GB2451723A

GB2451723A - A backwashed filter system

Info

Publication number: GB2451723A
Application number: GB0809992A
Authority: GB
Inventors: James Peter Hosford
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-06-02
Filing date: 2008-06-02
Publication date: 2009-02-11
Also published as: GB0809992D0; GB0710554D0

Abstract

A backwashed filter system comprises a filter 29, a backwashing means 34 for directing a backwashing flow to the filter in a generally opposite direction to the flow of fluid through the filter, a differential pressure sensor 16, 17 which in use senses a differential pressure across the filter and a valve (23, Fig 3) operated in response to the differential pressure sensed by the sensor to adjust and vary a relative proportion of the backwashing flow to the main flow to thereby adjust and vary the degree of backwashing. Preferably a pump 31 is provided to provide the flow through the filter system. The differential pressure sensor may be a moveable diaphragm connected to the valve such that movement of the diaphragm operates the valve. Also disclosed is method of controlling a backwashed filter system and a separate invention discloses a flow control valve in particular a balanced valve operated in response to a sensed increase in a differential pressure.

Description

Mechanical fluid valve to control fluid flow in response to differential pressure applied.

This invention relates to a control valve for self-cleaning filters used for liquids, although it is equally applicable to gases. The control valve may also find other applications.

There is disclosed in our granted prior patents GB 2 293 33313 and EP (1 1K) 1169103, EP (IT) 116910372514 BE/2(X)4, EP (FR) 1169103, EP (DE) 600 13 793.7-08, and US 6520,752B1 filter assemblies which are of the hackwashing type. In niany situations these work very well.

However in some situations the filters may become blocked with particulate matter. This can happen when there is an increase in the amount of particulate matter within the liquid and br over time there can be a slow build up of particulate matter on the filter screen, which the backwash is unable to remove, owing to an increase in the differential pressure across the filter screen. In this situation the flow of liquid through the lilter medium is severely reduced or stopped. In many situations it is important that the filter is able to automatically control itself when there is a surge in particulate matter in the fluid to be filtered and continues to With any flow of fluid across a filter medium there is a differential pressure, across the filter medium, the pressure on one side of filter medium is higher than on the other side. This is caused by the flow of liquid being impeded by the filter medium, the greater the impedance to the flow of liquid the greater the pressure differential. With any given filter, as particles settle on the screen some, or all, of the apertures in the filter medium become blocked and the differential pressure will increase, also at any given pressure the flow through the filter will decrease.

When the filters, as described in the granted prior patents, start to block, very quickly the differential pressure across the screen starts to rise. The backwash fluid finds it increasingly difficult to remove the particles that are adhering to the filter screen as they are pressed against the screen by the increased differential pressure.

As the backwashing is now less effective, more particles begin to adhere to the filter screen, the differential pressure rises even more quickly and soon the backwash fluid is unable to remove the particles and the filter is blocked.

To stop the filter blocking it is important to sense the rise in the differential pressure at an early stage in the process and take action to reduce the differential pressure. In the filters described in the patents they are often attached to a pump that sucks liquid through the filters.

The action required to reduce differential pressure across the filter is to increase the proportion of backwashing fluid in relation to the total flow through the filter.

In the case of Filters described in GB 2 293 333B where a "T" off the output of the pump directs a proportion of the pump's output back to the backwashing jets in the filter. A valve is required to increase the proportion of the pump's output that is directed back to the backwashing jets in response to an increase in differential pressure across the filter.

In the case of Filters as described in EP (UK) 1169103, EP (IT) 116910372514 BE/2004, EP (FR) 1169103 and EP (DE) 600 13 793.7-08, a valve is required to restrict the flow from the Page 1 main pump thereby increasing the backwash flow in relation to the total flow through the filler. The valve could also redirect sonic of the flow from the main pump and dump it hack inside the filter. This would be necessaiy where the self-cleaning filter is fitted to a positive displacement pump and the output froni the main pump cannot be reduced without overloading the pump.

The sensing of the differential pressure and adjustment of the how from the pump as described above can be done in a number of ways, for example, use a pressure transducer to sense the differential pressure across the filter, which, via an electronic circuit controls an actuated valve or solenoid valve. I have developed such a system hut it required a computer chip and associated electronics to provide the appropriate output to an actuated valve. This was complicated and expensive.

