1 Self Cleaning Strainer FIELD OF THE INVENTION The present invention relates to a pneumatically controlled, self cleaning strainer for particular use in the mining industry. 5 BACKGROUND OF THE INVENTION There are various environments in which water that may be contaminated with particulate material needs to be transported from one area to another using a pump or like equipment. One such environment is a typical underground mining environment in which ground water, which is know to slow production and damage machinery, needs to be pumped out effectively. 10 There exist various types of pump strainers that operate to ensure water that enters a pump is substantially free of particulate material which would otherwise block and cause damage to the pump. However, current strainers known to the present inventor have a number of inherent problems, including but not limited to the following: * the strainers become constantly blocked and thus require physical detection and manual clearing 15 of the blockages for the pump to draw efficiently, a process that is laborious and expensive for mine operators; * known strainers can involve a large number of parts, and generally be quite complex and expensive to manufacture; and * known strainers often do not comply with Fire Retardant Anti Static (FRAS) legislation for 20 underground mines in particular. It is therefore an object of the present invention to overcome at least some of the aforementioned problems or to provide the public with a useful alternative. SUMMARY OF THE INVENTION Therefore in one form of the invention there is proposed a strainer for filtering a pumped fluid, 25 said strainer comprising: a base; a strainer body rotatably supported above said base and having a circumferential wall provided with fluid inlet perforations; 2 at least one fixed scraper supported above said base, said scraper positioned such that an edge thereof extends across and contacts the cylindrical wall of the strainer body; a drive operatively connected to the strainer body for rotating the body relative to the fixed scraper such that in a single cycle the at least one scraper contacts the entire circumference of the 5 strainer body wall. In a further form of the invention there is proposed a pump strainer assembly for mining environments, said pump strainer including: a fluid pump adapted to pump ground water from said environment; a strainer in fluid communication with said pump and adapted to be placed in the body of ground 10 water to be pumped, said strainer including a base, a strainer body rotatably supported above said base and having a circumferential wall provided with fluid inlet perforations, at least one fixed scraper supported above said base, said scraper positioned such that an edge thereof extends across and contacts the cylindrical wall of the strainer body; and a pneumatic drive operatively connected to the strainer body for rotating the body relative to the 15 fixed scraper such that in a single cycle the at least one scraper contacts the entire circumference of the strainer body wall. Preferably the strainer includes two scrapers disposed on opposed sides of the strainer body, whereby each drive cycle constitutes rotation of the strainer body by 180 degrees. In preference said drive is configured to cause oscillatory rotation of the strainer body in 180 20 degrees cycles. Alternatively the strainer includes one scraper, whereby each drive cycle constitutes rotation of the strainer body by 360 degrees. Preferably said drive is configured to cause oscillatory rotation of the strainer body in 360 degree cycles. 25 In preference said strainer body is cylindrical and each scraper is an elongate body of friction rated anti-static rubber adapted to extend the length of the cylindrical body. Preferably said strainer body further including an outlet housing to which a hose to said pump is adapted to be connected, said outlet housing including an insert in which the strainer body is recessed and adapted to rotate.
3 Preferably said strainer body and said insert are manufactured from anti-spark/anti-static materials. Advantageously the strainer body is manufactured from a marine grade stainless steel such as 316 S/S and the insert in which the strainer body rotates is manufactured from a FRAS rated 5 polyurethane material. Stainless steel has an obvious advantage over say mild steel in that it has superior corrosion resistance and increased life span. Preferably said insert includes an opening disposed adjacent said base, said opening being of a similar dimension to that of said pump hose cross section. In preference said drive is in the form of a pneumatic control system to which compressed air is 10 supplied, said control system including a pneumatic control circuit and an actuator adapted to effect rotation of said strainer body. Preferably said actuator is supported above said base and communicates with said pneumatic control circuit via compressed air hoses. Preferably said pneumatic control circuit includes a means of providing a manual control over 15 timing of rotation of the barrel. In preference said pneumatic control circuit includes a means of preventing compressed air from reaching the actuator to enable the barrel to be manually rotated. Preferably said strainer further includes an outer mesh guard. Preferably said strainer is adapted to be placed in a body of water to be pumped, such as ground 20 water in an underground mine. In a still further form of the invention there is proposed a method for filtering pumped fluid, comprising: coupling a strainer as defined above to a pump; placing the strainer body in a pool of the fluid to be pumped; 25 operating the pump to draw fluid through the inlet perforations of the strainer body to the pump; rotating the strainer relative to the one or more scrapers in an oscillatory motion to ensure the entire circumference of the strainer body is scraped clean.
