GB2081874A - Control systems for gas appliances - Google Patents

Abstract

Gas controls, comprising a plug cock (5) and a thermostat (7) for a burner (1), are made as independent assemblies and mounted in a fire or cooker. They are operated by a knob (14) coupled to a rotatable rod (12). The rod extends through a hole in the thermostat, which can thus be mounted at any convenient position along the rod. A coupling pin (19) in the rod enters slots (20) in a rotatable element (18) formed with a temperature-setting cam (22) for the thermostat. The size of the hole and the nature of the coupling accommodate any slight misalignment. The end of the rod (12) is coupled to the input rod (9) of the plug cock by means of a flexible tube (11). In a modification the pin (19) is omitted and the element (18) is coupled to a co-axial sleeve around the upper part of the rod (12) and rotatable by a separate knob co- axial with knob (14). <IMAGE>

Description

SPECIFICATION Control systems for gas appliances This invention relates to control systems for gas appliances. The invention is particularly, but not exclusively, applicable to control systems for use in radiant gas fires. The invention is also applicable to control systems for cookers.

It is often convenient for several control devices of a gas appliance to be operated by a single knob, or by concentric knobs. The various control devices mechanically operated by the knob or knobs are normally provided in a single unit which may be of unitary construction or may comprise sub-units which are fastened together to form a single control unit.

Disadvantages of employing a single control unit are that the control unit tends to be bulky, and that the various control devices often have different or conflicting environmental requirements, such as temperature requirements.

Another disadvantage is that a single control unit is not readily adaptable to fit different gas appliances having different control requirements. In this connection it will be appreciated that it is highly desirable for a gas appliance manufacturer to be able to use identical control components in different gas appliances, and if a single unit that can perform several different functions is employed as a standard component it is necessary to render certain functions inoperative when it is used in gas appliances of some designs, and/orto provide auxiliary control devices to replace those devices embodied in the standard unit that are not suitable for the particular appliances.

An aim of the present invention is to enable these problems to be overcome or reduced.

According to one aspect of the invention a control system for a gas appliance comprises first and second mechanically operated control assemblies which are adapted to be independently mounted in spaced-apart relationship in a gas appliance, a first control connection actuable or adapted to be actuated at one end by manually operable actuating means for controlling both the first and second control assemblies and extending to an input of the first conrol assembly, and a second control connection extending from an output of the first control assembly to the second control assembly, the first control assembly being provided with transmission means arranged to transmit at least one component of movement of the input to the output so as to operate the second control assembly.

Thus, in use, the transmission means of the first control assembly serves to relay the control action for the second control assembly from the first control connection to the second control connection.

This arrangement enables the first and second control assemblies to be mounted in different locations of the gas appliance where the environmental conditions, such as the ambient temperatures, may be markedly different. Also, identical control assemblies may be used in different locations in different gas appliances, by employing control connections of appropriate lengths or kinds to suit the particular locations of the control assemblies.

Futhermore, the invention provides improved flexibility in that the system may be adapted to suit the control requirements of different gas appliances merely by replacing only one of the control assembly lies, or by omitting one of the control assemblies altogether.

A further advantage of such a system is that in the event of a fault in one of the control assemblies, that assembly alone may be replaced, possibly without disturbing the other control assembly.

Each of the control assemblies may be arranged to perform any of various functions, such as those of a gas tap, a thermostatically-controlled valve or a safety device.

Preferably the input and output of the first control assembly respectively comprise co-axial, rotatable input and output members.

Although the transmission means may comprise a plurality of force-transmitting members, when coaxial input and output members are employed the transmission means preferably comprises a single transmission member of which one end is connected to, coupled to or integral with the input member and of which the other end is connected to, coupled to or integral with the output member.

The control connections may be of any suitable kind, such as Bowden cables, but conveniently the control connections comprise elongate rigid members, preferably in the form of straight rods. Either rod may be of tubular form.

Preferably the transmission member is constituted by an intermediate length of a rod which extends through the first control assembly such that a part of the rod, on one side of the first control assembly constitutes, or forms part of, the first control connection, and another part of the rod, on the other side of that assembly constitutes or forms part of the second control connection.

This last arrangement is particularly advantageous since it enables the first control assembly to be disposed in any of a wide range of positions, as may be required in different gas appliances, merely by altering the location of the first control assembly along the rod.

