Abstract:
In a liquid filter of the reverse-flow flush-cleaning type, the present invention provides the improvement of mounting the pack of discs ( 170 ) intermediate to an assembly including a seat member ( 200 ) and screw-thread split-ring ( 202 ).

Description:
The present application is a non-provisional application of International Application No. PCT/IL2004/000862, filed Sep. 19, 2004. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to liquid filters, particularly for water irrigation systems, however also useful for other industrial or domestic applications. 
   More specifically, the invention concerns filter devices of the type disclosed in our U.S. Pat. No. 6,398,037 issued Jun. 4, 2002 which is hereby incorporated by reference (hereinafter called “the Patent”). 
   The Patent relates to filter devices utilizing a battery of filter discs with reverse flushing water flow cycles wherein the discs were caused to spin under the impact of water jets impinging thereon (hereinafter referred to as “Spin-Clean Filters”). 
   For better understanding of the invention herein disclosed, reference shall be made to  FIG. 1  which depicts the reverse flow spin-cleaning stage of the filter device (conforming  FIG. 10  of the Patent except that the spin-cleaning stage is provoked by the reverse flow proper rather than by an external pressure command, a feature which is understood to be encompassed within the scope of the Patent). 
   Using the same reference numerals as in the Patent, the water (or other liquid) admitted through the outlet port  20  flows into the conduit  30   a  (and conduits  30   b  and  30   c  that are not shown) and, through an opening  102   a  (not existing in the Patent exemplified embodiment) into the cylinder space  40  of the cylinder-and-piston assembly  28 . Under a pressure sufficient to overcome the force of the spring  52 , the piston  58  along with the cap member  60  will slide towards the distal end of the filter  10 , relieving the clamping of the filter discs battery  70 . The stroke of piston  58  is delimited by a protrusion  104  formed at the housing member  12  (shown but not referenced in the Patent drawings). As will be explained later on, this need for an extra, exterior element for stopping the progress of the piston has been found disadvantageous and hence remedied by one aspect of the present invention. 
   Turning now to the proximal end of the filter device  10 , there has been used a female screw-threaded ring portion  38  of the fixed member against which the filter discs are pressed for mounting the integral main filter core member  24  to the filter housing structure  14  intermediate female screw-threaded ring  82 . This mounting or coupling arrangement has also been found worthy of improvement as will be explained in detail below. 
   SUMMARY OF THE INVENTION 
   Thus provided according to one aspect of the invention is a liquid filtering device, particularly for irrigation water installations comprising a cylindrical housing with an inlet port and an outlet port; a cylindrical filter member installed within the housing so that, water flowing from the inlet port to the outlet port enters the filter member in a radial direction, and is discharged through the outlet port, and vice-versa during reversed, filter flushing flow cycles; a core member centrally mounted within the cylindrical space defined by, and forming a support for, the filter member; a fixed member abutting against the filter member at one axial end thereof; a piston assembly mounted to the core member comprising a piston and a displaceable member coupled to the piston and abutting against the filter member at the other axial side thereof; wherein said mounting of the core member comprises a female screw-thread forming part of the said fixed member; a female screw-threaded split ring matching the female screw-thread; and a circular convergent cone shaped trough encompassing the ring fixedly mounted to said housing; the arrangement being such that upon threading together, the ring becomes attracted towards the fixed member and thus self-tightened by frictionally clamping within the cone-shaped trough. 
