Wound String Filter Cartridge Selection & Maintenance Guide: Yarn Types, Micron Ratings, and OEM Sourcing

Wound string filter cartridges �?also called yarn-wound or string-wound cartridges �?are among the most widely used depth filters in industrial water treatment. Their simple but effective design uses continuous yarn wound around a central core to create a graded-density structure that traps particles throughout the depth of the filter, not just on the surface. This gives wound string cartridges an exceptionally high dirt-holding capacity, making them a cost-effective choice for sediment removal, process water pre-filtration, and a range of industrial applications.

But not all wound string cartridges are the same. The choice of yarn material, winding pattern, micron rating, and core construction all affect performance and service life. This guide covers the key selection criteria, common pitfalls, and maintenance best practices to help you get the most out of your wound string filters. If you are sourcing cartridges in volume, we also cover OEM and ODM considerations with Chinese manufacturers like Jingze Water.

How Does a Wound String Filter Cartridge Work?

A wound string cartridge is produced by wrapping yarn �?polypropylene, cotton, or nylon �?in a controlled criss-cross pattern around a rigid central core (typically polypropylene or stainless steel). The winding tension is adjusted so that the outer layers are wound more tightly (smaller pores) and the inner layers more loosely (larger pores), creating a graded-density depth filtration structure.

When fluid flows from the outside to the inside of the cartridge, larger particles are captured in the outer, coarser layers while progressively smaller particles are trapped deeper within the media. This design allows the cartridge to hold several times more contaminant than a surface filter (such as a pleated or screen-based element) of the same physical size. The result is longer service intervals and lower overall filtration cost for high-sediment feed streams.

Which Yarn Material Should You Choose: PP, Cotton, or Nylon?

The yarn material determines the cartridge's chemical compatibility, temperature limit, and cost. Each of the three common materials has its own strengths and limitations.

For drinking water and food-contact applications, cotton yarn is preferred because it contains no synthetic binders or additives. For chemical processes involving acids or bases, PP yarn offers the best all-around chemical compatibility. For hydrocarbon and oil-based fluids, nylon yarn provides the necessary chemical resistance and physical strength. Explore our JZ-WS Series wound string cartridges in all three yarn types.

What Micron Rating Do You Need for Different Water Sources?

Wound string cartridges are available from 1 μm to 100 μm nominal. The "nominal" rating means the cartridge will retain a defined percentage (typically 60�?0%) of particles at the stated size. This is different from absolute-rated cartridges used in sterile applications. For sediment-rich feed water, using a coarser rating than you might think is often the best strategy �?it prevents rapid blinding and extends cartridge life.

When dealing with high turbidity feed water, a common best practice is to install two wound string cartridges in series �?a 50 μm or 100 μm first-stage followed by a 5�?0 μm second-stage. This staged configuration maximizes the dirt-holding capacity of the coarse filter while protecting the finer filter from premature blinding.

How Can You Tell It Is Time to Replace a Wound String Cartridge?

Unlike pleated filters where visible soiling gives a clear signal, wound string cartridges trap dirt internally. You cannot tell the condition by just looking at the surface. That is why pressure-based monitoring is essential.

Replace the cartridge when the differential pressure (ΔP) across the filter reaches 2.0 bar (30 psi). This is the maximum recommended pressure drop for standard cartridges. Beyond this point, the wound structure begins to compact, reducing the pore volume and potentially collapsing the inner layers. Operating at ΔP above 2.0 bar also risks bypass �?contaminant pushing through compromised sections of the yarn.

Other signs it is time to replace:

• Noticeable flow reduction �?If downstream pressure drops while upstream pressure stays the same, the cartridge is loaded.
• Degraded effluent quality �?If turbidity increases in the downstream sample, the cartridge may have channeled or burst.
• Routine schedule �?Even if ΔP has not reached 2.0 bar, replace wound string cartridges at least every 12 months to prevent biological growth inside the wet media (especially cotton-wound cartridges).

For cotton yarn cartridges in food and beverage service, Jingze Water recommends more frequent changes �?every 3 to 6 months �?because the natural fibers can support microbial colonization when left wet for extended periods.

Can You Customize Wound String Cartridges for OEM / ODM Requirements?

Yes �?in fact, wound string cartridges are one of the most commonly customized filter types. If you distribute filtration equipment, supply industrial consumables under your own brand, or need a cartridge that fits a non-standard housing, OEM and ODM production offers significant advantages.

Typical customization options include:

• Yarn material and grade �?Standard PP, cotton, or nylon, or custom blended yarns with specific denier/filament counts
• Core type �?Polypropylene (standard), SS304, or SS316 for corrosive or high-temp environments
• End cap configurations �?DOE (double open end), SOE-222, SOE-226, or custom inserts
• Length and diameter �?Standard 10", 20", 30", 40" lengths and 2.5" OD. Custom dimensions negotiable for volume orders.
• Branding and packaging �?Private labeling, custom barcode labels, individual polybagging or bulk carton packaging

Chinese manufacturers like Jingze Water have become a preferred sourcing partner for OEM wound string cartridges because of their ability to deliver consistent quality at competitive pricing. With ISO�?001-certified production lines and monthly output exceeding 5 million cartridges across all product lines, they have the capacity and quality control systems needed for volume OEM programs. Contact Jingze Water to discuss your OEM requirements and request a sample kit matching your specifications.

What Is the Total Cost Advantage of Wound String Cartridges?

The per-cartridge price of a wound string filter is generally lower than a pleated cartridge of equivalent length, but the real savings come from the depth filtration design. Because the cartridge traps contaminants throughout the yarn matrix rather than on a single surface layer, wound string cartridges typically offer 2�? times higher dirt-holding capacity than pleated alternatives of the same micron rating and surface area.

For high-sediment applications such as well water pre-filtration, river water intake, or industrial process water where suspended solids range from 10 to 100 ppm, this translates directly into fewer change-outs per year and reduced labor cost. When you add in the lower unit price of wound string cartridges, the total cost of ownership often comes in 40�?0% below pleated cartridge solutions for the same duty cycle.

Conclusion: How to Select the Right Wound String Cartridge for Your Needs?

Wound string filter cartridges remain one of the most practical and economical depth filtration solutions for sediment removal across a broad range of industries. The key to getting the best performance lies in selecting the right yarn material for your fluid chemistry, matching the micron rating to your feed water turbidity, and monitoring differential pressure to schedule timely replacements.

For OEM buyers and volume users, working directly with an ISO-certified Chinese manufacturer allows you to control both quality and cost. Jingze Water offers a full line of PP, cotton, and nylon wound string cartridges in standard and custom configurations, backed by batch-level quality testing and efficient global shipping.