GB2125108A - Liquid supply vessel - Google Patents

Abstract

A container (5), capable of being pressurised, is arranged vertically with an inlet pipe (7) which is connected in use to a supply of liquid under pressure, opening into the top and with an outlet (9) near to the bottom of the container. The container (5) has an internal height (h) such that with the outlet (9) closed liquid will rise in the container (5) only up to a level (20) at which the gas in the top of the container (5) is compressed to a pressure equal to the liquid supply pressure and then inflow ceases automatically. The buffer vessel may be used in a domestic water system for pressurising a hot water tank to mains pressure. Alternatively, with a further inlet pipe (7A) two liquids can be supplied for mixing in the container. Flow into the container is self regulating to equal the quantity of liquid drawn from the container. <IMAGE>

Description

SPECIFICATION Buffer vessel for a liquid supply This invention relates to a buffer vessel for a liquid supply and to a liquid supply system incorporating such a buffer vessel, particularly, although not exclusively, a domestic water system. The term buffer vessel is used to mean a pressure vessel connectible to a supply of liquid under pressure and capable of being internally pressurised to a pressure dependent upon the liquid supply pressure, with a cushion of compressed gas inside the vessel.

In domestic water systems, the hot water supply is usually at a lower pressure than that of the cold supply because the hot system is merely pressurised by a header tank whereas the cold supply is usually at mains (high) pressure. For many circumstances, though, it is necessary or at least advantageous to have equalised pressures on the hot and cold supplies, and whilst to provide for this it is not uncommon for the cold supply pressure to be reduced to low pressure by using a cold water header tank, there are many applications when high pressure on both the hot and cold supplies is advantageous.

A direct connection of the mains pressure to the hot water system is, however, generally not permitted because of the risk of contamination of the mains supply.

The present invention provides means whereby a hot water system can be pressurised to mains pressure simply and reliably.

The invention may also be useful in other fields such as to provide means whereby two or more liquids can be brought together and mixed without risk of the mixed liquids or of the individual supplies coming into contact with the other, or another, one of the liquids.

According to the present invention, there is provided a buffer vessel for a liquid supply, comprising a closed container which is capable of being internally pressurised, at least one inlet pipe opening into the container at or near the top of the container in its use position, the inlet pipe being connected or connectible to a supply of liquid under pressure and being arranged so that gas in the container cannot escape from the container through the inlet pipe, and an outlet at or near to the bottom of the container, the container having an internal height from its outlet to its, or its lowest, inlet such that when liquid flow into the container through the inlet pipe is in excess of liquid flow out through the outlet, the gas which is trapped within the upper part of the container will be progressively compressed by liquid accumulating in the lower part of the container up to a pressure which equals the supply pressure (whereupon further flow of liquid into the container will cease) with the level of liquid in the container spaced downwardly from the inlet opening so that the liquid in the container will not come into direct contact with the liquid in the inlet pipe.

The cross-sectional area of the container may be uniform throughout its height. Thus, in a basic form the container comprises a cylinder closed at the top and bottom by sealed ends with inlet and outlet pipes opening into the container from a horizontal direction into the cylindrical side wall near the top and bottom respectively.

Alternatively, the cross-sectional area of the container may vary over the height in order to achieve certain operating characteristics or to suit space requirements for particular installations. The cross-sectional area may progressively decrease in the upward direction, or the cross-sectional area may include vertical portions of different uniform cross-section with a sudden transition from one to the other or with a progressively decreasing transition portion.

With a cross-sectional area that reduces in the upward direction, the rate at which the liquid level will rise within the container will increase for a given rate of net flow of liquid into the container, though in practice of course as the pressure of the gas within the upper part of the container approaches the supply pressure, the flow of liquid into the container will slow down.

With a reducing cross-sectional area the rate at which the liquid level will rise up to the cut-off point, at which the gas pressure equals the supply pressure, can be arranged to be approximately even.

A sudden transition from one cross-sectional area to another may be useful at a critical region just below the cut-off level so that the liquid level will not fall or rise particularly rapidly when the lever is below the transition at the larger crosssectional area - this condition may prevail when, for instance, the outlet of the container is continually being opened and shut as liquid is tapped off - but the level will rise more quickly when the cut-off point is approached above the transition, in the smaller cross-section portion; this will achieve a sharper cut-off.

If the liquid supply line is liable to pressure surges, it may be advantageous to have an upwardly increasing cross-sectional area. Thus, if during the static cut-off condition when the gas pressure equals the liquid supply pressure and there is no flow into the container, there were to be a sudden, perhaps momentary, pressure surge, an increasing cross-sectional area would reduce the risk that the liquid level could rise to the level of the inlet.

