EP0371715A1

EP0371715A1 - Modular gas burner assembly

Info

Publication number: EP0371715A1
Application number: EP89312256A
Authority: EP
Inventors: William John Lloyd; Stephen Roberts
Original assignee: Caradon Ideal Ltd; Stelrad Group Ltd
Current assignee: Caradon Ideal Ltd
Priority date: 1988-11-28
Filing date: 1989-11-27
Publication date: 1990-06-06
Anticipated expiration: 2009-11-27
Also published as: DE68925408T2; GB2225848A; ATE132958T1; EP0371715B1; GB8926777D0; GB8827729D0; DE68925408D1

Abstract

A gas burner assembly, such as for a boiler, is built up from easily assembled prefabricated units enabling the assembly configuration, the heat output and the control system to be selected at a relatively late production stage thereby facilitating the manufacture of a range of boilers of different kinds and with different requirements. The basic units are a control body (20) which mounts various control modules (22, 23,32) selected according to the desired control functions, a burner (1) which is sectioned to enable expansion to the required size, and a manifold (2) which interconnects the control body and burner and can be connected to each in different orientations.

Description

This invention relates to gas burner assemblies, especially but not necessarily exclusively for use in boilers intended for domestic heating and/or hot water systems. Different kinds of boiler are available and in use today. They include free standing boilers, wall hung boilers and back boiler units which are incorporated with gas fires, as well as other kinds. It is usual for a boiler to include a gas burner assembly which comprises a burner, a control arrangement, and a manifold interconnecting the burner and the control arrangement for conducting gas to the burner from the control arrangement, the control arrangement including means to control the supply of gas to the burner. (For convenience such an assembly is referred to hereinafter as "a burner assembly of the form initially described".) In the prior art assemblies the manifold takes the form of a rigid pipe which is bent to the required shape, having regard to the desired relative positioning of the control arrangement and burner in the completed assembly, and this pipe is provided with the necessary drillings and tappings for the gas connections. In addition a mounting or flange plate is welded to the pipe at a position intermediate its ends and in the finished boiler this plate is located at the interface between respective compartments defined within the boiler casing. The burners are made as complete prefabricated units dependent upon the particular design and kind of boiler as well as its heat output rating. Similarly, the control arrangement is at least for the most part pre-assembled into a finished unit ready for incorporation into the burner assembly and made in accordance with the type of control with which the boiler is to be equipped. In the manufacture of the prior art burner assemblies an auxiliary pilot burner, with its associated ignition device and pilot flame sensor probe (if provided), has to be mounted on or in the vicinity of the main burner, and the necessary gas and electrical connections have to be made with the control arrangement. These assembly operations are time consuming and there is the added disadvantage that the pilot burner sub-assembly interferes with the air flow around the main burner and has an adverse influence on its combustion performance.
From the foregoing it will be understood that in any given burner assembly the design and/or choice of the burner, the manifold pipe and the control arrangement are dictated by the particular boiler in which the assembly is to be accommodated. To put it another way, from almost the conception stage each burner assembly is dedictated for use in one given appliance. It is common for boiler manufacturers to supply a large range of boilers including boilers of various kinds and boilers of the same kind having different heat outputs and operating features. As a result a great number of mutually different burner assemblies are called for and the manufacturer is required to stock the necessary assemblies, or at least their component parts, to enable them to make the full range of boilers. This is uneconomical and a great inconvenience.
The present invention addresses the aforementioned problem and whereas the gas burner specifically described hereinafter and illustrated in the accompanying drawing embodies several novel features each of significant benefit in itself, when incorporated together in a single embodiment these features combine to ensure great versatility in the basic design whereby the assembly can be adapted so as to be dedicated to a given boiler at only a late stage in the manufacturing process. In other words several boilers can be made having different burner assemblies, but which assemblies share common basic components capable of being assembled together in different ways and adapted to receive further modules selected from a limited range in order to tailor the assembly according to the particular needs of that boiler into which it is to be fitted.
