Abstract:
The present invention discloses a system and method for self-cleaning filters without having to open the filter housing. Wash nozzles are integrated with the filter housings such that when the filters are clogged, both back-wash and regular washing can be performed with practically no down time. Moreover, without opening the filter housing, the hazardous components of the fluid to be filtered can be contained and dealt with before they escape the filter housing, thereby significantly reduces the environmental impact and harm to the working crew.

Description:
PRIOR RELATED APPLICATIONS 
       [0001]    This invention claims priority to U.S. 61/594,544, filed on Feb. 3, 2012 and incorporated by reference in its entirety herein. 
     
    
     FEDERALLY SPONSORED RESEARCH STATEMENT 
       [0002]    Not applicable. 
       FIELD OF THE DISCLOSURE 
       [0003]    The disclosure generally relates to a system and method for self-cleaning a filter, and more particularly to a system and method for self-cleaning a filter with a nozzle integrated to the filter housing such that the filter can be cleaned without opening the filter housing. 
       BACKGROUND OF THE DISCLOSURE 
       [0004]    Industrial filtration systems generally comprise multiple cartridge filters located within corresponding filter housings, and fluids to be filtered (influents) are supplied to the filter housings for the removal of debris, contaminants and particles. These cartridge filters generally have a cylinder shape with a hollow core. Influents are supplied to the hollow core and flowing outwards through the media of the cartridge filters, leaving debris, contaminants and particles at the surface of the media. After conducting such fluid processing for a period of time, the debris and particles will accumulate and clog the filter media, causing the drop of filter efficiency. In worse situations, a cake may aggregate at the inner surface of the filter cartridge and the filter will not function. Therefore, the cartridge must be cleaned and/or replaced after a period of operation. The cleaning of a filter generally involves shutting down the filtration operation, removing the cartridge, and manually spraying the surface to remove the residue so collected. 
         [0005]    Another often performed filter cleaning procedure is called “backwash,” where the fluid flow within the filter housing is reversed, and the accumulated debris and particles can be washed by the fluid and drained. However, such backwash procedure suffers a drawback in that the flow of the backwash fluid may not be strong enough to remove or blast the aggregated particulate material or debris on the filter. 
         [0006]    WO2009114128 discloses a spraying device that can move along a filter surface to emit a jet of cleaning fluid to remove residue from the filter surface. Specifically, the nozzle can move along the length of a filter cartridge to spray the cleaning fluid at the surface of the cartridge. However, such design fails to take into consideration the possible liquid/gas escape during cleaning, which may cause health and environmental concern when the influent contains hazardous components. Furthermore, the design cannot be used with a backwash cycle to improve the cleaning efficiency. 
         [0007]    Therefore, there is a need for a filter cleaning apparatus and method that is also able to work in combination with a backwash operation to improve the cleaning efficiency. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    The present invention relates to an apparatus for cleaning a filter within a filter housing without the need to first remove the filter from the filter housing. Specifically, the present invention discloses a wash nozzle integrated with the filter housing in a cylinder mounted on the filter housing so that the cylinder can move the wash nozzle up and down inside the filter housing within the hollow core of the filter cartridge. Moreover, the wash nozzle is connected to a source of wash fluid through a wash pipe, which is concentrically surrounded by a purge pipe that connects to a drain for purging the fluid and debris during backwash stage. A gas injection inlet is also provided for introducing a pressurized gas that causes turbulence inside the filter housing to “bubble off” (dislodge) the accumulated solids on the filter, especially the inner surface of the hollow core. A purge inlet is provided near the wash nozzle. Sealing mechanism is provided in the system especially where the cylinder is connected to the filter housing to prevent leaking that hinders regular filtration operation. 
