GB2527751A

GB2527751A - Accumulator system

Info

Publication number: GB2527751A
Application number: GB1411278.3A
Authority: GB
Inventors: Steven Burgess
Original assignee: Stuart Turner Ltd
Current assignee: Stuart Turner Ltd
Priority date: 2014-06-25
Filing date: 2014-06-25
Publication date: 2016-01-06
Anticipated expiration: 2034-06-25
Also published as: GB201411278D0; GB2527751B

Abstract

The system 1 comprises a pump 11 connected to a mains supply inlet 5, an accumulator 18 downstream of the pump, and a flow detector 17 downstream of the accumulator which operates the pump when flow is detected. There may be a second flow detector 15 between the pump and the accumulator, and both detectors may comprise a magnetic float inside a pipe and a detector coil outside the pipe. The system may comprise a flow limiter 58 for limiting flow from the accumulator, and a parallel one way valve 59 for allowing flow into the accumulator. Also claimed is a second system comprising an inlet for connection to mains supply, an accumulator downstream of the inlet and a flow limiter for limiting flow from the accumulator. The second system may comprise a pump and a one way valve parallel with the flow limiter. Also claimed are corresponding methods of supplying water to a property, and a connector for housing the parallel one way valve and flow limiter.

Description

Accumulator system The invention relates to water supply systems using accumulators to provide increased water pressure. In particular, the invention relates to systems including a pump supplemented by an accumulator.

An accumulator or pressure vessel in water supply systems is a tank which includes an expandable water storage compartment separated by a flexible membrane from a compressible gas compartment (typically filled with compressed air). As water is forced into the water storage compartment, the flexible membrane stretches, the storage compartment expands and the gas in the gas compartment compresses.

As the gas compresses, the pressure increases. At equilibrium, both the liquid and gas compartments are at the same pressure. Therefore the accumulator allows a significant volume of water to be stored at raised pressure. When water is drawn from the accumulator, the pressure begins to drop as the liquid volume reduces and the gas volume expands until the pressure reaches equilibrium with other fluids in the system.

In water supply systems, accumulators are typically used to provide elevated pressure in systems where the water pressure is otherwise low.

Mains water pressure at a property depends on a number of factors including the height difference between the property and the reservoir or local water tower, and the presence of any intermediate pumping stations. Throughout the day, mains water pressure can also fluctuate depending on upstream usage by other properties. For example in a residential area, mains water pressure will likely be higher during the night when everyone is asleep and maybe also during the day when most people are at work. Water pressure will be lower in the morning and evening when a lot of people are using the supply simultaneously. Although many properties have adequately high water pressure (e.g. 1 to 3 bar), towards the lower end of the spectrum in the United Kingdom, water suppliers typically guarantee an average mains water supply of around 0.7 bar. However, the actual supply pressure may vary e.g. from 0.3 bar during peak usage times up to 1 bar during low usage times.

At low pressures, properties will experience low flow rates that may not be sufficient for some purposes. For example, an average shower draws a flow of about 12 litres per minute. If system pressure drops, that flow rate cannot be sustained and the shower will be unsatisfactory. Even if a flow of 12 litres per minute can be sustained by the system, any simultaneous use of additional appliances (e.g. washing machines, dishwashers, flushing a toilet or turning on another tap) will lower the flow rate available for the shower, again leading to unsatisfactory performance. Eco-showers produce lower flow rates, but require higher operating pressures and can therefore suffer even more from low pressure.

Accumulators have been used to supplement a properties water pressure by providing a higher pressure storage vessel. Where the highest mains pressure (i.e. at low usage times) is sufficiently high, the pressure to pressurize the accumulator can come directly from the mains. In these scenarios the accumulator pressurizes to the highest available pressure e.g. overnight and retains that pressure until it is required. Subsequently when there is water demand within the property, the accumulator provides water at the higher pressure. In this set up, the accumulator needs to be large enough that the water pressure does not drop to an unacceptable level during normal demand. For example an 8 minute shower at 12 litres per minute draws nearly 100 litres of water from the accumulator and even with a large accumulator (200 litres or more) will cause a noticeable drop in pressure towards the end of the shower.

In cases where the mains pressure in a property never reaches sufficient levels, the accumulator needs to be pressurized by a pump. While there is no demand on the system, the pump forces water into the accumulator until a desired water pressure is reached, e.g. 3 bar. The pump can then be switched off until the accumulator requires repressurization. "Mien there is demand on the system, water is drawn from the accumulator at the elevated pressure. \Mien a significant quantity of water has been drawn from the accumulator, a pressure sensor senses the drop in pressure and causes the pump to engage to start repressurizing the accumulator.

