit the pilot burner or burners to continue to operate when the main valve is closed. The air extraction means may comprise an electric fan 7 and include flow detecting means 8. The bypass pipe may include a flow adjustment valve 5, and the pilot valve 6. Alternatively, the main control valve may open only in response to the combination of fan control switch (16 fig 2) supplying power and air flow detection.

Description

GAS BURNER INSTALLATION

Field of the Invention

This invention relates to a gas burner installation of the type having at least one main gas burner and a pilot burner for the or each main gas burner. For example, the installation may be cooking appliances in a commercial kitchen.

Background to the Invention

Safety standards, for example BS 6173:2001 in the UK, require that all new commercial kitchens utilising air extraction systems over the cooking appliances must have an interlock system between the air extraction system and the gas supply to ensure that the appliances cannot be operated without the extraction system being in operation.

Unlike most boilers or other automated plant including gas burners, cooking appliances are turned off and on not by an electrically controlled valve under the influence of a timer or the like, but by a person manually operating a control valve on the appliance. In order À.e - to meet the safety standards, therefore, it is necessary to control the closure of a main gas supply valve to the complete system in response to operation of the extraction or air extraction system, for example by putting a pressure sensor into the extraction system to detect the presence or absence of airflow, thus providing the required interlock.

Most catering establishments operate with peak periods of activity, for example the main meal times of breakfast, lunch and evening meals. Powerful air extraction systems can produce relatively high noise levels, and between these peak periods it is desirable for staff to be able to switch off the extraction systems to reduce noise and save energy. With the existing interlocking arrangements, this means that the pilot flames are also extinguished every time the fans are shut down, and there is thus a need to relight them several times a day. With most kitchens having a large number of burners, and with pilot burners typically being provided with flame failure devices, relighting the pilot burners can take a considerable time. In addition, repeated cooling and reheating of the flame failure devices will tend to shorten the life of these components. There is therefore a need for a safety system which can allow the pilot flames to remain alight when the extraction system has been turned off, but which ensures that the gas supply is fully shut down in the event of a leak or an attempt to operate an appliance without first starting the extraction system. - 2

A further problem encountered with existing systems is that pressure detectors for detecting air extraction air flow can become faulty with time as a result of exposure to grease and other pollutants in the extracted air. Additionally, it is a relatively simple matter to disable the switch, for example by by-pass wiring, to over-ride the safety lock out system, for example to avoid the necessity for constant re-lighting of pilot burners.

Summary of the Invention

According to the invention, there is provided a gas burner installation comprising at least one main gas burner and a pilot burner associated with the or each main gas burner, the or each main burner and the respective pilot burner being supplied with gas from a common supply controlled by a main gas control valve, air extraction means associated with the burner or burners, and control means arranged to allow the main control valve to open only when the air extraction means is operating, wherein a bypass is provided around the main valve, the bypass including a pilot valve and being dimensioned to supply sufficient gas only for the pilot burner or burners, and the control ÀÀ . means is linked to gas pressure means to cause the pilot valve to close in response to a pre- determined drop in pressure at the burner or burners, whereby the pilot valve may À.

remain open to permit the pilot burner or burners to continue to operate when the main À . valve has closed, but loss of gas pressure between the main valve and the burners will.... À

cause closure of the pilot valve. . . The gas pressure means may comprise differential detection means for detecting a pressure differential across the main valve, and pressure-sensing means for detecting the gas pressure in the system between the main valve and the burner or burners, the control means being arranged to cause the pilot valve and, if open, the main valve, to close if the pressure differential is greater than a first predetermined value or the detected gas pressure is below a second predetermined value.

In an alternative arrangement, a test bypass is provided around the main valve in parallel with the pilot bypass, the test bypass having a test valve therein, and being arranged to provide a gas flow rate therethrough, when the test valve is open, lower than that provided by the pilot bypass, whereby on start-up of the installation the test valve is first opened to pressurise the installation with the main valve and pilot valves closed, and the control means is arranged to monitor the pressure for a pre-determined period and to open the pilot valve only if pressure reaches a pre-determined value within said period.