         [0009]    The present invention also provides a method for self-cleaning a filter cartridge within a filter housing without opening the filter housing. A wash nozzle is integrated to the filter housing by a cylinder, a gas injection inlet is provided on the filter housing, and the method comprises closing the fluid inlet by terminating the fluid inlet to the inlet housing; closing the drain to the filter housing so that the filter housing is filled with fluid; initiating a back-wash by introducing a high-pressure gas into the interior of the filter housing through the gas injection inlet at a pressure capable of creating turbulence that will dislodge particulate matter or debris from the core of the filter while positioning the wash nozzle at proper location inside the filter housing; and forcing the fluid out of the filter housing with the gas whereby the particulate matters from the interior of the filter cartridge is purged from the filter housing through the purge pipe near the wash nozzle. 
         [0010]    This invention also provides a method for self-cleaning the filter cartridge without opening the filter housing, in which the filter cartridge has a hollow core and the filter housing further comprises a fluid inlet connected to the hollow core, and a wash nozzle and wash pipe mounted on the filter housing capable of traveling through the hollow core of the filter cartridge. The method comprises the steps of: closing the fluid inlet to the filter housing, washing the filter cartridge by spraying a high-pressure wash fluid from the wash nozzle to break the particulate build-up on the hollow core; and draining the wash fluid and debris from the fluid inlet by switching on a drain valve fluidly connected to the fluid inlet, wherein the drain valve directs the fluid from the fluid inlet to a drain pipe. 
         [0011]    A processor with sensors can detect pressure build up within the filter housing to determine the initiation of the self-cleaning process. A processor can control the backwash and washing process using sensors to detect fluid levels and operation of the apparatus. 
         [0012]    As used herein, a “pressurized gas” means a gas having a pressure equal to or greater than 20 psi. The exact pressure used may be adjusted based on system design and depending upon the type of particulate matter or debris being filtered, but in any case sufficient to dislodge particulate matter or debris from the filter core. 
         [0013]    As used herein, a “high-pressure fluid” means a fluid sprayed by the nozzle at a pressure equal to or greater than 100 psi. The exact pressure used may be adjusted based on system design and depending upon the type of particulate matter or debris being filtered, but in any case sufficient to clean the inside of the filter core. 
         [0014]    As used herein, “influent” means the fluid to be introduced to and filtered by the filter. 
         [0015]    The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise. 
         [0016]    The term “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated. 
         [0017]    The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive. 
         [0018]    The terms “comprise”, “have”, “include” and “contain” (and their variants) are open-ended linking verbs and allow the addition of other elements when used in a claim. 
         [0019]    The phrase “consisting of” is closed, and excludes all additional elements. 
         [0020]    The phrase “consisting essentially of” excludes additional material elements, but allows the inclusions of non-material elements that do not substantially change the nature of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a cross-section of the filter housing and the placement wash nozzle assembly during filtration stage with the arrows indicating flow during filtration. 
           [0022]      FIG. 2  is a detail cross-sectional view of the purge inlet near the wash nozzle. 
           [0023]      FIG. 3  is a detail cross-sectional view of the top of the wash pipe assembly showing the purge pipe and the wash pipe connections. 
           [0024]      FIGS. 4A-C  are cross-sectional views of the backwash stages. 
           [0025]      FIGS. 5A-C  are cross-sectional views of washing stages. 
           [0026]      FIG. 6A  is a schematic cross-sectional view of the system where the cylinder is fully extended and the wash nozzle is at the top of the filter housing and  6 B is a schematic cross-section with cylinder in the down position. 
           [0027]      FIG. 7  is a cross-sectional view of the present invention being used in two or more filter housings and wash assemblies. 