Until recently, such pump-fed accumulators in the United Kingdom had to be fitted downstream of a break tank as it was against regulations to pump directly from the mains. Recently the regulations have changed and it is currently permissible to pump directly from the mains at up to 12 litres per minute.

Many water pressure assistance systems now make use of a 12 litre per minute pump on its own with no accumulator. This guarantees a 12 litre per minute delivery to the property. If the mains pressure happens to be sufficient to support a greater flow, a pump bypass permits this. However, such systems are limited in that when the mains pressure is low, the flow rate is still restricted to only 12 litres per minute. This is enough to support a standard shower running on its own, but it cannot sustain the shower flow rate if other appliances are turned on at the same time. Thus such systems are not fully satisfactory.

The use of an accumulator together with a mains pumped system goes some way towards solving this problem as the accumulator can be pumped up to the desired pressure directly from the mains, storing a large volume of high pressure water.

Once the accumulator has fully pressurized, the pump is turned off. When water is drawn from the system, it is drawn from both the mains and the accumulator which together provide an adequate flow rate for the property (e.g. in excess of 20 litres per minute). A pressure sensor detects when the pressure in the accumulator has dropped below a certain level and triggers the pump to switch on and recharge the accumulator. The problem with such systems is that when the mains pressure is weak, the majority of the flow is drawn from the accumulator. Once the pressure drop in the accumulator has been detected, the volume of stored water in the accumulator has therefore already dropped significantly and the pressure and flow provided by the accumulator are already severely diminished. While the pump is now switched on and provides 12 litres per minute, the semi-drained accumulator is now unable to supplement this with much additional flow for very long. The accumulator quickly becomes exhausted and the available water pressure and flow within the property drops.

According to one aspect, the invention provides a water supply system comprising: an inlet for connection to a mains water supply; a pump connected to the inlet; an accumulator connected downstream from the pump; and a flow detector downstream of both the pump and the accumulator; wherein the system is arranged to operate the pump when flow is detected by said flow detector.

The use of a flow detector to activate the pump makes the system much more responsive. Traditional accumulator set ups have used pressure detectors to determine when to activate the pump. However, the pressure downstream of the accumulator does not change significantly when system demand first appears, e.g. when somebody turns on a tap or starts a shower. Instead, the accumulator maintains the pressure at all points downstream of itself until the accumulator itself has partially emptied enough for the pressure drop to be detected. A further problem is that pressure sensors have to be set to trigger at a certain pressure.

The sensors are not particularly accurate and so a reasonably conservative trigger value has to be set to avoid erroneous operation. Flow detectors on the other hand trigger as soon as system demand occurs. Any flow, regardless of pressure will trigger the flow detector and thus will activate the pump. Accordingly, as much of the demand as possible is fulfilled by the pump rather than the accumulator. The accumulator thus retains its water storage for longer and maintains its pressure for longer. The accumulator only comes into play when demand cannot be met by the pump alone, or where the pressure output from the pump is less than that in the accumulator. This allows a smaller accumulator for a given level of system assistance as the accumulator will not be drained as early as it would in a conventional set up and therefore provides useful flow addition for longer, improving the experience of the system user(s).

The mains inlet of the system is at an upstream end of the system and is typically connected to a water main at the property boundary. The outlets (e.g. taps, baths/showers, washing machines, dishwashers, etc. are connected to a downstream end of the system. The pump is connected directly to the mains inlet and pumps directly from the mains in use. The pump may be limited to a certain flow rate according to regulations (e.g. no more than 12 litres per minute to meet current UK regulations). The pump may include a mains bypass such that the pump does not need to be engaged if the mains pressure is sufficient to meet system demand.

The accumulator is a pressure vessel that can store liquid at an elevated pressure.

Any form of accumulator may be used, but for example the accumulator may have an expandable liquid compartment and a compressible gas compartment with an elastic membrane separating the two. Alternatively, a floating piston type accumulator may be used. The accumulator is typically mounted on a spur from a main supply pipe that feeds the rest of the downstream outlets. The accumulator may then be both charged and discharged via the spur.

The flow detector is downstream of both the pump and the accumulator, i.e. it is downstream of all potential water sources. The flow detector may be mounted in the main supply pipe downstream of the spur that connects the accumulator. The flow detector is upstream of all the appliances served by the system and therefore will detect system demand from any of them.

Any form of flow detector may be used, such as ultrasonic flow detectors or laser flow detectors. However, in preferred embodiments the flow detector comprises a magnetic float inside a pipe and a magnetic detector located outside the pipe. The magnetic float is weighted so as to sit in a first position when the system is at rest (no flow), but it is sufficiently finely balanced in that position that any flow will move the magnet from a first position to a second position (restricted from further movement by a stop or shoulder within the pipe) which can be detected by the external detector. Any magnetic detector may be used. As examples, the magnetic detector may be another magnet which can be attracted, thus generating movement, or it may be a coil in which a current is generated or it may be a reed switch. It will be appreciated that the float may have a buoyancy greater than its weight such that it sits in an upper position at rest, but by a sufficiently low margin that any flow will cause downward movement. Alternatively, the float's buoyancy may be just less that its weight so that it sinks to a lower position at rest, but any flow will move it to an upper position.

