GB2566094A

GB2566094A - Expansion vessel incorporating a foam core

Info

Publication number: GB2566094A
Application number: GB1714173.0A
Authority: GB
Inventors: David Kent Philip
Original assignee: Ideal Boilers Ltd
Current assignee: Ideal Boilers Ltd
Priority date: 2017-09-04
Filing date: 2017-09-04
Publication date: 2019-03-06
Anticipated expiration: 2037-09-04
Also published as: GB2566094B; GB201714173D0

Abstract

An expansion vessel 2, 3 comprises at least one opening 5 into which a liquid may enter, wherein the vessel comprises a compressible foam. The vessel may be used in a dosed water circuit, and in particular in a boiler system. It may comprise a composite shell having an upper portion 2 and a lower portion 3, and each portion may comprise support members 6b extending from its internal surface which are received by apertures 12 in the foam. The shell may be formed of glass-filled polyamide (GFPA) or carbon-filled polyphthalamide (CFPPA). A compressible foam core 13 for use in an expansion vessel is also disclosed. The core may comprise two layers of foam, with the internal layer possibly being a semi-closed cell silicone foam having higher compressibility. The external foam may be a laminated, closed cell, impervious, silicone or neoprene foam.

Description

Expansion Vessel Incorporating a Foam Core

Technical Field of the Invention

The present invention relates to an expansion vessel, especially an expansion vessel for a closed water circuit, in particular in a boiler system.

Background to the Invention

Domestic Combination boilers and System boilers in the UK and mainland Europe have an inbuilt expansion vessel, this has typically been the case for over 30 years. The expansion vessel allows for water expansion in closed water circuits.

An expansion vessel may act as a safety device to protect closed water circuits from excessive pressure rises above a defined maximum pressure. In closed water systems, if the defined maximum pressure is exceeded, components within the closed water circuit may suffer from excessive compressional load, plastic deformation, fatigue degradation from cyclic loading, and catastrophic failure.

The maximum pressure in a closed water system may be exceeded in a number of ways. One way is through water hammer (hydraulic shock). Water hammer commonly occurs when motion of a liquid in a closed system has a sudden momentum change i.e. is forced to stop or change direction. This can be attributed to a valve closing at the end of a pipeline in a system which causes a pressure wave to propagate in the pipe.

Another way in which the maximum pressure in a closed water system may be exceeded is due to thermal expansion. Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.

Water hammer and thermal expansion lead to drastic pressure changes and consequently to high stresses in the closed system. An expansion vessel accommodates both the excess volume of liquid resulting from thermal expansion, and the shockwave caused by water hammer. Thus, an expansion vessel allows for excessive pressure rises in a closed system.

The current convention for an expansion vessel in a closed water system is to have a gas / liquid divide within the structure of the vessel. The volume of gas is the compressible medium which accommodates and manages the hydraulic shock and/or thermal expansion within the liquid in the closed system within which the vessel is incorporated. Known expansion vessels are constructed from two pressed steel mating halves which are crimped together with a steel band around the outside. The two mating halves have a rubber diaphragm housed between them. The diaphragm is typically made of an ethylene propylene diene monomer (EPDM) rubber. One steel half of the vessel is fitted with a Schrader valve, this allows one side of the vessel to be pre-pressurised with a gas (typically nitrogen gas or air). The other side of the rubber diaphragm has a fluid connection to the boilers closed water circuit. Thus, a liquid / gas divide is produced within the vessel.

However, there are a number of disadvantages associated with known expansion vessels.

One disadvantage is that the actual usable volume (acceptance volume) of the expansion vessel is relative to its capacity. The acceptance volume is the volume of water that an expansion vessel can hold, taking into account the volume of the expansion vessel which is taken up by the diaphragm and the compressible gas. For example, the acceptance volume of an eight litre expansion vessel is 5.5 litres of water. This is a problem as the volume of the expansion vessel which water can expand into is reduced. Consequently, the internal stress increases in the system due to a higher operating pressure.