           [0028]      FIGS. 8A-B  combined are a flow chart illustrating the basic logics of the method of this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The invention is a novel system and method for self-cleaning filter cartridges without opening the filter housing. In one aspect of this invention, a system is provided for cleaning a filter cartridge located within a filter housing, the filter cartridge having a hollow core, the system comprising: a) a wash nozzle integrated in a filter housing, the wash nozzle on a movable cylinder mounted on top of the filter housing, wherein the wash nozzle is fluidly coupled to a source of wash fluid through a wash pipe located in the cylinder within the hollow core of the filter cartridge and capable of moving vertically within the hollow core by raising and lowering the cylinder; b) a purge pipe concentrically surrounds the wash pipe and forms a purge inlet to form an annular space around the wash pipe capable of fluid travel and terminates near the wash nozzle; c) the filter housing having a fluid inlet for introducing a fluid to be filtered, and a fluid outlet for draining filtered fluid, wherein the fluid inlet is fluidly coupled to the hollow core of the filter cartridge; and d) a processor controlling the movement of the wash nozzle. 
         [0030]    In another aspect of this invention, there is provided a method for self-cleaning a filter cartridge located within a filter housing without opening the filter housing, the filter cartridge having a fluid outlet, a hollow core fluidly connected to a fluid inlet of the filter housing, a gas injection inlet, and a wash nozzle and purge pipe mounted on the filter housing in a cylinder on top of the filter housing, the method comprising the steps of: a) terminating the fluid inlet to the filter housing; b) closing the fluid outlet to the filter so that the filter housing is filled with fluid; c) placing the wash nozzle and the purge pipe at the top of the filter housing; d) initiating a back-wash by introducing a high-pressure gas into the interior of the filter housing; and e) forcing the fluid out of the filter housing with the gas with particulate matter from the interior of the filter cartridge through the purge pipe. 
         [0031]    In yet another embodiment of this invention, there is provided a method for self-cleaning a filter cartridge located within a filter housing without opening the filter housing, the filter cartridge having a hollow core, the filter housing having a fluid inlet for introducing the influent, and a wash nozzle and wash pipe mounted on the filter housing capable of traveling through the core of the filter cartridge, the method comprising the steps of: a) closing the fluid inlet to the filter housing; b) washing the filter cartridge by spraying a high pressure wash fluid introduced through the wash nozzle to break the particulate build-up on the hollow core; and c) draining the wash fluid and debris from the filter housing through the filter inlet. 
         [0032]    In still another aspect of this invention, there is provided a method for self-cleaning a filter cartridge located within a filter housing without opening the filter housing, the method comprising the steps of: a) closing a fluid inlet to the filter housing so that the filter housing is substantially full of fluid; b) gradually introducing pressurized gas into the filter housing such that the gas creates turbulence that will dislodge particulate matter from the interior of the filter core; c) backwashing the filter core by purging the fluid inside the filter housing and the dislodged particulate matter by providing a purge exit from the filter housing utilizing the force of the pressurized gas; d) terminating the backwashing by ceassation of introduction of pressurized gas in the filter housing and closing the purge exit; e) washing the filter cartridge by spraying a high-pressure wash fluid to the interior of the filter core to remove any additional particulate matter; and f) draining the wash fluid with any particulate matter from the filter housing. 
         [0033]    In one embodiment, the purge pipe is not in fluid communication with the wash pipe, and the purge pipe is fluidly connected to a purge drain pipe. 
         [0034]    In one embodiment, the fluid inlet is connected to an inlet valve and a drain valve, both of which are operably connected to the processor, which controls the opening and closing of the valves. The fluid outlet is fluidly connected to an outlet valve that is also controlled by the processor. 
         [0035]    In one embodiment, the fluid housing further comprises a gas injection inlet for introducing a pressurized gas, which creates turbulence in the filter housing and forces the fluid through the annular space between the wash pipe and the purge pipe. 
         [0036]    In one embodiment, the method also includes detecting the pressure difference during the filtration process to determine when to start the self-cleaning method when the pressure difference reaches a predetermined value. The method also includes detecting the fluid level inside the filter housing and lowering the purge pipe at a position below the fluid level inside the filter cartridge as the fluid is forced out of the filter housing. 
         [0037]    In one embodiment, the method also includes, during backwash, moving the wash nozzle from the top to the bottom of the filter housing when purging fluid, thereby completing a backpulse. The method also includes, during washing, moving the wash nozzle from the bottom to the top of the filter housing and then back to the bottom, thereby completing a wash stroke. In one embodiment, the number of backpulses and wash strokes is preselected depending on the degree of clogging and the nature of the deposited particulate matter. 
