AU2008226325B2 - Pressure relief valve insulation device - Google Patents

Abstract

The invention relates to an insulating device for a pressure relief valve which valve includes an external body having an outlet for fluid expelled there through upon operation of the valve, the insulating device comprising a housing composed of material of low thermal conductivity that in use substantially surrounds and engages the pressure relief valve, the housing having an opening adjacent the outlet to permit fluid expelled from the pressure relief valve to pass through the opening.

Description

WO 2008/109941 PCT/AU2008/000337 Pressure Relief Valve Insulation Device Field of the invention The present invention relates to an insulation device for pressure relief valves. More specifically the present invention relates to an insulation device for pressure relief valves which retards thermal energy loss through the pressure relief valve without interfering with 5 function of the pressure relief valve or its operational parameters. Background of the invention In this specification where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known 10 to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned. While the present invention will be described with reference to relief valves for domestic hot water systems, it will be appreciated that the device is not so limited and can be used for relief valves for a wide range of domestic and industrial machines and systems. 15 In today's more environmentally aware society it is recognised that it is advantageous to minimise energy use and energy loss to preserve resources and limit environmental damage. Minimising energy use or loss also provides economic benefits. One of the largest energy consumers in the average home is the hot water system. The hot water system typically accounts for around one quarter of total household energy 20 consumption. Most domestic hot water systems have either storage water heaters, or continuous flow instantaneous water heaters. Storage water heaters heat and store water in an insulated tank ready for use. The most common heat sources are solar energy, off-peak electricity and natural gas. The storage tank capacity typically ranges from 90 to 440 litres, 25 depending on the heat source and supply demand (usually based on the number of residents in the household). Domestic hot water storage tanks invariably include a pressure relief valve, a requirement typically mandated by local law.

WO 2008/109941 PCT/AU2008/000337 2 Pressure relief valves are used not only in domestic hot water storage tanks, but are widely used in industrial processes, including processes of the petrol refining, petrochemical, chemical manufacturing, natural gas processing and power generation industries. Where used herein the term 'pressure relief valve' is intended as a generic term to include the type 5 of valves also known as 'pressure and temperature relief valves', 'pressure safety valves', 'safety release valves', 'safety valves' and the like. In general a pressure relief valve is a type of valve used to control or limit pressure in a system or vessel. This is particularly important in vessels or systems that can become pressurised due to process, instrument or equipment malfunction or other unplanned event. 10 Pressure relief valves have an internal valve that is designed or set to open when pressure or temperature exceeds a predetermined value and to allow pressurised fluid to be diverted through an auxiliary valve and out of the vessel or system. As the fluid is diverted, the pressure or temperature inside the vessel or system will decrease which may avoid or minimise damage caused by excess pressure. Usually, once the internal pressure or 15 temperature reaches the reseating pressure for the internal valve (usually within a few percent of the set-pressure) the internal valve will re-close. The pressure relief valves attached to domestic hot water storage tanks are designed to stop the tank from expanding, or even exploding under pressure build up. The pressure relief valve also releases water when the thermostat malfunctions and the temperature inside the 20 tank exceeds about 90 0 C. Pressure relief valves are also designed so that if the pressure or temperature in a vessel or system reaches extremes that challenge the integrity of the whole system or vessel, the pressure relief valve itself will become the point of least resistance for escape of fluid. Specifically, the pressure relief valve body will fail catastrophically and probably be 25 destroyed in order to provide immediate and significant pressure release that avoids damage to other parts of the vessel or system. Pressure relief valves, particularly those attached to insulated vessels, are a large source of heat loss. Current solutions for insulating pressure relief valves include piecemeal application of lagging or fabricating some type of cover from thermal blankets. This 30 fabrication involves the use of several tools and fixatives such as glues and is time consuming. In the past, Rheem Australia Pty Ltd has provided an 'insulation collar' to be WO 2008/109941 PCT/AU2008/000337 3 added to hot water system pressure release valves at the time of installation. However these collars are applied to only part of the valve and they do not address heat loss from the valve as a whole. Furthermore they can only be applied or removed by dismantling the pressure relieve valve or disengaging it from the system. 5 US patent 5,023,031 teaches a method of insulating a water heater by securing a jacket around the tank, and injecting an expandable polyurethane foam into the space between the tank and the jacket. A block of fiberglass insulation is positioned around the pressure relief valve. US patent 4,355,629 relates to a passive solar water heater having superior performance 10 and including an insulated pressure relive valve. Australian patent application 1992 18077 teaches the use of a thermally insulating cover for reducing heat loss from the pressure relief valve of a mains pressure hot water system, the cover being attached to the hot water heater (rather than the pressure relief valve) in such a way that the relief valve may be readily exposed for periodic manual operation. 15 These solutions typically do not address the operating requirements of the pressure relief valve. Furthermore, they are typically not convenient to install. They rely on the installer having a detailed understanding of the unique requirements of the pressure relief valve, thus limiting the persons who can install the valve insulation. If installation is time consuming or complicated, this often leads to the pressure relief valves either not being 20 insulated or being insulated in a manner that is likely to interfere with operation of the valve so that the system becomes dangerous. Most countries have legislation that makes it mandatory to have a pressure relief valve included in certain types of vessels or systems, such as domestic hot water tanks. Typically the legislation also requires that the pressure relief valves relief valves are 25 manufactured and installed according to certain standards, and that following installation, they remain fully functional at all times. For example, for hot water vessels it is mandatory that diversion of fluid through the auxiliary relief valve must not be retarded in any way. Furthermore, it is often mandatory that in the event of extreme pressurisation of the vessel, the auxiliary relief valve or the pressure relief valve is sacrificed to allow immediate, 30 significant pressure release to avoid explosion or damage to other parts of the vessel.