A second flow detector may be located downstream of the pump and upstream of the accumulator, and the system may be arranged to deactivate the pump when the second flow detector indicates no flow. This second flow detector may be used to keep the pump running until the accumulator has fully recharged after demand has ceased. During a period of demand, some water may be discharged from the accumulator such that it is below its maximum storage capacity. In such cases, the pressure in the accumulator will have dropped to below the pressure that can be supplied by the pump. Once all downstream outlets are shut, there will be no further flow out of the accumulator. The first flow sensor (downstream of the accumulator) will indicate no flow, but it will still be desirable to operate the pump so as to recharge the accumulator to maximum pressure. While the pressure output by the pump is greater than the pressure in the accumulator, water will flow into the accumulator and the second flow detector will indicate a flow. Thus the pump will continue to operate until a pressure equilibrium is reached between the pump output and the accumulator. Once equilibrium is reached, there will be no further flow, the detector will indicate this and the pump can be deactivated until it is required again.

The use of a flow detector rather than a pressure sensor for controlling recharge has the same advantages as described above in relation to the first flow detector.

Controlling the pump based on flow rather than pressure also means that the pump will always recharge the accumulator to the maximum currently available pressure rather than being limited to a preset pressure value. A pressure detector has to be set to a predetermined trigger value and that value has to be set sufficiently low that it can always be reached by the system, otherwise the pump may never switch off.

This limits the pressure that can be applied to the accumulator and thus limits the storage of the accumulator and its potential to assist the system at a later time. The flow detector avoids this by triggering at the equilibrium between the supply and the store.

As with the first flow detector, the second flow detector may comprises a magnetic float inside a pipe and a magnetic detector located outside the pipe.

The system may further comprise a flow limiter that limits the amount of water that can flow out of the accumulator. By limiting the flow out of the accumulator, the length of time that the accumulator supplements the pump (and/or the mains pressure) can be extended. Accumulators have traditionally been fitted with the goal of fully meeting the demand on the system. Thus, the user may open as many outlets as desired and the accumulator will endeavor to meet those demands.

However, this can lead to the accumulator draining down very rapidly, losing pressure and being unable to supplement the system at adequate pressure for more than a few minutes. To provide adequate storage for such circumstances, large accumulators are required typically with at least a 200 litre capacity. Such tanks take up a lot of space and are not suitable for smaller dwellings such as small flats. Unfortunately it is often the small flats that suffer badly from water pressure deficiency due to their elevation above ground level. The use of a flow limiter restricts the supply that is available within the dwelling compared with an unrestricted accumulator, but it can adequately supplement the input pressure for a longer period of time.

One of the most common scenarios where pressure loss is unacceptable is in the middle of a shower. A pumped mains system can provide 12 litres per minute which is about the required flow for an average shower. However, as soon as any other outlet in the system is opened (e.g. a toilet is flushed, or a tap is opened or a kitchen appliance is switched on), the supply to the shower drops significantly, reducing the shower flow to an unacceptable level. The flow restricted accumulator can provide a small, but long lasting supplement that mitigates this effect without requiring a large accumulator. For example, an accumulator with a 4 litre per minute flow limiter can provide a total of 16 litres per minute in combination with a 12 litre per minute pump. The shower alone will not require any supplement from the accumulator, being supplied by the pump alone. However when another outlet is opened, up to 16 litres per minute are available. This may be enough for both outlets to operate fully or it may result in a slightly restricted flow at each outlet, but the pressure drop is not too detrimental and an adequate shower experience can be had. Moreover, as the draw from the accumulator is restricted, a small accumulator can be used that is of an acceptable size for a small property while still providing its pressure and flow supplement for several minutes. The average shower length is about 8 minutes, so this is an important consideration.

The use of a flow limiter that maintains flow rate independent of pressure is advantageous because the accumulator pressure drops as water is drawn from it, however the supplementary flow rate can be maintained.

The system is advantageous in properties of any size. However, it provides particular benefits in smaller properties where the space in which an accumulator can be located is limited. Larger accumulators for larger properties may be fitted with larger flow limiters (i.e. that allow greater flow), whereas smaller accumulators for smaller properties may be fitted with smaller (more restricted) flow limiters. In some preferred embodiments the flow limiter limits the flow to not more than 15 litres per minute, preferably not more than 10 litres per minute. In some preferred embodiments the flow limiter limits flow to not more than 6 litres per minute, preferably 5 litres per minute, while in other preferred embodiments the flow limiter limits flow to not more than 4 litres per minute. More restrictive flow limiters limit the maximum available flow, but can maintain the flow from a given size tank for a longer period.