         [0038]    From here on, detailed explanation of the system and method of this invention will be made with reference to the drawings. The following examples are intended to be illustrative only, and not unduly limit the scope of the appended claims. 
         [0039]    Referring to  FIG. 1 , which shows the wash nozzle assembly  110  integrated with a filter housing  101 . Filter cartridges  104 ,  105  are located within the filter housing  101 , although more than two cartridges can be used. Also, if desired only one cartridge can be used. The filter cartridges have connected hollow core  103  that is fluidly coupled with a fluid inlet  122  at the bottom of the filter housing  101 . The filter cartridges are connected with a fluid tight seal  106 . The fluid inlet  122  is further connected to an inlet valve  124  and a drain valve (not shown). During filtration stage, the inlet valve will open to allow a fluid to be filtered being supplied to the filter through the fluid inlet  122 . During washing stage, as discussed later, the drain valve will open such that the wash fluid and debris can be drained through the fluid inlet. 
         [0040]    The filter housing further comprises a fluid outlet  120 , which is further connected to an outlet valve (not shown). During the filtration stage when the fluid enters core  103  under pressure, the outlet valve is open such that the filtered fluid can exit the filter housing through the fluid outlet  120 . 
         [0041]    The wash nozzle  110  is integrated with the filter housing through a cylinder  108  mounted on the top cover  107  of the housing  101 . The wash nozzle  110  is coupled to a wash tube  114  that is concentrically surrounded by a purge tube  112 . Both the wash tube  114  and purge tube  112  are fixed to the top of cylinder  108 , such that the cylinder can move with the wash nozzle along the hollow core  103 . The cylinder is preferably pneumatically operated, with the pneumatic fluid supplied to the cylinder. In  FIG. 1  two pneumatic fluid inlets  109   a ,  109   b  are shown. 
         [0042]    Details of the wash nozzle are shown in  FIG. 2 , to further illustrate the annular purge inlet  115  near the wash nozzle  110 . As discussed above, the wash nozzle  110  is connected to a wash pipe  114  that is surrounded by a purge pipe  112 . Toward the nozzle  110 , the purge pipe  112  is a bit shorter than the wash pipe  114  such that an annular opening  115  is present that serves as a purge inlet during back-washing stage. It is noted that the annular space between the wash pipe  114  and purge pipe  112  is not in fluid communication with the core of wash pipe  114  such that the fluid in each space will not be mixed. 
         [0043]    Also referring to  FIG. 3 , which shows the downstream/upstream piping connection for purge pipe  112  and wash pipe  114 . As shown in the figure, wash pipe  114  is connected to a path  118  that further connects to a wash fluid valve (not shown) and a wash fluid source. The purge pipe  112  is connected to a purge path  116  that further connects to a purge valve and a drain pipe. The functionalities of these pipes and valves will be discussed in further detail below. 
         [0044]    Referring back to  FIG. 1 , the filter housing  101  also comprises a gas inlet  102  for introducing high-pressure air or gas during the back-wash stage. As shown in the figure, the wash nozzle  110  rests at the bottom of the filter housing inside the hollow core. This is the preferred position for the wash nozzle  110  during especially the filtration stage, because the cylinders are in the lowered, more stable position. 
         [0045]    The system further comprises a processor (not shown) for controlling all the valves, the movement of the wash nozzle, and the gas injection. The system also comprises fluid level sensors for detecting the fluid level inside the filter housing, pressure sensors for detecting the pressure difference between the inside and outside of the filter cartridge, and position sensors for detecting the position of the wash nozzle. These sensors are also operably connected to the processor. The embodiments of the features are well known in the art and discussed below in detail of the operation. 
