Core points
- A string wound cartridge is a depth filter: density rises from the open outside to the dense core, so particles are captured through the whole wall, not just on a surface.
- The filtration rating is set by two winding parameters - yarn thickness and packing density. Finer yarn packed tighter means smaller pores and a finer rating.
- Best suited to low-viscosity, low-solids liquids; it is one of the most economical media per unit of dirt held.
- Yarn options - polypropylene, acrylic, degreased cotton - decide chemical compatibility; the core is PP or stainless steel.
- BROLERN winds to customer rating by controlling tension and density, with custom yarn/core combinations for export OEM programmes.
How the honeycomb density gradient works
A well-wound cartridge shows the true depth effect: the density increases from the outside towards the centre. During winding, density is controlled by the yarn diameter and the winding tension - finer yarn packs tighter, the pores become smaller, and the rating becomes finer. This inside-dense structure is what turns a spool of yarn into a graded filter: large particles stop at the surface layers, fine particles travel deeper before they are captured, and the whole wall shares the dirt load.
The practical consequence is longer service life at a given rating compared with a single-density media, and no surface blind spots that would restrict flow. Rating itself is a function of yarn diameter and winding density - the two levers a winder can set per order.
Typical parameters (BROLERN production range)
| Media (yarn) | Polypropylene, acrylic, degreased cotton; others on request |
|---|---|
| Core | Polypropylene or stainless steel |
| Filtration rating | 1-150 um nominal |
| Lengths | 5-70 inch (127-1778 mm) |
| Structure | Honeycomb, open-outside / dense-inside gradient |
Where they fit - and where they do not
String wound cartridges excel in low-viscosity liquids with low solids loading: water, RO pretreatment, coolants, condensate and similar duties. For high dirt loads, stage the train instead of loading one cartridge - a common industry practice is coarse-to-fine staging (for example 25 um to 5 um to 1 um), which typically lowers total cartridge cost per year even though more housings are involved [source: Scientific Edge cartridge selection guide]. For viscous or gelatinous media, a depth-wound media can blind quickly; pleated surface media or sintered metal is usually the better conversation.
FAQ
What controls the filtration rating of a string wound cartridge?
Yarn thickness and winding density. Finer yarn and higher packing density create smaller pores and a finer rating.
Which liquids suit string wound cartridges?
Low-viscosity liquids with low solids loading - water, RO pretreatment, coolants and light process liquids.
Can they be cleaned and reused?
Rinse and backflushing extends life in low-fouling duties, but they are economical enough to be treated as consumables in most programmes.
Conclusion
Specify a string wound cartridge by three things: yarn material (compatibility), rating (yarn + density), and length (dirt load). Get those three right and it remains the most cost-efficient depth media for clear liquids. BROLERN winds to customer rating with matched cores for OEM programmes - send the duty and we will propose the yarn.