The transmission means may be axially movable in addition to its being rotatable.

The relationship between the first control assembly and at least one of the control connections is preferably such as to accommodate some relative misalignment between them.

The manually operable actuating means may comprise independently operable knobs or levers for operating the respective control assemblies, in which case the first control connection comprises at least two operating components, such as a rod and a co-axial sleeve, the rod for example being arranged to operate the second control assembly, and the sleeve being arranged to operate the first assembly.

This permits the use of coaxially mounted operating knobs or levers.

Alternatively, the actuating means may comprise a single operating knob or lever which is arranged to operate both control assemblies.

The two control assemblies may then be arranged to be operated in tandem by one manual operation of the knob or lever and/or the arrangement may be such that one control assembly responds to one movement of the knob or lever while the other control assembly responds to a different movement of the knob or lever.

As indicated above, the first control connection may comprise at least two independently movable parts, one of which serves to operate the first control assembly and the other or another of which serves to operate the second control assembly. There may be two independently movable parts which are co-axial, one being disposed inside the other. In that case the arrangement is preferably such that the outer of the two co-axial parts serves to operate the first control assembly, and the inner of the two co-axiai parts serves to operate the second control assembly.

The first control assembly may incorporate an adjustable gas-valve, the adjustment of which can be effected by a rotary cam rotatable by the first control connection. The adjustable gas-valve may be such that it can also be operated by thermally-responsive means and constitutes part of a thermostat.

From another aspect the present invention consists in a gas appliance incorporating a control system as outlined above.

From yet another aspect the present invention consists in a thermostatic control valve assembly for a gas appliance comprises a housing, a sleeve mounted in the housing for angular displacement about its longitudinal axis, means mounted in the housing and responsive to angular displacement of the sleeve to alter the control temperature, and apertures in opposite sides of the housing coaxial with the sleeve axis to enable a control rod to extend through the sleeve and the housing.

The invention will now be futher described, by way of example only, with reference to the accompanying drawings in which: Figure I is a schematic view of a control system in accordance with the invention, incorporated in a radiant gas fire; Figure 2 is a view similar to the upper part of Figure 1 but showing a modification; Figure 3 is a section through a thermostatic control valve assembly in accordance with the invention; Figure 4 is a somewhat diagrammatic section through a slightly different thermostatic control valve assembly; Figures a view similar to Figure 4 but illustrates a modification; Figure 6 is a section through a valve forming part of a system in accordance with the invention, the section being along the line 6-6 of Figure 7; and Figure 7 is a section along the line 7-7 of Figure 6.

With reference to Figure 1 a radiant gas fire is provided with a main burner 1 of the well-known duplex kind provided with two injectors 2 and 3.

Injector 2 is supplied with gas directly from a first outlet 4 of a plug cock 5 having an inlet 6, and injector 3 is supplied indirectly by way of a thermostatically controlled valve assembly 7 which controls the gas supply from a second outlet 8 of the plug cock 5.

Plug cock 5 is controlled by a rotatable input rod 9 which also controls, in well known manner, an ignition device 10 for the main burner 1. Input rod 9 is connected by a suitable coupling, such as flexible sleeve 11, to the lower end of a main operating rod 12 which is keyed at its upper end 13 to a manually operable knob 14 provided on its underside with a boss 15 located with clearance in a hole 16 in the top wail 17 of the appliance casing. Sleeve 11 accommodates any slight misalignmentof rods 9 and 12.

Valve assembly 7 and plug cock 5 respectively constitute first and second control assemblies which are independently mounted in the gas fire. Plug cock 5 is carried by the main burner 1, and the valve assembly 7 is supported by a bracket, not shown, adjacent to the heat exchanger, not shown, which is of conventional form and is heated in the usual way by the hot gases coming from the radiant elements mounted on top of the burner 1. The valve assembly 7 is provided with a temperature-sensitive element so positioned that it responds to changes in temperaure of the heat exchanger. The valve assembly itself is mounted conveniently adjacent to the heat exchanger.