A further disadvantage associated with known expansion vessels is that the EPDM rubber diaphragm has a relatively high porosity. This leads to bleeding of the compressible gas (nitrogen/air) side into the water system. Consequently, there is a reduced volume of gas in the vessel so the minimum pressure is reduced, subsequently the expansion volume is reduced causing higher pressure in the system. To ameliorate this problem, the compressible gas in the vessel must be ‘recharged’ periodically (typically once a year) through the Schrader valve to replenish the compressible gas to the recommended pressure. This is a time-consuming and costly operation, as well as being a significant inconvenience to the owner of the water system.

Moreover, the high porosity of the EPDM rubber diaphragm allows gas to dissolve into the water from the compressible gas side of the vessel. The dissolved gas can be transported around the closed system and released at the highest point of the flow area. This can severely impact heat exchanger performance and can cause pumps to ‘bum out’ and become unusable.

As the age of the vessel increases, the EPDM rubber diaphragm degrades exponentially and becomes hydrolysed. Subsequently, gas dissolves into the water at an increasing rate up to the end of the serviceable life of the vessel.

Known vessels require regular servicing in order to maintain their efficiency and keep them in operation. Without regular servicing, the vessels quickly become redundant and need replacing, at a high cost to the owner. An expansion vessel suffering the abovementioned problems has the potential to cause other components in the system to fail and is, therefore, a detriment to the system as a whole.

It is therefore an object of the present invention to produce an expansion vessel which can ameliorate the abovementioned problems.

Summary of the Invention

According to a first aspect of the invention, there is provided an expansion vessel having at least one opening into which a liquid may enter, characterised in that the expansion vessel comprises a compressible foam. The present invention does not comprise a liquid / gas divide, as is the usual convention in known expansion vessels. Instead, the present invention provides a foam core which performs the function of the gas in the liquid / gas divide. Thus, the problems associated with closed water systems, such as hydraulic shock and thermal expansion, can be accommodated without having to tolerate the reliability problems associated with a liquid / gas divide system, namely bleeding of the gas through the diaphragm into the water system and degradation of the diaphragm itself.

The compressible foam may comprise at least two layers. The compressible foam may be of the form of a two-layered compressible foam structure.

The two-layered compressible foam structure may comprise an internal foam layer and an external foam layer.

The internal foam may have a higher compressibility than the external foam.

The internal foam may be formed of a closed cell foam, a semi-closed cell foam, or an open cell foam. The external foam may be formed of a closed cell foam or a semiclosed cell foam.

Foams are produced by forming gas bubbles in a liquid base which sets over a short period of time, the properties of the liquid and gas determine whether the foam is closed cell, semi-closed cell or open cell.

In a closed cell foam, the gas bubbles are completely encompassed within the liquid. When the liquid sets, the gases are entirely fixed within each individual bubble, thus creating a structure which is impervious.

In a semi-closed cell foam, the closed cells of the closed cell foam are physically burst to create a more open cell product which is softer and easier to compress than the closed cell foam.

In an open cell foam, the bubbles burst during the foam forming process. This creates an interconnection cellular network which gives rise to softer and breathable foams.

The internal foam may be a semi-closed cell foam or an open cell foam, and the external foam may be a closed cell foam. The internal foam may be a silicone foam and the external foam may be a silicone or neoprene foam. The external foam may be a laminated foam. The external foam may be impervious.

As the internal foam may be a semi-closed cell foam and the external foam may be a closed cell foam, the internal foam may be softer and more compressible than the external foam. Thus, the internal foam would be able to undergo greater deformation than the external foam. Further, the semi-closed cell foam exhibits a higher compression set than the closed cell foam. It is, therefore, the semi-closed cell foam which absorbs the hydraulic shock that may occur in a closed water system.