In accordance with a first aspect of the present invention there is provided a burner assembly of the form initially described wherein the control arrangement comprises a body which is capable of accepting prefabricated and fully assembled valve modules for controlling flow of gas through a passage formed in the body and connecting gas inlet and outlet ports.
In line with this same aspect the invention provides a gas burner assembly in the form initially described wherein the control arrangement comprises a body, and at least one prefabricated and fully assembled valve module mounted on the body as a unit for controlling flow of gas through a passage formed in the body and connecting gas inlet and exit ports.
In a preferred embodiment one valve module controls flow of gas from a gas inlet port of the body to a port which is connected to a pilot burner, and and a second valve module controls flow of gas through a passage leading to a gas outlet port which is connected to the manifold for delivering gas to the main burner. The valve modules are self-contained devices which can easily be secured to the body by a suitable mechanical connection or direct coupling and this assembly operation can be quickly and conveniently completed by unskilled personnel. Once fitted the valve modules can only be disassembled with the use of a tool. The or each valve module is selected from a range of modules which may include, for example solenoid valves, modulation valves and manually operable, e.g. manual preset flame failure, valves. In the case of electrically controlled valves the electrical connections can be made via the control body, the body and valve module being equipped with electrical contacts which are brought into cooperation upon mounting the module in place.
In the preferred construction the body of the control arrangement carries electrical terminal contacts for connection to control devices external to the boiler, such as a timer and/or room thermostat, and/or for connection to control devices, such as a water temperature sensor provided within the boiler in accordance with known practices. These terminals can take the form of contact blades arranged to receive push-on plug connectors of known design.
It is possible also for the body of the control arrangement to mount directly a sequencing module, i.e. an electrical/electronic unit for determining the mode of operation of the burner assembly in accordance with the control signals received from various internal and/or external devices, the necessary electrical connections to and from the sequencing module, and with the terminal contacts for example, being preferably made within the body of the control arrangement.
Another module which can be carried on the body of the control arrangement is a spark generating device and once again the necessary electrical connections to this device may be made through the body with contacts being provided on the respective parts and arranged to be brought automatically into correct cooperation when the spark generator is mounted in position.
With a control arrangement as proposed in accordance with the invention, the appropriate modules can be selected and be readily attached to the body at any convenient stage in the boiler manufacturing process, whereby the arrangement is adapted to meet the requirements of the control programme for the particular boiler being made. No special skills are required, the modules being prefabricated as complete, self-contained units. The body itself provides the necessary gas flow passages between the gas ports and the electrical connections between the electrical contacts, but it does not itself incorporate any of the control parts until it is equipped with selected modules. However, in order to eliminate need for a further separate component, the body could be modified to include a gas cock for isolating the valve modules and other parts of the burner assembly from the gas supply, e.g. during periods of maintenance.
At this point it should perhaps be mentioned that it is known to construct gas valves capable of receiving different types of actuator for operating the valve. As examples of such actuators solenoids and push button devices may be referred to. The present invention marks a significant departure from or extension to this principle in that the entire valve, i.e. including the valve seat and all the other working components are incorporated into a complete valve module which is fastened onto the basic control block. By virtue of this inventive concept it becomes possible for the boiler manufacturer to assemble a wide variety of different gas valve arrangements from a limited number of components consisting of the control block and the different modules which the block is adapted to receive.
In GB-A-2029564 there is proposed a control assembly for installation in a gas feed pipe of a gas burner, the assembly including prefabricated filter and gas control units connected directly together in series, each unit having a body with gas inlet and outlet ports on opposite faces. The assembly is intended to reduce the site work needed to connect the different forms of control device into the feed pipe during burner installation. It is not suited to use in a gas burner assembly in a boiler. The size of the assembly, and hence the relative positions of the gas inlet and outlet ports, is dependent upon the numbers and types of unit included. Furthermore, the assembly does not lend itself to incorporation of electrical control connections for valve actuators or external devices.