In some particularly preferred embodiments a flow limiter of about 4 litres per minute in combination with a 60 litre accumulator can provide a 4 litre per minute supplement for about 8 minutes (the typical shower time) before it is exhausted.

Such an accumulator can be fitted into a typical kitchen cupboard space and is therefore of particular value to small fiats or apartments.

Preferably the water supply system further comprises a one way valve in parallel with the flow limiter that allows flow into the accumulator. More preferably the one way valve permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator. While it is desirable to limit the flow out of the accumulator as described above, it is desirable that the accumulator can be recharged as quickly as possible once there is an available supply (i.e. once system demand is lower than the available supply). In the examples described above, when all outlets are closed, the pump can supply 12 litres per minute and it is desirable that all of that flow can be used to recharge the accumulator swiftly. The one way valve in parallel with the flow restrictor allows unlimited flow into the accumulator while leaving the only exit flow path from the accumulator through the flow restrictor.

Preferably the flow limiter and the one way valve are provided in a connecting component that connects the accumulator to a supply pipe downstream of the pump. The component then provides an interface between the accumulator and the supply pipe such that existing accumulators and existing supply pipes can be used simply by providing the connecting component in between. This reduces the cost of the system makes manufacture simpler.

For ease of installation, the accumulator, pump and detector(s) may all be mounted on a common frame (referred to as a skid). The system is then very easy for an installer to fit to an existing system as it merely requires connection to the mains inlet and the existing downstream architecture. All other connections can be made in the factory before the system is supplied. This is particularly useful in smaller properties, e.g. when mounting the system into a cramped space such as a kitchen cupboard as the number of awkward connections is minimized. The input and output connections can be made via flexible hoses and the skid then slid into position and fixed in place by simple fixing devices. Installation is therefore quick and easy.

In some preferred embodiments the frame, accumulator, pump and detectors together all fit within a cuboid box with one dimension of 80 cm and the other two dimensions of 60 cm. In other preferied embodiments, the frame, accumulator, pump and detectors together all fit within a cuboid box with one dimension of 80cm and the other two dimensions of 50 cm. These are the dimensions of a typical small kitchen floor unit and they are sufficient to house a 60 litre accumulator as discussed above.

Although larger accumulators may be used for larger properties, in some preferred embodiments the accumulator has a tank volume of no more than 120 litres, more preferably no more than about 100 litres. In other preferred embodiments the accumulator has a tank volume of no more than about 80 litres, more preferably no more than about 60 litres. It will be appreciated that these volumes refer to typical tank sizes as marketed. Actual tank sizes may be slightly larger due to manufacturing tolerances.

While the above system has been described in relation to a cold water supply, there is no reason why it could not also be applied to a hot water supply.

The use of a flow limiter is considered to be independently inventive and therefore according to another aspect, the invention provides a water supply system comprising: an inlet for connection to a mains water supply; an accumulator connected downstream from said inlet; and a flow limiter that limits the amount of water that can flow out of the accumulator. -10-

The use of the flow limiter in this system provides the same benefits as are described above in relation to the pumped system. Even where no pump is present in the system, the mains pressure can be supplemented for a longer period of time.

This may be of particular benefit in properties where the mains pressure fluctuates greatly over the course of a day, e.g. where the accumulator can be charged up to a good pressure over night and can then be used to supplement a weaker mains pressure during peak usage times such as the morning or evening.

The preferred features described above in relation to the first aspect also apply to this aspect. Thus the system may further comprise a pump connected to said inlet upstream from said accumulator. The flow detectors described above may also be used here.

The flow limiter may limit the flow to not more than 10 litres per minute, not more than 5 litres per minute or not more than 4 litres per minute as desired. A one way valve may be provided in parallel with the flow limiter that allows flow into the accumulator, preferably at a flow rate greater than the limited flow rate out of the accumulator. The flow limiter and the one way valve may be provided in a connecting component that connects the accumulator to a supply pipe downstream of the pump.

The accumulator may be mounted on a frame. The frame and accumulator (and any other components such as a pump, if used) together preferably fit within a cuboid box with one dimension of 80 cm and the other two dimensions of 60 cm.

The accumulator may have a liquid volume of no more than 100 litres or no more than 60 litres.

