GB2429416A

GB2429416A - A water filtering system for a washing machine

Info

Publication number: GB2429416A
Application number: GB0616741A
Authority: GB
Inventors: David James Dore
Original assignee: Quill International Industries PLC
Current assignee: Quill International Industries PLC
Priority date: 2005-08-26
Filing date: 2006-08-24
Publication date: 2007-02-28
Also published as: GB0517515D0; GB0616741D0

Abstract

A water filtering system for a washing machine 1 is provided for the filtration of effluent therefrom, comprises at least one gravel filter 7a, 7b, 8a, 8b and a pump 6 for pumping effluent through the gravel filter 7a, 7b, 8a, 8b, a holding tank 9 for storage of the filtered water from the effluent, valve means 15, 16, 21, 22 for controlling the flow of effluent through the gravel filter 7a, 7b, 8a, 8b and a control means 5 that controls operation of the pump 6 and the valve means 15, 16, 21, 22 such that during a washing process in the washing machine 1 a least a proportion of water from the effluent is pumped through the gravel filter 7a, 7b, 8a, 8b and thence to the storage tank 9 for subsequent re-use in the washing process. At predetermined intervals filtration of the effluent water by each the gravel filter 7a, 7b, 8a, 8b is suspended and the flow of water therethrough is reversed to backflush the gravel of the gravel filter 7a, 7b, 8a, 8b, the backflushed water being discharged to drain.

Description

IMPROVEMENTS TO WASHING MACHINES

The present invention relates to a water filtering system for a washing machine, in particular a continuous batch or tunnel washing machine such as is used in commercial laundries, to enable its effluent to be filtered for re- use by the washing machine.

In commercial laundries, industrial-size washing machines containing up to 100 kg of articles for washing are used which depend on a constant flow of pre-heated water and into which metered quantities of washing powder and adjuncts are pumped by dosing apparatus. Conventionally, in order to wash heavily soiled or biologically contaminated articles such as hospital linen, hospital workwear and the like, it is necessary to use hightemperature water, mechanical action within the washing machine, and high alkalinity and enzyme detergents. In addition, in order to disinfect the wash articles to predetermined standards, National Health Service protocols require that during the washing process the articles are subjected to a temperature of at least 65 C for at least ten minutes or a temperatures of at least 71 C for at least three minutes. As the washing cycle of such articles usually takes place at around 8o C, the washing process involves the use of a considerable quantity of water that requires heating to the appropriate temperature. The cost of pre-heating the water to temperatures of 6o C and greater for use in the washing process makes up a significant proportion of the total cost of the process. Typically, the water is heated by injecting steam into it and significant time and energy is taken up producing the steam for this purpose. Also, as the washing cycle itself is likely to be for times in excess of 20 minutes, steam continues to have to be generated throughout the washing cycle to ensure that the washing liquor is maintained at the correct temperature. Such heavy washing also typically requires at least two and sometimes more rinse cycles.

In order to reduce the cost of pre-heating the water for the washing process, it is common in such industrial processes for the waste rinse water to be re-used for the washing process. Typically such re-used water is first filtered to remove lint and other contaminants, which in a laundry washing heavily soiled or biologically contaminated articles such as hospital linen, hospital workwear and the like, consist primarily of hair, skin, proteins, body s fats and bacteria. The filtered water is then stored in a holding tank for addition to fresh, heated water for use in the main washing process. The filters used in such washing machines conventionally comprise cross-flow filters. The build-up of lint and the stickiness of the other constituents of the filtered residue eventually clogs such filters, which must, therefore, be cleaned on a regular basis. This means that the washing machine cannot be used during the cleaning time and the washing process must be suspended, adding to the cost of the washing process.

It is an object of the present invention to provide a washing machine in which the aforesaid problem is overcome or substantially mitigated.

