A pre-assembled drainage line unit includes a flexible longitudinally extending perforated sleeve member and a loose aggregation of lightweight elements contained within the sleeve member. A pliable, water permeable barrier material extends along the sleeve member and overlies at least a portion of the aggregation to prevent the passage of solid materials, such as sand and dirt, into the aggregation.

BACKGROUND OF THE INVENTION 
   This invention relates generally to liquid drainage systems used on site for footings, open trenches, or nitrification fields used as discharge points for septic tanks, and more particularly to a novel flexible preassembled drainage line unit which is an improvement over the flexible preassembled drainage line units illustrated in  FIGS. 2 and 3  of U.S. Pat. No. 5,015,123 (the “'123 patent”, owned by the assignee of this invention), the disclosure of which is incorporated herein by reference in its entirety. 
   The preassembled drainage line unit illustrated in  FIG. 2  of the '123 patent constitutes loose aggregate in the form of lightweight materials such as polystyrene beads provided in surrounding relationship to a perforated conduit and bound thereto by a perforated sleeve member such as plastic netting. These units, used in combination with preassembled units illustrated in  FIG. 3  of the '123 patent which do not include the perforated pipe, provide a storage chamber or area for example for effluent from a septic tank until it can be absorbed by the surrounding soil as illustrated in  FIGS. 4   b  and  4   c  of the patent and replaces the conventional gravel drainage system illustrated in  FIG. 1  of the patent. Drainage systems employing the preassembled drainage line units of the '123 patent represent a substantial improvement over prior conventional gravel systems for reasons set forth in the '123 patent and have enjoyed substantial commercial success. 
   While those preassembled drainage line units have enjoyed commercial success, in certain applications problems have presented themselves. For example depending on the type of fill soil placed on top of the preassembled units, solids such as sand or dirt may pass downwardly through the netting into the void area between adjacent aggregate, clogging that area and causing an undesirable reduction in liquid flow through the aggregate. In other applications it is sometimes desirable that the pre-assembled units which are normally very flexible along their length possess greater rigidity along that length and still in other applications it is sometimes beneficial to provide structure as part of those units which promotes the growth of microorganisms within the drainage units. 
   The improved drainage products of the invention as described hereinbelow have been developed to overcome the problems associated with the units described in the '123 patent and to fulfill the needs described above. 
   SUMMARY OF THE INVENTION 
   Accordingly, a primary object of the invention is to provide a preassembled drainage line unit in which loose aggregate in the form of lightweight materials is contained within and bounded by a perforated conduit such as a plastic mesh tube of construction netting and wherein a barrier material overlies at least a portion of the aggregate to prevent solids from passing through the netting and entering the storage area defined by the aggregate. 
   Another object of the invention resides in the provision of the above novel preassembled drainage unit which further includes a perforated conduit wherein the loose aggregate surrounds the conduit and is bounded thereby by the perforated sleeve member. 
   Depending upon the type of drainage application in which the novel preassembled units are to be used, the material from which the barrier is constructed may vary. For example, it may be paper, cloth, geo-textile such as nylon, or any other suitable pliable sheet material that can be inserted between the netting and the aggregate. The thickness of the sheet material can be varied. For example the thickness of the material may be thin so as to conform to the preferred cylindrical shape of the units or may be thicker to provide rigidity along the length of the units. In addition, the barrier material may extend around the aggregate through an angular distance of about 10 degrees through full coverage of 360 degrees. 
   The provision of the barrier material within the above described novel preassembled drainage units can be tailored to block the infiltration of outside media such as sand, dirt and soil through the net into the aggregate, to provide rigidity to the drainage units along their length and to provide structure which promotes the growth of microorganisms within the drainage unit. 
   It is also an object of the invention to provide a method and apparatus for manufacturing the novel drainage units. 