WO 2008/109941 PCT/AU2008/000337 4 Accordingly, there is a need for a safe, efficient and easy to install thermal insulation solution for pressure relief valves that takes into account the unique operating requirements of pressure relief valves. Summary of the invention 5 The invention relates to an insulating device for a pressure relief valve which includes an external body having an outlet for fluid expelled there through upon operation of the valve, the insulating device comprising a housing composed of material of low thermal conductivity that in use substantially surrounds and engages the pressure relief valve, the housing having an opening adjacent the outlet and wherein fluid expelled from the pressure 10 relief valve can pass through the opening. The opening may include a removable cover. In a further embodiment the invention relates to an insulating device for a pressure relief valve which valve includes an external body having an outlet for fluid expelled therethrough upon operation of the valve, the device comprising a housing composed of 15 material of low thermal conductivity that in use substantially surrounds and engages the pressure relief valve, the housing having an opening adjacent the outlet so that fluid expelled through the outlet can pass through the opening and wherein in the event of catastrophic failure of the pressure relief valve, the insulating device will disengage from the valve. 20 Typically the pressure relief value may automatically open once a preset pressure is reached. It may also be a manually operated pressure relief valve. It may incorporate a combination of both types of valves. The outlet may be, for example an auxiliary pressure relief valve or a drain outlet. Accordingly in another form of the invention the device includes at least one further 25 opening to permit fluid expelled through the associated outlet to pass through the opening. This may be appropriate where the pressure relief valve has more than one valve with an associated outlet through which fluid can be expelled when the valve is operated. Typically the pressure relief valve is activated by elevated pressure or temperature and discharges fluid in the form of liquid, vapour or gas. Typically the device of the present 30 invention is attached to a pressure relief valve of a domestic hot water system however the WO 2008/109941 PCT/AU2008/000337 5 invention is not limited to this application and may also be used for other domestic or industrial applications. Material of construction The device is typically constructed from an insulating material of low thermal conductivity 5 such as, for example polyurethane foam, however other suitable materials will be readily apparent to those skilled in the art. The material may include other properties (such as but not limited to, structural, aesthetic or weathering properties. Several materials may be combined to achieve these properties. For example, the device of the present invention could include an external layer of polyethylene material to withstand weathering and an 10 internal nitrile rubber layer providing insulation properties. The design of the device should also account for the weathering and deterioration of the thermal insulation material due to environmental conditions, such as an outside location. It should be resilient for usage in both low and high temperatures. Thus the device must take in account these requirements as well as the inherent mechanical properties of the material 15 of low thermal conductivity. Configuration In use, the housing of the device of the present invention encloses the pressure relief valve body such that heat loss and air flow around the pressure relief valve is minimised. For example, the housing may define a cavity that is of complementary shape to the body of 20 the pressure relief valve. Preferably the housing of the device is adapted to form a seal with the structure to which the pressure relief valve is attached. For example, when the pressure relief valve is adapted for use with a domestic hot water system the housing forms a seal with the outlet of the hot water tank and a seal with the drain line. 25 Preferably the housing of the device is adapted to receive pressure relief valves of different sizes. For example the housing may be elastically or permanently deformable to accommodate the dimensions of the pressure relief valve, or it may define one or more cavities that are large enough to accommodate different size pressure relief valves.