A mechanical valve that adjusts the liquid/gas flow through the valve in proportion to the differential pressure across the filter would be a simpler solution. The main problem to be overcome being that the output of the pump niay be at high pressure and the differential pressure across the filter needs to he maintained at relatively low levels usually less than 100mb and preferably below 50mb. Therefore to shut a valve with an orifice of, for example 50mm in diameter and for example >l0bar pressure with only a 50mb differential pressure presented some technical problems. Another problem is that the liquid that has been filtered may still contain some particles which particularly in the case of valves that are servo operated, i.e. are powered by the fluid pressure flowing through the valve can cause blockages. Servo operated valves nomially have small orifices which will block with detritus in the filtered fluid., causing malfunction of the valve.

I will now describe the valve that I have invented that overcomes these problems and achieves the desired result.

The valve consists of an orifice and a plunger that can either partially or completely obstruct the orifice. It has two rolling diaphragms that help to balance the forces on the plunger so that relatively little force is required to close the valve as the pressure is balanced by the diaphragms. Rolling diaphragms have been chosen instead of pistons to balance the forces as they have low friction and are easily sealed. Pistons would require tight machining tolerances and seals that require more force to overcome friction. Two diaphragms are used instead of one. In some balanced valves one piston or diaphragm is used with fluid pressure from the upstream side of the valve on one side of the diaphragm or piston and fluid pressure from the downstream side of the valve on the other side of the diaphragm or piston. This requires channels within the valve to direct fluid to both sides of the piston or diaphragm and these may become blocked with dethtus. The rolling diaphragms should have an effective area that is the same as the cross sectional area of the orifice, as this will balance the valve most effectively.

A rod runs through the valve connecting the two rolling diaphragms and plunger together.

This rod extends through one of the rolling diaphragms and connects to a further larger diaphragm that actuates the valve when a differential pressure is applied across this larger diaphragiii The size of the large diaphragm, to which the differential pressure across the filter is applied, depends on the force required to close, or partially close the valve and also the differential pressure available to close, or partially close the valve.

Page 2 The force required depends on a number of factors; the size of the orifice in the valve, the difference in the pressure across the orifice when it is closed, or partially closed, friction when the valve plunger, rod and rolling diaphragms are moved and the strength of the spring that normally holds the valve open. We have found that for a valve with a 50mm orifice, the large diaphragm needs to have an effective area of 300cm2, this will close the valve completely at approximately 50mb differential pressure across the filter with a 10 bar differential pressure across the valve orifice. The sensitivity of the valve, to the differential pressure applied from the filter can he achieved by altering the spring that holds the valve open.

With reference to Figure 1, I will now describe the operation of the valve. Fluid flows into the valve inlet (1) through the orifice (2) and out through valve outlet (3). The rolling diaphragm (4), on the upstream side balances the pressure on the valve plunger (5) from upstream fluid.

Rolling diaphragm (4) is vented to the exterior of the valve via vents 11 & 12. The rolling diaphragm (6) on the down stream side balances the pressure on the valve plunger from the downstream fluid. Rolling diaphragm (6) is vented to the exterior of the valve via vent (13) the spring (7) makes sure that the valve is kept in the open position. However the flow of fluid through the valve also tends to open the valve. . The outlet (14) is connected via a conduit to the interior of the filters as described in the patents. Applying a differential pressure to diaphragm 8, (the lower pressure in the space (9) and the higher pressure in space (10)), then the valve will start to close. This will increase the proportion of backwashing fluid to the total flow through the filter of the type described in the patents mentioned above. This increasing proportion of hackwashing fluid will decrease the differential pressure across the filter and the valve will open slightly. This will continue until the valve finds equilibrium and adjusts the proportion of backwashing fluid so that the filter will continue working without blocking.

The higher the solids levels in the tluid to he filtered the more the valve will close to keep the differential pressure across the filter within acceptable limits. What constitutes acceptable limits will depend on the pressure of the back flushing fluid, the open area and aperture size of the filter mesh and the differential pressure across the filter. I have found that with back flushing fluid pressures of 5 metres head, and filter apertures from 50 micron-300 microns and open areas of 30-60% the differential pressure across the filter should not exceed 50mb or the filter will block.