   According to another aspect of the invention, the piston assembly is provided with means for limiting the progress amount of the piston, such as a coil spring, the number and size of the coils being designed so as to limit the stroke of the piston following a predetermined compression thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and additional constructional features and advantages of the present invention will become more clearly understood in light of the ensuing description of a preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, wherein: 
       FIG. 1  is a longitudinal cross-sectional view of the filter device of the Patent in reverse flush flow, spin-cleaning mode of operation; 
       FIG. 2  is a cross-sectional view of a filter device incorporating the improvements of the preset invention; 
       FIG. 3  shows the split-ring before assembly; 
       FIG. 4  shows the seat member of the split-ring; 
       FIG. 5  shows the split-ring in the preparatory state for insertion into the seat member; 
       FIG. 6  shows the assembled state of the split-ring; 
       FIG. 7   a  is a partial cross-section showing the initial state of engagement of the core coupling ring and the split-ring; 
       FIG. 7   b  shows the final state of engagement; 
       FIG. 8  is a schematic view of a group of filter devices installed in parallel; and 
       FIG. 9  is a schematic view of several filter devices installed in series. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As clearly seen in  FIG. 2 , the mounting of the filtering discs battery  170  to the inlet/outlet housing member  114  has been modified. Rather than female screw-threaded ring  82  ( FIG. 1 ) there is provided an assembly comprised of seat member  200  and screw-threaded split-ring  202  shown in more detail in  FIGS. 3-7 . 
   The seat member  200  is formed with a circular trough portion defined by circular rim  200   a , convergent cone-shaped wall  200   b  and planar radial wall  200   c.    
   The seat member  200  is shown as integrally formed with the outlet fitting but other variations may be employed such as by welding. 
   The ring  202  is split as shown and made of an elastic or springy material to allow its closing by force ( FIG. 5 ) into a reduced diameter which must be smaller than the opening defined by the rim  200   a.    
   The outer surface  202   a  of the ring  202  is beveled by the same angle as the seat cone wall  200   b . The inner side is provided with a screw-thread matching that of the core member ring  138 . 
   The height of the ring  202  is less than the distance between the inner surfaces of the rim  200   a  and of the radial wall  200   c.    
   The mounting of the core member  124  is perfected in the following manner. First, the split-ring  202  is inserted into the trough portion by forcing it to close and placing thereinside, whereupon the ring will resume its partially open state ( FIG. 7   a ). It is designed so that in this position the screw threads of the ring  138  and of the split-ring  202  will match. 
   Upon relative rotation, the split-ring becomes dragged along the cone-shaped wall  200   b  up to a certain point ( FIG. 7   b ). Consequently, a self-tightening effect occurs whereby a highly secured and sealed coupling of the threaded members to each other is attained in a more effective way than in the Patent construction ( FIG. 1 ). 
   If necessary, stop means such as projection  200   d  may be provided to avoid the unison rotation of the two parts, at-least at the beginning of the operation where the friction between the beveled ring portions  202   a  and the seat wall portion  200   b  might be insufficient. 
   The dismantling of the core member  124  from the seat member  200  for maintenance or replacement purposes follows in the reverse order. 
   Turning now to the distal side of the filter device  110 , it will be readily seen that, by properly choosing the number and diameter of the coils, the spring  252  functions as an autonomic stop, limiting the stroke of the piston  158  (and cap member  160 ) of piston assembly  128 . 
   This seemingly minor and even almost obvious modification presents, however, the advantage of completely dispensing with the stop cap ( 104 — FIG. 1 ). Moreover, the length of the piston stroke can be governed and properly selected irrespectively of the housing(s) size. 
   This variability becomes even more significant where the filter devices are used in groups, either in parallel or in series. 
   In  FIG. 8  a battery of five filter devices  310  is shown (only three are seen) operating in parallel. The filters are mounted on a common base formed in inlet/outlet housing member  314 , either by the arrangement described above or otherwise. 
   Noteworthy in the present context is that the cylinder and piston assemblies  328  incorporate the integral piston-stroke limiting means rather than external stop-by-abutment means (cap  104  in  FIG. 1 ). This entails a significant saving in the design and structure of the other housing member  312 . 
   The filter devices  410  of  FIG. 9  operate in tandem between the common inlet and outlet, e.g. to achieve superfine quality of filtered liquid. 
   This type of construction is only enabled by implementation of the self-limiting piston-stroke means proposed according to the present invention. 
   Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be effected without departing from the true spirit and scope of the invention as defined in and by the appended claims.