Preferably, the air extraction means comprises an extraction fan, and the control means comprise a fan control switch for supplying electric power to the fan, air flow detecting means for detecting air flow caused by operation of the fan, and means responsive to the combination of closure of the fan control switch and detection of air flow to supply power to the main valve to permit the valve to open in response to the pressure differential detection means and pressure-sensing means.

Manually-operable means may be provided for selectively closing the main gas valve, for example in the event of an emergency.

According to another aspect of the invention, there is provided a gas burner installation associated with an air extraction system including an air flow detection means, the gas burner installation being supplied via a main gas valve provided with control means, and wherein the air extraction system has a fan control switch for supplying power thereto, the control means being arranged to allow the main gas valve to open only in response to the combination of the fan control switch supplying power to the air extraction system and the detection of air flow by the air flow detection means.

With this aspect of the invention, by-passing the fan air pressure detection means to permit the burners to be operated without the extraction system operating will not be successful.

Although reference is made herein to air extraction, it will be appreciated that the invention is applicable to installations having any sort of mechanical ventilation system.

Brief Description of the Drawings

In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a diagram of the main gas control valve and pilot valve; Figure 2 is a diagram illustrating a preferred embodiment of the control system for the installation; and Figure 3 is a diagram of an alternative embodiment to that shown in Figure 1.

Detailed Description of the Illustrated Embodiment

Referring first to Figure 1, a gas burner installation comprises a gas supply pipe 1 having a main solenoid-operated gas valve 2 connected to a controller 3. The gas supply - 4 pipe supplies gas to gas burners forming part of a commercial cooking range, for example, each burner having a respective pilot burner to maintain a pilot flame to ignite gas issuing from the associated main burner. The burners and their associated pipework are not shown in the Figure for the sake of clarity. A by-pass pipe 4 takes a small gas flow around the main valve 2 sufficient to supply the pilot burners when the main valve 2 is closed. The by-pass pipe 4 includes a flow-adjusting valve 5 to enable the flow rate to be adjusted according to the number of pilot burners in the system, and a solenoid- operated stop valve 6 also connected to the controller 3. The cooking range has an associated air extraction system, for example including an extractor hood above the range, the system comprising an electric fan 7 whose electricity supply is controlled by the controller 3 and an air- flow sensor/switch 8 adjacent to the fan and also linked to the controller. The controller 3 is also linked to a pressure differential detector 9 arranged to detect the pressure differential across the main valve 2, and a pressure sensor 10 À.. ..

which senses the pressure in the system between the main valve 2 and the burners. À À

The controller 3 is arranged to allow the main valve 2 to be open only when the À À.

following conditions are satisfied: À..

1. The fan is switched on; .. : À À 2. The air flow sensor 8 senses an air flow due to operation of the fan; .

...DTD: 3. The gas pressure in the system is not below a pre-determined value; and,, . 4. The gas pressure differential is below a pre-determined amount.

While the main gas valve 2 remains closed if the fan is not powered, or is not running, the pilot burners can still be supplied with gas and thus do not need to be re-lit after each shut-down of the extraction system. However, any attempt to operate any of the gas burners while the main valve is closed, or any leakage of gas, will cause a drop in pressure on the burner side of the main valve, and an increase in the pressure differential across the main valve. This will in turn cause the controller 3 to close the pilot stop valve 6.

A controller according to a preferred embodiment of the invention is illustrated by Figure 2. Power is supplied to the system via an emergency stop switch 11. When this switch is open, both gas valves 2 and 6 are in their no-power closed positions. Two 3-pole relays 12 and 13 are used to control all the switching in the system. The first of - 5 these 12 has only two poles in use. It will be appreciated that the relay arrangement could be replaced by solid-state switching, if desired.