According to a first aspect of the present invention there is provided a water filtering system for a washing machine for the filtration of effluent therefrom, the filtering system comprising at least one gravel filter, a pump for pumping effluent through the gravel filter, a holding tank for the storage of filtered water from the effluent, valve means for controlling the flow of effluent through the gravel filter, and a control means which controls operation of the pump and the valve means such that during a washing process in the washing machine at least a proportion of water from the effluent is pumped through the gravel filter and thence to the storage tank for subsequent re-use in the washing process, and at predetermined intervals filtration of the effluent water by each gravel filter is suspended and the flow of water therethrough is reversed to backflush the gravel of the gravel filter, the backflushed water being discharged to drain.

The advantage of such a backflushing arrangement is that the force of the backflushing water disturbs the gravel in the filter and thereby loosens the lint and other filtered residues from the gravel. These loosened particles are then caught up in the backflushing water and carried away to drain, leaving the gravel to re-settle within the filter ready for further use. Also, cleaning of the filters takes place during the washing process itself, which means that there is no downtime of the washing machine required to clean the filters.

Preferably, each gravel filter is backflushed using filtered water from the storage tank.

Preferably, at least one gravel filter is provided containing coarse gravel of the order of 8 mm in diameter and at least one other gravel filter is provided containing fine gravel or sand capable of filtering particles of the order of 75 microns in diameter, the two types of filter being arranged in series with one another.

Advantageously, two coarse-gravel filters containing gravel of the order of 8 mm in diameter are provided and arranged in parallel. Preferably also, two fine-gravel filters each capable of filtering particles of the order of microns in diameter are provided arranged in series with the two coarse- gravel filters and in parallel with one another.

Preferably also, the gravel of each gravel filter is angular in structure.

Preferably also, a storage tank is provided to store effluent discharged by the washing machine prior to its filtration by the filter system.

Preferably also, each gravel filter comprises a substantially upright tube containing the gravel, foraminous gravel retainers being located at the inlet and the outlet of the tube to retain the gravel in the tube.

Preferably also, each tube is filled with gravel to less than 8o% of its capacity to permit the gravel to be swirled around within the tube during the backflush to dislodge the filtered residue therefrom.

Preferably also, the tube of at least one of the gravel filters is transparent to permit the gravel and any filtered residue present therein to be seen.

Preferably also, the valve means controlling the flow of water through each of the gravel filters comprises two three-way valves that are respectively located at the inlet and the outlet of each said gravel filter.

Preferably also, the pump means comprises a first feed pump that pumps effluent from the washing machine through each gravel filter and a second pump that pumps filtered water from the storage tank to backflush each gravel filter.

Preferably also, the pump means comprises a third pump that can pump filtered water from the storage tank to the washing machine for re-use in a washing process.

Advantageously, during a washing process the control means is programmed to backflush of each of the gravel filters at least four times per hour.

According to a second aspect of the present invention there is provided a washing machine comprising a water filtering system in accordance with the first aspect of the present invention.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a diagram showing the water flow and general arrangement of a water filtering system for a washing machine in accordance with the present invention; and Fig. 2 is a vertical cross-section of a gravel filter containing coarse gravel for use in the filtering system shown in Fig. 1.

As shown in Fig. 1 a water filtering system is provided for a washing machine 1 such as a continuous batch or tunnel washing machine to enable effluent discharged by the machine i to be filtered for re-use therein. Effluent from the machine i is collected from the drain 2 of the machine 1 and retained within a storage tank 3. As shown in Fig. i, the storage tank 3 may comprise linked vessels a, 3b with an overflow 4 to drain. Under the control of a programmable control system 5, water from the tank 3 is pumped by a feed pump 6 to one or other of two coarse-gravel filters a and 7b and thence to one of two fine-gravel or sand filters 8a, 8b before being retained within a holding tank 9 ready for re-use. This system will now be described in further detail.

