GB2402994A

GB2402994A - Expansion chamber with flexible membrane

Info

Publication number: GB2402994A
Application number: GB0413362A
Authority: GB
Inventors: George Hanson-Graville
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-18
Filing date: 2004-06-15
Publication date: 2004-12-22
Anticipated expiration: 2024-06-15
Also published as: GB2402994B; GB0413362D0

Abstract

A hot water cylinder 1 is connected into a hot water central heating supply system which is fed from an elevated water storage tank sited to give a sufficient water supply head. In use the tank 1 is filled to only 90% of the volume with water 2 leaving 10% of the volume 3 as an air space. The top of the tank is in communication, through a pipe 4, with an expansion chamber 5 which comprises a flat casing 6 formed from two parts joined by a seam and closed-off from atmosphere on one side by a flexible membrane 7 forming a diaphragm with the periphery trapped in the seam. The membrane (Fig. 1) is in a relaxed concave state when the cylinder is filled with cold water. The top of the container 6, above the membrane 7, is open to atmosphere at 6a.

Description

Title: Unvented water storage tank apparatus.

This invention relates to a hot water storage tank or cylinder apparatus forming part of a hot water supply system, principally of the kind used for domestic hot water supply or central heating purposes. This invention also relates to an expansion vessel for use with hot water supply or central heating systems to form a closed system to prevent water loss through evaporation.

Known arrangements use a storage tank for hot water, the tank being filled to the maximum and having a hot water draw-off and an expansion pipe connected to the top of the tank, normally an upright cylinder. The expansion pipe rises to a level above a water storage reservoir feeding the hot water tank and into which water is discharged following expansion due to heating. In another system, which uses an unvented hot water tank, provision is made for an air pressure pocket to be trapped in the top of the hot water tank in order to s accommodate expansion. In these systems pressures of 2 Bar or greater can be experienced and protection systems are needed to avoid bursts or leakage when under pressure.

One object of this invention is to provide a hot water storage tank apparatus which allows expansion but without the generation of excessive no pressures should the water overheat to a dangerous level.

Another object of this invention in the alternative is to provide an expansion vessel which avoids loss of water through evaporation particularly in central heating systems.

According to a first aspect of this invention there is provided a hot water storage and supply system embodying an apparatus comprising a hot water storage tank associated with a water heating means, the tank being only partly filled with water and adapted to retain a defined volume of air above the water level in the tank, the top of the tank being in communication with the interior of a sealed expansion chamber, the expansion chamber comprising a container defined, in part at least, by a flexible membrane of which one surface, forming part of the interior of the chamber is in communication with the top of the hot water tank, the other surface of the membrane being in communication with o atmospheric pressure.

In an embodiment the volume of air in the hot water tank comprises approximately 10% of the tank volume when filled with ambient supply temperature cold water (nominally 7 degrees C) and the volume normally reduces to 6% of the volume of the tank at hot water temperatures of about 80 s degrees C. In this system, and according to the invention, the hot water tank is filled once only to the required level leaving an air space and connected to the expansion chamber without pressurization with the membrane being slack. As the water expands on heating then air is displaced into the expansion chamber whereby the membrane is displaced to permit the volume to expand but under little or no pressure. The expansion chamber will be located above the level of the storage tank supplying the hot water tank.

A safety relief valve is preferably provided connected with the expansion chamber to discharge any excess pressure should such occur.

In another and second aspect, this invention provides an expansion vessel comprising a casing having an upper part and a lower part with an internal medially disposed diaphragm defining, on one side thereof, a closed chamber in communication with a port for connection with the top of a hot water storage tank, the casing part overlying the other side of the diaphragm having an opening to atmosphere.

This invention also provides a central heating system with a closed water circuit incorporating the aforesaid expansion vessel.

Preferably the casing will be of a flat form comprising two halves joined To by a medially disposed seam. The seam will form a fixing for the diaphragm extending internally of the casing to form the closed chamber. The diaphragm may be of a flexible material and arranged to stretch under pressure from the closed chamber side. In a preferred arrangement the diaphragm will be slack having when at rest a concave profile and extending into the closed chamber s and adopting a convex profile when air is displaced form the top of a hot water storage tank into said chamber. The closed chamber may include an over- pressure relief valve associated therewith.