According to a further aspect, the invention provides a method of supplying water to a property comprising: detecting a change of flow caused by water demand within the property; upon detecting said change of flow, activating a pump to pump water from a mains water supply; and simultaneously supplying water from an accumulator connected downstream from said pump. -11 -

The preferred features described above in relation to the system also apply to the method. Thus the method may further comprise: detecting a reduction in flow downstream of the pump and upstream of the accumulator; and upon detecting said reduction in flow, deactivating the pump. The method may further comprise: limiting the rate at which water can flow out of the accumulator. The flow may be limited to not more than 10 litres per minute, not more than 5 litres per minute or not more than 4 litres per minute as desired. The method may further comprise a step of: recharging the accumulator by passing water through a one way valve that permits flow into the accumulator at a flow rate greater than the limited flow late out of the accumulator.

According to yet another aspect the invention provides a method of supplying water to a property comprising: drawing water from a mains water supply; simultaneously supplying water from an accumulator; wherein a flow limiter limits the rate at which water can flow out of the accumulator.

The step of drawing water may comprise pumping water from said mains supply.

The flow limiter may limit the rate to not more than 10 litres per minute, not more than 5 litres per minute or not more than 4 litres per minute as desired. The method may fuither comprise a step of: recharging the accumulator by passing water through a one way valve that permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator.

According to another aspect, the invention provides a connector part for connecting an accumulator to a water supply system, said connector part comprising: a one way valve; and a flow limiter; wherein said one way valve and said flow limiter are provided in parallel so as to provide parallel, but opposite flow paths through the connector. Preferably the one way valve permits a higher flow rate through the connector part than the flow limiter.

Certain preferred embodiments of the invention will now be described, by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of an embodiment of the system; -12-Fig. 2 shows a cross-section through the pump and sensors of an embodiment of the system; Fig. 3 shows a side view of an embodiment of the system with the accumulator partially cut away; Fig. 4 is an enlarged view of the connection to the accumulator; and Figs. 5A-5D illustrate operation of the system.

Figure 1 shows an embodiment of the water supply system 100. An incoming main 1 passes a stop cock 2 and a double check valve 3. These components are part of the standard water supply arrangement of the property. The system 100 includes a mains inlet connection 5 which connects to the property's mains supply 4.

Pump unit 10 includes a pump 11, a flow regulator 12 and a pump bypass 13 that includes a non-return valve 14. The flow regulator 12 limits the flow rate supplied by the pump 11 so as to prevent contravention of regulations. For example under current regulations in the United Kingdom, water cannot be pumped directly from the mains at greater than 12 litres per minute. Therefore for a UK system, flow regulator 12 is set to limit flow to 12 litres per minute.

Downstream from pump unit 10, water flows through a first flow switch 15, a non-return valve 16 and a second flow switch 17. Accumulator (pressure vessel) 18 is attached via spur 19 downstream of non-return valve 16 and upstream of second flow switch 17. System outlet 20 is a connection to all downstream outlets that are to benefit from the system 100, including all taps, showers, baths, kitchen appliances, etc. Figure 2 shows a cross-section through the pump unit 10 and associated pipes and connections of the system 100. As can be seen, in this embodiment the flow sensors 15, 17 are magnetic sensors. First sensor 15 comprises a magnetic float 30 that sits inside the supply pipe 40. Float 30 allows water to flow through a central channel in the middle of the float 30 and it has a buoyancy slightly less than its weight so that when there is no flow, the float 30 rests (under gravity) on shoulder 31 in supply pipe 40. When water starts to flow past float 30, the additional drag on float 30 causes it to rise upwards in supply pipe 40 where it will abut against stop 32. In this position the magnet causes reed switch 33 to make an -13-electrical connection which is detected by a controller (not shown) that control pump operation. Second flow sensor 17 comprises a similar arrangement with magnetic float 35, shoulder 36, stop 37 and reed switch 38.

Fig. 3 shows the pump unit 10 connected to pressure vessel (accumulator) 18. The pressure vessel 18 is shown partially cut away so as to show the elastic membrane that separates liquid compartment 51 from gas compartment 52. Fig. 3 also shows the connector part 55 which connects via flexible hose 54 to spur connection 19 on the main supply pipe 40.

Accumulator 18 is shown mounted to metal skid 53 for ease of installation. Pump unit 10 and associated components are shown separate from skid 53 in Fig. 3 for illustration purposes, but in actual implementations these components are also mounted on skid 53 so that the whole system can be slid into its target location as a single unit either before or after plumbing connections have been made.

Fig. 4 shows connector part 55 in more detail. Connector part 55 has a first interface 56 that fluidly connects to the inlet/outlet 60 of accumulator 18. Connector part 55 also has a second interface 57 that fluidly connects to main supply pipe 40 via spur connection 19. It should be noted that the embodiment of Fig. 4 shows the connector part 55 connected directly to the accumulator inletloutlet 60 and indirectly to supply pipe 40 via flexible hose 70. However both of interfaces 56, 57 can be made directly or indirectly according to circumstances.