Valve assembly 7 has been partially sectioned in Figure 1 in order to show a valve-operating sleeve 18 which is co-axially mounted on the main operating rod 12 and is coupled thereto by a transversely extending pin 19 which extends through a hole in the rod 12 and through diametrically opposed, axially extending slots 20 in the sleeve 18. The pin and slot coupling allows for any slight misalignment of rod 12 and sleeve 18. The sleeve 18 is journalled in a through-bore of a housing 21 of the valve assembly.

A cam 22 is provided on the outside of the sleeve and it co-operates with a cam-follower, not shown, which controls the temperature setting of the thermostat.

It will be appreciated that the upper portion 23 of the rod 12 constitutes a first control connection extending between the knob 14 and the input of the valve assembly 7 constituted by a portion 24 of the rod, that the portion 25 of the rod within sleeve 18 constitutes a transmitting member of the assembly 7 which connects the portion 25 with the output, constituted by a portion 26 of the rod, and that the lowermost portion 27 of the rod constitutes a second connection between the output of the valve assembly 7 and the plug cock 5.

Since the valve assembly 7 may be arranged at any convenient height along the rod 12, the system may be adapted with ease to fit a range of gas fires of different designs.

The operation of the system of Figure 1 will now be briefly described. On initial angular movement of knob 14the plug cock 5 is opened to supply gas to injector 2, and the ignition device 10 is operated by the rod 9 to ignite the burner 1. At this stage the injector 3 is inoperative, its gas supply being shut off by the plug cock 5. On further angular movement of knob 14 the plug cock operates to allow the passage of gas to the valve assembly 7, and the setting of the thermostat in that assembly is varied in dependence upon the angular position of cam 22. The supply of gas to the injector 3 is thus dependent on the cam-setting and on the temperature sensed by the thermostat element.

As shown in dotted outline in Figure 1,the plug-cock outlet 8 may be connected directly to the injector 3, and the valve assembly 7 may be dispensed with. The resulting system provides a simple control for a gas fire, and has no thermostatic control. This modified system is not within the scope of the present invention but it does illustrate the way in which the present invention enables standard components such as the plug cock 5 to be used without modification.

A modification within the scope of the present invention is illustrated in Figure 2. Those components that are similar to components used in the embodiment of Figure 1, have been given the same reference numerals as the corresponding components in Figure 1. In the arrangement shown in Figure 2 the sleeve 18 is operated, independently of the rod 12, by an operating sleeve 28 connected to the sleeve 18, coaxial with portion 23 of the rod 12 and controlled by a lever 29 carried by a cup 30 which is secured to the sleeve 28 and is arranged co-axially of knob 14.

It will be appreciated that in this arrangement the co-axial portion 23 of the rod 12 and the sleeve 28 together constitute said first control connection, and that the input to the assembly 7 is constituted by the upper end of sleeve 18 in conjunction with rod portion 24.

The thermostatic control valve assembly shown in Figure 3 may be used in place of the assembly 7 shown in Figures 1 and 2, but is primarily intended for use in controlling the supply of combustible gas to the oven burner or oven burners of a domestic cooker.

The control comprises a body 31 formed with a bore 32 and a gas inlet 33, through which gas enters the control in use. The gas inlet communicates with an open-mouthed cavity 34 in the top side of the body.

A control element is mounted for rotation in the tapered bore 32. Spaced portions of the element are cylindrical, while a portion 35, between the cylindrical portions constitutes a cam. O-ring seals are housed in circumferential grooves in the cylindrical portions of the element.

The body 31 thus corresponds to the body 21 shown in Figure 1, and the rotatable element with cylindrical end portions and a cam between them corresponds to the sleeve 18 with the cam 22.

An axially movable rod 36 is mounted in a hole formed in the body 31, and the lower end surface of the rod engages the surface of the cam 35. The upper end of the rod projects from the body 31 into the interior of a housing 37 secured to the top of the body by screws (not shown), a sealing gasket 38 being interposed between the housing and the body.

The upper end surface of the rod 36 engages a dome-shaped projection 39 formed on the underside of an end portion of a beam 40 which is disposed in the housing 37. The beam is formed from sheet metal and has down-turned stiffening flanges along is side edges. A second, upwardly facing, domeshaped projection 41 is formed in a central part of the beam. That end portion of the beam further from the rod 36 carries a valve component comprising a valve head or valve member 42 at the lower end of a rod from which projects a flange 43. The rod extends through an open-ended slot in the adjacent end portion of the beam 40, and the flange 43 normally engages the upper surface of the beam. A leaf spring 44 overlies the beam and is secured to the beam by rivets near one end thereof. There is a hole in the central part of the spring to allow the projection 41 to project through it.Near its other end the spring is formed with a hole which receives the upper end portion of the valve rod. The spring urges the valve component into a position or towards a position in which the flange 43 engages the upper surface of the beam.

