Filter drainage

Abstract

A filter system is for liquid effluent handling equipment including a drain pump 205 for emptying an effluent reservoir 207. The system includes a holding volume 201 for a quantity of effluent. The vo

Description

BACKGROUND Field of the Invention The invention relates to the field of the filtration of fluids, including effluent from laundering, cleaning and water treatment systems. In particular the invention relates to effectively draining liquids from the filter of such systems for improved usability. Description of Related Art Effluent produced during cleaning operations must be filtered to remove impurities before being released into the environment. For example, the handling of textiles in manufacturing and washing processes are performed using quantities of fluids to remove entrained debris and dirt. The resulting debris-laden fluid must itself be cleaned to prevent pollution of the environment. For example, the significant problem of the pollution of the world’s oceans by plastic is due substantially to the small fibres produced during the washing of clothes made of synthetic fibres in domestic and commercial washing machines. Advanced filters for domestic and commercial laundry devices are now being developed to deal with this problem, such as described in PCT / IB2022 / 061489. Existing filters in domestic washing machines are designed to trap large objects such as coins. The filters are called “penny trap” filters, and are intended to protect a drain pump from damage from these large objects. It is not common for a user to access the penny trap filter, so these filters are not designed to be easily accessible and other design considerations take priority; for example, it is preferable for the drain pump to remain full of waste-water between washes so that it is primed for its next use and therefore the penny trap filter would be full of waste water too between washes. This means that for a user to access the penny trap filter, they have to manually drain the waste-water from the drain pump and filter arrangement, which is a time-consuming and messy operation. This is not a problem when the filter is only rarely accessed, but with the 04 01 24 rarely accessed, but with the awareness of the need to filter out much more entrained debris, in particular the microplastics created during wash cycles, the need arises to access the filter to empty it more often. It is not realistic for a user to drain the filter frequently, so an automatically draining filter is 5 required, so that its contents are relatively dry when a user empties it. A similar problem exists in the field of cleaning systems, for example floor cleaners. The operation of a floor cleaner involves spraying clean soapy water onto a floor, sucking up dirty water and filtering the dirty water. Draining the io filter so that it is dry when it is emptied is preferable. A similar problem exists in the field of Waste Water Treatment Plants, where it is required to drain a filter unit prior to accessing and emptying the captured particles from the filter. In the commercial environment it is essential that this is is done in an efficient manner as any downtime is costly. Therefore, by draining the filter it is easier and quicker for the operator to remove captured particles and return the system to operation. Similarly, where a filter is used in textile manufacturing facilities to capture 20 particles during wet processing procedures, there is a requirement for an operator to access and remove these captured particles for the filter system periodically. It is advantageous to have drained the filter and capture area, to facilitate efficient operation in the commercial environment. 25 SUMMARY OF THE INVENTION In an embodiment, a filter system for liquid effluent handling equipment, such equipment including a reservoir for holding effluent and a drain pump for emptying the reservoir, wherein the filter system includes: a holding volume so for holding a quantity of effluent, the holding volume being in fluid communication with, and downstream from, an outlet of the drain pump, and a filter unit having an inlet in fluid communication with, and downstream from, the holding volume, the filter unit further having an outlet that is connectable CM to a sewerage system, the filter system characterised in having a non-return assembly between the holding volume and the filter unit for preventing effluent from returning to the holding volume, and an air inlet in fluid communication with the holding volume, the air inlet being arranged to allow air into the holding volume, and a control unit for controlling the drain pump. The liquid handling equipment could be textile processing or laundering equipment such as a washing machine, or the equipment could be a cleaning device such as a floor cleaner, or the equipment could be a large Waste Water Treatment plant, or textile manufacturing facility. The reservoir may be a sump in a washing machine or a tank for collecting dirty water in a floor cleaner. The holding volume could be a drain tank that is part of the drainage system of a washing machine or floor cleaner or Waste Water Treatment plant. The nonreturn assembly could be created by locating the holding volume above the filter unit so that a part of the draining fluid is prevented from flowing back into the holding volume and is instead replaced with air drawn into the system via the air valve. The advantage of the filter system is that it enables a filter unit to be drained and removed without flooding of water. The system also removes the need for an additional drain pump for the filter unit because the existing drain pump of a washing machine is used to create a piston effect that pumps air into the drainage system. This allows the filter unit to be located anywhere in the washing machine and prevents the build-up of microbiology associated with the usual drainage systems of washing machines that remains when between washes. In some cases, fluid processing systems, such as washing machines and specifically commercial washing machines, may not have a pre-existing drainage pump as they are designed to drain by gravity. When a filter is included in the design of these systems, a pump may be required to supply fluid through the filter and to the sewerage outlet, due to the additional restriction created by the filter system. The benefit of the drainage system described here is that this same pump can be used for two operations, both supply of fluid through the filter and also the drainage of the filter of that fluid. The drainage system can work with a filter system that is located both internally to an appliance, such as a washing machine, and externally. In the scenario with a filter system external to the appliance and the drainage pump internal to the appliance, the two systems can operate by being in both fluid communication and control communication with the drainage pump, despite components being housed separately. This can be advantageous as it allows for modularity and retrofitting of filter systems onto existing appliances or where there are design constraints to house the filter system internally to the appliance. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional diagram showing the components of a conventional washing machine. Figure 2 is a schematic diagram showing the components of an embodiment. Figure 3 is a schematic diagram showing the relative heights of the components of an embodiment. Figure 4 is a schematic diagram showing the relative quantities of fluid in a holding volume pump and a reservoir when a drainage pump is on and off. Figures 5a to 5i are schematic diagrams showing step-by-step the operation of a filter system in accordance with an embodiment. Figure 6a is a schematic diagram showing an embodiment with a filter unit located higher than a drain tank. Figure 6b is a schematic diagram showing an embodiment with an outlet located lower than a filter unit. Figure 7a is a drawing of a floor cleaner. Figure 7b is a cross section of the floor cleaner of Figure 7a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment that relates to domestic washing machines is described below. While the description that follows focuses on washing machines for clothes, it is to be understood that the teachings herein are not limited to use in washing machines as they are equally suited to other processing appliances, such as but not limited to driers, such as wash-dryer combination machines, tumble driers, dyeing machines, cutting machines, recycling machines, dry cleaning machines and so on. The washing machines or other processing appliances could be domestic or commercial. The teachings herein could also be used in other industries in which microparticles may be generated as a result of processing of items. References to washing machines herein are therefore to be understood as comprising any similar appliance of the types contemplated herein. Furthermore, the system could be applied in the broader context of filtration of effluent from floor cleaners, or in large-scale Waste Water Treatment Plants, or textile manufacturing facilities. A typical front-loading domestic washing machine is shown in Figure 1 in schematic form. The machine 100 includes a rotatable sealed drum unit 101 for receiving garments to be washed. The drum unit 101 has a perforated cylindrical rotatable drum mounted inside a static waterproof shroud. Clean water is fed into the drum 101 via a cold water or hot water inlet 102 connected to mains and under mains pressure of typically 1-5 bar. The water entering the drum 101 is managed by an electronic valve, under the control of a CPU 104. The inlet 102 is connected to a drawer 105 where liquid or powdered detergent can be added by a user. The drawer has an outlet that leads to the drum unit 101. The drum unit may include a heater controlled by the CPU to heat the water to the desired wash temperature, typically up to 90 degrees Celsius. The drum is rotatable by an electric motor 106 under the control of the CPU 104 at speeds of typically from 5 to 1600 rpm. The drum unit can be emptied via a drain pump 108 controlled by the CPU. The drain pump is rated with a given power to produce a known pressure at its output. The drain pump feeds into drain conduit 109 which is a section of tubing connected to an outlet point 110 on the outside of the washing machine. The outlet point is connected by a length of tubing 111 to the household or industrial drain 112 and eventually the wastewater network. In a household setting, the drain could bean upstanding open pipe, or a sink or a wall-mounted spigot, which allows wastewater to flow away under gravity into a sewer. The outlet point 110 of the drain conduit 109 of the washing machine is above the drain pump 108. In another embodiment the filter system could have a means of diverting the filtered water between sewerage and recirculating back into the reservoir. This could be achieved using a diverter valve. It is advantageous as by recirculating the filtered water, the overall water consumption of the appliance can be reduced. A typical top-loading machine will have the axis of the drum vertical but will otherwise share many of the features of the front-loading machine. In use, dirty laundry is placed in the drum, and a wash cycle initiated by a user. The CPU allows cold water to flow via the drawer to mix with detergent and then on into the drum, where the water is heated. The combined water, detergent and laundry is agitated by rotating the drum. During this process, dirt and grease is released into the water and fibres from the clothing too. If the clothing is synthetic, microfibers are typically released as the clothes rub against each other. The resulting effluent at the end of the wash cycle is a mixture of debris, dirt, grease and microfibers and potentially large objects such as coins or nails left in the clothing. This effluent is then drained and pumped out of the drum at a typical rate of 3-8 gallons per minute. Second or third rinse cycles with clean water may be performed, resulting in effluent with less concentrated contaminants. The drain rate of the washing machine is impacted by the level of water in the drum, the height of the outlet point and if a filter is connected to the outlet. A drain pump could be a centrifugal type. Centrifugal pumps can cavitate, i.e. when there is no fluid at the input, bubbles form around the rotor and collapse. Any other type of pump could be used, for example peristaltic or diaphragm pumps. Most drain pumps need to be primed to work. Therefore, it is important for a quantity of liquid to remain in the pump so that it is never operated in a dry condition, which can damage the seals and bearings in the pump. The waterproof shroud gathers waste water into a sump 