GB1601103A

GB1601103A - Gas taps

Info

Publication number: GB1601103A
Application number: GB10336/77A
Authority: GB
Original assignee: Concentric Controls Ltd
Current assignee: Concentric Controls Ltd
Priority date: 1977-03-11
Filing date: 1977-03-11
Publication date: 1981-10-28
Also published as: DE2810449A1; IT7821108A0; AU3401578A; FR2383370A1; IT1093220B

Description

(54) GAS TAPS (71) We, CONCENTRIC CONTROLS LIMITED, a British Company of Priory Road, Birmingham, B6 7LH, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: This invention relates to gas taps and in particular to gas taps of the kind comprising a body formed with a bore and a plug rotatable in the bore, a first gas-way extending through the body to a port in the bore, and the plug being formed with a second gas-way in communication with a helical or substantially helical groove in the outer surface of the plug, the arrangement being such that in use gas can flow from one gas-way to the other by way of the port and the groove, and that by rotation of the plug in the body the extent to which the groove overlaps the port, and thus the extent to which the flow of gas is restricted by the overlap, is gradually and progressively varied.

In practice, particularly when such gas taps are manufactured commercially, difficulties arise due to manufacturing tolerances, and it is found difficult to ensure that at any given angular relationship between the plug and the body the rate of flow of gas in exactly that required. This problem is explained in more detail below with reference to a particular embodiment of gas tap of the kind specified.

An aim of the present invention is to provide means whereby the adverse effects arising from this problem can be overcome or reduced.

According to the present invention a gas tap of the kind referred to above is characterised by the provision of a restrictor in the first gas-way operative to restrict the flow of gas through the groove, the restrictor being adjustable in such a manner that in use, at a predetermined angular position of the plug relative to the body, the rate of flow of gas, as determined at least in part by the combined effects of the groove and the restrictor, has a predetermined value.

The restrictor is preferably tubular, one end thereofbeing adjacent to the port, and the restrictor being adjustable so as to cause variation in the extent to which the gas flow through the groove is restricted in use when the plug is in said predetermined angular position. The restrictor is preferably so mounted that on rotation it moves axially, it being possible to effect adjustment by such rotation and axial movement. For example the restrictor may be externally screw-threaded and engage a corresponding thread in the first gasway. Alternatively the opening at the end of the tubular restrictor adjacent to the port may be eccentric or may be otherwise shaped or positioned that adjustment can be effected by rotation of the restrictor without axial movement thereof.

Gas taps embodying the present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an end view of a first gas tap, embodying the invention, Figure 2 is a section through the body of the gas tap, along the line 2-2 of Figure 1, Figure 3 is a view of one end part of the body as viewed from below in Figure 1, Figure 4 is a side view, to a larger scale, of the plug of the gas tap, Figure 5 is a section through the plug, along the line 5-5 of Figure 4, Figure 6 is a section to a larger scale of an insert, constituting a restrictor, shown in Figure 2, Figure 7 is an end view, from above, of the insert shown in Figures 2 and 6, Figure 8 is a section through a small part of a second gas tap embodying the invention, similar to part of the section of Figure 2 but to a much larger scale, and showing a different form of insert, Figure 9 is an end view, from above, of the insert shown in Figure 8, Figure 10 is a section along the line 10-10 of Figure 8, and Figure 11 is a graph illustrating the operation of the gas taps.

The gas taps illustrated largely resemble the gas tap that is the subject of British Patent No.

1 329 243 of Concentric Controls Limited, though whereas that earlier tap was capable of use with gases of different calorific values supplied at different pressures, the new gas taps, illustrated in the accompanying drawings, are primarily intended for use with gas of one calorific value supplied at a predetermined pressure. For example the taps illustrated may be used to control gas supplied at 8 inches water gauge (w.g.) with a calorific value of about 1000 B.Th.U per cubic foot. Similar taps may be used to control 1 .p. gas (liquid petroleum gas).

The gas tap shown in Figures 1 to 7 being largely similar to the gas tap described in the complete specification of the aforementioned British patent will not be described here in detail. Briefly, then, the tap comprises a body 10 made as an extrustion from brass or other suitable metal and formed with a longitudinally extending hole of which the central part constitutes a tapered bore 11. The body has a flat face 12 which can be secured against the mating face of other apparatus by means of screws which enter threaded holes 13. A gasway 14 extends in a direction radial with respect to the axis of the bore 11 and leads from an opening in the face 12 to a port 15 in the bore 11. At the narrower end of the bore 11 is a duct 16; at the broader end of the bore is a niting slot 17 of the shape shown in Figure 3.