The large diaphragm needs to be positioned close to the filter., or at least should remain submerged in the fluid in which the filter is working. It is safer to mount it very close to the filter as fluid levels, (in a tank for example), may fluctuate and could leave the large diaphragm (8) out of the fluid. In Fig 1 the large diaphragm (8) and the control valve are one unit. ibis makes for a compact and simple unit. However the whole unit needs to he positioned very close to the filter, i.e. it is immersed in the fluid along with the filter. The reason for this is, that if the whole unit is mounted away from the filter unit, a conduit is required from the filter unit to the connection (14) as shown in Fig 1. Fluid in this connecting pipe can exert a force on the diaphragm by its weight. For example if the whole valve unit as shown in figure 1 is mounted 50 cms above the fluid level in which the filter is immersed, then the weight of fluid in the tube will create a negative pressure of 50mb on the diaphragm (8).

Page 3 This will close the valve, even when there is little differential pressure across the filter.

Where the whole control valve unit is mounted veiy close to the filter, it is necessary to route the output of the pump back to the control valve, so that the control valve can regulate the ratio of backwash fluid to flow through the filter. This requires conduits from the pump outlet to the valve, which is positioned near the filter unit, and then back to where the fluid is required to be used. This can be expensive and cause extra pipe friction losses. If the main diaphragm unit is separated from the valve unit, then the valve can be mounted on the outlet of the pump and the diaphragm unit niounted on the filter. The movement of the diaphragm (8) needs to be transmitted to the valve unit. There are a number of ways that this can be done, and I have had some success with a Bowden cable to mechanically connect the diaphragm unit to the end of rod connecting the plunger and two rolling diaphragms together.

Although it worked, it was not very accurate. Very small movements of the diaphragm can make a big difference to the flow through the valve, especially when the valve is nearly closed. Bowden cables will work, hut are not ideal owing to the amount of "play" in them.

I have experimented using hydraulics, similar to a car brake system. This provides an accurate transfer of the movement from the main diaphragm to the rod connecting the plunger and two rolling diaphragms together in the valve unit. However the parts are expensive and the master cylinder on the main diaphragm is immersed in fluid that can cause corrosion problems.

Another preferred solution is that shown in Figure 2. Two diaphragm units as shown in Fig 1 are positioned back to back. The outlet of one diaphragm is connected to the filter at connection (15). This diaphragm (16) is connected to the second diaphragm (17) with a rod.

The outlet of the second diaphragm (17) is connected via outlet (18) to the control valve at outlet (14) as shown in Fig!. The other sides of diaphragms (16 & 17) are vented to the surroundings (vents 19 &20), which will normally he immersed in the fluid to be filtered.

Figure 3 shows the control valve with associated pipe work fitted to a submersible pump with self cleaning filter as described in EP(UK) 1169103, EP (IT) 116910372514 BF/2004, EP (FR) 1169103 and EP (DE) 600!3 793.7-08.

The submersible pump (21), self-cleaning filter unit (22) and control valve (23) a conduit (24) connects the inside of the filter to the connection (14) as shown in Figure 1. The outlet (25) of the pump (21) is routed back to the inlet of the valve (1) and then the outlet of the valve (3) back to a new outlet connection for the pump (26).

The T' pieces (27 and (28) are not connected internally and all the fluid from the outlet of the pump is routed via the control valve. The arrows show the route of the fluid flow. This submersible pump does not need to be completely submerged to operate and can operate as long as the filter unit is submerged. It is therefore necessary to mount the control valve so that there is very little distance between the control valve and the fluid surface level. If the control valve unit (23) is mounted any distance above the fluid level the weight of the fluid in conduit (24) will close or partially close the valve even when there is very little differential pressure across the filter.