In all cases, it is preferable that the crosssectional area of the container, or at least a portion of it, is greater than the cross-sectional area of the inlet pipe so that for a given volumetric flow the flow veiocity through the container, or that portion of it, is slower than the flow rate through the inlet pipe.

With two or more inlet pipes, different liquids can be supplied to the container where they will mix in its lower part. The pressurised cushion of gas in the upper part of the container ensures that the mixed liquid in the container can never rise to the level of the inlet openings, or to the lowest of them if they are at different levels, by arranging that the cut-off level when the gas pressure equals the supply pressures is apced below that inlet opening. The supply and mixing is completely selfregulating without the need for valves except that for controlling the outlet.

The supply pressure of the different liquids must themselves be equalised if the inlets open into the same portion of the container.

However to cope with different supply pressures the upper part of the container may be divided into downwardly open compartments the lower ends of which are below the respective cut-off levels appertaining to the volume in the respective compartments where the pressure equals the liquid supply opening into that compartment.

The invention maybe put into practice in a number of ways but certain specific embodiments will now be described by way of example only with reference to the drawings, in which: Figure 1 is a vertical section of a cylindrical buffer vessel in accordance with the invention; Figures 2A to F show vertical sections of further embodiments of buffer vessels with varying cross-sections; and Figure 3 shows a buffer vessel suitable for mounting on the side of a hot water tank of a domestic water system.

The buffer vessel shown in Figure 1 is a closed container 5 of uniform cross-section throughout its height - circular or rectangular for example having an inlet pipe 7 at or near to the top 8 which is flat and sealed to the side walls, and an outlet pipe 9 at or near to the bottom 10 also sealed to the container side walls. The inlet and outlet pipes 7 and 9 project generally horizontally, though they may in other embodiments extend vertically or inclined to the vertical.

The inlet pipe 7 is in use connected to a supply of liquid under pressure, for example a main water supply at pressure Pse The outlet pipe 9 is connected for example to a hot water tank which must also be closed and capable of being pressured up to pressure Psw Initialiy the container 5 will be empty of liquid containing only air at atmospheric pressure (though in other embodiments the container could initially contain some gas other than air and/or be at an initial pressure above - or even conceivably below -- atmospheric).

As water enters the container 5 from the supply via inlet pipe 7, the water will after filling the hot tank for example (and assuming no water is being tapped off) begin to accumulate in the bottom of the container 5 and as the water level rises first to cover the outlet pipe 9 so to trap an initial volume V, of air in the container 5 and then up the container, the air will be progressively compressed until at a volume V2 the pressure P2 equals the supply pressure Ps. Thereafter no further water will enter the container 5 from the inlet pipe 7 until the compressed air pressure falls below P2 when hot water is run off from the tank.

The hot water in the tank will thus be pressurised to pressure P2 equal to mains pressure P1.

The height h of the container 5 from the level of the outlet pipe 9 to the level of the inlet pipe 7 is designed to be such that the level 20 of water in the container 5 when the air is compressed to volume V2 - the so-called cut-off level when the flow of water into the container 5 ceases - is spaced downwardly well below the level of the inlet pipe 7. There is thus no risk of the water in the bottom portion of the container 5 coming into contact with the supply water because the level 20 can never normally rise to the level of the inlet pipe.

If the mains pressure were to fall, the air in the container 5 would simply expand into the inlet pipe 7 until the air pressure has decreased to the reduced mains pressure. Only in the event of a prolonged negative pressure in the mains could the water level in the container 5 ever rise above the level 20 but a non-return valve would in any case be fitted in the inlet pipe inside or outside the container to prevent back flow of water through the inlet pipe 7 to avoid contamination of the mains supply, even if that situation did occur.

If the container 5 is to be used for mixing two nasty liquids or ones which react together or must not otherwise contact each other, separate inlet pipes 7 and 7A can be provided, both supplies being at the same pressure. Both liquids will flow into the container 5 and mix but the mixed liquid level can only rise up as far as level 20 because by then the air/gas pressure P2 will equal the supply pressure at each inlet and inflow will cease.

As the mixed liquid is run off from the outlet pipe 9, the level of mixed liquid will fall below level 20, the air/gas pressure will decrease and the liquids will flow in again through the inlet pipes 7 and 7A to replenish the mixed liquid in the container 5 but again only up to the cut-off level 20.