A tapered plug 18 is rotatable in the bore 11. The plug is formed with an axial hole 19 extending into it from its narrower end, and a radially extending hole 20 which communicates with the inner end part of the hole 19. The holes 19 and 20 together constitute gas-way in the plug. The plug is also formed with a second radial hole, 21, which constitutes a bleed hole, the outer part thereof being of increased diameter as can be seen in Figures 4 and 5. A substantially helical groove 22 is milled in the outer face of the plug, one end of the groove communicating with the hole 20.

The plug 18 is also formed with an axial hole 23 which extends into it from the broader end. A helical compression spring (not shown) is provided in this hole and urges the plug axially into contact with the wall of the bore 11. A control rod 24 projects axially into the hole 23 and engages the spring. A radial pin 25 on the control rod projects through an axial slot 26 in the plug and enters the niting slot 17. A screw 27 prevents the disassembly of the tap after the pin 25 has entered the niting slot 17.

In normal use the gas-way 14 is connected to a supply of gas, and the duct 16 is connected to a gas burner. The operation of the tap is illustrated graphically in Figure 11. The x-axis of the graph represents the angle through which the plug is rotated from its fully off position, while the yaxis represents the rate of flow of gas through the tap; both scales are linear. In its fully off position part of the plug blocks the port 15. As the plug is rotated through an angle of about 30 the edge of the bleed hole 21 comes into register with the bore. On further rotation, to about 650, gas continues to flow through the bleed hole and the rate of flow remains substantially constant. The size of the bleed hole is such that combustion of the gas at the burner can just be maintained.When the plug is rotated beyond about 65" the groove 22 comes increasingly into register with the port 15 and permits a gradual and progressive increase in gas flow; this change is normally referred to as modulation. Finally, when the plug is rotated beyond about 1200 the radial hole 20 is largely or wholly in register with the port 15 so that the rate of flow is again substantially constant.

In the manufacture of gas type of this type problems tend to arise due to the normal manufacturing tolerances. The position of the substantially helical groove 22 in the outer face of the plug 18 is determined with reference to the broader end of the plug, but the diameter of the tapered plug 18, at any particular distance from that end of the plug, may differ slightly from plug to plug in normal manufacture. Likewise the position of the gas-way 14 in the body 10 of the gas tap, and thus the position of the port 15 constituted by the inner end of that gas-way is determined with reference to one end of the body 10, though the diameter of the tapered bore 11 at any particular distance from that end of the body may differ slightly from plug to plug.In a typical gas tap the taper of the plug is 1 in 6, so that the angle between the axis of the plug and the generatrix of a notional cone of which the outer surface of the plug forms a part is about 9.5 . In consequence, any slight variations in diameter as described above may lead to the plug being disposed lengthwise in the bore at a position differing significantly from the intended position. For example, an error in diameter of 0.001 inches would lead to a longitudinal displacement of about 0.006 inches. It will be appreciated that errors in the diameters of the plug and the associated bore may be additive and thus lead to a still larger longitudinal displacement from the intended relative longitudinal position of the plug in the body. This type of error will not, however, significantly affect the principal flowcharacteristics of the tap, for in use, when the plug is rotated in the body the radial hole 20 in the plug will progressively pass out of register with the port 15 in the body 10, and thereafter the groove 22 will likewise progressively pass out of register with the port 15.

Thus a curve on a graph corresponding to the graph 11 but for a tap in which the plug is axially displaced will be largely similar in shape from the curve on the graph shown in Figure 11 in spite of the fact that in the two taps concerned the relative longitudinal positions of the plugs in the housings differ considerably. Nevertheless, though the shapes of the curves are similar, part of the curve is shifted somewhat along the x-axis. In particular the curve for a tap in which the plug was displaced longitudinally from its intended position would be of largely similar shape to that in Figure 11 but part of it would be displaced along the x-axis so that modulation would start at (60 + n) ; nevertheless the rate of change of gas flow with plug angle would be the same as before.In a typical tap the groove 22 is cut at an angle of 130 at a plane normal to the axis of the plug. In that case n is approximately equal to the longitudinal displacement of the plug as measured in thousandths of an inch. Although that part of the curve corresponding to modulation of the gas flow would be displaced along the x-axis with longitudinal displacement of the plug, the cutoff point at 300 would remain substantially unaltered as it is determined by the angle at which the widened outer end of the bleed hole 21 passes out of register with the port 15. That angle scarcely alters with longitudinal displacement of the plug in the bore of the housing as the axes of the bleed hole 21 and the port 15 lie close to a common plane normal to the axis of the plug.