WO 2008/109941 PCT/AU2008/000337 6 The pressure relief valve typically has at least one port or opening for connection to the system or storage device. The port may be an inlet port or outlet port. For example, the pressure relief valve of a hot water storage tank has at least one port connected to the tank. Some are designed so that hot water can flow through and in this embodiment they include 5 an outlet port or drain line. The device of the present invention is adapted to enclose the one or more port. It is also typically configured to enclose other ports or associated features such as pipe unions of different sizes or configurations. Manual operation means 10 Typically the internal valve of a pressure relief device must be periodically manually released to check that it is operating properly and to dislodge any material that may cause the valve to stick or which obstructs any outlet. Accordingly, pressure relief devices often include an easing gear. If the pressure relief device includes an easing gear or other manual operation means, the device of the present invention may include an appropriately 15 shaped cavity which in use encloses the manual operation means. The cavity may include an opening that provides access to the manual operation means. The opening may have a resealable cover that allows access to the manual operation means, but otherwise impedes thermal loss through the opening. The cover may be attached by any convenient means such as hook and loop tape, hinge and latch or tongue and groove arrangements. The cover 20 may optionally have a handle to facilitate removal. Preferably the cover allows for movement in and/or deterioration of the housing material. The cavity and optional cover should be configured to allow necessary movement of the manual operation means. For example, when the manual operating means is an easing gear and the cover is closed, the cavity must allow the easing gear unhindered movement along 25 the easing gear direction of linear travel. When the cover is open it must allow the easing gear unhindered movement through the arc of travel. Assembly The device of the present invention may be installed in any orientation. In a further embodiment of the invention the device may include one or more parts that allow for ease 30 of assembly and installation. These could include, for example, locating guides to ensure WO 2008/109941 PCT/AU2008/000337 7 that the parts are properly aligned or surfaces on the parts that keeps them together in a thermally efficient manner. These surfaces may be constructed of a material other than the thermal insulation material. Auxiliary relief device 5 The outlet of the pressure relief valve may consist of an auxiliary relief device such as an auxiliary relief valve. The housing of the device includes a compartment which in use is located adjacent the auxiliary relief device and adapted to deflect fluid discharged from the auxiliary relief device at high pressure without interfering with its function. Fluid may be discharged from the auxiliary relief device at extremely high pressure (and temperature), 10 sufficient to cause damage or injury to anyone or anything it contacts. Accordingly, in a preferred embodiment the compartment is configured to include a surface or guide that is shaped to direct the flow of fluid discharge in a preferred direction. This may be, for example, a curved or straight channel or wall defining the compartment. Preferably the fluid is deflected away from any manual operation means such as an easing gear. It is 15 important that the compartment allows correct operation of the auxiliary relief device and does not interfere with its operation. The compartment may include an opening, optionally including a resealable cover constructed from insulating material that seals the said opening to prevent heat loss. The cover should automatically open or detach when the auxiliary relief valve discharges fluid 20 at high pressure. The cover may be attached to the housing using any convenient technique such as hinges (such as spring hinges), glue, hook and loop tape, tongue and groove. In an alternative embodiment, the cover may incorporate a one-way valve that allows the fluid flowing out of the auxiliary relief device to exit the housing while minimising air movement in and out of the housing. 25 Housing construction The housing of the device of the present invention can be constructed from one or more component parts. Preferably the body comprises two components however more may be used. The components can be joined at their mating surfaces by any convenient means such as an adhesive layer, friction fit, hook and loop tape, external strapping, magnets, 30 tape, zip or ties.