Connector part 55 includes a flow limiter 58 and a one way valve 59 provided in parallel and both providing fluid connections between the accumulator 18 and the supply pipe 40. Flow limiter 58 permits fluid flow out of accumulator 18 at no more than a predetermined flow rate (for example no more than 4 litres per minute).

Depending on construction, flow limiter 58 may or may not allow fluid flow into the accumulator 18. One way valve 59 allows fluid flow into accumulator 18 at a higher flow rate than is permitted to flow out of accumulator 18 via flow limiter 58. Thus accumulator 18 may be filled (or recharged) faster via one way valve 59 than it can be drained via flow limiter 58. One way valve 59 does not permit fluid flow out of accumulator 18. Thus all flow out of accumulator 18 must be through flow limiter 58. -14-

Operation of the system will now be described with reference to Figures 5A to 50.

Firstly, as shown in Fig. 5A, when the system is first installed, the pump 11 automatically starts and supplies the pressure vessel 18 with water until it is fully charged. The pressure vessel 18 will be charged to the maximum available pressure (including both the available mains pressure and the pressure boost provided by pump 11). During this phase, there is no demand from the system, so there is no flow downstream of the spur connection 19. Therefore second flow switch 17 registers no flow. Arrow 80 indicates the flow from the mains / pump 11 through spur connection 19 into pressure vessel 18. This flow causes first flow switch 15 to register a flow. All water entering pressure vessel 18 passes through one way valve 59. Flow is unrestricted and will be at the maximum flow rate provided by the mains / pump 11. This may be the maximum flow defined by flow regulator 12, e.g. 12 litres per minute.

Fig. 5B shows operation of the system when there is a demand of up to the limit of the pump unit 10 (e.g. 12 litres per minute for a UK installation). As shown by arrow 81, all water is supplied from the mains and/or pump unit 10. No flow is drawn from accumulator 18. As soon as one or more outlets are opened downstream of the system 100, flow will be drawn from system outlet 20 and this will be detected by second flow detector 17 (subject to a minimum detectable flow which can be set very low, e.g. greater 0.6 litres per minute). As soon as second flow detector 17 detects a flow, pump 11 is activated so as to draw water from the mains 1, providing increased pressure. When the outlet(s) draw less than the output capacity of the pump unit 10, all demand is met by the pump 11 and no water is drawn from the accumulator 18 which thus remains fully charged and pressurized.

Fig. 50 shows operation of the system when there is a demand greater than the limit of the pump unit 10 (e.g. greater than 12 litres per minute for a UK installation).

As shown by arrows 82 and 83, watel is now supplied via both the pump unit 10 (arrow 82) and via accumulator 18 (alrow 83). The total supply out of system outlet is now greater than either of the individual supplies from pump unit 10 and accumulator 18. In one embodiment, the pump unit 10 can supply up to 12 litres per minute and the accumulator 18 is flow limited (via flow limiter 59) to 4 litres per -15-minute. For this set up, Fig. 50 illustrates the scenario for between 12 and 16 litres per minute. Above 16 litres per minute, demand cannot be met and the pressure at an open outlets will be limited.

Fig. 50 shows the situation where system demand has dropped below the maximum capacity of the pump unit 10. The pump unit 10 will continue to supply its maximum flow rate (as determined by flow regulator 12). Some of that flow will be passed directly to the outlets (as indicated by arrow 84), while the rest will be fed into the accumulator 18 (as indicated by arrow 85) to recharge accumulator 18 back to its maximum pressure and storage capacity.

In all of the situations illustrated in Figs. 5B, 50 and 50, both the first flow detector and second flow detector 17 will register a flow. In Fig. 50, if demand then drops to zero, second flow detector 17 will register no flow, but the pump 11 will continue to operate while accumulator 18 is at less than maximum capacity. Once an equilibrium has been reached and no more water can be squeezed into accumulator 18, the flow shown by arrow 85 will cease and first flow detector 15 will sense a cessation of flow. Upon sensing this lack of flow, pump 11 will be deactivated and the system will remain in this state until there is further demand downstream.