4 Preferably the strainer includes two scrapers disposed on opposed sides of the strainer body, whereby each drive cycle constitutes rotation of the strainer body by 180 degrees. In preference said drive is configured to cause oscillatory rotation of the strainer body in 180 degrees cycles. 5 BRIEF DESCRIPTION OF THE DRAWING FIGURES The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings: Figure 1 illustrates in cross sectional view a ground water reservoir in an underground mine 10 including a groundwater pump arrangement and a pump strainer placed in the reservoir in accordance with the present invention; Figure 2a illustrates an enlarged perspective view of the strainer of the present invention; Figure 2b illustrate a perspective view of the strainer of Figure 2a with the outer mesh guard removed; 15 Figure 2c illustrates an exploded perspective view of the strainer of Figure 2a with outer mesh guard removed; Figures 3a-3d illustrate progressively how the meshed barrel of the strainer rotates in a 180 degree oscillatory motion against side mounted scrapers which clean the barrel; and Figure 4 illustrates a schematic control diagram of the pneumatic system used to control the barrel 20 actuator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever 25 possible, the same reference numbers will be used throughout the embodiments and the following description to refer to the same and like parts. The present invention relates to a self cleaning strainer 10 that allows for continuous flow of fluid (typically water) into a pump or other device located downstream of the strainer 10 by preventing 5 particulate material from entering the device. In particular, the strainer 10 is an automatic, pneumatically controlled strainer which by virtue of its configuration prevents particulate material from moving through the strainer and at the same time is self-cleaning. The example provided herein is the pumping of ground water 12 from an underground mining 5 environment using a fluid pump 14, the strainer 10 being used to ensure that particulate material 16 in the ground water 12 does not enter the pump 14. It is to be understood though that the present invention could equally well be used in other applications and environments. The above example is illustrated in Figure 1 which also shows an air control box 18 associated with the strainer 10 and whose purpose is described in more detail below. Hose 20 is adapted to carry compressed 10 air from the air control 18 to the strainer 10, while hose 22 is adapted to carry ground water 12 away from the mining environment when the pump 14 is in operation. Turning to Figures 2a-2c, the components forming the strainer 10 include: * a rectangular base plate 24 including a longitudinal axis, although the base plate could equally well be square; 15 * four supporting lugs 26 extending upright from the base plate 24 in a rectangular arrangement; e two braces 27 extending between longitudinally aligned supporting lugs 26; e two transversely aligned, inwardly directed scrapers 28 which are supported above respective braces 27, each scraper 28 being sandwiched the brace 27 and a plate 30 there above using bolts which for the purpose of brevity are not referenced with numerals in the drawings; 20 * a cylindrical mesh case or barrel 34 extending longitudinally between the scrapers 28, the barrel 34 being configured as per conventional strainers in that it includes a body having a wall provided with fluid inlet perforations and an outer surface, the barrel and scrapers positioned such that the scrapers contact the barrel outer surface; e a pneumatic actuator 36 whose shaft 38 engages the end of the barrel 34 such that rotation of the 25 shaft causes rotation of the barrel, the shaft being supported by a cross brace 39; e an outlet housing 40 located at the opposed end of the barrel 34 into which the cylindrical barrel 34 is recessed at one end, and to which hose 22 is fitted at the other end using known fastening means; 6 e an outlet housing wear insert 42 which fits into the mouth of the outlet housing 40, the wear insert including a partial "moon-shaped" opening 44 adjacent the bottom of the wear insert; and * an optional outer mesh guard 45 which provides a hard barrier from personal injury during operation. 5 One should already appreciate that the strainer 10 is adapted to be placed into a ground water reservoir and that operation of the pump 14 causes the water 12 to be sucked through hose 22 via the strainer 10. The meshed barrel 34 acts like a sieve and will only allow correctly sized material through so that the pump 14 downstream isn't blocked or damaged. The mesh size will be selected according to the strainer's application. 10 As mentioned in the preamble of the invention, such strainers 10 are prone to blockage themselves if particulate material builds up on meshed barrel 34. For this reason, the strainer 10 is made to be self cleaning and this is where the actuator 36 and scrapers 28 come into play. One can appreciate that if the entire circumference of the barrel 34 is meshed and is exposed to contaminated water, that the entire circumference is prone to blockage. For this reason, it is important that the entire circumference of the 15 meshed barrel 34 is cleaned. The strainer 10 of the present invention achieves this in a fully automated process which will now be described in more detail. The strainer 10 is self cleaning in the way the cylindrical mesh cage or barrel 34 is positioned between scrapers 28 and rotated by 180 degrees to ensure that the entire circumference of the barrel contacts the scrapers 28 and is thus cleaned. Once rotating, the barrel 34 is wiped clean by the two opposing scrapers 20 28 which as mentioned earlier are mounted 180 degrees apart. Figures 3a-3d illustrate the motion of the barrel 34 more clearly and how the scrapers 28 contact the outer surface of the barrel thus clearing the apertures of built up particulate material. Thus, every operation of the actuator 36 guarantees the barrel's circumference has been wiped clean through 360 degrees. The pneumatic actuator 36 is controlled from the air control box 18 which, as shown 25 in the schematic of Figure 4, contains: * an air intake regulator and filter 46; e a 5-port, 2-position duel piloted operated directional control valve 48; e two in-line pressure reducers 50 and 52; e two in-line flow controls 54 and 56; 30 e two air reservoirs 58 and 60; 7 * two "OR" valves (shuttle valves) 62 and 64; e a 5-port, 3-position toggle lever 66; and * two on/off taps 68 and 70. The function of the above components in the air control box 18 is to operate actuator 36 to rotate shaft 38 5 and hence barrel 34 in a 180 degree oscillatory motion. Underground mines typically have compressed air supplied throughout the mine which can be easily tapped into at various locations. The control box 18 is adapted to be tapped into such a line so that compressed air is supplied to the air intake regulator and filter 46 in the control box 18. The basic automatic pneumatic operation sequence is then as follows: (1) air reaches either port "A" or port "B" on the 5/2 pilot operated valve 48; 10 (2) assuming it's port "A", air travels to a first port on the actuator 36 which in turn rotates the barrel 34 in one direction until reaching a limit, at which point back air pressure is built up; (3) air then passes through the inline air pressure reducer 50 to start to reduce air flow and pressure for time delay; (4) air enters the inline flow control valve 54 which give control over timing manually; 15 (5) air passes through the reservoir 58 - the capacity of the air reservoirs determining the automatic delay time that the actuator 36 has between cycles; (6) air then travels to port "B" on the 5/2 pilot operated valve 48 and the steps (2) to (5) are repeated but via inline air pressure reducer 52, inline flow control valve 56 and reservoir 60. In fitting on/off air taps 68 and 70 in the lines between the 5/2 valve 48 and actuator 36, air can be 20 prevented from passing through the pressure reducer, flow control and reservoir, thus providing a manual control over timing of rotation of the barrel 34. The "OR" valves 62 and 64 are used operate the 5/3 toggle lever 66 to allow for manual rotation of the barrel 34. The reader will thus appreciate that when compressed air is supplied to the pneumatic control box 18, the actuator 36 will be triggered to rotate the strainer barrel 34 and effect self cleaning thereof by way of 25 engagement with the scrapers. The reader will also appreciate that operation of the strainer can be controlled and even halted by way of manual override. It is to be understood that while the above description relates to a preferred embodiment of the invention, variations are possible without necessarily deviating from its scope. For example, the extent of rotation of the barrel 34 is not intended to be limited to only 180 degrees. The strainer 10 would still function if there 8 was say one scraper used, with the barrel and associated control configured to cause barrel 34 to oscillate by 360 degrees instead. This would still result in the scraper contacting the entire circumference of the barrel 34. Referring back to the strainer components, the outlet housing wear insert 42 is used to provide a friction 5 reducing surface for the barrel 34 to rotate inside of, and to ensure that no spark can be made from metal rubbing on metal. The half-moon shaped opening 44 allows for fluid to pass through but also acts as an anti-cavitation component by reducing the volume of fluid drawn through the barrel down to the volume of the diameter of the pump hose 22 at the lowest possible level, i.e at ground level. It is to be understood that whilst the strainer 10 works best in ground water reservoirs as shown in the drawings, it could be 10 placed anywhere there is ground water deep enough to cover the half-moon shaped opening 44 of the insert 42. The wear insert 42 would typically be manufactured from a FRAS rated material such as a FRAS rated polyurethane (or at a minimum, an anti static ultra high UHMWPE material which is also often accepted at mines) for environments where there is not to be metal to metal contact, and brass, bronze and other suitable metals in other environments. 15 The size of the self cleaning strainer 10 is generally dictated by the capacity of the pump 14 to be used, material to be pumped, the required flow rates and the amount of air pressure available for supply to the actuator 36. The strainer 10 can be manufactured using a wide range of materials, however, when manufactured for underground mines typically coal mines, materials such as aluminium and non-FRAS rated products are not generally acceptable. In a preferred embodiment, the materials used are as follows: 20 - Parts 24, 26, 27, 34, 36, 39 and 40 - Stainless Steel; - Part 42 - FRAS rated polyurethane; - Part 28 - Friction rated anti-static rubber; The above materials comply with common regulations in most countries such as the Australian Coal Mine Health and Safety Regulation 2006 for example. 25 In above ground environments the use of different alloys, rubbers and plastics could be permissible to manufacture all parts in order for the invention to operate conventionally. This could help to reduce the chance of corrosion, reduce manufacturing costs and reduce the overall weight of the assembly. The skilled addressee should now appreciate that the self cleaning strainer 10 of the present invention has a wide range of operational advantages, including but not limited to: 30 - hardy construction; 9 - simple robust design; - pneumatically controlled; - minimal compressed air usage; - minimal maintenance; 5 - 360 degree barrel cleaning; and - anti-cavitation plate. The strainer 10 overcomes deficiencies present in prior art strainers in that it is designed and configured to be long lasting in a mining environment (owing to its construction and self cleaning capabilities), it is not overly complex or expensive to manufacture, and is capable of meeting occupational health and safety 10 standards in underground mines in that it is pneumatically controlled and constructed to avoid any chance of a spark occurring, which in coal mines is essential to preventing explosions. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the 15 scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of 20 the invention.