   Further objects and advantages of the invention will become evident from the reading of the following detailed description of the invention wherein reference is made to the accompanying drawings. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a preassembled drainage line unit constructed according to the invention which includes a plurality of lightweight aggregate surrounding a perforated conduit and bounded thereto by an outer perforated sleeve member, with a barrier material overlying at least a portion of the aggregate to prevent outside media such as sand, dirt or soil from infiltrating into the liquid storage area defined by the aggregate; 
       FIG. 2  is a cross-sectional view of the unit taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  illustrates a preassembled drainage line unit similar to  FIG. 1  with the perforated conduit removed; 
       FIG. 4  is a cross sectional view of the conduitless unit taken along line  4 — 4  of  FIG. 3 ; 
       FIG. 5  is a cross-sectional schematic view illustrating an alternative construction of the unit illustrated in FIG.  1 . 
       FIG. 6  is a fragmentary front perspective view of apparatus for manufacturing the novel drainage units of the invention; 
       FIG. 7  is a side view of the apparatus of  FIG. 6  illustrating the manner in which the rolls of barrier material are supported on the mandrel. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, the longitudinally extending, flexible preassembled drainage line unit  20  illustrated in  FIG. 1  includes a corrugated VC (polyvinyl chloride) perforated vent pipe  10  encased by an outer perforated sleeve member  22  of tubular nylon netting or mesh which is filled with an aggregation of discrete water impervious crush resistant lightweight plastic elements  21  and is secured to the pipe ends  24  and  25  by means of suitable conventional wires or tie fasteners  26  which prevent the escape of the loose aggregates  21 . 
   Unit  20  as described thus far corresponds to the drainage unit illustrated in  FIG. 2  in U.S. Pat. No. 5,015,123 and the detailed description set forth therein is incorporated herein by reference. 
   As mentioned hereinabove, in some applications employing the flexible drainage line units illustrated in the '123 patent, outside media solids such as sand, dirt or local soil placed on top of the units can penetrate into the units and thereby reduce the void space between the aggregates  21 , clogging the units and reducing the fluid flow through the units. 
   To alleviate this problem a liquid or water permeable barrier material  28  is placed between aggregates  21  and netting  22 , the barrier  28  extending longitudinally along unit  20  between ends  24  and  25  of the pipe and being secured at its ends to the pipes by fasteners  26  along with the netting  22 . 
   As shown n  FIG. 2  the barrier  28  extends through a predetermined desired angular distance across the top portion of unit  20  and depending upon the application it may extend through an angular distance within the range of 10 degrees to a complete 360 degrees of the unit. 
   Barrier  28  may be constructed of any suitable pliable water permeable sheet material such as paper or cloth, but is preferably a geo-textile material such as nylon having a fine weave to block the passage of the sand or dirt but sufficiently open to permit the passage of water therethrough. 
   Preferably barrier  28  is very thin so as to readily conform to the shape of the flexible unit  20  which is preferably generally cylindrical but it may be thickened as desired to provide rigidity to the unit if desired. 
   In operation water collected at one end of pipe  10  passes into the pipe and outwardly through the perforations of the pipe into the chamber defined by aggregates  21  and barrier  28  blocks infiltration of sand or dirt placed on top of units  20  into the void space containing the aggregates. 
   Referring now to  FIG. 3  the generally cylindrical drainage unit  30  is the same as unit  20  described in  FIG. 1  except that it has no conduit passing therethrough. The end of the netting  22  and barrier  28  are tied together at the ends of unit  30  to hold aggregates  21  in place within the units. The units illustrated in  FIG. 3  in this application containing the barrier  28  constitute an improvement over the conduitless units illustrated in  FIG. 3  of the '123 patent and described therein. 
     FIG. 5  an alternative construction to that illustrated and described above with respect to FIG.  1 . In the  FIG. 5  embodiment, a pipe  10   a  is surrounded by aggregate  21   a  which is bounded to the pipe by a first perforated net  22   a , with this structure described so far being essentially identical to the prior art unit illustrated in  FIG. 2  of the '123 patent. A barrier  28   a  extends longitudinally along the length of the unit outside of net  22   a  and around the unit through a predetermined angular distance and is fastened thereto by suitable means such as a second outer tubular nylon net or mesh  40  fastened at its ends along with the ends of barrier  28   a  to the ends of pipe  10  in the same manner as the unit of FIG.  1 . Instead of the tubular net  40 , barrier  28   a  may, for example, be fastened to the outside surface of net  22   a  by rope or cord at various locations along the length of the unit. 