In the initial rest position illustrated, when the emergency stop switch 11 is closed, power is routed by the first relay 12 only to the lockout indicator 14, which indicates that the system is in a lockout state and therefore no gas can flow. Power also flows to a lockout reset button15 which when pressed closed to perform a reset supplies power to the operating coil of the first relay 12, which in turn switches power to the pilot gas valve 6 to open this valve, allowing gas through the by-pass pipe 4 and into the burner system, and connects the line from the pressure and pressure differential switches 9 and 10, indicated together in the Figure, to the relay coil to supply power to the coil when the switches are both closed and the reset button has been released. In normal operation, and assuming that the main burners are all shut, the gas supply through the by-pass pipe 4 is sufficient to pressurise the burner system to its operating pressure, such that the differential across the closed main valve 2 is reduced to below its pre-set value, thereby allowing the differential switch 9 to close. Similarly, the pressure in the system causes the pressure switch 10 to close. At this point, the reset button can be released, since the power supplied through the pressure switches 9 and 10 (which can simply be connected in series) will hold the relay 12 in its operating position, so holding the pilot valve 6 open. If any of the burner valves is open at this point, the escape of gas prevents the pressure building up to the operating level, and so the switches 9 and 10 do not close, and release of the reset button will result in closure of the pilot valve 6.

With the pilot burners operating, the system can be set to its operational state by first switching on the fan control switch 16. This switches power to two of the poles in the second relay 13, both of which are isolated. The closure of the pressure switches 9 and 10 supplies power through the fan pressure switch 8 in the rest position thereof to a fan start button 17. When this button 17 is held pressed, power is switched to the operating coil of the second relay 13, causing the three poles of the relay to switch to their operating positions. The first pole switches power to the fan 7, while the second routes power to the relay coil, thereby permitting the fan start button to be released without causing the relay to close again. The third pole connects the fan pressure switch 8 to the main gas valve 2. However, the valve 2 remains closed until the fan pressure switch is activated by sufficient air flow from the fan to switch power from the gas pressure switches 9 and 10.

It will be seen that closing the fan switch 16 will return the system to its pilot state, provided that all the main burners are off and there is no gas leak in the system.

The pilot burners remain operational. If the fan is switched off with any of the burners open, or if any burner is opened or a leak occurs while the fan is off, then the fall in gas pressure or the change in the gas differential across the main valve 2 will immediately cause one or both switches 9 and 10 to open, removing power from the coil in the first relay 12 and causing a lockout condition to occur. If the fan should fail during operation, the fan pressure switch will go to its rest state, removing power from the main valve 2 and thereby causing it to close. If any of the burners is operating at the time, the resultant pressure drop/change of pressure differential will again result in a lockout state.

In an emergency, for example if a fire were to occur, the emergency stop switch 11 can be manually operated to revert the system immediately to a lockout state, with the gas supply isolated and the fan switched off.

It will be observed that the system incorporates a gas pressure differential switch 9 and a gas pressure switch 10, operating in series. It would be possible to operate the system with just a gas pressure switch. However, the sensitivities and consequently the response time of the system are determined by the value at which the low-pressure switch is set. Consequently if this switch is set close to the normal gas system pressure, nuisance shut downs may occur as a result of gas pressure transportation fluctuations. In these circumstances, although these fluctuations would result in system pressure variations as a whole, these would not result in differential pressures within the system.

By incorporating the differential pressure switch 9 across the main gas valve, the low pressure switch 10 can be set at a lower value, eliminating nuisance shut downs, while maintaining system sensitivity under these circumstances. In the event of an interruption of the incoming gas supply with the pilot system in operation or a small gas leak down stream of the main gas valve during a normal shut down period, a gradual loss of pressure would occur. This situation would be insufficient to affect the differential pressure switch, but the low- pressure switch would respond. The other advantage of the two pressure switches is that the system then incorporates a double safety feature.

