GB2176589A

GB2176589A - Expansion tank

Info

Publication number: GB2176589A
Application number: GB08513854A
Authority: GB
Inventors: Vincent Thomas Armstrong
Original assignee: Warmac Ltd
Current assignee: Warmac Ltd
Priority date: 1985-06-01
Filing date: 1985-06-01
Publication date: 1986-12-31
Also published as: GB8513854D0

Abstract

An expansion tank (10) for use with a liquid filled system such as a pressurised central heating system, includes a rigid closed vessel (11) which has a lower flow connection (13) for liquid to and from the system (not shown). The vessel (11) contains a flexible variable volume bag (27) having a neck (26) sealed to an upper air flow connection (23) through the vessel wall. Thus a liquid enters and leaves the vessel (11) the volume of air within the bag (27) falls and rises. The liquid (water) is thus isolated from atmospheric oxygen and contamination by foreign matter. The vessel (11) can have a replenishment connection (21) for fresh-liquid, an overflow (15) for excess liquid, and a vent arrangement (36, 37) for venting contained air upon commissioning or re-commissioning after servicing. <IMAGE>

Description

SPECIFICATION Expansion tank This invention relates to an expansion tank for use in pressurised liquid-filled systems wherein the volume of working liquid changes cyclically. The tank is particularly applicable to pressurised central heating systems.

A pressurised central heating system includes a heater, radiators, pressurisation unit and interconnecting pipework. Pressurisation increases the maximum operating temperature of the system and gives the system a greater heating capacity. However, it does mean that the change in volume of the working liquid varies very considerably as the system temperature varies from ambient up to high value.

The volume variation occurs cyclically as the system as a whole is switched on and off and as individual radiators are switched on and off. It is usual for the excess volume of water from a hot system to be transferred to an expansion or header tank whence it is drawn back into the system upon cooling. The pressure of oxygen in such water is most undesirable as its presence promotes electrochemical corrosion involving different metals (usually copper and iron) in the system. Accordingly it has been usual to attempt to reduce the amount of exposure to oxygen in ambient air which the water in the expansion tank undergoes. A "perfect" way of doing this is to provide a blanket of inert, oxygenless gas, such as nitrogen, above the level of the water in an expansion tank. However, such a provision requires an expensive installation and regular costly maintenance.

Other attempts to exclude air from water in expansion tanks have included floating lids on the water surface of an open tank and a layer of floating plastics balls on such surface. Although such provisions are to some degree effective, they still allow oxygenation of the water, with consequent corrosion, when expansion water is drawn back into the system.

It is an object of the present invention therefore to provide an improved expansion tank for a liquid-filled system whereby the problems associated with contamination of the liquid by air or foreign matter can be obviated or minimised.

The invention provides an expansion tank, for a liquid-filled system, comprising a closed vessel having a lower liquid-flow connection for entry and exit of liquid from and to the system and a flexible fluid impermeable container, within the vessel, communicating with external atmosphere via an upper gas flow connection sealed relative to walling of the vessel, the volume of gas within the flexible container varying cyclically, in use, between a "high" level wherein the volume of gas within the container is at a minimum and the volume of liquid in the vessel is highest, and a "low" level wherein the volume of gas within the container is at a maximum and the volume of liquid in the vessel is lowest.

The invention also provides a liquid-filled system including an expansion tank comprising a closed vessel accommodating a flexible fluid-impermeable container of variable volume whose interior is in gas-flow connection with atmosphere and whose exterior contacts liquid in the vessel enabling the volume of liquid in the tank to vary without contact of the liquid with atmospheric oxygen.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a vertical cross-sectional view of a preferred tank of the invention in a "full" condition; Fig. 2 is a similar view with the tank in a "half-full" condition; Fig. 3 is a similar view with the tank "empty" and Fig. 4 is a cross-sectional elevation of a flexible container used in the tank of Figs. 1 to 3.

A preferred embodiment of tank 10 of the invention is suitable for use as an expansion tank for a liquid-filled system, such as a pressurised central heating system, wherein the volume of the working liquid, usually water, varies in use and needs to be protected from contact with atmospheric oxygen and contaminents such as dust.