The feed pump 6 has an isolation valve 10 fitted on its inlet pipe 11 so that it can isolated from the washing machine for servicing. An outlet pipe 12 leads from the valve 10 and is divided to form two inlet pipes ia, 12b that lead to the two coarse gravel filters a and 7b. The flow of water into and out of each of the gravel filters a and 7b via inlet and outlet orifices 13 and 14 respectively is controlled by an upstream three- way valve 15 and a downstream three-way valve 16. Associated with each of the valves 15 and 16 is an isolation valves 17 so that each gravel filter a, 7b and three-way valve 15, i6 can be isolated from the filtering system for servicing or replacement.

The passage of water through the three-way valves 15 and i6 is controlled by the control means 5. When effluent is to be filtered and the pump 6 is operational, the three-way valves 15 are arranged such that the water flows from the inlet pipes i2a, 12b into pipes i8 leading to the filters a, 7b.

Thereafter, the water flows out of the filters a, 7b along pipes 19 to the three-way valves 16 and thence along outlet pipes 2oa, 20b. The outlet pipes 2oa, 20b leading to other inlet three-way valves 21 controlling the flow of water into the two sand filters 8a and 8b via their inlet pipes 18. Water that has been filtered through the filters 8a and 8b then passes via outlet pipes 19 to further outlet three-way valves 22 into a conduit 23 leading to the holding tank 9. A flow indicator 24 may be located in the conduit 23 to indicate the flow of water through the filters a, 7b, 8a, 8b.

The holding tank 9 retains the filtered waste water from the washing machine i for re-use. It will be appreciated that the water it holds will have been heated when it was first used within the washing machine and is therefore likely to have a temperature in the region of 40 C. The tank 9 is provided with a main outlet pipe 25 leading back to the inlet of the washing machine i. A pump 26, isolatable by isolation valves 27, is located in the pipe and is under the control of the washing machine's control system in order that filter water from the tank 9 can be pumped to the washing machine i when required.

In case of emergency, for example if for any reason the level of the water in the holding tank 9 becomes low, as determined by a series of floatoperated switches 28 located therein, the flow of water along the pipe 25 can be switched to come from a mains supply 29 rather than the tank 9 by means of a three-way valve 30. A flow indicator 31 may also be provided in the pipe 25 downstream of the valve 30 to indicate a flow of water along the pipe 25.

The filtering system is also designed to enable the filters a, 7b, 8a, 8b to be cleaned by backflushing.

The holding tank 9 for the filtered water is also provided with a second outlet pipe 32. A pump 33, isolatable by an isolation valve 34, is located in the pipe 32 and is under the control of the control system 5 such that at regular intervals during the washing process, the filters a, 7b, 8a, 8b can be cleaned by backflushing. The backflushing arrangement is such that the two coarse-gravel filters a and 7b can be backflushed sequentially along with one or other of the fine-gravel filters 8a and 8b so that at any one time one of the coarse-gravel filters and one of the fine-gravel filters can be in use filtering the effluent from the washing machine i whilst the other filters are being backflushed. The control means 5 is programmable such that it causes each of the filters a, 7b, 8a, 8b, to be backfiushed at predetermined intervals, which are preferably every ten to fifteen minutes during the washing process, for a predetermined length of time. This arrangement will also now be described.

During a backflushing operation, filtered water is pumped by the pump 33 along a pipe 35 that leading to each of the outlet three-way valves i6 and 22. These valves 16 and 22 have been switched by the control system 5 to close off flow along the pipes oa, 20b and 23 and to permit flow into the filters a, 7b, 8a, 8b along the pipes 19 in the opposite direction to that during water filtration. Water therefore leaves the filters a, 7b, 8a, 8b along with the filtered residue which the backflushing has dislodged along the pipes through pipes 18 in the direction of the three-way valves 15 and 21.

These valves 15 and 21 have also been switched such that the backflushing water egresses therefrom along pipes 36a, 36b, 36C, 36d that combine into a single outlet pipe 36 that leads to a drain.