         [0046]    Referring to  FIG. 6A , which shows the cylinder  150  fully extended and the wash nozzle  110  is therefore at the top of the filter housing  101  within the hollow core  103 . In  FIG. 6B , the cylinder  150  is fully refracted and the wash nozzle  110  is therefore at the bottom of the filter housing  101  within the hollow core  103 . The cylinder is preferably pneumatically operated with seals (not shown) preventing the gas and/or fluid from escaping the filter housing. 
         [0047]    With configuration of the present invention, especially the feature that the wash nozzle is integrated within the filter housing, whenever a cleaning of the filter cartridge is necessary, there is no need to open the housing and remove the filter cartridge for cleaning as conventional design, which would cause significant downtime for the filtration operation and increase and operational cost. As explained below, the backwash and washing stages of the present invention ensures the satisfactory cleaning without the downtime. Furthermore, in the case where the fluid to be filtered contains hazardous gas or particles, such as greenhouse gases, the present invention effectively prevents those gases or particles from escaping the filter housing into the atmosphere. This feature has significant application for a greener and safer environment. 
       Filtration Stage 
       [0048]    Referring back to  FIG. 1 , which shows the filter system of the present during regular filtration operation. The processor opens the inlet valve  124  such that the fluid to be filtered can enter the filter housing through the fluid inlet  122 . The arrows indicate the direction of the fluid to be filtered. After the fluid enters the filter housing, it will flow radically outward from the hollow core  103  to pass through the filter medium  105 . As noted above, the wash nozzle  110  is lowered to the bottom of the filter housing for better stability. 
         [0049]    The particles or other impurities in the fluid cannot pass through the filter medium  105  and therefore remain on the surface of the hollow core  103 . After filtering for a period of time, the accumulated particles and impurities aggregate to block and clog the available passageway for fluid in the filter. As clogging worsens, the pressure difference between the hollow core and outside of the filter will increase, and when the pressure difference reaches a detectable predetermined maximum, self-cleaning can be activated. 
       Back-Wash Stage 
       [0050]    Referring now to  FIGS. 4A-C , which illustrates the back-wash stage of the present invention. It is called the “back-wash” because the fluid is now flowing in the direction opposite to the filtration stage. The fluid inlet  122  from the filter housing is closed, as is the fluid outlet for filtered fluid. Referring to  FIG. 4A , which shows the beginning of the back-wash stage. As shown in the figure, the wash nozzle  110  is first raised to the top of the filter housing  101 , while the filter housing is filled with air through inlet  102  and creates pressure and turbulence on the fluid inside the filter. This forces fluid and particles from the inside of the filter through the annular purge inlet  115  and out of the purge pipe  116  as discussed below. The position sensor and fluid level sensor detects the position of the wash nozzle  110  and the fluid level inside the filter housing, respectively. The processor ensures that the wash nozzle  110  and the purge inlet  115  stays below the fluid level during the backwash stage. In this embodiment the wash fluid is water, but other wash fluids are possible, depending on the accumulated solids to be cleaned. 
         [0051]    High pressure air is then injected into the filter housing through the gas inlet  102 . Although in this embodiment air is used, other high-pressure gas can also be used. The high pressure air will cause violent turbulence in the water inside the filter housing, especially in the hollow core, and thereby knocking off a portion of solids accumulated on the inner surface of the hollow core. At the same time, the processor will open the purge valve that connects to the purge pipe  112  and the purge inlet  115 , thereby providing a low pressure exit. The high pressure air and the turbulent water will naturally flow to the low pressure exit, and thereby drain by the purge pipe. 
         [0052]    As shown in  FIG. 4B , the water level drops with the water being drained through the purge pipe. The injection of high pressure air continues and further removes solids accumulated on the hollow core. The empty space above the water level will be occupied by high pressure air which further pushes the water to leave through the purge pipe.  FIG. 4C  shows that the water level continues to drop. The back-wash stage will complete when the position sensor senses that the wash nozzle reaches the bottom of the filter housing. At that point the processor will stop air injection and close the purge valve. 