The tank 10 includes a closed sheet metal vessel 11 which may be of overall cylindrical configuration and may vary in size from 0.6M in diameter and 1.3M in height up to 3.6M in diameter and 6M in height. The vessel 11 has adjacent its base 12 a side flow connection 13 which connects with a conduit 14 connecting to the system (itself not shown) and allowing liquid (usually water) to flow toand from the vessel 11. The vessel 11 has an overflow connection 15 including an upright conduit 16, a vent conduit 17 protected by a cowl 18, and a drain spout 19. An "upwardsonly" nonreturn valve 20 allows flow in only one direction in conduit 16.A replenishment liquid entry 21 is provided and is controlled by a solenoid valve 22 which operates automatically in response to activation of a lowlevel sensor means (not shown) when the level of liquid falls below a predetermined low level and allows the water to replenish the vessel 11 until the low level is exceeded once again.

At its upper end (Fig. 4) the vessel 11 has a gas flow connection in the form of a spigot 23 having an upper outwardly-extending flange 24. Overlying flange 24 and secured thereto by adhesive, and/or clamping or other means is a complementary flange 25 on a wide (typically 150-200mm wide) neck 26 of a container or bag 27 made of fluid impermeable inelastic sheet material whose body 28 is ac commodated within the vessel 11 and whose lower end 29 is secured by a flexible member such as a cord 30 to the base of vessel 11.

Cord 30 has some slack to allow the bag 27 to move inside the vessel 11 to facilitate flow of air to and from the bag 27. The bag 27 is made from a pair of layers each consisting of woven polyamide coated with butyl rubber and adhered together with a two component butyl adhesive. The bag 27 is relatively inelastic and is completely air and liquid impermeable and resistant to attack by atmospheric ozone. As an alternative to this bag a thicker rubber bag which is intrinsically elastic (like a balloon) could be used, but its weight would limit it to use in smaller tanks. The air flow connection through spigot 26 can be protected by a cowl 33 against ingress of dust etc, and more comprehensively, if required, by a filter (not shown).

As seen in Fig. 4, the bag 27 has a generally cylindrical body 28 and part-spherical end portions 31, 32. As illustrated the end portions 31, 32 are hemispherical and this is preferred, but less than a hemisphere can be used to suit different vessels 11. However, the angle between the cylindrical walls of body 28 and the end portions 31, 32 at their junction should be 120 degrees or more to avoid excessive stress at this point in use.

The lower end of bag 27 has connected thereto one end of a flexible tube 34 whose other end connects with side walling of vessel 11 at 35. Egress of water from point 35 indicates puncture of the bag 27 and the need to replace or repair it.

When the vessel 11 is initially filled or refilled after servicing, contained air needs to be released and this is achieved using a bleed connection 36 having a valve at 37. Upon filling of vessel 11, or during use to remove expelled gas, the valve 37 can be opened manually to vent air or gas until liquid flows.

Alternatively an automatic venting valve can be used.

At its bottom lower left as shown the vessel 11 has a liquid flow connection 38 whereby the tank 10 can be connected to an adjacent comparable tank 11 a. This expedient will normally be adopted when the expansion volume of a system is greater than a single tank can accommodate, or when a system is enlarged and it is cheaper to add a second tank than to replace an existing tank, or where a larger tank cannot be accommodated for space reasons.

In use, the tank 10 of the installation, or a battery thereof, replaces and has the same function as a conventional expansion tank in a pressurised or even non-pressurised central heating or other liquid filled system. It allows liquid to flow from and to the system as the volume of the working liquid changes, and it prevents any substantial ingress of atmospheric oxygen to the working liquid. Figs. 1 to 3 illustrate the various states of the vessel 11 from "full" to "empty" It will be appreciated that the interior of vessel 11 should be free from protrusions, and/or roughness and/or discontinuities to reduce the possibility of damage to the bag 27 during its cyclic inflation and deflation. The view of the bag 27 in Figs. 1 and 2 are schematic as the bag 27 does not actually contract as shown, but flattens in the manner of a paper bag as it goes towards minimum internal volume.

The invention is not limited to the details of the apparatus described above and variations can be made thereto within the scope of the following claims.

