WO2005097289A1

WO2005097289A1 - Self cleaning fluid filter

Info

Publication number: WO2005097289A1
Application number: PCT/GB2005/050047
Authority: WO
Inventors: Lee Moore
Original assignee: Lee Moore
Priority date: 2004-04-07
Filing date: 2005-04-07
Publication date: 2005-10-20
Also published as: GB0407888D0

Abstract

A self-cleaning fluid filter, comprising a tubular filter element (1) the external surface of which is exposed, in use, to an outlet through which the filtered fluid can be withdrawn from within the filter element, and at least one nozzle (6b, 6c) rotatably mounted within the filter element, motor means (7, 8, 9) for rotating the nozzle or nozzles, and connector means (10) communicating with the nozzle or nozzles and connectable to a supply of clean fluid to be ejected from the nozzle or nozzles, characterised in that the or each nozzle is arranged to direct fluid substantially perpendicularly on to the inner surface of the filter element, thereby dislodging therefrom solids adhering to the exterior surface of the filter element.

Description

SELF-CLEANING FLUID FILTER Field of the Invention This invention relates to a self-cleaning fluid filter, for example for use in filtering fish-pond water, and to a filter system including such a filter. Background to the Invention Fluid filters become progressively less effective during use as a result of clogging of the filtration medium with the materials being filtered from the fluid. There have been various proposals for the backwashing of filters to maintain their filtration efficiency in use, but these typically require the filter to be withdrawn from service during the back- washing operation. Examples of such an arrangement are disclosed in GB 1 485 989 and GB 2 157 964A. Each of these filters requires special flow arrangements to stop the filtration operation and initiate the reverse flow to effect cleaning of the filter. This has the disadvantage of making the control of the filter complex and of downtime on filtration while cleaning is taking place. For some applications, for example filtration of fish-pond water, it is impractical to use a mechanism requiring a high degree of control automation, from the point of view both of initial cost and operating maintenance. GB 2 293 333A discloses a simpler arrangement in which clean water withdrawn from within a tubular filter element is pumped through rotating nozzles within the element, the nozzles being driven by expulsion of water through them at an angle, and the expelled water impinging on the inner surface of the filter element with a view to dislodging blocking materials from the exterior of the element. In this way, cleaning can be carried out continuously during use of the filter, the nozzles sweeping progressively over the filter element as they rotate. In practice, however, it has been found that relatively low cleaning efficiency is achieved because of the difficulty of balancing the flow rate necessary to effect cleaning of the filter with a low enough rotational speed to ensure that a cleaning effect is achieved before the jet moves away from the particular area being affected. Further, the nozzles are arranged to span the height of the tubular filter element by providing a fan-shaped jet, and so need to be spaced inwardly from the surface of the filter element by a sufficient distance to allow the jet to spread. In consequence, there is substan- tial dissipation of the energy in the jet by the time it impinges on the filter element, especially towards the axial ends of the element In addition, in certain industrial or automotive applications involving high levels of dust, problems can be experienced with clogging of conventional gas or air filters, requiring their frequent replacement. This is expensive not only in component and labour costs but also in downtime of the process or engine. The present invention seeks to overcome these disadvantages.