In use in a typical commercial laundry, a tunnel washing machine i will produce approximately ooo litres of effluent per hour. The holding tank 3 is designed to hold approximately iooo litres at any given time because water is continually being drawn off for re-use within the washing machine.

Typically, the backflushing operation uses approximately 500 litres of water per hour leaving around 4500 litres per hour to be re-used within the washing process. As this water normally has a temperature of around 40 C it will be appreciated that considerable energy savings can be made by using the filtering system without any enforced downtime of the washing process having to take place to permit the filters to be cleaned because the backflushing operation takes places regularly during the washing process itself.

In order to ensure that the used water retained within the holding tank 3 and the surfaces of the tank 3 itself do not act as a breeding ground for bacteria, the water entering it can be treated by the addition of suitable additives from a dosing machine 37 linked to that of the main washing machine. Similarly, each of the gravel filters a, 7b, 8a, 8b can be individually flushed with appropriately treated liquid via inlet/outlet valves 38 located adjacent their respective inlet and outlet orifices 13, 14 once the gravel filter in question has been isolated from the rest of the system by appropriate control of the valves 15, 16, 21, 22.

The structure of the gravel filters a, 7b, 8a, 8b will now be described with particular reference to Fig. 2.

Each of the filters comprises a substantially upright tube 39 containing gravel 40 and defining the water inlet and outlet orifices 13 and 14 at the top and the bottom of the tube 39 respectively. The gravel 40 is retained within the tube 39 by foraminous gravel-retention members 41 that are located at the top and bottom of the tube 39. These members 41 are perforated such that they can retain the gravel, which is all of a similar grade as described below, but not particles that are much smaller than the gravel 40. Hence, the members 41 do not act as filters in their own right.

Preferably, the gravel 40 in the filters a and 7b that contain coarse gravel is of the order of 8 mm in diameter. Such gravel can filter from the effluent lint, hair and larger particles. Also, as the contaminants tend to be sticky, small particles tend to be trapped by any sticky residues that adhere to the gravel and filtered lint and hair. In contrast, the filters 8a and 8b contain fine gravel or sand capable of filtering particles of the order of 75 microns in diameter. These filters 8a, 8b can trap bacteria and small contaminants to prevent their build-up within the water being used within the washing machine 1. It will be appreciated that the two types of filter 7a, 7b and 8a, 8b are arranged in series with one another with the effluent being filtered first through one of the coarse-gravel filters a or 7b and then through one of the fine-gravel filters 8a or 8b.

The size of the gravel 40 selected for use within the tubes 37 can be as appropriate for any given washing situation. It will be appreciated, however, that in different systems it may be appropriate to have more or fewer coarse- gravel filters a and 7b and, likewise more or fewer fine-gravel filters 8a and 8b dependent on the type of laundry being washed and the size of the washing machine.

In order that the efficiency of the filtering operation to be monitored, preferably the tubes 39 of the filters a, 7b, 8a, 8b, particularly those containing coarse gravel, are made from a transparent plastics material to permit the gravel 40 and any filtered residue present therein to be seen. This enables an operator to judge visually the operation of the filter in order that he can program the control means 5 to carry out backflushing more or less frequently or to adjust the length of time the backflushing operation takes in order, for example, to deal adequately with the residues from any given type of soiled material being washed.

During filtration, water enters each tube 39 through the uppermost orifice 13 and passes downwards through the gravel 40 to egress via the lowermost orifice 14, leaving the filtered residue behind trapped in the gravel 40. However, during backflushing of the filter, water is forced into the tube 39 through the lowermost orifice 14 under the force of the pump 32. The water disturbs the gravel 40 and carries it up the tube 39 towards the uppermost orifice 13 where it is prevented from egressing therefrom by the uppermost retention member 41. The swirling of the gravel 40 in the tube during this operation dislodges the lint and other filtered residues from the gravel so that it can be carried out of the filter with the egressing water and flushed away to drain. The gravel 40 then re-settles within the tube 39 ready for filtration to be recommenced.