Page 4 Figure 4 shows a control valve in use with a self-cleaning filter as described in my patent GB 2 293 33313. The Filter (29) is shown, for example purposes, submerged in a tank or lagoon containing particles in the fluid to be filtered. There is a conduit (30) connecting the filter to the pump's (31) inlet. The outlet (32) of the pump is connected to a conduit, which has a T' (33), which directs some of the pump's output to the cleaning jets (34) inside the filter via conduit (35). There is a conduit that connects the inside of the filter to the connection 15 on the double diaphragm unit. A further conduit. which is connected at one end, to the double diaphragm unit at connection 18, and the other end to the complete control valve unit at connection (14). In this situation when the pressure in the filter (29) reduces below the pressure in the tank or lagoon, i.e. there is a pressure differential across the filter, the diaphragms (16) & (17) in the double diaphragm unit move and produce a reduced pressure in the space (9) of the control valve, and move diaphragm (8) which closes or partially closes the control valve. This the sends more fluid to the cleaning jets (34) of the filter. Therefore there is an increased proportion of the total flow through the filter, which is used for the backwashing jets. This reduces the differential pressure across the filter to a level where it will continue to operate without blocking.

The valve unit as described in figure 1 is a "normally open" valve, by moving the large diaphragm unit to the other end of the valve, and also moving spring (7) to the other end of the valve, so that the spring (7) keeps the valve closed, the valve will then he opened in response to a differential pressure applied across diaphragm (8).

This could be useful for example in the example shown in Fig 4. In some situations where the fluid to be filtered contains only small amounts of suspended matter, the filter may operate for periods without the requirement for any backwashing. By positioning the "normally closed" control valve unit in conduit 35, it will only start to open and provide backwash fluid to backwash jets 34 when a differential pressure is sensed across the filter. This will mean that none of the pump's output is used to backflush the filter unless the filter is beginning to block and output of the pump is not wasted backflushing the filter unnecessarily.

The valve may well find other applications, in particular other self-cleaning filter units where a simple mechanical controller is required to control the supply of backflushing fluid in response to a differential pressure across the filter.

Another possible application would be control of fluid in flow into a tank in response to level changes in the tank and could replace float valves. The fact that the weight of fluid in conduit (24) can either open or shut the valve, (depending on its configuration, either normally open or normally closed), can he made use of in a tank which has an incoming flow which must he stopped when the tank is full.

Page 5

Claims

1. A backwashed filter system comprising: a filter for filtering, in use, a main flow of fluid through the filter to a filter outlet; a backwashing means for directing a backwashing flow to the filter in a generally opposite direction to the flow of fluid through the filter; a differential pressure sensor which in use senses a differential pressure across the filter; and a valve operated in response to the differential pressure sensed by the sensor to adjust and vary the relative proportion of the backwashing flow to the main f low to thereby adjust and vary the degree of backwashing. * S S...

*

2. A backwashed filter system as described in claim 1 wherein the valve is operated to increase a relative proportion of the backwashing flow to the main flow W.. through the filter in response to a sensed increase in the sensed differential pressure.

3. A backwashed filter system as described in claim 1 or 2 wherein the valve is connected to a backwashing fluid supply to control the backwashing flow.

4. A backwashed filter system as described in any preceding claim wherein the filter outlet is connected to the backwashing means to supply a portion of an outlet flow from the filter to the backwashing means as said backwashing flow.

5. A backwashed filter system as described in any preceding claim wherein the valve is connected to the filter outlet to control a main outlet flow from the filter.

6. A backwashed filter system as described in claim 5 wherein the valve thereby controls the main flow through the filter to thereby vary the proportion of the backwashing flow to the main flow through the screen.

7. A backwashed filter system as described in any preceding claim further comprising a pump connected to the filter outlet and configured to draw at least a portion of the main flow of fluid through the filter to a pump outlet.

8. A backwashed filter system as described in claim 7 wherein the valve is connected to the pump outlet.

*.:s

9. A backwashed filter system as described in claim 7 or 8 wherein the valve is connected to the pump outlet to redirect a portion of the outlet flow back to an inlet : side of the pump.

10. A backwashed filter system as described in claim 7 wherein the pump outlet is connected to the backwashing means to supply a portion of the pump outlet flow to the backwashing means as said backwashing flow.

11. A backwashed filter as described in any preceding claim wherein the differential sensor is mechanically, hydraulically or electrically connected to the valve to operate the valve.

12. A backwashed filter system as described in claim 11 wherein the differential sensor is connected to a valve actuator to operate the valve.

-

13. A backwashed filter as described in any preceding claim wherein the valve is located remotely from the filter and/or sensor.