Summary of the Invention The invention provides a self-cleaning fluid filter, comprising a tubular filter element the external surface of which is exposed, in use, to an outlet through which the filtered fluid can be withdrawn from within the filter element, and at least one nozzle ro- tatably mounted within the filter element, motor means for rotating the nozzle or nozzles, and connector means communicating with the nozzle or nozzles and connectable to a supply of clean fluid to be ejected from the nozzle or nozzles, characterised in that the or each nozzle is arranged to direct fluid substantially perpendicularly on to the inner surface of the filter element, thereby dislodging therefrom solids adhering to the exterior surface of the filter element. Preferably, the or each nozzle is spaced from the inner surface of the filter element by a small distance such that the velocity of the fluid ejected by the nozzles is substantially undiminished on striking the surface. More preferably, the distance of the or each nozzle outlet from the filter surface is less than 35mm and, depending on the power of the pump, more preferably less than 15mm. A gap of less than 3mm may in some circumstances give rise to reduced cleaning efficiency. In a preferred embodiment, the filter comprises a pair of nozzles extending from a central spindle extending axially of the tubular filter element, the nozzles being separated from each other by 180 degrees. The nozzles are preferably displaced axially rela- tive to each other, whereby the nozzles act on axially displaced regions of the filter element as they rotate. It will be appreciated that there may be more than two nozzles, and these may be displaced from each other radially around the axis and/or along the axis. It is desirable to ensure that the nozzles are evenly spaced around the axis to balance any mechanical loading on the spindle. The output of the pump will need to be increased where a greater number of nozzles is provided and the resultant total cross-sectional area of the nozzles is thus increased. The motor means may comprise a turbine driven by fluid flowing between the connector means and the nozzle or nozzles. In a preferred embodiment, end closure plates are provided which close the ends of the tubular filter element A pump may be mounted on one of the end plates to be connected between the outlet and the connector means. The invention also provides a fluid filter system, comprising the filter of the invention, arranged in a filter chamber communicating with a source of fluid to be filtered, and a pump connected between the outlet and the connector means. While the fluid will typically be a liquid, for example water, the filter of the inven- tion may be applied to the cleaning of gases, for example air. Thus, while one application of the filter system of the invention is in cleaning pond water, it will be understood that the invention is not limited to such a use. For example, the filter could be used in industrial filtration processes, or in cleaning gas flows, for example on the air intake of an internal combustion engine used in especially dusty conditions, such as in a desert. The filter of the invention is suitable for continuous unattended use, maintaining filtration efficiency for long periods. Maintenance of the filter system is simple, and complex control systems are avoided. Brief Description of the Drawings In the drawings, which illustrate an exemplary embodiment of the invention: Figure 1 is a sectional elevation of a filter in accordance with the invention; Figure 2 shows a filter system including the filter of Figure 1 ; Figure 3 is a top plan view of the rotating nozzles of the filter of Figure 1 , and Figure 4 is a top plan view of the turbine motor drive of Figure 1 with the casing removed. Detailed Description of the Illustrated Embodiment The filter comprises a tubular filter element 1 having at each end a respective closure plate 2 and 3 to define within the element an enclosed space from which filtered fluid passing through the filter from outside may be withdrawn via an outlet 4 passing through the upper end plate 3. An axial spindle 5 extends through the filter element and carries a rotating nozzle assembly 6. The nozzle assembly 6 consists of a central annular pipe 6a surrounding the spindle 5, and a pair of nozzles 6b and 6c extending radially outwardly therefrom on opposite sides thereof, each nozzle having an axial length, relative to the filter element 1 , just greater than half the length of the element 1 so that, as the nozzles 6b and 6c rotate about the spindle 5 they sweep overlapping portions of the filter element 1 to ensure substantially full coverage of the element. It will be understood that where embodiments are used which have more than two axial ly-displaced nozzles, each might sweep over a smaller proportion of the axial length of the filter element. The central annular pipe 6a opens into a motor chamber 7 containing a fluid- powered turbine wheel 8 and reduction gearing 9, described in more detail hereinafter with reference to Figure 4. Clean fluid enters the motor chamber through an inlet pipe 10 and impinges on the turbine wheel 8, causing it to rotate, before flowing into the pipe 6a and thence to the nozzles 6b and 6c. The rotation of the turbine wheel 8 is transmitted to the nozzle assembly through the reduction gearing 9 so that the nozzle assembly 6 rotates more slowly than the turbine, sweeping the nozzles over the inner surface of the filter element The openings to the nozzles 6b and 6c are spaced from the surface of the filter element 1 by a short distance such that the velocity of the fluid expelled from the nozzles is substantially undiminished as it impinges on the element The fluid velocity is such as to pass through the filter element and to dislodge any solid material adhering to the exterior of the element As may be seen from Figure 2, the filter may be installed in a filter chamber 1 1 to which fluid, typically liquid, to be filtered may be supplied so that the filter is wholly immersed in the fluid. A pump 12 is attached to the outlet 4 and serves to withdraw some of the clean fluid from within the filter element 1 , returning it to the inlet pipe 10 to the motor chamber 7 to drive the turbine and to perform the filter cleaning action. A sepa- rate pump (not shown) may be used to withdraw the main part of the filtered fluid from within the filter element, driving the filtering process and passing the filtered fluid to where it is required. For example, if the filter is used for filtering fish-pond water, then the filtered water will be returned to the pond. In an alternative arrangement a single pump is used, part of the flow from the pump being diverted back to the inlet 10, while the remainder is discharged as output from the filter. The pump is shown in Figure 2 as being located remotely from the filter. It will be appreciated that it would be possible to integrate the pump with the filter element to form a single package, mounting the pump on the end wall of the filter element, for example. Referring now to Figure 4, the drive between the turbine wheel 8 and the nozzle assembly 6 is effected through reduction gearing 9 so that the nozzles sweep over the filter element sufficiently slowly to maximise the cleaning effect The turbine wheel 8 has a smaller gear wheel 9a fixed thereto, driving a larger gear wheel 9b mounted on a separate shaft and fixed to a smaller gear wheel 9c, which in turn drives a larger gear wheel 9d attached to the nozzle assembly. By this means, a typical speed reduction of 2.6:1 is achieved, with the result that the nozzle assembly rotates at a speed of around 30 rpm. It will be understood that when the filter of the invention is used with fluids other than water, for example air, different turbine speeds may be necessary to achieve the desired rotation of the nozzles, and thus different speed reduction gearing.