   Another embodiment constructed according to  FIG. 5  but without the conduit  10   a  may be provided as an alternative to the conduitless unit illustrated in  FIGS. 3 and 4 . 
   From the description herein above it is apparent that the provision of the barrier  28  in the preassembled drainage line units advantageously prevents the passage of outside media such as sand, dirt or soil into the void space defined by the lightweight plastic aggregates; the barrier provides structure for the growth of microorganisms within the drainage unit; and the barrier may be constructed to provide rigidity to the unit when desired. The flexible pliable barrier material may extend a varying angular distance around the unit. For example, it may extend through a small angular distance of about 10 degrees to full circumferential coverage of 360 degrees of the unit depending upon the application in which the unit is to be used. 
   The apparatus shown in  FIGS. 6 and 7  is of the type illustrated and described in detail in U.S. Pat. No. 6,173,483 which is owned by the assignee of this application, and the disclosure of U.S. Pat. No. 6,173,483 is incorporated herein by reference in its entirety. The apparatus is used to make both of the units of  FIGS. 1 and 2 . 
   Briefly, the apparatus includes a tubular mandrel  50  having an inner bore or cavity, a rear opening, a front opening, and an upper opening, with each opening communicating with the inner cavity. 
   A pipe feeder is positioned for feeding a predetermined length of perforated length pipe through the inner cavity of the mandrel  50  in a direction of manufacture from the rear opening to the front opening and therethrough. As it is fed into the mandrel  50  the vent pipe is positioned within the inner cavity so as to define a void space between the pipe and the inner wall of the mandrel. 
   A hopper assembly containing the plastic aggregate bodies is connected via conduit  52  to the upper opening in the mandrel to feed the plastic aggregates into the cavity. 
   A blower  54  is positioned in communication with the inner cavity of the mandrel for producing the sufficient air flow therethrough for moving the aggregate from conduit  52  through the inner cavity to substantially fill the void space between the vent pipe and the wall of the mandrel so that the pipe is surrounded by the aggregate as it emerges from the from opening of the mandrel. 
   A sleeve feeder is connected to the front end of the mandrel for feeding a continuous sleeve of netting  22  over the plastic aggregate and the vent pipe emerging through the front opening of the mandrel. As it is fed the continuous sleeve of netting  22  substantially encases the plastic aggregate around the vent pipe thereby forming a drainage unit. 
   The apparatus operates substantially the same for producing the conduit units of  FIG. 3  but with no perforated vent pipe being fed through the unit. 
   For a more detailed description of this type of apparatus, reference is made to the specification of U.S. Pat. No. 6,173,483. 
   In accordance with the invention one or more rolls  56  of barrier sheet material  28  are mounted on top of mandrel  50 , the leading end  58  of which is located underneath the netting  22  in contact with the mandrel and is fed with the netting over the plastic aggregate and is fastened with the netting around the vent pipe for manufacturing the units of  FIG. 1 , or is simply tied together with the end of the netting for producing the conduitless units of FIG.  3 . The apparatus as illustrated in  FIGS. 6 and 7  is producing conduitless units. When drainage units larger in diameter for example, 10 inches, 12 inches, 14 inches, etc. are being produced instead of using a single roll  56  of barrier material it is better to use a plurality of rolls which are angularly offset as shown in  FIGS. 6 and 7  with overlapping side edges so that the barrier material is able to extend for a larger angular distance, for example approximately 180 degrees in the unit shown in FIG.  6 . 
   The operation illustrated in  FIGS. 6 and 7  produces the units of  FIGS. 1 and 2  and  FIGS. 3 and 4  wherein the barrier material  28  is placed between netting  22  and aggregates  21 . 
   To produce the embodiments illustrated in  FIGS. 5 and 6 , the operation of  FIGS. 6 and 7  may be modified by placing the leading edges of barrier material  28  on top of the netting  22  on mandrel  50  and then placing a second netting  40  around barrier  28  and the first netting  22  and continue the operation as described above. 
   The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.