To enable the gravel 40 to be swirled around in each of the tubes 39 during backflushing, preferably each tube 39 is only filled with gravel 40 to no more than 8o% of its capacity and preferably to less than this. In - :iU - addition, the gravel 40 used is preferably angular or sharp so that as the pieces of gravel collide with one another during the backflushing operation, each piece tends to scrape off debris sticking to other pieces of gravel. The gravel 40 is, therefore, self-cleaning.

Claims

- 11 - CLAIMS

1. A water filtering system for a washing machine for the filtration of effluent therefrom, the filtering system comprising at least one gravel filter, a pump for pumping effluent through the gravel filter, a holding tank for the storage of filtered water from the effluent, valve means for controlling the flow of effluent through the gravel filter, and a control means which controls operation of the pump and the valve means such that during a washing process in the washing machine at least a proportion of water from the effluent is pumped through the gravel filter and thence to the storage tank for subsequent re-use in the washing process, and at predetermined intervals filtration of the effluent water by each gravel filter is suspended and the flow of water therethrough is reversed to backflush the gravel of the gravel filter, the backflushed water being discharged to drain.

2. A system as claimed in Claim 1, wherein each gravel filter is backflushed using filtered water from the storage tank.

3. A system as claimed in Claim 1 or Claim 2, wherein at least one gravel filter containing gravel of the order of 8 mm in diameter is provided.

4. A system as claimed in Claim 3, wherein two gravel filters containing gravel of the order of 8 mm in diameter are provided and are arranged in parallel with one another.

5. A system as claimed in any of Claims 1 to 3, wherein at least one gravel filter capable of filtering particles of the order of 75 microns in diameter is provided.

6. A system as claimed in Claim 5, wherein two gravel filters are provided that are capable of filtering particles of the order of 75 microns in diameter arranged in parallel with one another.

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7. A system as claimed in any of Claims 1 to 6, wherein at least one gravel filter is provided containing coarse gravel of the order of 8 mm in diameter and at least one other gravel filter is provided containing fine gravel or sand capable of filtering particles of the order of 75 microns in diameter, the two filter types being arranged in series with one another.

8. A system as claimed in any of Claims 1 to 7, wherein the gravel of each gravel filter is angular in structure.

9. A system as claimed in any of Claims 1 to 8, wherein a storage tank is provided to store effluent discharged by the washing machine prior to its filtration by the filter system.

10. A system as claimed in any of Claims 1 to 9, wherein each gravel filter comprises a substantially upright tube containing gravel, foraminous gravel retainers being located at the inlet and the outlet of the tube to retain the gravel within the tube.

ii. A system as claimed in Claim 10, wherein each tube is filled with gravel to no more than 80% of its capacity to permit the gravel to be swirled around within the tube during the backflush to dislodge the filtered residue therefrom.

12. A system as claimed in Claim 10 or Claim ii, wherein the tube of at least one of the gravel filters is transparent to permit the gravel and any filtered residue present therein to be seen.

13. A system as claimed in any of Claims 1 to 12, wherein the valve means controlling the flow of water through each of the gravel filters comprises two three-way valves that are respectively located at the inlet and the outlet of each said gravel filter.

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14. A system as claimed in any of Claims 1 to 13, wherein the pump means comprises a first feed pump that pumps effluent from the washing machine through each gravel filter and a second pump that pumps filtered water from the storage tank to backflush each gravel filter.

15. A system as claimed in any of Claims 1 to 14, wherein the pump means comprises a third pump that can pump filtered water from the storage tank to the washing machine for re-use in a washing process.

16. A system as claimed in any of Claims 1 to 15, wherein the control means is adapted to cause backflushing of each of the gravel filters at least four times per hour.

17. A washing machine comprising a water filtering system as claimed in any of Claims 1 to i6.