Moreover, forming the external foam as a closed cell foam prevents bleeding of gas from the cavities comprised in the internal foam into the closed water system. Further, the external foam provides a comparatively high rigidity which, together with the relatively high compression set of the internal layer, allows the foam to resist maximum operating pressures with minimal compression in order to maintain a substantially constant pressure in the system.

The expansion vessel may comprise a composite shell having an upper portion and a lower portion. The upper portion and the lower portion may be formed by injection moulding. Each of the upper portion and the lower portion may comprise a lip extending around the perimeter of the base of each portion.

The upper portion and the lower portion may each comprise a plurality of support members. The support members may extend from the internal face of the upper portion and/or the internal surface of the lower portion. The support members may be arranged in any configuration or formation on the internal surface of the upper portion and/or the internal surface of the lower portion. The support members extending from the internal surface of one portion of the shell may have a corresponding support member extending from the internal surface of the other portion of the shell. The support members extending from the internal surface of the upper portion may have a height which is substantially equal to the depth of the upper portion. The support members extending from the internal surface of the lower portion may have a height which is substantially equal to the depth of the lower portion. The support members may be any shape, such as, but not limited to cylinder, cuboid, and pyramid. The support members allow for induced loads and stresses to be distributed throughout the entire expansion vessel. In conventional known steel expansion vessels, induced loads and stresses are only distributed around the perimeter of the expansion vessel. Thus, compared with known expansion vessels, the present invention provides a stronger and more robust structure which is able to withstand greater induced loads and stresses.

The support members may be positioned so that when the upper portion and the lower portion are assembled, each support member extending from the upper portion is in contact with the corresponding support member extending from the lower portion. The support members may be shaped so that a support member extending from the internal surface of, for example, the lower portion, comprises a groove or indentation on its surface which is contactable by a corresponding support member extending from the internal surface of the upper portion. The corresponding support member extending from the internal surface of the upper portion may comprise a ridge or point of elevation. The ridge or point of elevation may be inserted into the groove or indentation on the support member from the lower portion when the upper portion is assembled onto the lower portion. The support members may further comprise notches or other connecting means to facilitate the connectivity of a support member with its corresponding support member.

The corresponding interconnection of the support members from each portion provides a stronger and more secure fit between the two support members, thus providing a stronger and more robust structure which is able to withstand greater induced loads and stresses.

At least 50% of the internal cavity of the shell may be occupied by the foam, alternatively at least 70% of the internal cavity of the shell may be occupied by the foam, alternatively at least 80% of the internal cavity of the shell may be occupied by the foam, alternatively at least 90% of the internal cavity of the shell may be occupied by the foam, alternatively substantially all of the internal cavity of the shell may be occupied by the foam. The at least one opening in the expansion vessel may be occupied by the foam.

The foam may be shaped to substantially correspond to the interior cavity of the shell.

The foam may comprise a plurality of apertures. The apertures in the foam may be positioned to receive the plurality of support members.

The expansion vessel may be used as an expansion vessel as part of a boiler system. The boiler system may be a domestic boiler system.

The expansion vessel may be formed integral with the boiler system or domestic boiler system.

The shell may be formed of a glass-filled polyamide (GFPA) or a carbon-filled polyphthalamide (CFPPA). Forming the shell from one of these materials provides for a shell manufacturing process which allows additional features to be incorporated into the shell moulding. Such features may allow ancillary boiler components to be affixed to the shell. This may provide for a more efficient manufacturing process of the expansion vessel and a reduction in the quantity of sheet steel brackets required in the boiler system. Consequently, this will reduce the manufacturing time and overall production cost when compared with the manufacture time and cost of producing known expansion vessels. Further, the expansion vessel of the present invention provides a significant component weight reduction when compared to known steel expansion vessels. This may reduce transport costs and make the expansion vessel of the present invention easier to handle and install.

Moreover, the expansion vessel of the present invention does not require periodic re-pressurising. This is because the expansion vessel of the present invention does not utilise a diaphragm and a liquid / gas divide system which uses gas as a compressible medium such as is found in known expansion vessels.