The beam 40 is located in the housing 37 by means of a locator 45 which is made from spring steel sheet. One end portion of the locator has lateral wings which enter vertical grooves in opposite side walls of the housing. The adjacent end portion of the beam extends horizontally through a slot in that end portion of the locator. The central part of the locator lies beneath the beam, one end thereof abutting the gasket and the other end thereof abutting the underside of the beam adjacent to the valve component and urging the adjacent part of the beam upwards. An upturned tag 46 at the upper end of the inclined central part of the locator projects upwards through the slot in the beam and through a slot in the leaf spring 44.

The projection 41 in the central part of the beam is urged upwards by the locator 45 into engagement with an abutment 47 at the centre of the lower face of a concentric bellows assembly 48 constituting part of a thermally-responsive device. Atubular mounting 49 extends axially upwards from the upper face of the bellows assembly, extends through a hole in the housing and is held in place by a circlip 50 which enters a circumferential groove in the mounting. The hole is sealed around the mounting to prevent the escape of gas. A tube 51 is connected to the mounting 49 and leads to a vial (not shown). The interiors of the vial, tube 51, mounting 49 and bellows assembly 48 intercommunicate and contain an oil which expands when heated. In use the vial is situated in or near the oven enclosure.When the temperature in the enclosure rises, the oil expands and causes the bellows assembly to expand and to push the central part of the beam downwards.

The valve member 42 co-operates with a valve seating constituted by the upper end portion of a tubular component 52 which is externaily screwthreaded and is mounted in a correspondingly tapped bore in the body 31. The interior of the tubular component 52 communicates with a gas way 53 terminating at a gas outlet port in an outside face of the body 31.

The axial position of the valve seating can be adjusted by rotating the tubular component 52. This rotation can be effected by means of a ring of teeth 54 formed on the outside of that end portion of the component further from the seating, the teeth engaging complementary teeth 55 at the inner end of a drive member constituted by a pin 56 and rotatably mounted in a bore in the body 31 parallel with the bore containing the tubular component 52.

A screw-driver slot 57 is formed in the outer end of the pin 56. An O-ring 58 is housed in a circumferential groove in the pin and serves both as a seal and as a friction element to retain the pin in position both axially and rotationally. A resilient plug 59 normally closes the end of the bore containing the pin. In use, when the plug 59 is removed the pin 56 can be rotated with the aid of a screw-driver to adjust the axial position of the seating 51. The screw-thread on the tubular component is of a relatively small pitch and is coated with a film of grease so that little or no gas can pass along the thread between the component and the body, and there is sufficient friction to prevent unintentional rotation of the component in use.

The rotatable element incorporating the cam 35 is formed with an axial hole which extends right through the element. There is also formed a through hole in the body 31 co-axial with the element so that there is an unbroken hole extending through the entire assembly. An operating rod 60, similar to the rod 12, extends through the hole. The rod may be coupled to the element so that the element rotates in unison with the rod, or the element may be coupled to a sleeve, similar to the operating sleeve 28 (Figure 2), by means of which it can be rotated.

To simplify the foregoing description the control has been described as if it were in one particular orientation, that is with the housing 37 at the top; it is to be understood, however, that the control may equally well be positioned in any other desired orientation when in use.

In use, the rod 60 can be coupled to a gas tap by means of which a supply of gas to the thermostat control shown in Figure 3 can be turned on and off.

The gas tap constitutes a second control assembly and part of the rod 60 constitutes the second control connection. The gas tap is initially in its off position to prevent any flow of gas to the thermostat control.

When the gas tap is turned on gas can flow from the tap and through the inlet 33.