Hitherto, therefore, two taps may have differed from each other in the angles through which the plugs had to be tumed to bring about the same rate of gas flow, but the rate of change of flow with angular rotation was the same for each tap substantially throughout its modulating range of operation. Such taps are often quite satisfactory, but they can cause difficulty if the extent of the angular rotation of each plug from the off position is indicated by means such as a co-operating pointer and a numberbearing dial. For example a gas cooker may be provided with two similar gas burners controlled by nominally similar taps, but one tap may permit a certain rate of gas flow when its pointer and dial indicate a certain angular position, while the other tap permits a different rate of gas flow when adjusted to the same angular position.The user may note that a setting of a particular number of one dial is suitable for a particular purpose, but would find that if the same number were set on the other dial the associated burner would operate at a different rate from the burner associated with the former dial.

The present invention aims to overcome or reduce that difficulty by providing means whereby the rate of flow through the groove can be adjusted after assembly of the gas tap.

In the embodiment illustrated in Figures 1 to 7 there is a restrictor 28 disposed in the gas-way 14. The restrictor is made from a plastics material such as an acetal resin or a nylon. The outer end part of the restrictor is externally screw-threaded and engages a corresponding intemal thread in the outer end part of the gas-way. The inner end part of the gas-way 14 is not threaded and is of slightly reduced diameter. This is entered by the inner end portion of the restrictor which has a peripheral bead 29 which seals against the unthreaded wall of the gas-way. The restrictor has has an axial hole 30, the outer end of which is enlarged to form a hexagonal socket 31 for a correspondingly shaped key.

Taps of the kind illustrated are such that in the absence of any restrictors modulation starts at various angular positions of the plug within a range of angular positions determined by the predetermined manufacturing tolerances. The design of the taps is such that the maximum angle of that range is equal to or less than the angle at which modulation is required to start.

When a restrictor is inserted into the gas-way 4 of such a tap its inner end can be brought close to that part of the port 15 which cooperates with the groove 22 to control the rate of flow of any gas during modulation. If the axial position of the restrictor is varied the position of the inclined part of the curve of Figure 10 corresponding to the modulation of the gas flow moves bodily along the x-axis, while the position of the cutoff point remains substantially unaltered. Thus by adjusting the axial position of the restrictor in each of the taps, all the taps can be caused to have gas flow characteristics resembling quite closely those of the ideal characteristics illustrated in Figure 10.

In manufacture each tap is mounted on a test bench so that air at a predetermined pressure is introduced into the gas-way 19, 20 in the plug through the axial duct 16 in the body 10. The plug is rotated to a predetermined angular setting in relation to its off position.

Conveniently the angle is such that in a perfect tap it corresponds to a certain point on the inclined, modulation portion of the gas flow curve. For example the angle might be 76".

To assist the user to locate readily a setting corresponding to a predetermined point near the lower end of the inclined portion of the curve the niting slot 17 is formed with an intermediate notch 32 for the pin 25 to enter when the plug has been rotated to this angle.

Thus, in a convenient method of manufacture, the plug is rotated to bring the pin 25 into the notch 32, and the restrictor 28 is adjusted until a predetermined rate of air flow is achieved. There is of course a simple relationship between the gas flow that occurs in use and the air flow used when the insert is being adjusted, and that relationship is taken into account when the appropriate predetermined rate of air flow is initially decided upon.

A second construction is illustrated in Figures 8 to 10. Here the body 33 (which is similar to the body 10) has a cylindrical gasway 34 (equivalent to the gas-way 14). There is also a plug 35 (similar to the plug 18) with a substantially helical groove 36 (similar to the groove 22). A restrictor 37 is inserted into the gas-way 34. The restrictor is made from a suitable plastics material such as an acetal resin or a nylon. The restrictor has a cylindrical bore 38 of which the axis is parallel to but spaced from the axis of the outer cylindrical surface of the restrictor. At its outer end the restrictor is formed with screw-driver slots 39, while at its inner end the restrictor is chamfered to present a frustoconical end surface. The cone angle is the complement of the cone angle of the plug and is therefore about 80.5Q.

