Abstract:
A fluid pressure vessel has a filter cartridge with spaced headers positioning cylindrical pleated filter media. The headers form an inlet chamber communicating with the inlet upstream side of the filter media and an isolated outlet chamber communicating with the downstream side of the filter media. A hollow piston with a toothed periphery having a circumferential slot is positioned closely adjacent the upstream side of the filter media. The piston hollow communicates with a drain chamber isolated from the inlet and outlet chambers. Upon opening of the drain chamber to atmospheric pressure, the pressure in the piston hollow and slot causes a lower pressure in a localized area of the media and back flushing of trapped material on the upstream side of the media to the drain chamber. An actuator is connected to selectively progressively move the piston and slot along the entire surface of the media.

Description:
BACKGROUND 
     The present disclosure relates to fluid filtration, particularly filters employed in line for filtering pressurized fluid such as encountered in petro chemical refining, chemical processing, hydraulic fluid systems and filtration of water and aqueous solutions. In such filtration applications, barrier filters comprised of wire mesh, fabric or screens, and combinations thereof, have been employed in a pressure vessel disposed in-line in a fluid system. Typically, the pressure vessel has a removable lid openable for permitting removal and replacement of a filter cartridge. 
     In service, the filter media or barrier causes filtered particles of contamination to accumulate on the inlet or pressure side of the filter and causes an increase in differential pressure across the filter media which, in turn, creates a reduction in the process flow. 
     Heretofore, backwashing by reverse flow has been employed as a means of dislodging filtered particles and contaminates from the surface of the filter media and discharging same to a drain. This often requires shutting down process flow and applying reverse flow pressure to effect the backwashing and also may result in a high volume of contaminated process liquid to be disposed of with the trapped material removed from the filter. 
     In some filtration systems employing a cylindrical configuration for the barrier or filter media, a rotating member has been heretofore employed with a drain port disposed closely adjacent the inlet pressure side of the filter media and rotated thereabout with the port being open to a drain at substantially atmospheric pressure. This has provided a reverse pressure differential between the discharge pressure side of the filter media and the drain port thus providing localized back flushing or backwashing as the ported member is rotated about the cylindrical filter media. This technique is applicable to cylindrical filter media having a generally smooth interior inlet pressure side; however, where the filter media is formed in a cylindrical pleated configuration, the discharge port of the rotating member is ineffective to create a substantial pressure differential in the pleated regions and thus the backwashing is less effective for such filter configurations. 
     Accordingly, it has been desired to provide a way or means for removing trapped particles and contaminants from a pleated cylindrical fluid filter in service without the need to shut down the system and apply backwashing pressure to the outlet or the need for removing the filter media cartridge from the pressure vessel. 
     SUMMARY 
     The present disclosure describes a fluid filtration assembly with a pressure vessel having an inlet and outlet respectively for connection to a fluid pressure supply and discharge line and a drain port for connection to a valve selectively operated for backwashing filtering media disposed in the pressure vessel. A generally cylindrical filter cartridge having round or pleated filter media is disposed in a pressure vessel and defines therein a fluid inlet chamber communicating exclusively with the interior of the filter media and the inlet. The exterior of the filter media is isolated from the inlet chamber in an outlet chamber and communicates exclusively with the outlet. A depending wall portion of the pressure vessel, which may be formed as part of a removable lid, forms a drain chamber isolated from inlet chamber and communicating with a drain. 
     In the presently described filtering assembly a piston with a periphery configured to conform to the pleated configuration of the filter media is disposed in the interior of the filter cartridge and has a peripheral slot formed thereabout which communicates with a hollow in the piston and a purge tube having one end connected to the piston. The opposite end of the purge tube is slidably received into the drain chamber and has a discharge port provided in the end within the drain chamber. An operating member or rod is connected to the end of the discharge tube in the drain chamber and the operating rod extends exteriorly of the pressure vessel through a sliding seal and is connected to an actuator for effecting movement of the operating member discharge, tube and piston along the length of the filter media in the cartridge. In the disclosed version, the actuator comprises a pair of fluid pressure cylinders connected via a yoke member to the exterior end of the operating rod. 