The position of the valve member 42 relative to the valve seating is initially determined by the position of the rod 36 which is in turn determined by the rotational position of the cam 35. Initially the valve is likely to be open, enabling gas to pass freely to the burner where it is ignited. As the temperature in the oven rises the vial is heated and the bellows assembly 47 expands accordingly and tends to move the valve member towards the valve seating or onto thevalve seating thus reducing or cutting off the flow of gas through the valve. The temperature to which the vial must be heated to cause the valve member 42 to engage the valve seating depends on the rotational position of the cam 35. The element of which the cam forms a part can be rotated manually through the intermediary of the first control connection.

There is a gas bypass (not shown) from the interior of the housing 37 to the gas outlet permitting gas to flow at a relatively slow rate, even when the valve member engages the seating, that slow rate being sufficient to enable the burner to remain alight, though with a reduced heat output. Thus the control serves as a thermostat for the oven. Owing to the inevitable time delays in the system there are occasions when the bellows assembly continues to expand for a short while even after the valve member 42 has engaged the valve seating. When this occurs the beam 40 continues its downward movement and is temporarily parted from the flange 43 of the valve component, the leaf spring 44 yielding appropriately.

Figures 4 and 5 illustrate in somewhat diagrammatic form other possible arrangements. In Figure 4 a thermostat body 61 is formed with a cylindrical bore containing a rotatable control element 62. Circumferential grooves in the element contain O-ring seals 63. A portion of the element between the seals is formed with a cam surface 64 which engages a rod (not shown) which acts in a manner similar to the rod 36 (Figure 3). Adjacent to one of its ends the element 62 is formed with a longitudinally extending slot 65. One end of a pin 66 projects into the slot, the other end thereof being housed in an operating rod 67 which extends axially through the element and through the body 61. Rotation of the rod 67 causes rotation of the element 62, but the rod is free to move axially. Rotation of the rod may also operate a gas-valve or other control assembly as in the system illustrated in Figure 1.In addition, however, the axial movement of the rod may be employed for any of a number of purposes. It may, for example, be connected to ignition means, to a flame-failure device of the kind in which a valve opened by axial movement is retained open by an electro-magnet powered by a thermocouple orto niting means to prevent or resiliently resist rotation of the rod.

The arrangement illustrated in Figure 5 is in part similar to that illustrated in Figure 4, and similar parts in the two Figures are given the same reference numerals. In the arrangement illustrated in Figure 5 there is a blind axial hole in the sloted end of the element 62, and the rod 67 terminates in the hole. A compression spring 68 in the hole urges the rod axially relatively to the control element. At the other end the element is formed with an axial spigot 69 which projects from the body 61 and carries a transverse pin 70. The ends of the pin enter longitudinal slots 71 in one end of a second operating rod 72 so that rotation of the element 62 causes rotation of the rod 72. The operating rod 67 (which constitutes the first control connection) can be rotated to rotate the element 62 (which constitutes the transmission means) and can also be moved axially.

Rotation of the rod 67 also brings about rotation of the rod 72 (which constitutes the second control connection) but, unlike the situation with the arrangement illustrated in Figure 4, axial movement of the rod 67 does not cause axial movement of the rod 72. Any device dependent on axial movement must therefore be coupled to the rod 67 rather than to the rod 72.

It is to be understood that the assembly shown in Figure 3 can be modified to incorporate the principles described above with reference to Figures 4 and 5.

The gas-valve shown in Figures 6 and 7 comprises a generally tubular body 73 with a laterally extending gas inlet 74 near one end and a gas outlet 75 at the other end. The inlet 74 leads into a chamber 76 which is closed at the end by a cap 77. The chamber 76 contains a valve member 78 with a resilient annular sealing flange urged towards a planar, annular valve seat 79 by a spring 80 which acts between the cap 77 and the valve member. An axially movable rod 81 engages the valve member 78, extends through a fixed guide 82 and engages a cam 83 formed on an operating member 84 which is rotatable about an axis normal to and intersecting the axis of the rod.

The operating member 84 is provided at its right-hand end, in Figure 7, with a driving spigot 85 of D-shape in transverse cross-section which is received with clearance within a bore of complementary, but slightly larger, cross-section in one end of a shaft 86 of which the opposite end is connected to a manually operable knob, not shown, arranged in a manner similar to the knob 14 of Figure 1. At its left-hand end 87 the operating member 84 is provided with a bore 88 in which is loosely received one end of a further shaft 89 which is keyed thereto by a transverse pin 90 which projects from one side of shaft 89 through a single axial slot 91 in end 87. The shaft 89 is used to operate a further valve unit, not shown.