       Washing Stage 
       [0053]    Referring to  FIGS. 5A-C , which shows the washing stage of the present invention. Generally speaking in the washing stage the wash nozzle  110  will travel from bottom to the top of the filter housing and then travel back down to the bottom to complete a “stroke.” However, multiple strokes of moving up and down the filter housing may also be preferred if that enhances the cleaning efficiency. Referring to  FIG. 5A , which shows the start of the washing stage. The processor opens the wash valve and the discharge valve (both not shown for well known in the field) such that high-pressure wash fluid is supplied to the nozzle  110  through wash line  118 , and the pressurized sprays the interior hollow core to remove any additional particulate accumulated. The processor also opens the drain valve for draining the water and debris through the fluid inlet. As shown in  FIG. 5B , the processor controls the cylinder such that the wash nozzle  110  gradually moves up the filter housing  101  along the hollow core  103  while spraying high pressure water to continuously break down the accumulated solids. As shown in  FIG. 5C , half of the washing stage cycle is marked by once the position sensor detects that the wash nozzle  110  reaches the top of the filter housing  101 . The processor then brings the wash nozzle  110  gradually down to the bottom, while still spraying. This cycle, beginning from the wash nozzle  110  from the bottom to the top and back to the bottom of the filter housing, is called “one stroke.” If an operator determines that one stroke is sufficient to clean the hollow core of the filter cartridge, the washing stage ends and the processor then closes the wash valve, the discharge valve and the drain valve. If, however, the operator determines that more strokes of washing are required, for example because the accumulated solids are stubborn to be removed, then a stroke counter will add “1” after each stroke and the washing stage will not stop until the stroke count reaches what the operator sets. 
       Employing the System in Two or More Filters 
       [0054]    Referring now to  FIG. 7 , which shows the system being employed in two parallel filters. It is to be noted that the system can be employed in an array of filters by the same configurations, and it is for simplicity purpose to show only two filters. In this figure, two filter housings  101 ,  201  are joined together, and most configurations are the same as in  FIG. 1 , except that the fluid inlets from both housings are jointly controlled by the same inlet valve  144  and drain valve  142 , the fluid outlets from both housings are jointly controlled by the same outlet valve  140 , and the gas injection inlets are jointly controlled by the same gas injection valve  130 . This way, the filtration, backwash and washing stages are activated and controlled together by the same processor for both filters. By this pairing up configuration, the self-cleaning system and method of this invention can easily be employed for an array of filters. 
       Method of the Self-Cleaning Method 
       [0055]    Referring now to  FIGS. 8A and 8B , which combined shows the basic logics of the filter self-cleaning method of the present invention. In step  801 , the system is activated in auto-run mode, and the processor will execute a predetermined plan for self-cleaning, including the backwash stage and washing stage. In step  802 , the processor reduces the flow rate to 66% (2/3) of normal setting by partially closing the inlet valve. This is done especially in the filter array setting where some filter housings are undergoing self-cleaning, and the flow rate is therefore reduced for other on-line filters in order not to overload them. The number is variable depending on the settings and actual conditions. In step  803 , the processor will determine whether the current station (station  1 ) is locked out. This means that any command sent to the filter station will be ignored. The station has to be locked out before the self-cleaning can begin and there will be no filtration, back-wash or washing at this step. If station  1  is locked out, the system proceeds to step  846 , where the processor will determine if the next available filter station  2  is locked out. This is because the system is configured such that lock-out only occurs when a problem exists in the filter housing, which makes it unable to take command until the problem is fixed. But if station  1  is not locked out, the system proceeds to step  804 . With regard to the current station  1 , step  846  is a place holder in the logic, as is station  2 . 
