The latest development in string-wound cartridges has overcome problems with roving and friction-spun yarns and has all the features of melt-blown cartridges. The media of the new string-wound cartridge is made from the continuous filaments-each individual filament that continues throughout the entire length. There are no short fibers, making the cartridge free from any media migration. These continuous filaments are melt-spun in a way that no chemicals like spin-finish, wetting, and antistatic agents, surfactants, emulsifiers, etc., are required. These chemical-free continuous filaments are then randomly oriented to each other, intermixed, looped, and entwined forming a non-round, highly stable, bulky yarn.

Random short loops protrude from the surface of the yarn. As the filter is wound, every single yarn traps part of the loops of the adjacent yarn giving a highly stable structure. The yarns get locked in place and will not roll or move aside. This stable structure also gives excellent sealing. It easily passes the paper clip test. Yarn that doesn’t shift easily also makes the filter resistant to particle unloading. With advancements in winding technology (computer controls) and pitch, the number of crossings and space between each yarn can be continuously varied and controlled from start to finish of the cartridge winding. The inner layers of yarn can be wound closer together and the distance between the yarns can be gradually increased toward the outer layers. This achieves density grading without changing the winding tensions for more consistent performance in string-wound cartridges. Coarser particles are trapped in the outer layers and finer particles in the inner layers. In this cartridge, the liquid flows through the entire yarn structure-there are no typical diamond-shaped holes.