113 below the drum. In some washing machines, a hollow ball 114, is provided that can float on top of the water in the sump and thereby close off the drum housing. This is provided to conserve detergent; when a wash is initiated, the first water to arrive in the drum contains the detergent rinsed out of the drawer; without the ball, this fluid would go straight to the sump and not be available for the wash. Therefore, it is preferable that the sump is full at the end of the wash so that the ball is actively closing off the bottom of the drum housing. The requirement for a full sump and a wet drain pump means that the drainage section of a typical washing machine is full of waste water. This means that any equipment in the drainage line will also be wet. This has the disadvantage that, if access to this equipment is required by a user, then they must drain the line, which is time consuming and messy and can lead to flooding. Furthermore, if the washing machine is unused for long periods of time, then microbiological build-up can occur, leading to odours and further mess. Equipment that is desirable to include in the drainage conduit 109 is a filter, in particular a microplastics filter, such as that described in PCT / EP2022 / 061489. This unit sits in the drain line and removes fine debris from the flow of waste water. The unit needs to be periodically emptied and therefore it is desirable that the drain line has no waste water in it. An embodiment of the present invention provides an arrangement for draining a portion of the drainage conduit 109, using the existing drain pump of a washing machine, as shown in Figure 2. The drainage conduit 109 includes three regions: a waste-water holding region 201, an equipment region 202 and an outlet region 203. In this embodiment, the equipment in the equipment region is a microplastics filter 204 having an inlet 204a and an outlet 204b. The waste-water holding region 201 is a section of conduit that connects the drain pump 205 to the inlet 204a of the filter 204 in the equipment region 202. The outlet region 203 comprises a length of conduit that connects the outlet 204b of the filter 204 to the outlet point 206 of the washing machine. The outlet region includes a one-way valve 211 at the lowest point, to prevent the flow of waste water back from the outlet region to the equipment region. This one-way valve is optional and an embodiment without this valve is described in more detail later. The waste-water holding region 201 includes a drain tank 207 of volume Vt. The volume of the drain tank Vt is approximately equal to the volume of the sump 208 Vs. The drain tank 207 has a drain tank outlet pipe 209 that connects to the equipment region 202. The drain tank outlet pipe 209 is located at the top of the drain tank and rises up from the drain tank and then down towards the equipment region 202 to create a high point in the drain tank outlet. An air inlet 210 is located at the high point in the drain tank outlet. The air inlet 210 includes a one-way valve to allow air into the drain tank 207 but not out. The relative heights of the various elements of the drainage conduit are significant for operation of the drainage system. These relative heights are shown in Figure 3. The centre of the drain pump 301 defines the zero height H1. The top of the sump is at height H2, which is the same height as the bottom of the drain tank 303. The air inlet is at H3, which is greater than H2. The portion of the outlet region that is above H3, contains a volume Vx. The lower end of Vx is defined as H3 and the upper end H4, is the highest point of the upstanding household drain pipe 112 in Figure 1. In a conventional system with a centrifugal drain pump, the drain pump operates until the sump is empty. Then the pump cavitates and cannot push any more waste-water out of the drain conduit. At this point, the drain conduit is full of waste-water, up to the maximum height. When the pump is turned off, the waste-water in the drain conduit falls back through the pump and into the sump where it reaches an equilibrium, such that the sump and drain conduit is partially filled with waste water at rest. In the present embodiment, an arrangement downstream of the drain pump is provided that utilises some of the waste-water to act as a piston in a pump operation that can continue to operate with a limited volume of waste-water remaining in the drainage system. This is done by ensuring that waste-water that has left the drain tank does not return to it and instead is replaced by air. The principle of operation is shown in Figure 4, where the volume of wastewater Vt held in the holding tank when the drain pump cavitates is allowed to drain back under gravity into the sump, of volume Vs while the vacant volume Vt is allowed to fill with air. When the drain pump is activated again, the volume Vt of air is then pumped into the drainage system. When the cycle is repeated, another volume Vt of air is pumped into the drainage system. The cycle is repeated until all of the waste-water downstream from the drainage tank is replaced by the air that is pumped into the drainage system. In the present embodiment, when a wash is completed and the drain pump 205 is first activated, the sump 208 is emptied into the drainage conduit and the entire drainage conduit is full of flowing waste-water under pressure, as shown in Figure 5a. When the sump 302 becomes empty, the drain pump 205 cavitates and the pressure in the drainage conduit drops to zero as fluid flow towards the outlet 206 stops. The drainage conduit is full along its length with waste-water from the drain pump outlet to the highest point in the outlet region 203, as shown in Figure 5b. When this state is detected, either by detecting the lack of waste-water in the sump 208, or the change in the performance of the drainage pump 301 as it cavitates, or by timing, or the drop in pressure in the drainage conduit, the drain pump 205 is turned off, as shown in Figure 5c. The system is now not in equilibrium because there is a volume of water in the drainage tank 207 at height H2 above the empty sump 208 at height H1. At this stage, the body of waste-water in the drainage conduit would move backwards to fill the sump 208, but the one-way valve 211 prevents this. The drainage conduit upstream of the one-way valve 211 experiences a negative pressure, which causes the air valve 210 to open to