A tubular member and method of supporting same

Abstract

 A method of supporting an elongate frangible bulb typically of the kind used in a thermally responsive triggering device such as a fire extinguishing sprinkler, the method comprising the step of coating, wrapping or encapsulating one or both end regions of the bulb in a material which provides a compliant interface between the bulb and its supporting structure. The bulb may be seated in a material which conforms to the outer surface thereof and is subsequently cured to provide a rigid support, or alternatively it may be wrapped in one or more layers of a compliant tape or still further it may be dipped into a liquid material which dries to provide the compliant interface.

Description

[0001] THIS INVENTION concerns a technique for supporting an end region of a tubular member, for example an elongate glass bulb which in use will sustain a longitudinally applied mechanical load and particularly, though not exclusively, of the type defining an internal chamber filled with a thermally expansive liquid, for use in thermal release devices such as a fire extinguishing sprinkler unit. In such a unit the bulb forms a trigger member placed under longitudinal compression and acting on a seal to prevent the release of a fire extinguishing medium, usually water. When the ambient temperature reaches a critical level the resultant expansion of the liquid within the bulb causes the glass to break thus releasing the seal and permitting the water to escape.

[0002] Such a bulb typically comprises a generally cylindrical glass tube supported endways within a framework having adjustable means to apply a compressive force longitudinally of the bulb to maintain the seal. The bulb is produced by a technique which closes the filling end of the tube in a manner which usually produces a tapered or nib-like configuration, and it is typically this end of the bulb which is seated in a device, usually of metal, which acts upon the water seal.

[0003] Conventionally such bulbs have been in excess of 5mm in diameter but there is an increasing requirement for slimmer bulbs, the belief being that a slimmer bulb responds more rapidly at the designated operating temperature.

[0004] As the bulbs become smaller to meet market requirements so there is increasing difficulty in supporting them mechanically in the body of the thermal release device and in minimising the risk of premature failure either in manufacture, installation or subsequent use.

[0005] Conventionally, such bulbs are supported in a seating ring which presents to a tapering wall portion of the bulb, an annular shoulder of right-angled cross-section with the result that the bulb is typically supported circumferentially around a single narrow line.

[0006] Certain measures have been taken to increase the mechanical strength of the bulb itself particularly in the end regions where it is seated in the supporting framework. One such measure as described in United States patent US 4796710 is to increase the thickness of the glass locally in the contact regions where the bulb is supported.

[0007] An object of the present invention is to improve the load bearing capability of a bulb not by increased thickness, but by providing a compliant interface between the bulb and its supporting structure.

[0008] The invention is not limited to bulbs for use in thermal release devices and is to be construed as including any frangible tubular member containing a reactive substance.

[0009] According to the present invention there is provided a method of supporting an end region of a tubular member, the member defining an internal chamber containing a reactive substance and being adapted to carry a mechanical load applied longitudinally of the member; characterised by the steps of seating one or both end regions of the member in a material which is capable of conforming to the outer surface of the member in said region thus to support the member in said region under the mechanical load to be applied.

[0010] Further according to the present invention the aforesaid method is adapted to support an elongate frangible bulb in a thermally responsive triggering device, the bulb defining an internal chamber containing a thermally expansive liquid.

[0011] Further according to the invention the method comprises the step of selecting a material which is fluid to conform to the outer surface of the member in said region, and subsequently curing the material to support the member under the mechanical load to be applied.

[0012] Preferably substantially an entire end region of the member is seated within such material and is fully supported thereby.

[0013] Further, the material is preferably one which forms a bond with the outer surface of the member in said region thus to increase its supporting properties.

[0014] Still further, the invention includes an elongate glass bulb produced and supported as aforesaid.

[0015] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Fig. 1 is a cross-sectional view of a conventional fire extinguishing sprinkler unit incorporating an elongate glass bulb in a known manner;

Fig. 2 is a cross-sectional view of an elongate glass bulb made in accordance with a first embodiment of the present invention for use in a sprinkler unit;

Fig. 3 is a similar view of a second embodiment;

Fig. 4 is a similar view of a third embodiment;

Fig. 5 is a similar view of a fourth embodiment;

Fig. 6 is a similar view of a fifth embodiment;

and Fig. 7 is a similar view of an elongate glass bulb incorporating the concept of the present invention at the opposite end of the bulb.

[0016] Referring now to Fig. 1, a typical sprinkler unit comprises an externally threaded tubular body 10 to be inserted into the open end of a pressurised water supply duct and having a resilient annular sealing ring 11 adapted to be seated against a shoulder 12 to prevent the escape of water. A pair of side members one of which is shown at 13 extend between radially opposite portions of the body 10 and a spreader device 14, axially within the centre of which is an adjusting screw 15 which bears against one end of a liquid filled elongate glass bulb 16. The other end of the bulb 16 is tapered to a nib shape and is centrally located within a seating ring 17, itself centrally located within a soft, typically non-ferrous, button 18 which bears against the inner circumference of the sealing ring 11 to maintain it in sealed engagement with the outlet orifice of the body 10.