         [0056]    In step  804 , the operator will determine the number of backpulse and strokes to be performed in the self-cleaning cycle. A backpulse is one round of backwash, meaning the wash nozzle  110  travels in the backwash step shown in  FIGS. 4A-C  from top to bottom once and stops. A stroke is one round of washing, meaning the wash nozzle  110  moving from the bottom of the filter housing to top and back to the bottom. The number of backpulse and stroke may vary, depending on how clogged the filter is or the nature of the solids. If the filter is very clogged or the accumulated solids are known to be hard to break, the operator may choose to perform more than one backpulse or more than one stroke for the cleaning cycle. Whether the predetermined number of backpulse/stroke has been performed will be tracked by the backpulse counter and the stroke counter later in the cycle. 
         [0057]    Steps  805  to  814  are related to the backwash stage as illustrated in  FIGS. 4A-C . In step  805 , the cylinder is raised to move the wash nozzle to the top of the filter housing in preparation of the backwash purge. In step  806 , the position sensor will confirm that the cylinder (and the wash nozzle) is raised to the top of the filter housing. In step  807 , the system starts preliminarily inject air through the gas injection inlet for 10 seconds, so as to build up sufficient air pressure inside the housing, and then in step  808  the gas pressure sensor will determine whether the gas pressure within the housing is sufficiently high. As discussed above, the gas pressure is important both to create violent turbulence in the fluid to break off the solids, and also pushes the fluid toward the purge pipe. Typically the system will determine a 25 psi gas pressure to be sufficient, but it can vary depending on different system requirement, for example in some instance 20 psi may be sufficiently high for backwash to proceed. If in step  808  the processor determines that the pressure is high enough, the system proceeds to step  812 . If in step  808  the system determines that the gas pressure is not high enough, in step  809  the system will continue the preliminary air injection for another 30 seconds, and check the pressure again in step  810 . If the pressure is still not reached, the self-cleaning cycle may be terminated due to the loss of air pressure from external air supply, and the process cannot continue until the problem is addressed. If the pressure is sufficiently high, the system will proceed to step  812 , where the processor will open the purge valve for draining the fluid within the filter housing, and gradually lower the cylinder to keep the wash nozzle and purge inlet below the fluid level for purging the fluid through the purge inlet and purge pipe. In step  813 , the position sensor will confirm that the cylinder and thus the wash nozzle are down to the bottom of the filter housing to complete one “backpulse,” and in step  814  the processor stops the air injection and closes the purge valve. 
         [0058]    Steps  815  to  821  are preparation for washing stage. In step  815 , a fluid level sensor at the wash fluid source detects whether enough wash fluid is present. If there is, the system proceeds to step  816 , and if not the system proceeds to step  820 , where the processor determines that no wash fluid is available, and closes all the valves and returns to the main screen with an “error warning” in step  821 . In step  816 , where previously determined that sufficient fluid is available, the processor will open the source and suction valves near the fluid tank. This is simply a designer&#39;s choice to have more than one fluid tank as the fluid source, and each tank has its own source and suction valve for proper fluid supply. For example, if one fluid tank is low in reserve the system can switch to the other fluid tank for washing while the first tank is filled up. Alternatively, the system can be equipped with one larger fluid tank that will not be depleted. Or in another embodiment, the wash fluid is supplied from the already filtered fluid from other filters in the filter array such that continuous and replenishing supply of wash fluid can be accomplished. In step  817 , the system will determine whether the wash pump is primed, and if it is the system proceeds to step  822 , but if not the system proceeds to step  818 . By “primed” it means that there is sufficient fluid in the pump for proper fluid supply, and that there is no air present in the pipelines, because air will cause pressure drop in the pump, which in turn results in insufficient pumping. If the system determines that the wash pump is not primed, the system proceeds to step  818 , where the wash pump prime vent will be opened for 1 minute to vent off the existing air in the wash pump and continues to prime the pump. In step  819  the system will check the wash pump primer level again, and if it is satisfactory, the system proceeds to step  822 . If the primer level of the wash pump is still not high enough, it means no wash fluid is available in step  820 , and the processor closes all valves and return to main screen with an “error” warning in step  821 . 