WO 2008/109941 PCT/AU2008/000337 8 To facilitate the mating and alignment of the components a guide may be incorporated in the components. The guide can take any convenient form such as locating pins and holes, locating slots, grooves or magnets at one or more locations on the components. The housing can be provided with signage that indicates the correct orientation of the 5 pressure relief valve within the housing. This can take the form, for example, of a pictogram. Drawings Various embodiments/aspects of the invention will now be described with reference to the following drawings in which; 10 e Figure 1 is a schematic representation of a typical hot water system, * Figure 2 is a schematic representation of a pressure and temperature relief valve, * Figure 3 is a cross sectional view of one embodiment of the thermal insulating device according to the present invention, e Figure 4 is a perspective view of a further embodiment of assembled thermal 15 insulating device according to the present invention, * Figure 5 is an isometric view of the right hand component of the thermal insulating device of Figure 4, * Figure 6 is a front view (viewed from the hot water tank) of the right hand component of Figure 5, 20 e Figure 7 is an isometric view of the left hand component of the thermal insulating device of Figure 4, * Figure 8 is a front perspective view of the thermal insulating device of Figure 4 containing the pressure relief valve of Figure 2, * Figure 9 is an internal view of the right hand component of the thermal insulating 25 device of Figure 8 containing the pressure relief valve of Figure 2, e Figure 10 is the same view as Figure 9, showing an open relief cover, and * Figure 11 is a rear perspective view of the thermal insulating device of Figure 4 containing the pressure relief valve of Figure 2, with an open relief cover.

WO 2008/109941 PCT/AU2008/000337 9 Key to Figures 1 Hot water storage system 2 Hot water storage tank 3 Pipe fittings (inlet and outlet) 5 4 Access panel 5 Pressure relief valve 6 Pressure relief valve outlet 7 Hot water outlet pipe. 8 Drain line 10 9 Auxiliary relief device 10 Easing gear 11 Pressure relief valve 12 Connection to drain line 13 Connection to hot water outlet of the water storage tank 15 14 Valve seat 15 Valve disc 16 Pipe union 17 Temperature element 18 Easing gear arc of travel 20 19 Easing gear direction of linear travel 20 Auxiliary relief device direction of linear travel 21 Direction of auxiliary relief device discharge flow 22 Insulating device of the present invention 23 Pressure relief valve compartment 25 24 Pipe union extension cavity 25 Hot water outlet opening WO 2008/109941 PCT/AU2008/000337 10 26 Hot water outlet opening flange 27 Drain line outlet 28 Drain line opening flange 29 Easing gear cavity 5 30 Auxiliary relief device compartment/cavity 31 Discharge flow guide 32 Discharge flow opening 33 Locating guides 34 Mating surface adhesive layer 10 35 Mating surface 36 Pressure relief valve orientation pictogram 37 Easing gear cavity cover 38 Easing gear cavity cover fixture 39 Auxiliary relief device discharge cover 15 40 Easing gear cavity opening 41 Easing gear cavity cover handle 42 Housing 43 Left hand component of the housing 44 Right hand component of the housing 20 45 Hinged cover Figure 1 Figure 1 shows a schematic representation of a hot water storage system (1) including a storage tank (2) and fittings. This is a generic representation of the typical hot water storage systems such as a solar boosted hot water system. Analysis of the heat loss from 25 such hot water storage systems (1) shows that the principle heat loss areas are the hot water storage tank (2), the pipe fittings (3) (particularly the inlet and out-let), the access panels (4) and the pressure relief valve (5). Thermal insulation solutions exist to minimise heat loss from the hot water storage tank (2) (through use of thermal blankets), the pipe fittings WO 2008/109941 PCT/AU2008/000337 11 (3) (through the use of lagging) and the access panels (4) (through the use of thermal blankets or improvement in manufacture). However no safe, efficient and easy to install solution exists in the prior art for thermal insulation of the pressure relief valve (5) that takes into account its unique operating requirements. 5 Figure 2 Figure 2 shows a schematic representation of a pressure relief valve (11) of the type typically used with the device of the present invention. The insulating device (22) must allow the proper operation of the pressure relief valve (11) including the auxiliary relief device (9). Preferably it will also be adapted to allow operation of the easing gear (10). 10 The connection to drain line (12) and connection to hot water outlet of the water storage tank (13) must also be permitted to operate normally. To enable proper operation of the auxiliary relief device (9), the insulating device (22) must allow the internal valve to open without altering the set pressure threshold of the pressure relief valve beyond normal tolerances. Furthermore, the insulating device (22) 15 should not deflect any fluid discharged (21) from the auxiliary relief device (9) toward the easing gear (10). When the pressure relief valve (11) includes an easing gear (10) the insulating device (22) must allow a user access to the easing gear (10) to perform periodic lifting of the internal valve disc (15) off its seat (14). The movement of the easing gear (10) should not be 20 restricted by the insulating device (22). To enable proper operation of the pressure relief valve (11) the insulating device (22) shall not impede the connection of the pressure relief valve (11) to the drain line (12). Additionally the insulating device (22) shall not impede any fluid discharge from the drain line (12). 25 The insulating device (22) is shaped to allow unhindered connection of the hot water inlet (13) of the pressure relief valve (5) to the hot water outlet (6) of the water storage tank. Figure 3 Figure 3 shows a cross sectional view of one embodiment of the insulating device (22) of the present invention which is suitable for removable attachment to a pressure relief valve 30 (11) of a domestic hot water system.

