What Is a Cartridge Filter?

A cartridge filter is a tubular element inside a housing that removes particles, and sometimes dissolved contaminants, from a liquid or gas as it flows through. What decides its performance is not the tube shape, it is five specific choices underneath it.

What a cartridge filter is actually made from

Every cartridge is built from the same five kinds of parts, whatever the brand or the media. The filter media does the actual capturing: polypropylene, polyester, cellulose, activated carbon or ceramic, each suited to different fluids and duties. A support core runs through the centre so the media does not collapse under differential pressure. End caps seal the media into a fixed shape that fits the housing, and a gasket or O-ring closes that seal so liquid cannot bypass the media entirely. Some designs add an outer protective cage for extra mechanical strength in high-flow or high-pressure duty. Get any one of these wrong for the application and the media choice barely matters.

The five media types, and what each one is actually for

Cartridge filter media types

Polypropylene is the general-purpose choice: broad chemical resistance at moderate cost, suited to most industrial and water filtration. Polyester holds up at higher temperatures where polypropylene would soften. Cellulose is the economical option for basic filtration where the stream is not aggressive. Activated carbon works on an entirely different principle, adsorption rather than straining, and is chosen specifically to pull out odour, chlorine and dissolved organic compounds rather than suspended solids. Ceramic is the specialist choice for ultra-fine filtration and sterility-sensitive duty, at a correspondingly higher cost.

Surface or depth: read the full comparison elsewhere

Cartridges also split by mechanism: surface filters (like pleated cartridges) stop particles at the outer layer; depth filters (like string wound and sintered metal cartridges) trap particles throughout the thickness of the media, usually lasting longer at a higher unit cost. We cover that comparison, and when each mechanism is the right call, in the filtration and separation guide and in bag filters versus cartridge filters.

When to actually replace a cartridge

The right trigger is a pressure reading, not a date on the calendar. Most systems work against a differential pressure limit, commonly around 10 psi above the clean element's baseline; once the reading crosses it, the element is loaded enough that flow and filtration quality both start to suffer. A day-based guideline, every 30 or 45 days for example, is only a starting estimate based on an average contaminant load; your actual stream may load the element faster or slower than that average. Replacing on a fixed schedule without checking the pressure gauge risks changing too early, which wastes element life, or too late, which runs degraded filtration in the meantime. When it is time, shut the system down, depressurise and drain it, remove the housing lid and the old cartridges, check the housing for corrosion or residue, fit the new cartridges with a clean and lubricated seal, reinstall the lid, and purge air from the system before bringing it back online.

Direct answers

What is a cartridge filter made from?

A cartridge is built from filter media (polypropylene, polyester, cellulose, activated carbon, or ceramic, chosen for the fluid and duty), a support core that stops the media collapsing under pressure, end caps that seal it into the housing, and a gasket or O-ring that closes the seal against bypass. Some cartridges add a protective outer cage for mechanical strength.

What is the difference between a surface cartridge and a depth cartridge?

A surface cartridge, such as a pleated element, stops particles at the outer layer of the media. A depth cartridge, such as string wound or sintered metal, traps particles throughout the thickness of the media, which usually gives it a longer service life at a higher unit cost. Our filtration and separation guide covers the comparison in full.

When should I replace a cartridge filter?

Replace on the pressure reading, not the calendar. Most systems set a differential pressure trigger, commonly around 10 psi, above the clean element's baseline; once the reading crosses it, the element is loaded to the point where flow and filtration quality both suffer. A day-based guideline (every 30 or 45 days, for example) is only a starting estimate: actual life depends on the contaminant load in your specific stream.