         [0059]    Steps  822  to  834  discuss the washing stage, especially one “stroke” of washing. In step  822 , the processor opens the discharge valve near the wash pump, the drain valve connected to the fluid inlet, the water wash valve and the wash prime vent. As discussed above, the discharge valve is the result of having two alternate fluid tanks, and may be omitted if only one fluid tank is used. The wash prime vent is a vent for excluding air from the wash pump. When all valves are opened, the wash prime vent is closed to prevent air from entering the wash pump. The system then proceeds to step  823  to start wash pump for 5 seconds for the wash fluid to fill up the pipelines. In step  824 , the system checks the output pressure of the wash pump. If the output pressure is not enough, the system proceeds to step  826  with a wash pump error, and stops the pump and closes all valves in step  827 . The self-cleaning cycle will be terminated. If the output pressure is sufficient in step  824 , the system proceeds to step  825 , where the cylinder and thus the wash nozzle will be gradually raised while spraying high-pressure wash fluid to the surface of the hollow core to break off the solids. The sprayed wash fluid and debris is drained through the fluid inlet. 
         [0060]    During this washing stage, the wash pump pressure is still continuously checked in step  828 , and if insufficient pressure is found in step  829 , the cycle is again terminated. If the system determines that the pump pressure is sufficient, in step  830  the position sensor determines whether the cylinder and wash nozzle are all the way to the top of the filter housing. Once reaching the top of the filter housing, the processor lowers the cylinder and the wash nozzle while continuously spraying high-pressure wash fluid to the surface of hollow core. The entire stroke is completed when the cylinder and wash nozzle is at the bottom of the hollow core in step  832 , and the processor will confirm that the cylinder and wash nozzle are down in step  833 . In step  834 , the processor determines whether the predetermined number of strokes has been reached, and if not, the processor will add “1” to the stroke counter and starts over from step  825  to run another stroke. If, however, the predetermined number of strokes is reached, the system proceeds to step  836  where the wash pump is stopped and all valves are closed except for the drain valve. 
         [0061]    In step  837 , additional air is injected for 10 seconds to push any remaining wash fluid and debris down the fluid inlet. Then, the system confirms that low level sensor is off, which means that the filter housing is now empty. Then air injection is stopped, and the drain valve is closed. 
         [0062]    In step  838 , the processor determines whether the predetermined number of backpulse has been reached. If not, in step  839  the processor adds “1” to the backpulse counter, and reset the stroke counter to 1 for the next cycle. Then in step  840  the processor opens the fluid inlet and vent valves to re-fill the vessels to get ready for the next round of backwash. In step  841 , the system confirms that the high fluid level sensors are on, which detect the fluid level inside the filter housing. At this stage water is introduced into the filter housing through the fluid inlet and fill up the filter housing before the air is injected. The air originally existed in the filter housing leaves through the vent. In step  842 , the filter housing is full of water, and the processor closes the vent valve, and the system is now ready for another round of backwash and wash. 
         [0063]    In step  843 , the system opens the fluid inlet and the system vent, readying the filter housing to be filled. The fluid to be filtered will be introduced through the fluid inlet, until in step  844  the level sensors confirms that the filter housing is full, i.e. the high level sensor in the filter housing is on, while the air leaves through the system vent. The processor then closes the vent and open the fluid outlet, and the filtration can begin. 
         [0064]    Based on the discussion above, the self-cleaning filter system and method can clean the filter without opening the filter housing. This significantly reduces the cost for cleaning the filters because there is practically no down time comparing to conventional cleaning because the time for the self-cleaning backwash and washing cycles is minimal compared to shutting down the whole filter, open the filter housing, manually remove the filter and clean it and then put it back. In addition, in an array of filter housings having the self-cleaning apparatus of the present invention, most filters in the array can continue the filtration operation while some filters are being cleaned by the self-cleaning apparatus and method, thereby maintaining the operation output for the array. More importantly, the self-cleaning system assures that the hazardous gases from the filtration process do not escape to the atmosphere and do not harm the working personnel or environment. What is claimed is: