Cartridge Filter Selection: Micron Rating, Media and Housing
Depth, pleated, membrane and metal cartridges; bag filters; filter housings and end caps: engineering steps for selecting the right filter for liquid and gas lines.
Five Decisions That Determine Filter Selection
- Micron rating: which particle size is to be retained, and at what efficiency? Absolute rating (measured 99.98% efficiency) and nominal rating are not the same thing.
- Material: fluid chemistry and temperature. Polypropylene, PES membrane, PTFE-impregnated glass microfiber, nylon, polyester, stainless steel.
- Construction: depth, pleated, membrane, metal or bag; dirt load and flow rate determine this choice.
- Housing and end cap: length (10–40 inch), 222/226 O-ring, DOE, Big Blue; housing style and collar ring for filter bags.
- Sterilization or sanitization requirement: steam, autoclave, hot water limits and integrity testing.
See EDI system selection for 5 micron pre-filtration ahead of EDI, and filtration systems for general filtration equipment.
Micron Rating, Absolute vs Nominal, Pressure Drop
Values are taken from ChemTech manufacturer catalogs.
The micron rating indicates which particle size a cartridge retains; the real question is at what efficiency. ChemTech CHT cartridges are defined as absolute rating, 99.98% efficiency; Megapleat efficiency is verified by multipass testing and a laser particle counter; POLYFIL PP determines its absolute micron rating by measuring ACFTD particles with a multichannel laser counter. A finer rating means higher pressure drop: in the CHT catalog, the pressure drop of a 10 inch cartridge at 1 m³/h water flow (25°C, 1 cP) is as follows:
| CHT micron rating (µm) | Pressure drop (mbar), 10 inch, 1 m³/h |
|---|---|
| 0.5 | 730 |
| 1 | 410 |
| 3 | 230 |
| 5 | 130 |
| 10 | 30 |
| 20 | 15 |
| 30 and above | 10 |
Therefore, when a fine-rated cartridge is required, either the number of cartridges is increased for the flow rate or a coarser pre-filter stage is placed upstream. Catalog rating ranges: CHT 0.5–120; POLYFIL PP 0.3–20; Megapleat 2–100; POLYFIL PES 0.20–0.80; TEFPOR GF 0.01–0.5 (0.01, 0.3, 0.5); CHTM metal cartridge 1–100; bag filters BNMO 1–1500, felt 1–100 (up to 200 in polyester), BPOMF 1–90.
PP, PES, PTFE and Metal: Which Media Goes Where?
| Media | Product | Operating limits | Chemistry and application |
|---|---|---|---|
| Polypropylene depth | CHT | Max 82°C continuous; 4 bar (40°C); hot water sanitization 85°C (PP core) / 105°C (nylon/glass core) | General water, chemical, food & beverage, pre-RO; European Pharmacopoeia compliant, PZH |
| Polypropylene pleated | POLYFIL PP, Megapleat | POLYFIL PP: 80°C continuous, 121°C autoclave, 4 bar (20°C); Megapleat: 82°C (max 90°C in operation), 3.5 bar | Compatible with acid, base and aliphatic solutions; pre-filtration and final clarification |
| PES membrane (sterile) | POLYFIL PES | 0.20–0.80 µm; 70°C continuous; 130°C steam/autoclave; 90°C hot water; 5 bar (20°C) | Full pH range, many organic solvents; low protein binding; integrity testable |
| PTFE-impregnated glass microfiber | TEFPOR GF | 90°C continuous; 121°C autoclave; 4 bar (21°C), 2.4 bar (70°C) | Air and gas, tank venting; hydrophobic; 0.01 µm grade validated for bacteria and microorganism retention |
| Stainless steel | CHTM | SS 304 and 316L: max 480°C; Hastelloy C-276: 540°C; Inconel 600: 815°C | Hot gas, steam, aggressive chemicals; backwashable and reusable; 1–100 µm absolute |
| Large diameter, coreless | MP-CHT | Polypropylene or nylon media | High-flow water and air lines; fewer cartridges, smaller housing |
In TEFPOR GF, PTFE is not a pure PTFE membrane but a PTFE-impregnated glass microfiber surface; it prevents condensed water from passing through and keeps the filter from wetting out and blinding. Besides 316L and 304, metal cartridges can be manufactured in Monel, Inconel, Hastelloy or Fecralloy on request.