[0017] In operation, with a rise in ambient temperature the liquid within the glass bulb 16 expands to an extent which, at a designated critical temperature, causes the bulb to break thus releasing the seating ring 17, the button 18 and the sealing ring 11, to activate the sprinkler.

[0018] During assembly of the unit, a compressive force is applied by the screw 15, via the bulb 16 to the seating ring 17, and the tapered (nib) end region of the glass bulb bears against the annular internal shoulder of the seating ring 17 causing considerable compressive stress upon the wall of the bulb around a circumferential line.

[0019] To comply with international regulations the bulb must withstand a compressive force of up to six times greater than its normal in-service load, and with continuously reducing diameters of glass bulb, the mechanical precision of the assembly is of increasing importance thus to prevent the bulb from fracturing either in assembly or prematurely in use due to, for example, non-uniform loading at its point of contact with the seating ring 17.

[0020] Referring now to Figs. 2 to 5, in accordance with the present invention a seating ring similar in principle and general configuration to the conventional ring 17 in Fig. 1, is shown at 30, and in this case, the bulb 16 although similarly located upon a right-angled bearing shoulder 31 is also seated within and supported by a material 32 which, in manufacture of the device is sufficiently fluid to conform to the outer surface of the bulb throughout the entire recess defined by the ring 30, above and/or below the loading point at shoulder 31. The material is of a type which once cured is sufficiently rigid to support the bulb throughout the seated region, and preferably forms a good bond with the outer glass surface in that region thus to occupy any imperfections in the configuration of the glass and provide an overall protective support. Thus when a bulb made in accordance with this embodiment is longitudinally loaded mechanically within a device similar to that illustrated in Fig. 1, a point or line loading of the glass structure within the end region of the bulb is avoided.

[0021] Referring now to Fig. 3, in this example the seating ring 33 has a stepped internal supporting shoulder 34 which increases the area over which the bulb may be in contact with the seating ring and also permits the filling material 32 to flow into the so formed steps thus further to enhance its supporting role.

[0022] Fig. 4 illustrates a simplified arrangement in which the seating ring 34 is simply bored internally to receive a complete filling of the material 32 whereby no contact between the glass and the seating ring 34 remains. In Fig. 5 a further modified seating ring 35 includes a recess the configuration of which more closely resembles the outer configuration of the end region of the bulb but wherein the filling material 32 still fully supports the bulb without contact with the seating ring.

[0023] Referring now to Fig. 6, there is shown an example wherein the seating ring has been omitted altogether and replaced by a seating formed entirely from the filling material 32. In this example the end region of the bulb is placed within a mould to be filled with the material 32 and then removed from the mould leaving the material formed as the seating ring.

[0024] Fig. 7 illustrates that the opposite end of the bulb may similarly be supported in a filling material 36 with or without an outer seating ring 37 or the screw 15. This may apply to any of the previously described embodiments.

[0025] Thus it can be seen, that at least a part of one or both end regions of an elongate glass bulb may be encapsulated within a material which increases the load contact area and eliminates point loading forming, preferably, though not always necessarily, a bond between the glass and the encapsulation material and accommodating any geometrical or surface imperfections in the glass. Several, readily available materials have been found satisfactory for the purpose of this invention including the following which are given by way of example only:-

Permabond E15 epoxy

Araldite 2011 Toughened epoxy

Araldite 2020 Structural Glass Adhesive

Araldite 2021 Toughened Methacrylate

Araldite 2022 Toughened Methacrylate

3M Vitremer - Glass Ionomer Cement

Fortafix Cement WB12RB

Fortafix Cement WBSP/21

[0026] The material may be selected from types which are cured, for example, chemically, thermally, or by exposure to light.

[0027] It will be appreciated that the present invention is not specifically restricted to fire sprinkler applications and can be used wherever a frangible tubular member containing a reactive substance is required to be loaded longitudinally, compressively and/or in tension. While the invention has been generated out of the need to provide support for so-called "fast response" glass bulbs with minimal diameter, it is nevertheless equally applicable to larger diameter bulbs, or a bulb of any geometry since the encapsulation technique of this invention renders the geometry immaterial.

[0028] Whilst it is preferable for the filling material to form a bond with the glass, nevertheless any material which provides additional support by conforming, at least partially, to the outer shape of the bulb, is intended to be included within the scope of the invention.

[0029] Cement types may vary according to application and ambient conditions and may include additional fillers such as glass powders or other strengthening additives.

[0030] Several advantages accrue from glass "trigger" bulbs manufactured in accordance with the invention. In addition to increased load bearing capability for any such bulb, and the safe accommodation of imperfections in the manufacture of such bulbs there is increased protection for the bulb end regions against shock and mechanical damage in service and the potential for a considerable reduction in conductivity of heat away from the bulb through adjacent metal components. Also, a bulb seated and supported in this manner may be used in existing sprinkler devices normally intended to receive larger diameter bulbs. The encapsulation may thus accommodate an oversized or undersized orifice.