Claims

CLAIMS 1. A self-cleaning fluid filter, comprising a tubular filter element the external surface of which is exposed, in use, to an outlet through which the filtered fluid can be withdrawn from within the filter element and at least one nozzle rotatably mounted within the filter element motor means for rotating the nozzle or nozzles, and connector means communicating with the nozzle or nozzles and connectable to a supply of clean fluid to be ejected from the nozzle or nozzles, characterised in that the or each nozzle is arranged to direct fluid substantially perpendicularly on to the inner surface of the filter element thereby dislodging therefrom solids adhering to the exterior surface of the filter element.

2. A filter according to Claim 1 , wherein the or each nozzle is spaced from the inner surface of the filter element by a small distance such that the velocity of the fluid ejected by the nozzles is substantially undiminished on striking the surface.

3. A filter according to Claim 2, wherein the distance of the or each nozzle outlet from the filter surface is less than 35mm.

4. A filter according to Claim 3, wherein the distance of the or each nozzle outlet from the filter surface is less than 15mm.

5. A filter according to any preceding claim, comprising a pair of nozzles extending from a central spindle extending axially of the tubular filter element the nozzles being separated from each other by 180 degrees.

6. A filter according to Claim 5, wherein the nozzles are displaced axially relative to each other, whereby the nozzles act on axially displaced regions of the filter element as they rotate.

7. A filter according to any preceding claim, wherein the motor means com- prises a turbine driven by fluid flowing between the connector means and the nozzle or nozzles.

8. A filter according to any preceding claim, wherein the fluid is a liquid.

9. A filter according to any of Claims 1 to 7, wherein the fluid is a gas.

10. A filter according to Claim 9, wherein the gas is combustion air supplied to an internal combustion engine.

11. A filter according to any preceding claim, comprising end closure plates closing the ends of the tubular filter element.

12. A filter according to Claim 11 , comprising a pump mounted on one of the end plates and connected between the outlet and the connector means.

13. A fluid filter system, comprising a filter according to any of Claims 1 to 11 arranged in a filter chamber communicating with a source of fluid to be filtered, and a pump connected between the outlet and the connector means.

14. A fluid filter system according to Claim 13, wherein the pump is mounted on an end closure plate on the filter element.

15. A fluid filter system according to Claim 13, wherein the pump is located outside the filter chamber.

16. A fluid filter system according to Claim 14 or 15, wherein the fluid connection between the pump and the connector means is divided, whereby a portion of the fluid withdrawn from within the filter element can be delivered to a filter system outlet.