In some circumstances, the use of the differential pressure switch can give rise to unwanted lockouts where abrupt pressure changes arise from the sudden shut-down of high-load appliances, for example boilers, supplied by the same supply. Figure 3 illustrates an alternative embodiment, in which the differential switch is omitted, and a secondary or test bypass 20 is provided in parallel with the pilot bypass 4. The test bypass includes a solenoid valve 21 connected to the controller 3, and a manual balancing valve 22, and is arranged to provide a gas flow rate substantially lower than that through the pilot bypass 4. On startup of the installation, all valves are initially closed. Operation of the Start control initiates a timer in the controller 3 and opens the test bypass solenoid valve 21, allowing gas into the installation at a very low rate sufficient to pressurise the installation to its working pressure within a pre-determined time. The pressure in the installation is monitored by a gas-pressure switch 10, which is set to close at the working pressure. Failure to reach the working pressure level within the pre-determined time À - ..

period means that the necessary signal from the switch 10 is not received, and the controller 3 then goes to lockout, preventing any of the other valves from opening Thus, the system cannot be used until the leak causing the pressure loss has been rectified and the system has been re- set.

In the absence of a leak (or a burner valve left open, for example), the installation reaches working pressure within the pre-determined time interval and the pressure switch 10 closes, permitting the controller to send current to the pilot solenoid 6, which then supplies sufficient gas to the installation just to supply all the burner pilot flames.

The flow rate is adjusted by means of manual balancing valve 5 on initial set-up according to the number of pilot flames to be included in the installation. The remainder of the start-up then follows the system hereinbefore described. It will be understood that the pressure switch 10 continues to serve as a monitor for satisfactory operation of the system, so that the pilot valve 6 will be closed if, on standby mode, an attempt is made to open a burner valve without the fan 7 first being started satisfactorily. - 8

Claims

1. A gas burner installation comprising at least one main gas burner and a pilot burner associated with the or each main gas burner, the or each main burner and the respective pilot burner being supplied with gas from a common supply controlled by a main gas control valve, air extraction means associated with the burner or burners, and control means arranged to allow the main control valve to open only when the air extraction means is operating, wherein a pilot bypass is provided around the main valve, the pilot bypass including a pilot valve and being dimensioned to supply sufficient gas only for the pilot burner or burners, and the control means is linked to gas pressure means to cause the pilot valve to close in response to a pre-determined drop in pressure at the burner or burners, whereby the pilot valve may remain open to permit the pilot burner or burners to continue to operate when the main valve has closed, but loss of gas pressure between the main valve and the burners will cause closure of the pilot valve.

2. An installation according to Claim 1, wherein the gas pressure means comprise differential detection means for detecting a pressure differential across the main valve, and pressure-sensing means for detecting the gas pressure in the system between the main valve and the burner or burners, the control means being arranged to cause the pilot valve and, if open, the main valve, to close if the pressure differential is greater than a first predetermined value or the detected gas pressure is below a second predetermined value.

3. An installation according to Claim 1, comprising a test bypass around the main valve in parallel with the pilot bypass and having a test valve therein, the test bypass being arranged to provide a gas flow rate therethrough, when the test valve is open, lower than that provided by the pilot bypass, whereby on start-up of the installation the test valve is first opened to pressurise the installation with the main valve and pilot valves closed, and the control means is arranged to monitor the pressure for a pre-determined period and to open the pilot valve only if pressure reaches a pre-determined value within said period.

4. An installation according to Claim 1, 2 or 3, wherein the air extraction means comprises an extraction fan, and the control means comprise a fan control switch for supplying electric power to the fan, air flow detecting means for detecting air flow - 9 - caused by operation of the fan, and means responsive to the combination of closure of the fan control switch and detection of air flow to supply power to the main valve to permit the valve to open in response to the pressure differential detection means and pressure-sensing means.

5. An installation according to any preceding claim, comprising manually operable means for selectively closing the main gas valve.

6. A gas burner installation associated with an air extraction system including an air flow detection means, the gas burner installation being supplied via a main gas valve provided with control means, and wherein the air extraction system has a fan control switch for supplying power thereto, the control means being arranged to allow the main gas valve to open only in response to the combination of the fan control switch supplying power to the air extraction system and the detection of air flow by the air flow detection means.

7. A gas burner installation, substantially as described with reference to, and/or as shown in, the drawings. À À c ce c e À. À À-. bees