To illustrate the benefits of this system, consider a 60 litre pressure vessel with a 30 litre working capacity (i.e. it can store up to 30 litres of water, with the remainder of the tank being occupied by compressed gas). This is a very small pressure vessel compared with conventional systems which typically use accumulators of 150 litres or more. We will also assume a typical United Kingdom installation with a 12 litre per minute flow regulator limiting the flow that can be pumped directly off the mains and a flow limiter limiting the accumulator output to no more than 4 litres per minute. This system provides particular benefits to small properties such as a 1 bedroom house or flat with low mains water pressure. The pump can supply up to 12 litres per minute which is adequate for a typical shower providing that no other demands are placed on the system. The additional pressure provided by the pump (typically adding 1.5 bar to the mains pressure) also ensures sufficient pressure for a satisfactory shower. If another outlet is now opened (e.g. a tap is turned on elsewhere in the property or a toilet is flushed), there will be an additional demand -16-on the system. This additional demand will typically be in the range of 4 to 8 litres per minute. The accumulator now comes into play and supplies an additional 4 litres per minute resulting in a total supply of 16 litres per minute. If the additional demand placed on the system is up to 4 litres per minute, there will be no reduction in flow of the shower. If the additional demand is greater than 4 litres per minute then there will be some loss of flow in the shower, although this should be minimal and should thus be acceptable. If an eco-shower is fitted, the shower may only draw 8 litres per minute and thus the system could fully meet the demands of the showel and an 8 litre per minute additional draw. The additional pressure supplied by the pump means that the system is capable of supporting an eco-shower (as these typically require a higher operating pressure).

The accumulator 18 is a 60 litre tank which starts out with about 30 litres of water stored at high pressure. When the system is supplying at full capacity of 16 litres per minute, the flow limiter 58 means that the accumulator can operate for about 7.5 minutes before it is exhausted. This is about the length of the average shower and thus even a small 60 litre accumulator can provide a significant improvement to system performance. At 14 litres demand, the accumulator can operate for about minutes before the supply drops and at 12 litres per minute, the accumulator is not required and the supply is continuous. Once completely drained, the accumulator can recharge within about 3 minutes provided there is no other demand on the system. The 16 litre per minute combination of accumulator 18 and pump 11 and the 30 litre capacity of accumulator 18 are also well suited to filling a bath via two 9 litre per minute taps. At 16 litres per minute for 7.5 minutes, 120 litres of water can be supplied before the accumulator is exhausted. This is adequate for an average bath. It will be appreciated that a 60 litre tank will typically contain about 30 litres of water when fully charged. However, this value may vary slightly in different systems as it depends on the mains water pressure, the pump and the pressure vessel's precharge.

With the accumulator 18 limited to an output of no more than 4 litres per minute, it is necessary for the pump 11 to respond swiftly to demand, otherwise the system will be limited to the combination of the accumulator's 4 litres per minute with whatever is available via the non-pumped mains supply (which may be very low). The use of flow detectors rather than pressure detectors in the system makes the system very -17-responsive to demand. Pressure detectors have typically been used in conventional accumulator systems with much larger accumulators so as to detect when the accumulator is losing pressure. However, the combination of the fact that the accumulator itself maintains the pressure for a significant period and the fact that pressure sensors are not particularly accurate means that a significant proportion of the accumulator's stored water will have been emptied before the system engages a pump for additional supply. This is acceptable with larger accumulators, but with a small accumulator, this would result in the tank being practically empty before the pump was engaged, so the system would not achieve the goal of maintaining supply for a significant period. Essentially, the combination of rapid pump response and limited accumulator supply give the user the impression of having a much larger accumulator as compared with conventional systems.

It should be noted that the flow limited accumulator 18 can be used without the pump unit 10 in situations where the mains pressure can reliably provide a flow roughly equivalent to the pump unit 10 (e.g. 12 litres per minute). The accumulator 18 is still advantageous for supplementing this supply to meet an increased demand within the property and the flow limiter 58 ensures that the accumulator does not get discharged quickly, thus maintaining improved supply for longer.

Once demand has ceased, the mains pressure will recharge the accumulator via the one way valve 59. -18-