The body of the control arrangement according to the present invention serves as a basic distribution unit providing the necessary gas connections and enabling flow control modules to be added in a simple manner to achieve a control arrangement exhibiting the desired operating features. In addition the body can provide at least some of the electrical connections of the control circuitry with modules mounted on the body becoming automatically connected upon being mounted thereon. In this regard it is convenient to mention at this time that the manifold may be connected to the body through a releasable coupling, which in addition to providing the necessary gas connections may include electrical connectors for coupling a pilot burner ignition electrode and a pilot flame sensor probe in the control circuitry. The coupling may be of a quick release type to facilitate detachment of the burner for servicing.
In accordance with a second aspect of the present invention there is provided a gas burner assembly of the form initially described, wherein the manifold comprises a member having extending therethrough a plurality of non-communicating conduits defining a main gas passage for conveying gas to the burner, and a further gas passage isolated from the main passage for conducting gas to a pilot burner.
The composite manifold eliminates the need for respective pipes connecting the main and pilot burners. The manifold member can be conveniently made as an extrusion or as a casting. Additional channels, either open or closed, may be provided in the manifold member and serve as cable ducts for electrical wiring connected to a pilot ignition device and a pilot flame detector/monitor.
In a preferred assembly the manifold member comprises at one end a connection flange having openings which communicate with the respective gas passageways. This connection flange is secured by suitable mechanical fastening means (such as a quick release coupling as previously mentioned) to a face of the control arrangement body, which face has gas ports located therein to register with the gas openings of the flange. The connection flange and the corresponding face of the control body are so arranged that the manifold member can be turned through 180° and the necessary gas connections are still maintained. For example, the connection flange may have two pilot gas openings located uniformly either side of the main gas opening so that one of the openings will register with the pilot gas port and the other opening will be sealed closed when the flange is fastened to the control body. It will be understood that this feature enables the control arrangement to be reversed, whereby the configuration of the burner assembly may be chosen to suit a given boiler.
At its end opposite the control arrangement the manifold member is secured to the burner, and the manifold member may carry a gas injector nozzle for delivering gas from the main manifold passage into a main burner inlet shroud which also acts to connect the burner to the manifold member. Also, the manifold member may be fitted with a pilot gas injector nozzle to deliver gas from the pilot gas passageway, e.g. into an air mixing tube leading to the pilot gas burner.
In accordance with a third aspect of the present invention there is provided a gas burner assembly of the form initially described wherein the burner is connected to the manifold by means permitting the the angular disposition of the manifold with respect to a substantially horizontal axis determined by the burner to be selected.
The correct disposition of a gas burner is fixed and predetermined by the burner design. Thus, the orientation of the burner is one factor which cannot be changed. However, by virtue of the manifold having different possible angular dispositions relative to the burner the overall configuration of the burner assembly is easily adapted to suit a given boiler. For example, in one boiler, such as a free standing boiler, it will be appropriate for the manifold to extend generally vertically upwardly from the burner, whereas in another boiler, such as a wall hung boiler it will be appropriate for the manifold to extend downwardly from the burner. In other cases it may be appropriate and more convenient for the manifold to extend at other angles, for example generally horizontally.
In a preferred construction the means connecting the burner to the manifold comprises a cylindrical part, so that the angle of the manifold may be selected to have any value within the range of 0 to 360°. Conveniently the connecting part is provided by an inlet shroud of the burner, in which case a main injector nozzle fitted to the manifold may be positioned to direct the jet of gas along the tube axis, which is coincident with and serves to define said substantially horizontal axis. If the manifold is also equipped with an injector for delivering gas to a pilot burner as mentioned above, a series of connection points for this injector may be included in the manifold at locations set by predetermined angular dispositions for the manifold, the injector being applied at the appropriate connection point when it has been decided which angular disposition the manifold is to take.
The attachment of the main gas inlet shroud to the manifold can be achieved by a suitable means which will enable the angular disposition of the manifold to be easily adjusted to that required and then firmly secured or locked to prevent undesirable subsequent relative movements.
In accordance with a fourth aspect the invention provides a burner assembly of the form initially described wherein the burner comprises a primary burner section having an upstream end connected to the manifold, and a downstream end, a gas duct extending through the burner being open at said downstream end of the primary section, and said downstream end of the primary burner section having means connecting thereto one or more optional additional burner sections or a closure member to close the end of the gas duct.
In FR-A-2196058 there is described a burner assembly in which a manifold of modular construction provides different mounting locations for injection nozzles to supply gas to respective burner units. Similarly FR-A-1422286 discloses a burner made up of separate blade elements supplied with gas through respective nozzles distributed along a manifold tube, so that by extending the length of the manifold and providing a greater number of blade elements the burner size can be increased. In contrast, the burner of the present invention allows its size to be tailored to the need of a particular boiler without modification to the manifold. DE-A-1551819 suggests a gas burner made up from a range of basic modules allowing various burner configurations to be obtained from the range of modules available. A more simple solution is achieved with a primary burner section and optional secondary burner sections which connect directly to the primary section in accordance with the invention.
In practice the primary burner section will conveniently be arranged to suit the boiler having the lowest maximum heat output of the range of boilers to be produced. One or more additional or add-on burner sections will be provided and by fitting them to the primary burner section the burner rating can be increased to the highest maximum heat output desired. Intermediate heat ratings of course can also be catered for. Thus, the burner of desired size is readily assembled from a limited number of basic components, and the basic primary burner section is adapted to comply with the requirements of a particular boiler in which the burner assembly is to be incorporated.
Any suitable form of mechanical connection may be utilised to connect the additional burner section or end cap to the primary burner section although it will be appreciated that a sealed connection will be required.
The additional burner sections preferably include extensions for the air and gas mixing tube which passes through the primary burner section, whereby the assembly procedure for the enlargement of the burner is further facilitated.
According to yet another aspect the invention provides a gas burner assembly of the form initially described wherein the burner includes an integral minor portion isolated from a main gas supply feeding the burner and connected to a pilot gas supply.
In this way the minor portion of the burner acts as a pilot burner, whereby the need to mount subsequently the pilot burner sub-assembly is obviated as is the deleterious affect which such separately mounted pilot burner assemblies commonly have on the air flow characteristics around the main burner creating bad combustion areas.
In the case of a burner comprising a series of parallel blade elements, the integral pilot burner may conveniently be provided by the first blade in the series. This blade may be of reduced length and used entirely as the pilot burner or only part, e.g. the central region of this blade may be utilised for the pilot burner with the other parts thereof being connected to the main gas supply. In such a construction a main gas inlet shroud may extend into the burner and serve to seal the pilot gas burner from the main gas and air mixture supply.
The several aspects of the invention provide benefits which are functionally independent, but which are nonetheless related in that they all share the same fundamental objective, namely that of achieving a basic construction for a burner assembly which is adaptable to the demands of a range of different appliances having regard to the configuration of the assembly, the performance required and the type of control system to be employed. Furthermore, the necessary adaptation can be performed at a late stage in the production of the appliance by straightforward assembly techniques, whereby the extra assembly steps required can be easily incorporated into the normal assembly line procedures.
To assist a clear understanding of the invention an exemplary embodiment will now be described with reference to the accompanying drawing, in which:

Figure 1 is a schematic side view of a gas burner assembly in accordance with the invention;
Figure 2 is a front view of the assembly;
Figure 3 is a top view of the assembly; and
Figure 4 shows a control or sequencing module which may be used with the assembly.

Illustrated in the drawing is a gas burner assembly which includes a burner 1, a manifold 2, and a control arrangement 3. The burner comprises a series of fins or blades (five as shown), the first one 5 which constitutes a pilot burner while the remaining blades 6 form a main burner. Extending through the burner are two ducts, namely an inner, i.e. venturi tube and an outer duct formed by the burner itself. At the end of the burner remote from the blade 5 this outer duct is closed off by a separate cap fastened to the burner. The burner can be expanded to provide a greater heat output in which case one, or possibly more extra flame distributing burner sections may be fitted in place of the closure cap, the primary burner section and extra burner sections being equipped with appropriate coupling means to facilitate such enlargement of the burner. (Part of an extra burner blade 6′ is shown in broken line in Figure 3). The interior of the pilot burner blade 5 is isolated from the main gas and air mixture supply duct, which is conveniently achieved by the forward end of a cylindrical main burner inlet shroud 7 telescoping into the burner and terminating between the pilot blade 5 and the next adjacent blade 6. As a modification to the construction shown, the blade 5 could be made with the same length as the blades 6, and have the outermost regions arranged to form main burner elements. In this case the forward end of the inlet shroud can be shaped to provide the necessary connections between the end portion of the blades and the main gas/air mixture supply.
Carried on the pilot burner blade are an ignition device in the form of an electrode 8, and a flame monitoring or detecting device, such as a thermocouple 9. The mounts for receiving these devices are integral with the bade 5 and provided during prefabrication of the primary burner section 1, thereby facilitating the subsequent mounting of the devices 8, 9 at a later production stage.
Projecting rearwardly from the pilot burner 5 is an air mixing tube 10 into the open rear end of which a stream of gas is directed by an injector 11 fitted to the manifold 2.
The burner 1 is firmly supported on the manifold 2 by the cylindrical main burner inlet shroud 7, a lower portion of which is removed to define an inlet for air. A main gas injector (not shown) supported by the manifold 2 is arranged to direct a main gas stream into the shroud and along its axis. The rear end ofthe shroud is fastened to the manifold by a suitable mechanical attachment means which allows pre-selection of the angular disposition of the manifold 2 relative to the axis of the shroud 7. The vertically downward orientation of the manifold as depicted in the drawing is suitable for a wall hung boiler. A vertically upward orientation would be appropriate for a free standing boiler.
To cater for the variety of manifold dispositions which are to be available for selection, a number of sealed tapping points (not shown) may be provided on the manifold with the pilot injector 11 being fitted to the tapping point corresponding to the chosen manifold disposition.
As shown in the drawing the manifold comprises a member of generally rectangular configuration, thereby presenting a planar face for mounting the burner. Defined within the manifold member are two mutually separated conduits constituting main gas and pilot gas passageways connecting corresponding inlet openings provided in an end coupling 13 with the main gas and pilot gas injectors, respectively. The manifold member may comprise an extrusion or alternatively a casting having appropriate end fittings fastened to it. The precise cross-sectional configuration of the manifold member is unimportant and it can for example include additional channels which may serve as the pilot gas passageway should a different orientation of the manifold on the control arrangement be selected as described below. Extra channels can be included to accommodate electrical leads which are connected to the pilot burner ignition electrode 8 and the thermocouple 9. These extra channels may be enclosed or could be open. In either case the electrical leads may be installed ready for appropriate connections to be made when the manifold is assembled with the burner and the control arrangement. In the illustrated embodiment an open channel 15 for the wiring associated with the electrode 8 is shown at one side of the manifold.
The end coupling 13 is adapted for quick release from and attachment to a connection face of a body 20 of the control arrangment 3, this face being provided with main and pilot gas exit ports. The precise form of the connection means is unimportant. The gas ports and openings are arranged to be brought into register upon assembly of the manifold with the control body 20. Preferably the gas ports/openings and the connection means allow the manifold to be fastened to the body in different rotational positions about an axis perpendicular to the connection face of body 20, e.g. turned through 180° from the position shown in the drawings. This allows further variation in the precise configuration of the burner assembly. Instead of the manifold being reversible on the control body, the manifold 2 could be adapted to enable the burner 1 to be mounted on either side.
The body 20 has a gas inlet port, e.g. at the left hand face as seen in Figure 2, and internal galleries connecting this inlet to the pilot and main gas exit ports. Although not included in the illustrated embodiment, the body could be equipped with a tap for shutting off the gas supply, such as during servicing periods. For controlling the gas flow during periods of normal operation, valve modules are mounted on the block, preferably by means of snap action (or other quick attachment) type fastenings which require the use of a tool for removal. The valve modules are fully assembled, complete valve units. A range of modules will be available and those appropriate for the appliance being manufactured will be selected and fitted to the body. There can be one, such as a solenoid valve module 22, for controlling the main gas feed to the burner and another, such as a manual preset flame failure module 23, to control the flow of gas to the pilot burner and to the inlet side of the valve of module 22.
The body is preferably equipped with electric contacts and internal conductors for interconnecting the contacts as appropriate. Thus, contacts may be located at the valve module reception places so that the electrical connections for electrically operated valve actuators possibly incorporated in the valve modules will be made automatically when mounting the modules.
Similarly, contacts can be provided at the connection face of the control body 20 for cooperation with contacts included on the coupling 13 and connected to either or both of the pilot ignition and flame detection devices 8,9.
The body 20 may be equipped with one or more electrical connectors, e.g. comprising contact blades and adapted for receiving push-on electrical plug connectors 25 which are wired to control means located internally and externally of the appliance, respectively. One connector could for example be wired to a sequencing module 30 which contains the logic circuitry for controlling the operation of the burner assembly in accordance with predetermined programme requirements. While the sequencing module may be mounted remotely of the burner assembly and connected to it in this way, the sequencing module can instead be mounted on the control block and have input/output contacts arranged to be brought into proper cooperation with corresponding contacts provided on the body 20 and connected electrically to other contacts for the appropriate connections to be made.
Another module shown carried on the control body 1 is a spark generator 32. A wire is shown leading from this device (and to the electrode 8 via a conduit within the manifold) but as with the other modules the necessary connections can be achieved by appropriate contacts on the spark generator and the body 20. By avoiding separate wiring connections the necessary assembly steps involved in the construction of the control arrangement from the body 20 and the selected modules is reduced to a minimum.
From the description which has been given it will be appreciated that starting from three basic parts consisting of the primary burner section, the manifold and the control body it becomes readily possible by connecting these parts in different orientations and adding appropriate parts selected in accordance with the particular requirements, to produce a wide range of different burner assemblies capable of satisfying a need for different configurations as well as a variety of control systems. Consequently a boiler manufacturer is able to produce assemblies to meet with existing production demands without having to carry large stocks of components as has been necessary with the prior art constructions.

Claims

1. A gas burner assembly characterised in that the body (20) of the control arrangement (3) is arranged to accept prefabricated and fully assembled valve modules (22, 23) selected from a range of such modules for controlling the flow of gas through a passage formed in the body and connecting gas inlet and exit ports.

2. A gas burner assembly comprising a burner (1), a control arrangement (3) for controlling the gas flow to the barrier, and a manifold (2) interconnecting the burner and the control arrangement for conducting gas to the burner from the control arrangement, the control arrangement including a body (20) with gas inlet and outlet ports and at least one valve housed in the body, characterised in that the body (20) of the control arrangement (3) has mounted thereon as a unit at least one prefabricated and fully assembled valve module (22 or 23) selected from a range of such modules for controlling flow of gas through a passage formed in the body (20) and connecting gas inlet and exit ports.

3. An assembly as claimed in claim 2 wherein the two valve modules (22, 23) are attached to the body (20) for controlling flow of gas to main gas and pilot gas exit ports, respectively.

4. An assembly as claimed in claim 2 or 3, wherein at least one valve module (22 or 23) includes an electrically operable actuating means, and said module and the body (20) have electric contacts brought into cooperation upon mounting the module on the body.

5. An assembly as claimed in claim 2, 3 or 4, wherein the body includes electrical conductors therein interconnecting contacts located on the body (20) at reception places for the valve modules (22, 23) and/or other operating or control modules (30, 32), at the connection with the manifold (2) and/or at terminal positions (25) for the connection of electrical wiring.