allow the fluid in the drain tank 207 to drop back through the drain pump 205 and back into the sump 208. Therefore, by turning the drain pump 205 off, an air pocket 501 is introduced into the drain tank 207. The sump is now full and the drainage pump is primed. The drain pump 205 is then turned back on, as shown in Figure 5d. The sump empties and the drain tank 207 fills again, pushing the air pocket 501 through into the equipment region 202. This in turn pushes waste-water out of the outlet 206. The drain tank 207 fills until the sump 208 is empty and the drain pump 205 cavitates again. When the empty sump 208 is detected, as described above, the drain pump 205 is turned off again, as shown in Figure 5e. The fluid in the outlet region and the equipment region remains static, while the waste-water in the drain tank 207 flows back through the drain pump 205 into the sump 208, drawing a volume of air in again through the air inlet valve 210 to create a larger air pocket 502 in the system. When the sump is re-filled, the drain pump 205 is turned back on again, as shown in Figure 5f, and the larger air pocket 502 is pushed into the drain tank outlet pipe 209 and a further volume of waste-water is purged from the outlet 206. The movement of waste-water from the drain tank to the sump as the pump is switched off, and then back from the sump to the drain tank, defines a single ‘pump stroke’. The volume of water that is purged from the system during this single pump stroke is defined as the stroke volume, Vstroke and is equal to the volume of waste-water held in the sump, Vs. The process of switching on the drain pump when the sump is full and off when it is empty is repeated, as shown in Figures 5g and 5h to introduce a larger and larger air pocket into the equipment region and outlet region, until almost all of the waste-water is drained from the system, as shown in Figure 5g. Alternatively, the filter unit 601 can be located above the drainage tank 602, as shown in Figure 6a. Alternatively, the outlet 603 can be located below the filter 601, as shown in Figure 6b. The one-way valve 211 at the filter unit outlet 206 can be omitted if the sump volume Vs is large enough to accommodate all of the waste-water that flows back out from the outlet region 203. This would be the case if the highest point of the outlet is lower than the top of the drain tank 207. Alternatively, a holding tank could be used at the outlet of the filter to accommodate the backflow from the outlet region. The CPU 104 of the washing machine is arranged to control the drain pump. A separate control apparatus for the drain pump could be provided. The switching of the drain pump on and off provides the piston effect of the waste-water moving between the sump and the drain tank. The timing of the switching can be controlled in a number of ways: 1. Detecting when the drain pump is cavitating, e.g. using a pressure sensor at the outlet of the drain pump to detect when the pressure of wastewater drops, or detecting when the power consumption of the drain pump decreases. 2. Detecting when the waste-water in the sump has reached a pre-defined level using a fluid level sensor. 3. Calibrating the drainage rate of the washing machine and arranging for the pump to switch off after a pre-defined time. Calibrating the flow of wastefluid back into the sump from the drainage tank and arranging for the pump to switch on again after a pre-defined time. The timing parameters or fluid level detectors could be arranged to provide shorter stroke lengths; this would allow the use of a smaller drain tank and cavitation of the drain pump to be avoided. In this case, the volume of the stroke Vstroke is the volume of fluid displaced by one “on” pulse of the drain pump.The benefit of the invention is that it allows drainage of a system downstream from a drain pump, particularly when the system is lower than the drain pump and the outlet of the system. The air valve 210 could be a one-way valve that operates when the pressure in the drain tank is less than atmospheric pressure, or it could be an electronic valve operated by the CPU 104. In a further embodiment, the raised drain tank could be replaced with a nonreturn valve and a drain pump that could be operated in reverse. The pump would be operated to drain the sump and then operated in reverse to refill the sump with waste-water upstream of the non-return valve; the non-return valve would prevent waste-water downstream from returning and instead air would be drawn into the space. Forward operation of the pump would then pump this air into the drainage system and repeated cycling would pump air into the drainage system until all of the waste-water downstream from the no-return valve was displaced. In a further embodiment, a floor cleaner is provided with an embodiment of the forced-air filter drainage system, as shown in Figures 7a and 7b. The floor cleaner 700 is a mobile unit that includes a system of tanks and brushes to apply soapy water to a dirty floor. A clean water tank 701 feeds clean water to a rotating brush 702. As the unit is moved along the floor, dirty water is sucked up through inlet 703, through ducting 704 and deposited into a dirty water holding tank 705, by means of a vacuum pump 706. The holding tank has a sump 707 that is drained by means of drain pump 708. A drainage tank 709 is provided downstream of the drain pump 707 and a one-way air inlet valve 710 is provided in the drainage tank 709. Dirty water from the drainage tank is pumped through a filter unit 710 and the resulting clean water is returned to the clean water tank 701. To empty the filter, the vacuum pump is turned off so that no new effluent is entering the dirty water tank. The dirty water tank is emptied until only the sump is full. Then the drainage pump is operated in the same way as described for the washing machine filter above, i.e. the drainage pump is periodically turned on and off so that the waste-water is cycled between the sump and the drain tank to create a piston effect, whereby air is sucked into the system through the air valve. This water-piston drives air through the system until all of the waste water is evacuated from the filter. A larger-scale embodiment of the invention can be applied to the treatment of 5 effluent in Wastewater Treatment Plants. For example, the chamber of the filter could be 1 meter in diameter or 2 meters or greater.