Claims

Claims 1. A water supply system comprising: an inlet for connection to a mains water supply; a pump connected to the inlet; an accumulator connected downstream from the pump; and a flow detector downstream of both the pump and the accumulator; wherein the system is arranged to operate the pump when flow is detected by said flow detector.
2. A water supply system as claimed in claim 1, wherein said flow detector comprises a magnetic float inside a pipe and a detector coil located outside the pipe.
3. A water supply system as claimed in claim 1 or 2, further comprising a second flow detector downstream of the pump and upstream of the accumulator, and wherein the system is arranged to deactivate the pump when the second flow detector indicates no flow.
4. A water supply system as claimed in claim 3, wherein said second flow detector comprises a magnetic float inside a pipe and a detector coil located outside the pipe.
5. A water supply system as claimed in any preceding claim, further comprising a flow limiter that limits the amount of water that can flow out of the accumulator.
6. A water supply system as claimed in claim 5, wherein the flow limiter limits the flow to not more than 10 litres per minute.
7. A water supply system as claimed in claim 6, wherein the flow limiter limits the flow to not more than 5 litres per minute.
8. A water supply system as claimed in claim 7, wherein the flow limiter limits the flow to not more than 4 litres per minute. -19-
9. A water supply system as claimed in any of claims 6, 7 or 8, further comprising a one way valve in parallel with the flow limiter that allows flow into the accumulator.
10. A water supply system as claimed in claim 9, wherein the one way valve permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator.
11. A water supply system as claimed in claim 9 or 10, wherein the flow limiter and the one way valve are provided in a connecting component that connects the accumulator to a supply pipe downstream of the pump.
12. A water supply system as claimed in any preceding claim, wherein the accumulator, pump and detector(s) aie all mounted on a common frame.
13. A water supply system as claimed in claim 12, wherein the frame, accumulator, pump and detectors together all fit within a cuboid box with one dimension of 80 cm and the other two dimensions of 60 cm.
14. A water supply system as claimed in claim 13, wherein the accumulator has a tank volume of no more than aboutl2o litres, preferably no more than about 100 litres.
15. A water supply system as claimed in claim 14, wherein the accumulator has a tank volume of no more than about 80 litres, preferably no more than about 60 litres.
16. A water supply system comprising: an inlet for connection to a mains water supply; an accumulator connected downstream from said inlet; and a flow limiter that limits the amount of water that can flow out of the accumulator.

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17. A water supply system as claimed in claim 16, further comprising a pump connected to said inlet upstream from said accumulator.
18. A water supply system as claimed in claim 16 or 17, wherein the flow limiter limits the flow to not more than 10 litres per minute.
19. A water supply system as claimed in claim 18, wherein the flow limiter limits the flow to not more than 6 litres per minute
20. A water supply system as claimed in claim 19, wherein the flow limiter limits the flow to not more than 4 litres per minute.
21. A water supply system as claimed in any of claims 18, 19 or 20, further comprising a one way valve in parallel with the flow limiter that allows flow into the accumulator.
22. A water supply system as claimed in claim 21, wherein the one way valve permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator.
23. A water supply system as claimed in claim 21 or 22, wherein the flow limiter and the one way valve are provided in a connecting component that connects the accumulator to a supply pipe downstream of the pump.
24. A water supply system as claimed in any of claims 16 to 23, wherein the accumulator is mounted on a frame.
25. A water supply system as claimed in claim 24, wherein the frame and accumulator together fit within a cuboid box with one dimension of 80 cm and the other two dimensions of 60 cm.
26. A water supply system as claimed in claim 25, wherein the accumulator has a tank volume of no more than about 120 litres, preferably no more than about 100 litres. -21 -27. A water supply system as claimed in claim 26, wherein the accumulator has a tank volume of no more than about 80 litres, preferably no more than about 60 litres.28. A method of supplying water to a property comprising: detecting a change of flow caused by water demand within the property; upon detecting said change of flow, activating a pump to pump water from a mains water supply; and simultaneously supplying water from an accumulator connected downstream from said pump.29. A method as claimed in claim 28, further comprising: detecting a reduction in flow downstream of the pump and upstream of the accumulator; and upon detecting said reduction in flow, deactivating the pump.30. A method as claimed in claim 28 or 29, further comprising: limiting the rate at which water can flow out of the accumulator.31. A method as claimed in claim 30, comprising limiting the flow to not more than 10 litres per minute.32. A method as claimed in claim 31, comprising limiting the flow to not more than 6 litres per minute.33. A method as claimed in claim 32, comprising limiting the flow to not more than 4 litres per minute.34. A method as claimed in claim 31, 32 or 33, further comprising a step of: recharging the accumulator by passing water through a one way valve that permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator.35. A method of supplying water to a property comprising: drawing water from a mains water supply -22 -simultaneously supplying water from an accumulator; wherein a flow limiter limits the rate at which water can flow out of the accumulator.36. A method as claimed in claim 35, wherein the step of drawing water comprises pumping water from said mains supply.37. A method as claimed in claim 35 or 36, wherein the flow limiter limits the rate to not more than 10 litres per minute.38. A method as claimed in claim 37, wherein the flow limiter limits the rate to not more than 6 litres per minute.39. A method as claimed in claim 38, wherein the flow limiter limits the rate to not more than 4 litres per minute.40. A method as claimed in claim 37, 38 or 39, further comprising a step of: recharging the accumulator by passing water through a one way valve that permits flow into the accumulator at a flow rate greater than the limited flow rate out of the accumulator.41. A connector part for connecting an accumulator to a water supply system, said connector part comprising: a one way valve; and a flow limiter; wherein said one way valve and said flow limiter are provided in parallel so as to provide parallel, but opposite flow paths through the connector.42. A connector part as claimed in claim 41, wherein the one way valve permits a higher flow rate through the connector part than the flow limiter.