How to choose a filter cartridge: wound, melt-blown, pleated, carbon or sintered

Most liquid filtration problems come down to choosing the right cartridge. The same housing can hold a cheap wound cartridge that clogs in a week or a membrane cartridge that protects a pharmaceutical line, so the choice matters more than the hardware around it. This guide explains how each type of cartridge works and when to use it.

At a glance

• Depth cartridges (string wound and melt-blown) hold dirt through their full thickness. They cost little, hold a lot of dirt and suit pre-filtration.

• Pleated cartridges filter at the surface of a pleated medium. They give sharper ratings and a lower pressure drop, and suit final filtration.

• Membrane cartridges (PTFE, PES, nylon, PFA) are pleated cartridges rated down to 0.04 µm, for sterile and ultra-pure duties. The membrane is chosen for the liquid.

• Activated carbon cartridges adsorb chlorine, organic compounds and odours rather than sieving out particles.

• Sintered metal elements take high pressure and temperature, and can be cleaned and reused.

• High flow cartridges are large-diameter pleated cartridges that cut the number of elements in large systems.

Depth or surface filtration

A depth cartridge is a thick wall of fibres. Large particles are caught near the outside and smaller ones further in, so the whole wall does the work and the cartridge holds a lot of dirt before the pressure drop rises. The rating is nominal: most particles at the rated size are held, but some pass. That is fine for protecting pumps, reverse osmosis membranes and downstream filters.

A surface cartridge has a thin medium, pleated to give a large area. Particles larger than the rating are held at the surface. The rating is sharper and, with membranes, absolute, which is what sterile and high-purity processes need. Pleating also keeps the pressure drop low for the flow.

In many systems the two work together. A depth cartridge upstream takes the bulk of the dirt, and a pleated or membrane cartridge downstream gives the final rating and lasts much longer as a result.

The cartridge types compared

Type	How it filters	Vens range and ratings	Best for	Keep in mind
String wound	Depth: yarn wound on a core; the winding density sets the rating	AquaFil, 1 to 150 µm, polypropylene or cotton	Pre-filtration, RO pre-filters, process water	Nominal rating; replaced, not cleaned
Melt-blown	Depth: polypropylene fibre, dense inside and open outside	HydroFil S, H and M, 1 to 150 µm	Pre-filtration of pure water, food and chemicals	Fine-fibre grade removes more than 99%; up to 80 °C
Pleated polypropylene	Surface: graded polypropylene membrane	PolyFil, 0.1 to 100 µm	Final filtration of acids, alkalis and salts; pharmaceuticals; food	Up to 80 °C; steam sterilisable
Membrane	Surface: microporous PTFE, PES, nylon or PFA membrane	FlouroFil, FlouroFil X, SulfoFil, NylonFil, FlouroFil K; 0.04 to 0.45 µm	Sterile and ultra-pure liquids and gases, solvents, semiconductor chemicals	Choose the membrane for the liquid
Glass fibre	Depth: high-porosity glass fibre, pleated	SulfoFil X, 0.5 to 5 µm	Pre-filtering viscous or colloidal liquids ahead of a membrane	High dirt load at a low pressure drop
Activated carbon	Adsorption	CarboFil, 0.5 to 10 µm	Chlorine, organic compounds and odour in water	Up to 52 °C; not a particle filter on its own
High flow	Surface: large-diameter pleated	PermeaFil, 10 to 60 inch, 0.02 to 80 µm	Large flows with few elements	Needs a high flow housing
Sintered stainless steel	Depth: fused metal powder	0.1 to 100 µm, in the VH-HPF housing	High pressure and temperature, gases, purge systems	Cleanable and reusable; the highest cost

Choosing a membrane

• Hydrophobic PTFE (FlouroFil): repels water. Used for gases, vents and aggressive solvents, including sterile filtration of nitrogen and argon.

• Hydrophilic PTFE (FlouroFil X): the chemical resistance of PTFE for water-based liquids, with no pre-wetting.

• PES (SulfoFil): binds little protein and stands repeated steam sterilisation. Used for ultra-pure water and sterile liquids, and for weak acids and alkalis.

• Nylon 66 (NylonFil): hydrophilic and alkali resistant. Used for alkaline organic solvents and ultra-pure chemicals.

• PFA (FlouroFil K): all-fluoropolymer and rated to 170 °C, for semiconductor acids, solvents and strong oxidisers.

What else decides the choice

• Particle size and efficiency: match the rating to the smallest particle you must remove. A nominal depth cartridge is fine where some passage is acceptable; use a pleated or membrane cartridge where it is not.

• Flow and pressure drop: too few cartridges for the flow means a high pressure drop and a short life. Size the number and length of cartridges so the clean pressure drop is low.

• Chemical compatibility: check the medium, the core and cage, the end caps and the seals against the liquid.

• Temperature: polypropylene cartridges are generally limited to 80 °C. PFA and sintered metal go higher.

• End fittings and seals: the cartridge must fit the housing. Common fittings are double open end (DOE) and 222 or 226, flat or with a fin. Seals are nitrile, EPDM, silicone or Viton.

• Change-out: fit pressure gauges either side of the housing. We recommend changing depth cartridges at 0.8 to 1.5 bar differential pressure.

What to send us for a quotation

• The liquid, its temperature and pressure

• The flow rate

• The particles to remove, or the rating you use now

• Your housing, or the cartridge length, diameter and end fitting you use now

• Any hygiene or sterility requirement

Need an equivalent for a cartridge from another brand? Search FilterDex by part number or size.

Frequently asked questions

Can a filter cartridge be cleaned and reused?

Polypropylene, cotton, glass fibre and carbon cartridges are disposable. Sintered stainless steel elements can be cleaned and reused, and some membrane cartridges can be sanitised in place.

What is the difference between a nominal and an absolute rating?

A nominal rating means most particles of that size are held. An absolute rating means essentially all of them are held, which is what membrane cartridges are tested for. Use absolute ratings for sterile and critical duties.

Why does a fine cartridge need changing so often?

A fine cartridge collects everything larger than its rating. A coarser depth cartridge upstream takes most of that load, so the fine cartridge lasts much longer.

Vens filter cartridges

• String wound filter cartridges (AquaFil)

• Melt-blown filter cartridges (HydroFil)

• Activated carbon filter cartridges (CarboFil)

• Pleated polypropylene filter cartridges (PolyFil)

• Hydrophobic PTFE pleated filter cartridges (FlouroFil)

• Hydrophilic PTFE pleated filter cartridges (FlouroFil X)

• PFA pleated filter cartridges (FlouroFil K)

• PES pleated filter cartridges (SulfoFil)

• Nylon 66 pleated filter cartridges (NylonFil)

• Glass fibre pleated filter cartridges (SulfoFil X)

• High flow filter cartridges, 10 to 60 inch (PermeaFil)

• High pressure purge filter housing with sintered element (VH-HPF)

Related guide: How to size a bag filter housing. See the full Vens filter range.

Customers in the EU are supplied and supported through our European company, VDT Europa OÜ in Tallinn, Estonia.