14. A backwashed filter as described in any preceding claim wherein sensor is located close to the filter.

15. A backwashed filter system as described in any preceding claim wherein the differential pressure sensor comprises a moveable diaphragm across which the differential pressure across the filter is applied to move the diaphragm. * **

*.I

16. A backwashed filter system as described in claim 15 in ** which the moveable diaphragm divides a chamber into a first space connected to one flow side of the filter, * ** and a second space connected to the other side of the filter.

17. A backwashed filter system as described in claim 15 or 16 wherein the moveable diaphragm is connected to the valve such that movement of the diaphragm operates the valve.

18. A backwashed filter system as described in any preceding claim wherein the valve comprise an orifice and a moveable plunger that can either partially or completely obstruct said orifice to thereby allow or restrict a flow of fluid through said orifice and thereby through said valve.

19. A backwashed filter system as described in any preceding claim wherein the valve comprises a balanced valve.

20. A backwashed filter system as described in any preceding claim wherein the filter comprise a filter screen.

21. A method of controlling a backwashed filter system comprising a filter, and a backwashing means for directing a backwashing flow to the filter, the method comprising: sensing a differential pressure across the filter; and varying the relative proportion of the backwashing flow to a main flow through the filter to thereby adjust and vary the degree of backwashing, in response * ** *** to an increase in the sensed differential pressure. **** * S ****

22. A method as described in claim 21 comprising increasing * ** a proportion of the backwashing flow in relation to a main flow of fluid through the filter in response to an 2*0*, increase in the sensed differential pressure. S...

23. A method as described in claim 21 or 22 wherein varying the proportion of the backwashing flow in relation to the main flow of fluid through the filter comprises varying the main flow of fluid through the filter.

24. A method as described in any of claims 21 to 23 wherein varying the proportion of the backwashing flow in relation to the main flow of fluid through the filter comprises varying the backwashing flow.

25. A method as described in any of claims 21 to 24 further comprising supplying the backwashing flow from a portion of an outlet flow from the backwashed filter system.

26. A flow control valve comprising: an inlet; an outlet; a flow orifice defining a flow passage between the inlet and outlet; a moveable valve member that is moveably mounted to move relative to the flow orifice from an open to a closed position to at least partially open or close the flow passage; a first balance member configured in use to be acted on by an inlet pressure and connected to the moveable valve member to apply a closing force to said moveable valve member; * .* a second balance member configured in use to be **.

acted on by an outlet pressure and connected to the * *. moveable valve member to apply an opening force to said moveable valve member in an opposite direction to said closing force; and 20'.. a valve actuator connected to the moveable valve * member to move the moveable valve member between the open and close positions.

27. A flow control valve as claimed in claim 26 wherein the first balance member is located upstream of said orifice.

28. A flow control valve as claimed in claim 26 or 27 wherein the second balance member is located downstream of said orifice.

29. A flow control valve as claimed in any of claims 26 to 28 further comprising a biassing spring biassing the moveable valve member towards a closed or open position. *

30. A flow control valve as claimed in any of claims 26 to 29 wherein the first and/or second balance members comprise a moveable diaphragm.

31. A flow control valve as claimed in any of claims 26 to wherein the actuator comprises a moveable actuator member that is connected to the moveable valve member, the actuator member being acted on by an actuator pressure to move the actuator member.

32. A flow control valve as claimed in claim 31 wherein moveable actuator member comprises a inoveable diaphragm. * *S

* ic * **-*** .*

33. A flow control valve as claimed in claim 30 or 32 wherein the moveable diaphragm comprises a rolling * .S diaphragm.

34. A backwashed filter system as described in of claims 1 to 20, wherein the valve comprises the flow control valve of any of claims 26 to 33.

35. A method as described in any of claims 21 to 25 wherein the backwashed filter system comprises the backwashed filter system of any of claims 1 to 20.

36. A flow control valve substantially as hereinbefore described with reference to, and/or as shown in any one or more of figures 1 to 4.

37. A backwashed filter system substantially as hereinbefore described with reference to, and/or as shown in any one or more of figures 1 to 4.

S \1

38. A method of controlling a backwashed filter system substantially as hereinbefore described with reference to, and/or as shown in any one or more of figures 1 to 4. * ** a * S. S... * S 5.. * a. 4* * * S. S...

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