[0031] It is not intended to limit the invention to the above examples, variations such as might readily occur to a skilled person, being possible without departing from the scope of the invention.

[0032] For example, in the embodiments illustrated in Figs. 2 to 4, an aperture may be provided in the base of the seating ring 30, 33 to allow the nib of the bulb 16 to protrude through the aperture if required.

[0033] Furthermore, in place of a compliant and curable material one or both ends of the bulb may be covered with one or more layers of material such as PTFE tape which will afford sufficient compliance and resilience with the seating ring to afford adequate support for the compressive load to be applied.

[0034] Still further, in place of a thick material in which the end of the bulb is to be encapsulated as illustrated in Figs. 2 to 6, it may be sufficient, in some applications, merely to dip the end or the whole of the bulb during manufacture into a material which is thus applied as a thin film over the surface of the bulb, the film having compliant properties sufficient to absorb and distribute the compressive load applied to the ends of the bulb in use. A multiple process may be used for this purpose in which two or more different materials are applied as thin films on the surface of the glass bulb. In one such example, the base film may be of a material which does not form a bond with the glass and thus affords a degree of slip between the material and the glass when the assembly is seated in a supporting ring.

[0035] By protecting a frangible glass bulb in accordance with the invention an increase of 20% or more of the crush strength and thus the permitted compressive load to be applied to the bulb may be achieved.

[0036] In the following example, a comparative test was conducted to measure the crush strength (maximum force applied longitudinally before fracture) of two batches of glass trigger bulbs comprising a first untreated control batch and a second batch in which one end of each bulb was encapsulated or seated in Araldite 2011. The results are given in Table I below.

TABLE I

Untreated control Bulbs		Bulbs encapsulated in Araldite 2011
Sample	Crush Strength (kN)	Sample	Crush Strength (kN)
1	5.07	11	5.60
2	4.11	12	5.17
3	3.85	13	4.10
4	2.98	14	4.18
5	4.39	15	4.61
6	2.98	16	5.19
7	3.83	17	5.08
8	4.35	18	4.65
9	3.99	19	4.79
10	4.09	20	5.11
Mean:		Mean:

[0037] With control samples 1 to 10, the resultant mean crush strength was 3.96kN whereas with treated Samples 11 to 20, the resultant mean crush strength was 4.85kN, an increase of 22.47%.

[0038] A further advantage of supporting the bulb against its compressive load in accordance with the invention is that an otherwise weaker bulb, perhaps having a thinner wall thickness, may be used to support the load, and being inherently weaker, perhaps with thinner wall thickness, will fracture more readily when required in the event of an increase in temperature. A bulb which will fracture in service more rapidly upon attaining the trigger temperature, is more thermally responsive and thus more efficient in its application as a fire extinguishing sprinkler unit.

Claims

1. A method of supporting an end region of a tubular member, the member defining an internal chamber containing a reactive substance and being adapted to carry a mechanical load applied longitudinally of the member; characterised by the steps of seating one or both end regions of the member in a material which is capable of conforming to the outer surface of the member in said region thus to support the member in said region under the mechanical load to be applied.

2. A method according to Claim 1, adapted to support an elongate frangible bulb in a thermally responsive triggering device, the bulb defining an internal chamber containing a thermally expansive liquid.

3. A method according to Claim 1 or Claim 2, including the step of selecting a seating material which is fluid to conform to the outer surface of the member in said region, and subsequently curing the material to support the member under the mechanical load to be applied.

4. A method according to any preceding claim, wherein substantially an entire end region of the member is seated within such material and is supported thereby.

5. A method according to any preceding claim, wherein the seating material is selected to be one which forms a bond with the outer surface of the member in said region thus to increase its supporting properties.

6. A method according to any preceding claim, wherein one or each end region of the member is located within a seating ring, the material occupying a space between the member and the seating ring whereby no contact between the member and the seating ring remains.

7. A method according to Claim 1 or Claim 2 or any one of Claims 4 to 6, comprising the step of selecting a seating material in the form of at least one layer of a preformed tape adapted to afford sufficient compliance to provide adequate support for the compressive force to be applied.

8. A method according to Claim 7, wherein the tape is of PTFE.

9. A method according to any one of claims 1, 2, 4 and 5, wherein the or each end region of the member is dipped into a liquid material which is thus applied as a thin film over the surface of the bulb, the film having compliant properties sufficient to absorb and distribute the compressive load applied to the member.

10. A method according to any one of Claims 1 to 4 or 6 to 9, wherein the seating material is selected to be one which does not form a bond with the outer surface of the member in said region thus to afford a surface of the member in said region thus to afford a degree of slip between the material and the surface.

11. A tubular member supported in at least one end region thereof by a method according to any one of the preceding claims.

12. An elongate glass bulb containing a thermally expansive liquid, and supported in at least one end region thereof by a method according to any one of Claims 1 to 9.

Drawing