WO 2008/109941 PCT/AU2008/000337 12 The insulating device (22) includes a housing that defines a cavity that substantially encloses the body of the pressure relief valve (5) and the port by which it is attached to the hot water outlet opening (25) of the water storage tank. The cavity also encloses the flange (26) on the pressure relief valve outlet that is shaped to allow a contact seal with the 5 pressure relief valve (5). The stepped design of the flange (26) also allows for a tight seal with any thermal insulation lagging on the pressure relief valve (5) to minimise heat loss. The cavity is further shaped to allow the pressure relief valve (5) to be connected to a drain line (8) via an opening (27) and a flange (28) of a stepped design that allows a contact seal between insulating device (22) and the drain line (8). The stepped design of this flange 10 also allows for any thermal insulation lagging on the drain line (8) to mate with the insulating cover (22) to ensure a tight seal to minimise heat loss. Preferably the flange is created by a very flexible foam rubber gland on the hot water outlet (25) and the drain line opening (27). In this embodiment each gland will comprise two halves with each half being seated in the two cover halves. (These glands can be more clearly seen in Figures 9 15 and 10). A further embodiment of the invention may be an allowance for several openings to allow for different drain line configurations. Any unused drain line openings are covered to ensure a tight seal to minimise heat loss. In this embodiment, the housing of the insulating device (22) is also adapted to enclose a pipe union (16). 20 The insulating device (22) includes locating guides (33) to ensure that the components of the housing are properly aligned. To further enhance the ease of assembly the components have a surface (35) which keeps them together in a thermally efficient manner. Orientation signage (36) ensures correct installation of the pressure relief device (22). An opening (40) in the insulating device (22) allows access to and manual operation of the 25 easing gear (10). The easing gear must be allowed unhindered movement along the easing gear direction of linear travel (19) and through the arc of travel (18). The housing of the insulating device (22) includes a compartment (30) shaped to allow correct operation of the auxiliary relief device (9) of the pressure relief valve (5). In order to simplify construction the compartment (30) may be approximated by use of cylindrical 30 or cubic voids or any other convenient (20).

WO 2008/109941 PCT/AU2008/000337 13 The compartment (30) is further shaped to prevent the discharge flow (21) from the auxiliary relief device (9) from being deflected toward the easing gear (10). Specifically, the compartment includes a guide (31) that is shaped to direct the flow away from the easing gear level (10) to one or more openings (32) in the thermal insulating device (22). 5 An opening (32) in the thermal insulating device (22) allows the unimpeded flow of any fluid discharged from the auxiliary relief device (9). This opening (32) prevents the deflection of the discharge towards the easing gear (10). The auxiliary pressure relief opening (32) may have a cover (39) constructed from insulating material that seals the said opening to prevent heat loss. This said cover shall be 10 automatically opened or removed when the auxiliary relief device (9) discharges. This cover may be removed without removing the thermal insulating device (22) from the pressure relief device (5). In this embodiment the cover is attached to the thermal insulating device (22) via a spring. Thus it can be opened by someone but not physically removed. In an alternative embodiment the cover could be attached by hook and loop tape 15 or other means which allow the cover to be completely removed. The easing gear opening (40) has a cover (37) constructed from insulating material that seals the said opening to prevent heat loss and is removable to allow access to operate the easing gear (10). The cover is provided with a handle (41) to facilitate easy removal and replacement of the cover. 20 The housing comprises two components joined at their mating surfaces (35) with an adhesive layer (34). To facilitate the mating and alignment of the component parts a guide is incorporated in the components in the form of locating pins and holes (33). Signage in the form of a pictogram (36) is provided to indicate the correct orientation of the pressure relief valve (5) within the insulating device (22). 25 Figure 4 Figure 4 is a perspective view of a further embodiment of assembled thermal insulating device (22) according to the present invention. In this view can be seen the housing (42) composed of material of low thermal conductivity, the housing (42) being assembled from two components - a left hand component (43) and a right hand component (44) which meet 30 at a mating surface (35), a hot water outlet opening (25) through which a pressure relief device may be attached to a hot water system.