Claims

1. A filter system for liquid effluent handling equipment, such equipment including a reservoir for holding effluent and a drain pump for emptying the reservoir, wherein the filter system includes:a holding volume for holding a quantity of effluent, the holding volume being fluidly communicable with an outlet of the drain pump, anda filter unit having an inlet in fluid communication with, and downstream from, the holding volume, the filter unit further having an outlet that is connectable to a sewerage system,the filter system characterised in havinga non-return assembly between the holding volume and the filter unit for preventing effluent from returning to the holding volume, andan air inlet in fluid communication with the holding volume, the air inlet arranged to allow air into the holding volume, anda control unit for controlling the drain pump.

2. The filter system of claim 1, wherein the non-return assembly comprises arranging the filter unit below the top of the holding volume.

3. The filter system of claims 1or 2, wherein at least a part of the holding volume is located above the drain pump.

4. The filter system of any preceding claim, wherein the holding volume is of substantially equal volume to the reservoir.

5. The filter system of any preceding claim, wherein a non-return valve is provided at the outlet of the filter unit.

6. The filter system of any preceding claim, wherein a sensor is provided to detect a condition of the reservoir or drain pump.

7. The filter system of any preceding claim, wherein the detected condition is whether the reservoir is empty or whether the drain pump has cavitated.

8. The filter system of claim 7, wherein the control apparatus is arranged to deactivate the drain pump on detecting the condition.

9. A washing machine having the filter system of claims 1 to 8.

10. A floor cleaner having the filter system of claims 1 to 8.

11. A waste-water treatment plant having the filter system of claims 1 to 8.

12. A textile manufacturing facility having the filter system of claims 1 to 8.

13. A method of operating the filter system of claims 1 to 8, comprising the steps ofoperating a drain pump to drain effluent from a reservoir into a holding volume and then into a filter unit and from the filter unit to an outlet, determining when the reservoir has drained to a pre-determined level, then operating the drain pump so that a pre-determined volume of effluent returns to the reservoir,allowing air into the holding volume as the effluent returns to the reservoir from the holding volume, while preventing effluent from returning from the filter unit to the holding volume.

14. The method of operating the filter system of claim 13, including repeating the steps of operating the drain pump to drain effluent from the reservoir into the holding volume and then operating the drain pump to allow effluent to flow back into the reservoir and allowing air into the holding volume, while preventing effluent from returning from the filter unit to the holding volume.CM15. The method of claim 14, further including the steps of operating the drain pump periodically, until substantially all of the effluent is removed from the filter unit.5 16. The method of claim 15, further including the step of periodicallyoperating the drain pump in dependence on the amount of effluent present in the reservoir.

Images