Contamination of the individual supplies by either the mixed liquid or the other (or another, if there are more than two inlet pipes and supplies) one of the liquid cannot occur, and moreover the supply of both (or all) of the liquids and the mixing is completely self-regulating as determined by the drawing off of the mixed liquid from the outlet pipe 9.

The proportions of the liquid making up the mixture can be determined by appropriate sizing of the inlet pipes 7 and 7A, and either or both could be provided with a valve so that the relative proportions of the liquids one to another can be varied.

Figures 2A to 2F show various different container shapes with a cross-section which varies over the height of the container, as will be explained. In other respects the operation of the buffer vessel in accordance with the invention using these variants of containers is essentially the same as that described above with reference to the Figure 1 embodiment, and where possible similar reference numerals have been used to identify those parts with similar functions.

In Figure 2A an upwardly tapering cross section is shown. The progressively upwardly reducing cross-sectional area may be arranged approximately to match the progressively decreasing inflow rate of liquid as the cut-off level 20 is approached so to keep the rate of rise of the liquid level generally even. The container 5 shown in Figure 2A may be frusto-conical, frustotetrahedral, or frusto-pyramidal for example.

In Figure 2A, also, a variant is shown for the inlet pipe 7' which extends upwardly inside the container 5, the upper end opening just below the top 8 of the container 5.

Figure 2B shows a container with upper and lower portions 5B and 5A each of uniform crosssection which may each be any one of circular, rectangular or triangular for example, with a sudden transition between the two cross-sections.

In the lower portion 5A the rise and fall of the liquid level as liquid is replenished or run off will be slow but once the level of liquid rises into the upper portion 5B the rate of rise will suddenly get quicker giving a more rapid increase in the gas pressure as the level 20 is approached thereby giving a sharper cut-off. The actual and relative cross-sectional areas of the portions 5A and 5B will depend upon particular use conditions and rates of inflow and drawing off.

Figure 2C shows a container which in principle is exactly similar to that of Figure 2B, the only difference being that the container portions 5A and 5B are centred on the vertical axis whereas in Figure 2B the upper portion 5B is eccentrically located on the lower portion.

Figures 2D and 2E correspond to Figures 2B and 2C except that in these cases the upper and lower container portions 5B and 5C are not directly adjacent but a tapering cross-section intermediate portion 5C, again of any suitable cross-sectional shape, is provided. This combines the progressively reducing cross-section characteristics, as described in relation to the embodiment of Figure 2A, for the transition region, with the characteristics of the larger and smaller uniform cross-sections of the lower and upper portions as described for the embodiments of Figures 2B and 2C.

Figure 2F shows a container 5 for mixing two liquids the supplies of which are at different pressures. The respective inlet pipes 7B and 7C here open into different compartments 5X and 5Y formed in the top of the container 5 by a partition 14, these compartments being downwardly open.

In use, as the level of mixed liquid, which may be stirred by an agitator 1 5 to assist mixing, rises in the container 5 it eventually closes the bottom of the compartments 5X and 5Y. Thereafter, the liquid levels in the two compartments rise to their different cut-off levels 20B and 20C dependent upon the respective supply pressures at the inlet pipes 7B and 7C. The difference in those pressures will be equal to the hydrostatic pressure corresponding to the difference between the levels 20B and 20C.

Finally, the buffer vessel of Figure 3 is one specially shaped to fit onto the side wall 22 of a domestic hot water tank, so as to pressurise the latter to mains pressure. The container 5 here is elongate and vertically oriented and of closed U channel section 23 closed at each end 25, 26 and with a cut-away vertically-extending mid portion which is closed by panels 27, 28 and 29 to leave a vertical portion 30 within the container and somewhat nearer to the top portion of it, of reduced, semi-circular cross-sectional area.

The inlet pipe 7, connected to the mains water supply, enters and opens into the upper portion of the container 5 through panel 29, and the outlet pipe 9 exits from the lower portion of the container 5 from the panel which closes the U channel section of that portion directly into the hot water tank through the side wall 22.

The principle of operation is the same as that explained above in relation to the Figure 1 embodiment. The water from the mains supply will enter the container through the inlet pipe 9 and will accumulate in the lower portion of the container as the hot tank fills. Once the outlet pipe 9 is covered, the air in the container will be trapped and as the level of water rises the air will be compressed until, at a level which should not be higher than that of the panel 29 through which the inlet pipe 7 projects (and is preferably arranged to be only part way up the reduced cross-section portion 30), the air pressure will equal the supply pressure and no more water will flow from the mains into the container. This condition will remains until the air pressure in the container is reduced when the water level falls after water is drawn off from the hot water tank.

The reduced cross-section container portion 30 may have a clear, e.g. glass, panel to enable the water level in the container 5 to be seen.