WO 2008/109941 PCT/AU2008/000337 14 Figure 5 Figure 5 is an isometric view of the right hand component (44) of the thermal insulating device of Figure 4. In this view can be seen a mating surface (35) which acts as a locating guide shaped to receive a complementary shaped guide or surface on the left hand 5 component (not shown in this view). Typically, in the event of catastrophic failure of a pressure relief valve within the thermal insulating device, the mating surface (35) will provide a line of least pressure resistance, allowing the two components to part without interference to the operation of the pressure release valve. In this view can also been seen the drain line outlet (27) and the discharge flow opening 10 (32) that permits passage of fluid expelled from a valve located within in the assembled housing (42). Figure 6 Figure 6 is a front view (viewed from the hot water tank) of the right hand component of Figure 4 showing, the right hand component (44) of the housing, the hot water outlet 15 opening (25) through which a pressure relief device may be attached to a hot water system. Figure 7 Figure 7 is an isometric view of the left hand component (43) of the thermal insulating device of Figure 4. In this view can be seen a mating surface (35) which is shaped to receive a complementary shaped surface on the right hand component of Figure 5. In this 20 view can also been seen the drain line outlet (27). Figure 8 Figure 8 is a front perspective view of the thermal insulating device (22) of Figure 3 containing the pressure relief valve (11) of Figure 2. In this view can be seen the housing (42) comprising two components - a left hand component (43) and a right hand component 25 (44), a hot water outlet opening (25) through which projects the temperature element (17) of the pressure relief valve. Figure 9 Figure 9 is an internal view of the right hand component of the thermal insulating device of Figure 8 containing the pressure relief valve of Figure 2. In this view can be seen the right WO 2008/109941 PCT/AU2008/000337 15 hand component (44) of the housing (42) and the hot water outlet opening (25) through which projects the temperature element (17) of the pressure relief valve (11). The right hand component (44) defines half of a cavity within the housing, the cavity being of complementary shape to the body of the pressure relief valve (11). The cavity is shaped to 5 enclose the easing gear lever (10). The cavity is also shaped to include a compartment (30) adjacent the auxiliary relief device (9) that has surfaces configured to deflect any fluid discharged from the auxiliary relief device at high pressure, without interfering with its function. The surface is configured to direct the flow of fluid downwards in the direction of the opening (32) which in this view is sealed by a hinged cover (45). 10 Figure 10 Figure 10 is the same view as Figure 9, except that the hinged cover (45) is open so that water discharged from the pressure relief valve (11) can escape through the opening (32). The hinged cover (45) would typically be configured to open at a specific pressure inside the insulation device, or under a particular head of water. 15 Figure 11 Figure 11 is a rear perspective view of the thermal insulating device of Figure 4 containing the pressure relief valve of Figure 2. In this view the cover (45) is open to allow outflow of water from inside the thermal insulating device (22). The word 'comprising' and forms of the word 'comprising' as used in this description and 20 in the claims does not limit the invention claimed to exclude any variants or additions. Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.

Claims (5)

1. 9. An insulating device according to claim 8 wherein the cover opens automatically in response to elevation of pressure and discharge from the pressure release valve within the housing without interfering with the operation of the pressure release valve.
2. 10. An insulating device according to any one of the preceding claims which forms a seal with fixtures to which the insulating device is attached.
3. 11. An insulating device according to any one of the preceding claims wherein the housing is adapted for use with a variety of pressure relief valves.
4. 12. An insulating device according to any one of the preceding claims wherein the housing is adapted for removable attachment to the pressure relief valve.
5. 13. An insulating device according to claim 1 and substantially as herein described with reference to Figures 4 to 11.