In this construction the restrictor 37 is pushed to the inner end of the gas-way 34, and adjustment is effected by rotating the restrictor with the aid of a screw-driver. The presence of the screw driver blade in the screw-driver slots during adjustment is found not to affect significnatly the flow-rate of the air used during the adjustment. As the insert is rotated the extent to which its inner end restricts the air flow through the groove 36 varies.

To understand more fully the operation of the restrictor 37 it is necessary to consider in detail the relationship between the inner end of the restrictor and the plug 35. It will be appreciated that if, in the absence of the restrictor, one looks axially down the gas-way 34 one will see a portion of the outer surface of the plug, that surface being frustoconical in shape. If then a flat-ended restrictor is inserted axially down the gas-way, its inner end, which lies in a plane normal to the axis of the gas-way, meets the portion of the frustoconical surface of the plug at the uppermost point of the exposed surface. The remainder of the flat end of the restrictor, however, is spaced away from the frustoconical surface due to the inclination and curvature of that surface.The situation is quite similar when the inner end of the restrictor is chamfered, as in the embodiment illustrated in Figures 8 to 10, though the inner end of the restrictor can now come into line contact with the plug. Figure 8 is a section through the plane in which the line contact can occur, though in that Figure the presence of the groove 36 prevents such contact. From Figure 10,however, it can be seen that the curvature of the plug results in the groove being only partially restricted by the restrictor; further the inner end of the restrictor is spaced some way from that edge of the port which co operates with the bleed hole to start the gas flow, so that the angle of the plug at which gas flow starts is independant of the presence of the restrictor.

The relative dimensions of the components are such that when the plug is at the angular setting at which adjustment of the restrictor is effected (again typically 760) the maximum extent to which the groove 36 overlaps the port at the inner end of the gas-way 34 is less than the maximum wall-thickness of the restrictor.

When the restrictor is inserted, therefore, it cannot be inadvertently pushed into the groove.

It is desirable that the restrictor should not be able to enter the groove, for it its inner end were to project into the groove it might be severed from the remainder of the restrictor on rotation of the plug towards its off position.

The effect on the restrictor itself would be negligible, but the small speck of plastics material might move from the groove and cause trouble elsewhere.

In each of the two embodiments illustrated the inner end of the restrictor is chamfered so as to be slightly frustoconical. This is not essential, however, and the inner end could be flat, in a plane normal to the axis of the insert.

Both restrictors are made of a plastics material. Such a material is preferred as its resilience enables the restrictor to be retained in position merely by friction and makes it unnecessary to provide an adhesive or locking medium to secure the insert in position, and it avoids the formation of any metal swarf that might interfere with the correct operation of the tap. Nevertheless the inserts might be made of metal or other materials as desired.

WHAT WE CLAIM IS: 1. A gas tap of the kind comprising a body formed with a bore and a plug rotatable in the bore, a first gas-way extending through the body to a port in the bore, and the plug being formed with a second gas-way in communication with a helical or substantially helical groove in the outer surface of the plug, the arrangement being such that in use gas can flow one gas-way to the other by way of the port and the groove, and that by rotation of the plug in the body the extent to which the groove overlaps the port, and thus the extent to which the flow of gas is restricted by the overlap, is gradually and progressively varied, characterised by the provision of a restrictor in the first gasway operative to restrict the flow of gas through the groove, the restrictor being adjustable in such a manner that in use, at a predetermined angular position of the plug relative to the body, the rate of flow of gas, as determined at least in part by the combined effects of the groove and the restrictor, has a predetermined value.

2. A gas tap according to Claim 1 in which the restrictor is tubular, and one end thereof is adjacent to the port, the restrictor being adjustable so as to cause variation in the extent to which the gas flow through the groove is restricted in use when the plug is in said predetermined angular position.

3. A gas tap according to Claim 2 in which the restrictor is so mounted that on rotation it moves axially, it being possible to effect adjustment by such rotation and axial movement.

4. A gas tap acording to Claim 2 in which the opening at that end of the tubular restrictor adjacent to the port is so shaped or positioned that adjustment.can be effected by rotation of the restrictor without axial movement thereof.