     When back flushing is desired, the drain port is opened to the atmosphere creating a pressure in the piston peripheral port significantly less than the outlet pressure on the exterior side of the filter media thereby creating a localized back flow through the filter media in the region of the peripheral port and the piston causing trapped contaminant material in the localized region to enter the hollow of the piston, the discharge tube for flow outwardly through the discharge port into the drain chamber and out through the drain port. The filter assembly of the present disclosure thus enables backwashing of the filter media interiorly around its circumference at a given station of the piston which is progressively moved along the entire length of the filter media for complete backwashing and which may be accomplished in service without interrupting the process flow. The filter assembly of the present disclosure provides effective backwashing with a minimal amount of contaminated flow to the drain during the backwashing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one version of a filter assembly according to the present disclosure; 
         FIG. 2  is a section view taken along section indicating lines  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an enlarged view of a portion of the section view of  FIG. 2  illustrating the discharge port and drain chamber; 
         FIG. 4  is an enlarged view of another portion of the cross-section of  FIG. 2 ; 
         FIG. 5  is an enlarged view of a portion of  FIG. 1  with the vessel wall and filter media broken away; 
         FIG. 6  is a perspective view of the piston of the filter assembly of  FIG. 1 ; 
         FIG. 7  is a section view taken along section indicating lines  7 - 7  of  FIG. 6 ; and, 
         FIG. 8  is a section view taken along section indicating lines  8 - 8  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , filter assembly in accordance with the present disclosure is illustrated in one exemplary version generally at  10  and includes a pressure vessel having a generally cylindrical wall  12  closed at one end by a flanged header  14  and at the opposite end with a lid  16  secured to a flange ring  18  by suitable fasteners such as bolts  20  extending through the flange ring  18  and the lid  16 . The vessel wall  12  has an inlet fitting  22  provided thereon with an inlet passage  24  communicating with the interior of the pressure vessel wall  12  in a region adjacent the flange  18 . An outlet fitting  26  is provided on the pressure vessel wall  12  adjacent the flanged header  14  and has therein an outlet passage  28  communicating with the interior of the pressure vessel wall  12 . The fittings  22 ,  26  are respectively provided with flanges  30 ,  32  adapted for bolting connection to respectively a pressurized fluid inlet line (not shown) and a fluid pressure discharge on outlet line (not shown). 
     A filter cartridge indicated generally at  34  is received within the pressure vessel and has a generally cylindrical configuration with the filter media formed in a pleated arrangement as denoted by reference numeral  36  in  FIGS. 5 and 8 . 
     Referring to  FIG. 3  and  FIG. 4 , the filter cartridge  34  has formed thereon at the upper end thereof an annular flange  38 , which may be molded onto the pleated filter material  36 , and may include dispersed therein graphite particles for effecting ease of assembly into the pressure vessel and sealing against the inner periphery of the wall  12  between the inlet port  24  and the outlet port  28  and spaced adjacent the inlet port  24 . The annular flange  38  thus divides the interior of the pressure vessel  12  into an inlet chamber  40  in which the interior of the pleated filter material  36  communicates exclusively with the inlet port  24  and is isolated from the outlet port  28 . The annular flange also forms an outlet chamber  42  which is isolated from inlet chamber  40 . The exterior of the pleated filter material  36  communicates exclusively with the outlet port  28  and is isolated from the inlet port  24 . In service, the inlet chamber is exposed to an inlet pressure P i ; and, the outlet chamber  42  is at a discharge pressure P o  which differs from P i  by the amount of the pressure differential due to filtering across the pleated filter material  36 . 
     Referring to  FIGS. 4 ,  5 ,  6  and  7 , a piston indicated generally at  44  is disposed in the interior of the cartridge  34  and has the outer periphery thereof configured in a generally toothed configuration as denoted by reference numeral  46  and piston  44  has a centrally disposed tubular hub  48  formed thereon which has the inner periphery  50  thereof communicating with a hollow chamber  52  formed in the piston  44 . The piston also has a plurality of fluid flow apertures  54  formed therethrough for permitting free passage of fluid to opposite sides of the piston. 
     Referring to  FIGS. 6 and 7 , the piston  44  has formed about its periphery in teeth  46  a peripheral slot  56  which extends through the teeth  46  and communicates the exterior of the teeth with the hollow  52  of the piston. In the present practice, for filtering fluids at elevated temperatures, the piston may be formed of a cast metal such as alloy or stainless steel. For applications filtering only unheated fluids, the piston may alternatively be formed of suitable polymer material. The slot  56  thus ports the hollow  52  of the piston to the pressure P i  in the interior inlet chamber  40  during service. In the present practice it has been found satisfactory to space the piston slot  56  about 2.0 mm from the interior surface of the pleated filter material  36 . 