The expansion vessel may be formed as a stressed member of the boiler system. The structural shape and space utilisation of the composite shell within the boiler system would allow careful design of the boiler layout at the concept stage. Incorporating the expansion vessel of the present invention into a boiler system as a stressed member of that system would provide an overall stronger boiler structure. This would allow the gauge thickness of the boiler chassis components to be reduced.

The expansion vessel may be for use in closed water circuits.

In forming the expansion vessel, the foam core may be positioned within one of the upper portion or the lower portion of the composite shell. The other portion of the shell may then be assembled onto the portion containing the foam core. The two portions may be assembled such that the lips of each portion can be connected around the entire perimeter of each shell portion. The lips may be connected by vibration welding. Each support member may be connected to its corresponding support member. This connection may be formed by vibration welding. Subsequently, a robust and fluid tight shell encapsulating the compressible foam core is produced.

According to a second aspect of the present invention, there is provided a compressible foam core for use in an expansion vessel.

The compressible foam may comprise at least two layers. The foam may comprise a first layer of an internal foam and a second layer of an external foam.

The internal foam may have a higher compressibility than the external foam.

The internal foam may be a semi-closed cell foam or an open cell foam, and the external foam may be a closed cell foam or a semi-closed cell foam.

The internal foam may be a silicone-based foam. The external foam may be a silicone foam or a neoprene foam.

The external foam may cover at least 50% of the outer surface of the internal foam, alternatively the external foam covers at least 70% of the outer surface of the internal foam, alternatively the external foam covers at least 80% of the outer surface of the internal foam, alternatively the external foam covers at least 90% of the outer surface of the internal foam, alternatively the external foam covers substantially all of the outer surface of the internal foam.

The compressible foam core may comprise any of the abovementioned features that have been stated in accordance with the expansion vessel of the first aspect of the present invention.

Detailed Description of the Invention

In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1	is a plan view of a lower portion of an expansion vessel;
Figure 2	is a cross section view of an expansion vessel according to a first aspect of the present invention, without the foam core, taken along line A-A shown in figure 1;
Figure 3	is a cross section view of an assembled expansion vessel according to the present invention;
Figure 4	is a schematic exploded lateral cross section view of a whole expansion vessel; and
Figure 5	is a schematic exploded perspective view of a whole expansion vessel.

With reference to figure 1, there is shown a lower portion 3 of an expansion vessel according to the present invention. The lower portion 3 is substantially rectangular and comprises a plurality of support members 6b, in the present embodiment sixteen support members 6b are included. The support members 6b extend from the internal surface 9 of the lower portion 3. Together, the upper portion 2 and the lower portion 3 form the composite shell of the present invention. The upper portion 2 and the lower portion 3 are made of a glass-filled polyamide (GFPA) or a carbonfilled polyphthalamide (CFPPA).

A lip 4b is provided around the perimeter of the base of the lower portion 3.

The opening 5 can be positioned anywhere on the outer surface of the expansion vessel and is arranged to connect to the piping of a closed water system. In the present embodiment, the opening 5 is positioned below the lip 4b on a shorter side of the substantially rectangular lower portion 3 (see figure 2).

With reference to figure 2, an expansion vessel 1 according to the present invention is shown, but without the foam core. The expansion vessel comprises the lower portion 3 shown in figure 1 and an upper portion 2. The upper portion 2 is substantially rectangular and has a perimeter which coordinates with the perimeter of the lower portion 3. The upper portion 2 comprises a lip 4a around the perimeter of the base of the upper portion 2. Upper portion 2 also comprises a plurality of support members 6a. Support members 6a, 6b are substantially rectangular. Support members 6a, 6b comprise either a ridge 10 or a groove 11. A support member 6a, 6b comprising a ridge 10 has a corresponding support member 6a, 6b comprising a groove 11. As shown in figure 2, support members 6a are distributed on the internal surface of the upper portion 2 so that they are positioned over the support members 6b extending from the internal surface of the lower portion 3 when the upper portion 2 is positioned on top of lower portion 3 with lips 4a and 4b abutting. Consequently, upon assembly of the expansion vessel, the ridges 10 are inserted into grooves 11 to form a strong and secure fit.

As shown in figures 3 to 5, the present invention comprises a compressible foam core 13. The compressible foam core is a two-layered compressible foam structure comprising an internal layer 7 and an external layer 8. The compressible foam core 13 comprises apertures 12 for receiving support members 6a, 6b. The apertures 12 are distributed within the compressible foam core 13 in a manner so that the distribution of the apertures 12 in the compressible foam core 13 correspond to the distribution of the support members 6a, 6b - such that the support members extend through the apertures and meet in the middle of the compressible foam core. The external foam 8 encapsulates the internal foam 7, so the external foam 8 is arranged adjacent to each aperture as well as at the outer surface.

The internal foam 7 is a semi-closed cell silicone compressible foam. The external foam 8 is an impervious closed cell silicone or neoprene foam. Substantially all of the internal cavity of the composite shell is occupied by the compressible foam core 13.

The compressible foam core 13 removes the need to incorporate a diaphragm (for example a EPDM diaphragm) which provides a liquid / gas divide. Thus, the problems associated with known expansion vessels, as previously described, are ameliorated through the use of a compressible foam core 13, as in the present invention.

The shape of the compressible foam core 13 substantially corresponds to the shape of the internal cavity of the composite shell (figure 5). As shown in figure 3, the upper portion 2 is assembled on the lower portion 3. The support members 6a are inserted into apertures 12 in the compressible foam core 13. The upper portion 2 and the lower portion 3 are joined by vibration welding of the lips 4a, 4b, and the support members 6a, 6b. A tight and secure fit between the compressible foam core 13 and the upper portion 2 and lower portion 3 is formed. By way of example, figure 3 shows a support member 6a which provides a ridge 10 connected to a support member 6b which provides a groove 11. Upon assembly of the expansion vessel, the ridge 10 is inserted into the groove 11. The interconnection between corresponding support members 6a and 6b provides for a strong and robust expansion vessel structure which is able to withstand greater induced loads and stresses.

The expansion vessel of the present invention is connected to the piping of a water system via the opening 5. In the event of water hammer or thermal expansion, water may enter the expansion vessel through opening 5. The water may surround the compressible foam core 13. The external foam 8 is impervious and thus prevents the water from contacting the internal foam 7. The internal foam 7 exhibits high compressibility due to its semi-closed cell structure. Thus, when water surrounds the compressible foam core 13 and exerts pressure onto the compressible foam core 13, the foams compress, internal foam 7 compressing to a greater extent, increasing the acceptance volume of the expansion vessel and thus decreasing the internal stress in the closed water system, therefore, ameliorating the high operating pressure in the system.

When the effects of water hammer or thermal expansion have subsided and the operating pressure in the system is reduced, the pressure exerted on the compressible foam core 13 is diminished. The foam layers 7, 8 subsequently expand and the compressible foam core 13 returns to occupying substantially all of the internal cavity of the composite shell.

The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. An expansion vessel having at least one opening into which a liquid may enter, characterised in that the expansion vessel comprises a compressible foam.

2. An expansion vessel according to claim 1, wherein the compressible foam comprises at least two layers.

3. An expansion vessel according to claim 2, wherein the compressible foam is a two-layered compressible foam structure.

4. An expansion vessel according to claim 3, wherein the two-layered foam structure comprises an internal foam and an external foam.

5. An expansion vessel according to claim 4, wherein the internal foam has a higher compressibility than the external foam.

6. An expansion vessel according to claim 4, wherein the internal foam is a semiclosed cell foam.

7. An expansion vessel according to any of claims 4-6, wherein the internal foam is a silicone foam.

8. An expansion vessel according to claim 4, wherein the external foam is a closed cell foam.

9. An expansion vessel according to any of claims 4-8, wherein the external foam is a laminated foam.

10. An expansion vessel according to any of claims 4-9, wherein the external foam is a silicone foam or a neoprene foam.

11. An expansion vessel according to any of claims 4-10, wherein the external foam is impervious.

12. An expansion vessel according to any of the preceding claims, wherein the vessel comprises a composite shell.

13. An expansion vessel according to claim 12, wherein the shell comprises a composite upper portion and a composite lower portion.

14. An expansion vessel according to claim 13, wherein each of the upper portion and lower portion comprise a lip extending around the perimeter of the base of the upper portion and the lower portion.

15. An expansion vessel according to claim 13 or 14, wherein the upper portion and lower portion each comprise a plurality of support members.

16. An expansion vessel according to claim 15, wherein each of the plurality of support members extending from the internal surface of the upper portion and/or the internal surface of the lower portion.

17. An expansion vessel according to claim 16, wherein the support members extending from the internal surface of the upper portion have a corresponding support member extending from the internal surface of the lower portion.

18. An expansion vessel according to any of claims 15-17, wherein each of the plurality of support members in each of the upper portion and lower portion have a height which is substantially equal to the depth of the respective upper portion or lower portion.

19. An expansion vessel according to any of claims 15-18, wherein the corresponding support members are positioned so that when the upper portion and lower portion are assembled, each of the plurality of support members extending from the upper portion is in contact with the corresponding support member extending from the lower portion.

20. An expansion vessel according to any of claims 12-19, wherein at least 50% of the internal cavity of the shell is occupied by the foam.

21. An expansion vessel according to any of claims 12-20, wherein the foam is shaped to substantially correspond to the interior cavity of the shell.

22. An expansion vessel according to any preceding claim, wherein the foam comprises a plurality of apertures.

23. An expansion vessel according to claim 22 when dependent upon any of claims 15-19, wherein the apertures in the foam are positioned to receive the plurality of support members.

24. An expansion vessel according to any preceding claim, wherein the at least one opening is occupied by the foam.

25. An expansion vessel according to claim 24, wherein the vessel is for use as an expansion vessel in a boiler system.

26. An expansion vessel according to claim 25, wherein the boiler system is a domestic boiler system.

27. An expansion vessel according to claim 25 or 26, wherein the vessel is formed integral with the boiler system or domestic boiler system.

28. An expansion vessel according to claim 25, wherein the shell comprises ancillary components of the boiler system.

29. An expansion vessel according to claim 25, wherein the vessel is formed as a stressed member of the boiler system.

30. An expansion vessel according to any preceding claim, wherein the vessel is for use in closed water circuits.

31. An expansion vessel according to any of claims 12-30, wherein the shell is formed of a glass-filled polyamide (GFPA) or a carbon-filled polyphthalamide (CFPPA).

32. A compressible foam core for use in an expansion vessel.

33. A compressible foam core according to claim 32, wherein the foam comprises at least two layers.

34. A compressible foam core according to claim 33, wherein the foam structure comprises a first layer of an internal foam and a second layer of an external foam.

35. A compressible foam core according to claim 34, wherein the internal foam has a higher compressibility than the external foam.

36. A compressible foam core according to claim 35, wherein the internal foam is a semi-closed cell foam.

37. A compressible foam core according to claim 35 or 36, wherein the external foam is a closed cell foam.

38. A compressible foam core according to any of claims 34-37, wherein the internal foam is a silicone foam.

39. A compressible foam core according to any of claims 34-38, wherein the external foam is a silicone foam or a neoprene foam.

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40. A compressible foam core according to any of claims 34-39, wherein the external foam covers at least 50% of the outer surface of the internal foam.

41. A compressible foam core according to any of claims 32-40 for use in the vessel according to any of claims 1-31.

42. A boiler system comprising the expansion vessel of any of claims 1-31.

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43. A boiler system comprising the compressible foam core of any of claims 32-40.