Such a buffer vessel installed in this way obviates the need for a header tank completely thus making it especially suitable for bungalows and single storey buildings, and moreover its use advantageously pressurises the hot water system to a high pressure equal to the cold (mains) pressure making possible the use of more effective high-pressure water fittings such as mixer units for showers, baths or basins.

Although the container 5 shown in Figure 3 is attached to the hot tank, it will be appreciated that the buffer vessel could be installed in the water system at any convenient location.

Claims (23)

1. A buffer vessel for a liquid supply, comprising a closed container which is capable of being internally pressurised, at least one inlet pipe opening into the container at or near the top of the container in its use position, the inlet pipe being connected or connectible to a supply of liquid under pressure and being arranged so that gas in the container cannot escape from the container through the inlet pipe, and an outlet at or near to the bottom of the container, the container having an internal height from its outlet to its, or its lowest, inlet such that when liquid flow into the container through the inlet pipe is in excess of liquid flow out through the outlet, the gas which is trapped within the upper part of the container will be progressively compressed by liquid accumulating in the lower part of the container up to a pressure which equals the supply pressure (whereupon further flow of liquid into the container will cease) with the level of liquid in the container spaced downwardly from the inlet opening so that the liquid in the container will not come into direct contact with the liquid in the inlet pipe.

2. A buffer vessel as claimed in claim 1 , in which the cross-sectional area of the container is uniform throughout its height.

3. A buffer vessel as claimed in claim 2, in which the container comprises a cylinder, or other body of constant cross-section, closed at the top and bottom by sealed ends with inlet and outlet pipes opening into the container from a horizontal direction into the side wall near the top and bottom respectively.

4. A buffer vessel as claimed in claim 1, in which the cross-sectional area of the container varies over its height.

5. A buffer vessel as claimed in claim 4, in which the cross-sectional area of the container progressively decreases in the upward direction.

6. A buffer vessel as claimed in claim 4, in which the container has vertically extending portions of different uniform or progressively varying cross-section with a sudden transition from one to the other or with a progressively decreasing transition portion.

7. A buffer vessel as claimed in claim 6, in which the transition portion is arranged below the cut-off level.

8. A buffer vessel as claimed in claim 4, in which the cross-sectional area of the container decreases in the upward direction such that the rate at which, in use, the liquid level rises to the cut-off point, at which the internal gas pressure equals the liquid supply pressure, is approximately even.

9. A buffer vessel as claimed in claim 4, in which the container includes at least a portion with an upwardly increasing cross-sectional area.

1 0. A buffer vessel as claimed in any one of the preceding claims, in which the cross-sectional area of the container, or at least a portion of it, is greater than the cross-sectional area of the inlet pipe.

11. A buffer vessel as claimed in any one of the preceding claims, in which two or more inlet pipes are provided.

12. A buffer vessel as claimed in claim 11, in which the upper part of the container is divided into downwardly open compartments into which separate inlet pipes open and the lower ends of which are below the respective cut-off levels appertaining to the volume in the respective compartments when the pressure equals the liquid supply opening into that compartment.

13. A buffer vessel as claimed in claim 11 or claim 12, in which an agitator is provided for mixing liquid in the bottom part of the container.

14. A buffer vessel as claimed in claim 11, in which means is provided for equalising the pressures at the two or more inlet pipes.

15. A buffer vessel as claimed in any one of the preceding claims, in which the container includes a clear panel to enable the liquid level in the container to be seen.

16. A water supply system including a buffer vessel as claimed in any one of claims 1 to 10, in which the inlet pipe of the container is connected to a water supply, in which the container is arranged vertically, and in which the container outlet is connected to delivery means controlled by a valve.

1 7. A water supply system as claimed in claim 16, in which the container outlet is connected as the inlet to a tank e.g. a hot water tank.

18. A water supply system as claimed in claim 17, in which the container is mounted on the side of the tank.

19. A water supply system as claimed in any one of claims 16 to 18, in which the water system is a domestic water system.

20. A water supply system as claimed in any one of claims 1 6 to 19, in which the inlet pipe is connected to a mains water supply.

21. A system for mixing and supplying two liquids, including a buffer vessel as claimed in any one of claims 11 to 14, in which two or more liquid supplies are connected to respective inlet pipes of the container, and the container outlet is connected to delivery means for delivering a mixture of the liquids from the container.

22. A buffer vessel substantially as specifically described herein with reference to any one of Figures 1 to 3 of the accompanying drawings.

23. A liquid supply system having a buffer vessel as claimed in claim 22.