This construction avoids the need for a separate ball-valve and header tank with overflows to replenish loss of water as used in conventional central so heating systems and requires only filling once. Thus long term build-up of lime scale through repeated replenishment of water due to evaporative losses is prevented An embodiment of this invention is described, by way of an example, and with reference to the accompanying drawings, wherein: Fig 1 shows an arrangement according to this invention when the water is cold, and Fig. 2 shows the arrangement when the water is hot.

As shown in the drawings a hot water cylinder 1 is connected into a hot water supply system, not shown here, and the system is fed from an elevated water storage tank sited to give a sufficient water supply head, also not shown.

In use the tank 1 is filled to only 90% of the volume with water 2 leaving 10% of the volume 3 as an air space. The top of the tank is in communication, through a pipe 4, with an expansion chamber 5 forming the second aspect of this invention and which comprises a flat casing 6 formed from two parts joined by a seam and closed-off from atmosphere on one side by a flexible membrane 7 forming a diaphragm with the periphery trapped in the seam. The membrane, as shown in Fig. 1, is in a relaxed concave state when the cylinder is filled with cold water at nominally 7 degrees C. The top of the container 6, above the membrane 7, is open to atmosphere at 6a.

When the water in the tank is heated then air will be displaced to lift the membrane as shown in Fig. 2 to a convex state. At the maximum normal temperature the pressure contained by the membrane will be minimal and typically 2 inches water pressure will be the maximum. Included is a pressure so relief valve 8 which opens at 1-2 Ibs. pressure and which then operates should any fault occur resulting in over-expansion or boiling of the water. Even in this case only steam is discharged due to the retention of the air volume.

The membrane in the expansion vessel will be slack such that little pressure is needed to move same This construction permits expansion without displacement of hot water and avoids loss by evaporation. The expansion vessel may be connected with and form part of a closed water circuit central heating system of a conventional kind and not shown here.

Claims

Claims: 1. A hot water storage and supply system embodying an apparatus

comprising a hot water storage tank associated with a water heating means, the tank being only partly filled with water and adapted to retain a defined volume of air above the water level in the tank, the top of the tank being in communication with the interior of a sealed expansion chamber, the expansion chamber comprising a container defined, in part at least, by a flexible membrane of which one surface, forming part of the interior of o the chamber is in communication with the top of the hot water tank, the other surface of the membrane being in communication with atmospheric pressure.
2. A hot water storage and supply system in accordance with claim 1, wherein a safety relief valve is connected with the expansion chamber to discharge any excess pressure should such occur.
3. A hot water storage and supply system in accordance with claim 1 or 2, wherein the expansion chamber comprises a casing having an upper part and a lower part with an internal medially disposed diaphragm defining, on one side thereof, a closed chamber in communication with a port for connection with the top of a hot water storage tank, the casing part overlying the other side of the diaphragm having an opening to atmosphere.
4. An expansion vessel for use in a hot water storage and supply system comprising a casing having an upper part and a lower part with an internal medially disposed diaphragm defining, on one side thereof, a closed chamber in communication with a port for connection with the top of a hot water storage tank, the casing part overlying the other side of the diaphragm having an opening to atmosphere.
5. A hot water storage and supply system in accordance with claim 3 or an expansion vessel in accordance with claim 4, wherein the casing is of flat form comprising two halves joined by a medially disposed seam.
6. A hot water storage and supply system or an expansion vessel in accordance with claim 5, wherein the seam forms a fixing for the To diaphragm extending internally of the casing to form the closed chamber.
7. A hot water storage and supply system or an expansion vessel in accordance with claim 5 or 6, wherein the diaphragm is of a flexible material and arranged to stretch under pressure from the closed chamber side.
8. A hot water storage and supply system or an expansion vessel in accordance with claim 5 or 6 or 7, wherein the diaphragm is slack having, when at rest, a concave profile and extending into the closed chamber and adopting a convex profile when air is displaced form the top of a hot water storage tank into said chamber.

so
9. A hot water storage and supply system or an expansion vessel in accordance with any one of claims 5 to 8, wherein the closed chamber includes an over-pressure relief valve associated therewith.
10. A central heating system with a hot water storage tank and a closed water circuit, the system incorporating the expansion vessel according to any preceding claim 4 to 10.
11. A central heating system In accordance with claim 10, wherein the expansion vessel is mounted on the top of the tank.
12. A hot water storage and supply system as described herein and exemplified with reference to the drawings.
13. An expansion vessel as described herein and exemplified with reference to the drawings.
14. A central heating system incorporating a hot water storage tank and an expansion vessel as described herein.