     Referring to  FIGS. 2 ,  4  and  5 , the pressure vessel wall is provided with a depending portion  58  which may comprise a lower end portion  58  of a tubular member  60  which extends upwardly and outwardly through the lid  16 . The upper end of the tube  60  is closed by a cover plate  62  secured to an annular flange  64  formed about the upper end of the tube  60  by suitable means such as bolt  66 . The lower end  58  of the tube  60  has an annular plug  68  provided therein; and, the plug  68  has received therein the upper end of a purge tube  70  which has its lower end attached to the hub  48  of the piston  44  such that the inner periphery of the tube  70  communicates with the hollow  52  of the piston. The upper end of the purge tube  70  has a discharge port  72  formed therein which communicates the interior of the tube  60 . The upper end of tube  70  is slidably received in and sealingly engaged with the inner periphery of the annular plug  68  so as to define a drain chamber  74  within the tube  60 . The interior of tube  70  thus is communicated with drain chamber  74  through discharge port  72 . In the present practice the purge tube also may be formed of alloy or stainless steel. 
     Referring to  FIG. 3 , the annular plug  68  is shown as having an annular sliding seal  76  provided thereon for slidably engaging and sealing against the outer periphery of tube  70 . 
     The lower end of tube  70  is secured onto the hub  48  of piston  44  by any suitable expedient as, for example, adhesives or weldment in such a way that the hollow  52  of the piston and the interior of tube  70  are isolated from the fluid pressure P i  in the inlet chamber  40 . 
     Referring to  FIGS. 2 and 3 , the upper end of the purge tube  70  is connected by a suitable main such as annular coupling  78  to an operating member or rod  80  which extends upwardly through the cover plate  62  in sliding sealed engagement so as to maintain the integrity of the drain chamber  74  isolated from the atmosphere. 
     Referring to  FIGS. 1 and 2 , the drain fitting  82  is provided on the exterior of the tube  60  and has a drain port formed therethrough which communicates through the wall of tube  60  to the drain chamber  74 . The outer end of the fitting  82  has a flange  86  provided thereon which is adapted for connection to a drain line such as shown in dashed outline at  88  in  FIG. 2 . The drain line  88  may be connected to a remotely operated valve indicated in dashed outline at  90  in  FIG. 2  which, upon opening connects the drain chamber  74  to substantially atmospheric pressure P ATM  for discharge of backwash and filter contaminants. Valve  90  is normally closed. 
     Referring to  FIG. 1 , the operating rod  80  has its upper end connected to a yoke  92  which has its opposite ends connected to respectively piston rods  94 ,  96  which rods extend from respectively fluid power cylinders  98 ,  100  which if desired, may be mounted on the lid  62  as shown in  FIG. 1 . Upon the selected introduction of pressure into the fluid power cylinders  98 ,  100 , the piston rods  94 ,  96  move the yoke  92  upwardly to raise the operating rod  80  and pull the discharge tube  70  and piston  44  upwardly along the inner surface of the pleated filter media  36 . 
     In operation, process flow enters inlet port  24  at the supply pressure P i  in the inlet chamber  40  and flows outwardly through the pleated filter media  36  into the discharge chamber  42  and to the discharge port  28  at the outlet pressure P o . In service debris or solids filtered from the fluid accumulate on the interior surface of the fitter media  36  thus causing changes in the pressure differential between P i  and P o  thereby necessitating a cleaning operation as will be hereinafter described. 
     When it is desired to backwash the filter material  36  and cartridge  34 , the drain valve  90  is opened causing a sudden reduction of pressure to atmospheric in the drain chamber  74  and discharge port  72  and the interior of the discharge tube  70  and piston hollow  52 . The sudden reduction of pressure in the piston hollow  52  is applied through the peripheral slot  56  to the teeth  46  of the piston and locally to the inner surface of the pleated material  36  adjacent the slot  56  in each pleat. The sudden drop of pressure in the local area between the inner surface of the pleated media and the face of the teeth of the piston creates a pressure differential between the interior of the pleat in the local area of the slot  56  and the external pressure P o  in the chamber  42  thereby causing back flow in the localized region adjacent the slot  56  and removal of contaminant from the interior surface of the pleated material in the localized region and flow into the hollow  52  of the piston upwardly through discharge tube  70  and through discharge port  72  into chamber  74  and outwardly through the port  84  and drain tube  88 . When the drain valve  90  is opened to initiate back flow through the slot  56  in the piston  44 , the yoke  92  is raised by actuation of the power cylinders  98 ,  100  and movement of rods  94 ,  96  which moves the piston  44  upwardly progressively along the interior surface of the pleated material  36  such that the entire inner periphery of the cartridge  34  is purged of contaminant with minimal affect on the process flow because the balance of the filter cartridge  34  not exposed to the back flow is undisturbed and the filtering can continue in a normal operative manner. 
     The present disclosure thus describes a filter assembly which, upon activation of the remotely operated drain valve and power actuators, is operative to progressively remove contaminates from the interior of the cylindrical filter cartridge having pleated filter media material along the length of the cartridge without interrupting the normal process flow through the filter assembly. 
     The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.