6. A gas burner assembly comprising a burner (1), a control arrangement (3) for controlling the gas flow to the burner, and a manifold (2) interconnecting the burner and control arrangement for conducting gas to the burner from the control arrangement, characterised in that the manifold (2) comprises a member defining a plurality of non-communicating conduits providing a main gas passage for conveying gas to the burner (1), and a further gas passage isolated from the main gas passage for conducting gas to a pilot burner (5).

7. An assembly as claimed in claim 6, wherein at one end the manifold (2) has a coupling member (13) including gas openings communicating with the respective passages, and said coupling member (13) is secured to a body (20) of the control arrangement (3) at a face of said body including main gas and pilot gas exit ports arranged to register with said openings.

8. An assembly as claimed in claim 7, wherein the manifold coupling member (13) has a releasable connection to said body.

9. An assembly as claimed in claim 7 or 8, wherein the coupling member (13) has electrical contact means connected to a pilot burner ignition device (8) and/or a pilot flame sensing means (9), and the body (20) of the control arrangement (3) includes corresponding contact means brought into engagement therewith upon connection of the manifold to the control body.

10. An assembly as claimed in claim 7, 8 or 9, wherein the coupling member (13) is arranged to enable the manifold (2) to be secured to the control body (20) in any selected one of a plurality of positions.

11. A gas burner assembly comprising a burner (1), a control arrangement (3) for controlling the gas flow to the burner, and a manifold (2) interconnecting the burner and control arrangement for conducting gas to the burner from the control arrangement, characterised in that the burner (1) is connected to the manifold (2) by means permitting the angular disposition of the manifold with respect to a substantially horizontal axis determined by the burner (1) to be selected.

12. An assembly as claimed in claim 11, wherein the burner (1) is connected to the manifold (2) by a cylindrical part (7) having an axis coincident with said substantially horizontal axis.

13. An assembly as claimed in claim 12, wherein the cylindrical part is constituted by a main gas inlet shroud (7).

14. An assembly as claimed in claim 13, wherein the manifold (2) supports a main gas injecting means for directing a stream of gas axially along the shroud (7), and a pilot gas injector means (11) selectively positionable at one of a number of attachment points in accordance with the selected angular position of the manifold (2).

15. A gas burner assembly, comprising a burner (1), a control arrangement (3) for controlling flow of gas to the burner, and a manifold interconnecting the burner and control arrangement for conducting gas to the burner from the control arrangement, characterised in that the burner (1) comprises at least a primary burner section having an upstream end connected to the manifold (2) and a downstream end, a gas duct extending through the burner being open at said downstream end of the primary burner section, and said downstream end of the primary burner section having means connecting thereto one or more optional burner sections (6) or a closure member for closing the gas duct.

16. An assembly as claimed in claim 15, wherein at least one additional burner section (6′) is fitted to the primary section and includes an extension piece arranged to extend a gas and air mixing tube passing through the primary section.

17. A gas burner assembly comprising a burner (1), a control arrangement (3) for controlling flow of gas to the burner, and a manifold (2) interconnecting the burner and the control arrangement for conducting gas to the burner from the control arrangement, characterised in that the burner (1) includes an integral minor portion (5) isolated from a main gas supply feeding the burner (1) and connected to a pilot gas supply means (10).

18. An assembly as claimed in claim 17, wherein the burner comprises a series of blade elements (6) and said minor portion is provided by the first blade element (5) of said series.

19. An assembly as claimed in claim 18, wherein a main gas inlet shroud (7) extends into the burner (1) and serves to isolate the minor portion (5) from the main gas supply.

20. An assembly as claimed in claim 17, 18 or 19 wherein said minor portion of the burner (5) has integral therewith means for mounting thereon an ignition device (8) and/or a flame sensing device (9).

21. An assembly as claimed in any one of claims 1 to 5 and also in accordance with any of claims 5 to 19.