Claims

1. An expansion tank, for a liquid-filled system, comprising a closed vessel having a lower liquid-flow connection for entry and exit of liquid from and to the system and a flexible fluid impermeable container, within the vessel, communicating with external atmosphere via an upper gas flow connection sealed relative to walling of the vessel, the volume of gas within the flexible container varying cyclically, in use, between a "high" level wherein the volume of gas within the container is at a minimum and the volume of liquid in the vessel is highest, and a "low" level wherein the volume of gas within the container is at a maximum and the volume of liquid in the vessel is lowest.

2. A tank as claimed in claim 1 wherein the container is in the form of a bag made from inelastic air and gas impermeable material.

3. A tank as claimed in claim 1 wherein the container is of elastic resilient material.

4. A tank as claimed in claim 2 wherein the material of the bag is a textile coated and/or impregnated with a rubber or plastics.

5. A tank as claimed in claim 4 wherein a butyl rubber is coated on the textile which is a woven polyamide cloth.

6. A tank as claimed in claim 5 wherein two layers of polyamide textile material, each coated with butyl rubber, are adhered together.

7. A tank as claimed in any of claims 2 to 6 wherein the upper gas flow connection includes a tubular spigot on the vessel wall which surrounds a tubular neck on the bag.

8. A tank as claimed in claim 7, wherein the spigot has an outwardly extending annular flange to which is clamped, adhered or otherwise secured a complementary flange on the neck of the bag.

9. A tank as claimed in any preceding claim wherein the upper gas flow connection is in direct flow connection with ambient atmosphere.

10. A tank as claimed in claim 9 wherein the upper gas flow connection is shrouded to allow gas flow but to discourage entry of foreign matter into the interior of the bag.

11. A tank as claimed in claim 9 or 10 wherein the gas flow connection includes a filter to exclude all or larger dust and the like from entry to the bag.

12. A tank as claimed in any preceding claim wherein the vessel is at least substantially free of internal irregularities and/or protruberances and/or discontinuities to minimise the danger of damage to the container in use.

13. A tank as claimed in any preceding claim and having an inlet for replacement supply liquid.

14. A tank as claimed in claim 13, wherein the inlet for replacement liquid is normally closed, being operable in response to the activation of sensor means capable of detecting a low liquid level.

15. A tank as claimed in claim 14 wherein the sensor means is connected to operate the inlet valve automatically when replenishment is needed.

16. A tank as claimed in any preceding claim and having an overflow connection operative to discharge liquid to drain in the event of a superfluity of liquid being supplied to the tank by the liquid flow connection.

17. A tank as claimed in claim 16 wherein the overflow connection includes a non-return valve and a shrouded exit.

18. A tank as claimed in any preceding claim and including a vent connection to allow gas within the vessel to be removed when it is first filled after installation or servicing.

19. A tank as claimed in any preceding claim wherein the container has a flexible member attached at a low part thereof and secured to the base of the vessel to anchor the container within the vessel.

20. A tank as claimed in claim 19, wherein the flexible member provides a degree of slack to allow container movement.

21. A tank as claimed in any preceding claim, wherein the container has connected to a lower part thereof one end of a flexible tube whose other end connects with walling of the vessel, egress of liquid from said other end signifying puncture of the container and the need to replace or repair the container.

22. A tank as claimed in any preceding claim and having a further lower liquid flow connection allowing the tank to be connected to an adjacent comparable tank when the expansion volume of the system is greater than can be accommodated by a single tank.

23. A tank as claimed in any preceding claim wherein the container has a generally cylindrical body and part-spherical end portions.

24. A tank as claimed in claim 23, wherein the end portions are hemispherical.

25. A liquid-filled system including an expansion tank comprising a closed vessel accommodating a flexible fluid-impermeable container of variable volume whose interior is in gas-flow connection with atmosphere and whose exterior contacts liquid in the vessel enabling the volume of liquid in the tank to vary without contact of the liquid with atmospheric oxygen.

26. A system as claimed in claim 25 wherein the liquid is water.

27. A system as claimed in claim 25 or 26 and having a pressurised portion, a pressurisation unit effecting connection between the pressurised portion and the expansion tank.

28. A system as claimed in claim 25, 26 or 27 and being a central heating system.

29. A liquid filled system substantially as hereinbefore described with reference to the accompanying drawings.