Abstract: A method for manufacturing preassembled drainage line units comprises feeding a length of perforated vent pipe along a direction of manufacture longitudinally through a tubular mandrel, feeding a continuous sleeve of netting concentrically over the vent pipe along the direction of manufacture from a front end of the mandrel and continuously supplying quantities of artificial aggregate into the space between the sleeve of netting and the vent pipe. A low friction coating is applied to the inside surface of the mandrel to reduce the surface friction of the artificial aggregate caused by compaction, and to permit high speed manufacture.

Abstract: A method for manufacturing preassembled drainage line units comprises feeding a length of perforated vent pipe along a direction of manufacture longitudinally through a tubular mandrel, feeding a continuous sleeve of netting concentrically over the vent pipe along the direction of manufacture from a front end of the mandrel and continuously supplying quantities of artificial aggregate into the space between the sleeve of netting and the vent pipe. A low friction coating is applied to the inside surface of the mandrel to reduce the surface friction of the artificial aggregate caused by compaction, and to permit high speed manufacture.

Abstract: A method for manufacturing preassembled drainage line units comprises feeding a length of perforated vent pipe along a direction of manufacture longitudinally through a tubular mandrel, feeding a continuous sleeve of netting concentrically over the vent pipe along the direction of manufacture from a front end of the mandrel and continuously supplying quantities of artificial aggregate into the space between the sleeve of netting and the vent pipe. A low friction coating is applied to the inside surface of the mandrel to reduce the surface friction of the artificial aggregate caused by compaction, and to permit high speed manufacture.

Abstract: Preassembled drainage line units for a septic tank nitrification field employ a predetermined length of perforated conduit having an aggregation of discrete, crush resistant, light-weight elements surrounding the length of conduit and a perforated sleeve member enveloping the aggregation and bounding the same relative to the conduit with the ends of the conduit extending beyond the sleeve. The drainage line unit is provided with connecting means at each extending end, for end-to-end interconnection with an adjacent drainage line unit.

Abstract: A preassembled unit for a sewage nitrification field has minimum outward dimensions of loose, lightweight plastic aggregate material enveloped and bound by a plastic sleeve around a horizontal conduit. In one embodiment, the unit takes a bag form with an aggregate-filled netting sleeve concentrically surrounding and fastened to the ends of corrugated plastic vent pipe. In another form, the sleeve is a plastic extrusion of rectangular cross-section and the conduit can be formed integrally with the sleeve. Cross-webbing is added for strength. In ground installation, conduitless units make up the insufficiency of aggregate dimension. Mating male and female end caps are used to interconnect the conduit of adjacent units end-to-end. Apparatus for manufacturing the concentric netting sleeve/vent pipe version has a hopper that discharges aggregate into the top of a mandrel and an annular disc or helical auger blade that pushes the aggregate forward into the sleeve.

Abstract: A preassembled unit for a sewage nitrification field has minimum outward dimensions of loose, lightweight plastic aggregate material enveloped and bound by a plastic sleeve around a horizontal conduit. In one embodiment, the unit takes a bag form with an aggregate-filled netting sleeve concentrically surrounding and fastened to the ends of corrugated plastic vent pipe. In another form, the sleeve is a plastic extrusion of rectangular cross-section and the conduit can be formed integrally with the sleeve. Cross-webbing is added for strength. In ground installation, conduitless units make up for insufficiency of aggregate dimension. Mating male and female end caps are used to interconnect the conduit of adjacent units end-to-end. Apparatus for manufacturing the concentric netting sleeve/vent pipe version has a hopper that discharges aggregate into the top of a mandrel and an annular disc or helical auger blade that pushes the aggregate forward into the sleeve.

Abstract: A preassembled unit for a sewage nitrification field has minimum outward dimensions of loose, lightweight plastic aggregate material enveloped and bound by a plastic sleeve around a horizontal conduit. In one embodiment, the unit takes a bag form with an aggregate-filled netting sleeve concentrically surrounding and fastened to the ends of corrugated plastic vent pipe. In another form, the sleeve is a plastic extrusion of rectangular cross-section and the conduit can be formed integrally with the sleeve. Cross-webbing is added for strength. In ground installation, conduitless units make up insufficiency of aggregate dimension. Mating male and female end caps are used to interconnect the conduit of adjacent units end-to-end. Apparatus for manufacturing the concentric netting sleeve/vent pipe version has a hopper that discharges aggregate into the top of a mandrel and an annular disc or helical auger blade that pushes the aggregate forward into the sleeve.