The connections between the operating member 84 and the shafts 86 and 89 permit a certain amount of misalignment of the shafts 86 and 89 so that the positioning of the valve units in the gas appliance is not critical.

That part of the body 73 adjacent to the cam 83 is enlarged laterally, as shown in Figure 7 to accommodate the cam. O-rings 92 serve to prevent the escape of gas. The central part of the cam 83 is so shaped as to engage the rod 81 and cause the valve member 78 to be lifted from its seat 79 as the operating member 84 is rotated, the valve being fully open after a relatively small rotation. At the same time the outer parts of the cam co-operate with the adjacent walls of the interior of the body 73 to afford constrictions which gradually become wider as the operating member is rotated. In this way the principal function of the valve member 78 is to turn the supply of gas on and off while that of the cam 83 is to vary the supply when the gas is on. A blind axial hole 93 is formed in the cam 83 and serves to join two radial holes 94 and 95 which are mutually offset axially of the cam. Athreaded pin 96 enters the hole 93, closes its outer end, and by co-operating with a shoulder in the hole controls the passage of gas from hole 94 to hole 95. When the valve is just open, but the cam surface does not allow gas to flow past the cam, the holes 94,93 and 95 allow a controlled flow of gas through the cam, sufficient to permit combustion.

This form of gas-valve is particularly suitable for controlling the supply of gas to a gas fire.

Claims (19)

1. A control system for a gas appliance comprising first and second mechanically operated control assemblies which are adapted to be independently mounted in spaced-apart relationship in a gas appliance, a first control connection, actuable or adapted to be actuated at one end by manually operable actuating means for controlling both the first and second control assemblies and extending to an input of the first control assembly, and a second control connection extending from an output of the first control assembly to the second control assembly, the first control assembly being provided with transmission means arranged to transmit at least one component of movement of the input to the output so as to operate the second control assembly.

2. A control system according to claim 1 in which the input and output of the first control assembly respectively comprise co-axial, rotatable input and output members.

3. A control system according to claim 2 in which the transmission means is rotatable as a unit so that rotation of the input member causes corresponding rotation of the output member.

4. A control system according to claim 3 in which the transmission means is constituted by a portion of a rotatable rod or tube which extends through the first control assembly and extends beyond that assembly to form at least part of at least one of the control connections.

5. A control system according to either of claims 3 and 4 in which the transmission means is axially movable in addition to its being rotatable.

6. A control system according to any of claims 2 to 5 in which the relationship between the first control assembly and at least one of the control connections is such as to accommodate some relative misalignment between them.

7. A control system according to claim 2 in which the first control connection comprises at least two independently movable parts, one of which serves to operate the first control assembly and the other or another of which serves to operate the second control assembly.

8. A control system according to claim 7 in which there are two independently movable parts which are co-axial, one being disposed inside the other.

9. Acontrol system according to claim 8 in which the outer of the two co-axial parts serves to operate the first control assembly, and the inner of the two co-axial parts serves to operate the second control assembly.

10. A control system according to any of the preceding claims in which the first control assembly incorporates an adjustable gas-valve, the adjustment of which can be effected by a rotary cam rotatable by the first control connection.

11. A control system according to claim 10 in which the adjustable gas-valve can also be operated by thermally-responsive means and constitutes part of a thermostat.

12. A control system substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

13. A control system according to claim 12 but modified substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

14. A control system according to claim 1 incorporating a valve assembly substantially as herein be fore described with reference to Figure 4 of the accompanying drawings.

15. A control system according to claim 1 incorporating a valve assembly substantially as herein be fore described with reference to Figure 5 of the accompanying drawings.

16. A control system according to claim 1 incorporating a valve assembly substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

17. Agas appliance incorporating a control system in accordance with any one of the preceding claims.

18. A thermostatic control valve assembly for a gas appliance comprising a housing, a sleeve mounted in the housing for angular displacement about its longitudinal axis, means mounted in the housing and responsive to angular displacement of the sleeve to alterthe control temperature, and apertures in opposite sides of the housing co-axial with the sleeve axis to enable a control rod to extend through the sleeve and the housing.

19. An assembly according to claim 18 and substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.