5. A gas tap according to any of Claims 2 to 4 in which the restrictor is retained in position merely by friction.

6. A gas tap according to any of Claims 2 to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. resin or a nylon. The restrictor has a cylindrical bore 38 of which the axis is parallel to but spaced from the axis of the outer cylindrical surface of the restrictor. At its outer end the restrictor is formed with screw-driver slots 39, while at its inner end the restrictor is chamfered to present a frustoconical end surface. The cone angle is the complement of the cone angle of the plug and is therefore about 80.5Q. In this construction the restrictor 37 is pushed to the inner end of the gas-way 34, and adjustment is effected by rotating the restrictor with the aid of a screw-driver. The presence of the screw driver blade in the screw-driver slots during adjustment is found not to affect significnatly the flow-rate of the air used during the adjustment. As the insert is rotated the extent to which its inner end restricts the air flow through the groove 36 varies. To understand more fully the operation of the restrictor 37 it is necessary to consider in detail the relationship between the inner end of the restrictor and the plug 35. It will be appreciated that if, in the absence of the restrictor, one looks axially down the gas-way 34 one will see a portion of the outer surface of the plug, that surface being frustoconical in shape. If then a flat-ended restrictor is inserted axially down the gas-way, its inner end, which lies in a plane normal to the axis of the gas-way, meets the portion of the frustoconical surface of the plug at the uppermost point of the exposed surface. The remainder of the flat end of the restrictor, however, is spaced away from the frustoconical surface due to the inclination and curvature of that surface.The situation is quite similar when the inner end of the restrictor is chamfered, as in the embodiment illustrated in Figures 8 to 10, though the inner end of the restrictor can now come into line contact with the plug. Figure 8 is a section through the plane in which the line contact can occur, though in that Figure the presence of the groove 36 prevents such contact. From Figure 10,however, it can be seen that the curvature of the plug results in the groove being only partially restricted by the restrictor; further the inner end of the restrictor is spaced some way from that edge of the port which co operates with the bleed hole to start the gas flow, so that the angle of the plug at which gas flow starts is independant of the presence of the restrictor. The relative dimensions of the components are such that when the plug is at the angular setting at which adjustment of the restrictor is effected (again typically 760) the maximum extent to which the groove 36 overlaps the port at the inner end of the gas-way 34 is less than the maximum wall-thickness of the restrictor. When the restrictor is inserted, therefore, it cannot be inadvertently pushed into the groove. It is desirable that the restrictor should not be able to enter the groove, for it its inner end were to project into the groove it might be severed from the remainder of the restrictor on rotation of the plug towards its off position. The effect on the restrictor itself would be negligible, but the small speck of plastics material might move from the groove and cause trouble elsewhere. In each of the two embodiments illustrated the inner end of the restrictor is chamfered so as to be slightly frustoconical. This is not essential, however, and the inner end could be flat, in a plane normal to the axis of the insert. Both restrictors are made of a plastics material. Such a material is preferred as its resilience enables the restrictor to be retained in position merely by friction and makes it unnecessary to provide an adhesive or locking medium to secure the insert in position, and it avoids the formation of any metal swarf that might interfere with the correct operation of the tap. Nevertheless the inserts might be made of metal or other materials as desired. WHAT WE CLAIM IS:

1. A gas tap of the kind comprising a body formed with a bore and a plug rotatable in the bore, a first gas-way extending through the body to a port in the bore, and the plug being formed with a second gas-way in communication with a helical or substantially helical groove in the outer surface of the plug, the arrangement being such that in use gas can flow one gas-way to the other by way of the port and the groove, and that by rotation of the plug in the body the extent to which the groove overlaps the port, and thus the extent to which the flow of gas is restricted by the overlap, is gradually and progressively varied, characterised by the provision of a restrictor in the first gasway operative to restrict the flow of gas through the groove, the restrictor being adjustable in such a manner that in use, at a predetermined angular position of the plug relative to the body, the rate of flow of gas, as determined at least in part by the combined effects of the groove and the restrictor, has a predetermined value.

6. A gas tap according to any of Claims 2 to

S in which that end of the restrictor adjacent to the port is chamfered to conform with the taper of the plug.

7. A gas tap according to any of the preceding claims in which the plug is provided with at least one hole that leads from the second gas-way to the outer surface of the plug and co operates with the port in a certain range of angular position of the plug, the arrangement being such that the co operation between the hole or each hole and the port is substantially unaffected by the presence or adjustment of the restrictor.

8. A gas tap according to any of the preceding claims which includes means enabling the plug to be releasably located at said predetermined angular position.

9. A gas tap substantially as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings.

10. A gas tap substantially as hereinbefore described with reference to Figures 8 to 10 of the accompanying drawings.