Patent ID: 8668828

Claim:
A method of making a spiral wound membrane cartridge of about 7.9 in. diameter for a sanitary application, which method comprises the steps of: providing a central permeate collection tube and a plurality of sheets of feed spacer material, permeate carrier material, and semipermeable membrane filtration material, said membrane filtration material sheets each having a length about twice as long as said other sheets and being folded approximately in half, adhesively attaching each of said permeate carrier sheets between half-sheets of two different semipermeable membrane filtration sheets along both longitudinal side edges of said permeate carrier sheet and across the free end edge thereof to create 3-ply leaves, disposing a feed spacer sheet between each two facing half-sheets of different filtration membrane material, which feed spacer sheet is of bi-planar construction and formed of two groups of parallel filaments, spirally wrapping said plurality of sheets about said central permeate collection tube to form an assemblage, following curing of said adhesive, partially unrolling said spiral wound assemblage and trimming a free end edge of each of the 3-ply leaves to provide an adhesive-filled end edge surface, affixing overwrap material sheeting to an end portion of one of said feed spacer sheets which feed spacer sheet is juxtaposed in surface to surface contact with facing membrane filtration sheets within said spiral wound assemblage, said overwrap material sheeting having a substantially greater tensile strength than the feed spacer, which greater tensile strength is at least about 1250 N/m in the longitudinal direction, tightly re-winding said plurality of sheets of said partially unrolled assemblage about said central permeate collection tube with said overwrap sheeting attached to one feed spacer sheet to create several wraps of overwrap sheeting around the spiral wound assemblage, while applying gradually increasing tension to at least 7 lbf/in (1250 N/m) to said overwrap sheeting to thereby tighten the wrapped assemblage about said central permeate collection tube and place the assemblage of sheets in radial compression, joining two juxtaposed regions of said overwrap sheeting to each other in surface to surface contact to retain the resultant tightly wrapped final filtration element in substantially cylindrical form having a selected outer diameter, and associating a thin tubular shell having a textured exterior surface with said tightly wrapped element to provide a filtration cartridge designed to allow a controlled bypass flow of liquid feed between a pressure vessel interior surface and said textured exterior surface of said shell.