Depth, Pleated, Membrane or Bag?
- Depth cartridge (CHT): layers with porosity decreasing from outside to inside; coarse particles are trapped in the outer layer and fine particles in the inner layer, holding dirt within the depth of the cartridge. Economical for pre-filtration with high dirt loads.
- Pleated cartridge (Megapleat, POLYFIL PP): much larger filtration area within the same housing volume; fewer changeouts on low-dirt-load, high-flow lines. Megapleat uses inside-to-outside flow and conforms to the HFU standard, allowing drop-in use in existing HFU installations without changing the housing.
- Membrane (POLYFIL PES): sterile filtration; asymmetric pore structure provides high flow rate and dirt-holding capacity. Integrity testing is straightforward and repeatable, required in validated manufacturing.
- Metal cartridge (CHTM): pleated microfiber (70–87% porosity), sintered metal powder (1 micron for culinary-grade steam), pleated mesh and wedge-wire screen types; cleanable and reusable an almost unlimited number of times.
- High flow (MP-CHT): in the large-diameter coreless construction, the stainless steel support core remains in the housing; no metal is present in the disposed cartridge.
In lines with both high dirt load and high flow rate, two stages are used in series: a depth or bag filter first, followed by a pleated cartridge.
Bag Filters: Media, Sizes and Welded Seams
There are three bag families: BNMO nylon monofilament mesh (surface filtration only, 1–1500 micron, no fiber or contaminant migration, unaffected by metal fatigue); PONG/PENG glazed-surface polypropylene or polyester felt (1–100 micron; 75 and 200 also available in polyester); and BPOMF three-layer microfiber (1, 2, 10, 25, 90 micron; FDA-compliant material). In felt bags, welded seams are critical: needle holes in sewn bags can reach up to 1200 microns and allow unfiltered liquid to bypass.
| Bag size | Diameter (mm) | Length (mm) | Surface area (m²) |
|---|---|---|---|
| 1 | 180 | 420 | 0.25 |
| 2 | 180 | 815 | 0.50 |
| 3 | 102 | 203 | 0.07 |
| 4 | 102 | 360 | 0.12 |
| 4L | 102 | 380 | 0.12 |
| 30 | 102 | 250 | 0.08 |
| 65 | 102 | 560 | 0.18 |
In felt bags, polypropylene is highly resistant to acids and bases; polyester is weaker in strong alkalis but outperforms polypropylene in solvents. Catalog temperature limits are 200–220°F (approximately 93–104°C) for polypropylene and 275–325°F (approximately 135–163°C) for polyester. As a bag filter housing, HDB plus XL features a side-entry design accepting standard Size 1 and Size 2 bags, rated for 8 bar / 60°C under PED. See filtration systems for bag filter options.
Filter Housing and Ordering Code
LSH is a sanitary single-cartridge housing (316L or 304; from laboratory scale up to large industrial sizes; with vent and drain valves). TLSH is a sterile multi-cartridge housing operating with pharmaceutical-standard code 226 cartridges in 10, 20, 30 and 40 inch lengths; its inline construction simplifies disassembly and autoclave sterilization. HDB plus XL is used for filter bags. The housing and cartridge end cap must match.
The ChemTech ordering code follows the sequence length + type + micron + end cap + O-ring. End-cap codes (per CHT, POLYFIL PP, POLYFIL PES and TEFPOR GF catalogs): DOE/M double open end; 2 = 222, 6 = 226 O-ring style; FL flat, FN fin. O-ring codes: B NBR, E EPDM, S silicone, V Viton, P PFA/Viton. Length codes: 5 = 5 inch, 1 = 10, 2 = 20, 3 = 30, 4 = 40. Example: 30CHT-5-6FNS = 30 inch CHT, 5 micron, 226 fin end cap, silicone O-ring. For cartridges with an uncertain code, share the label or photo and we will verify the equivalent.
Which Filter for Which Line?
| Application | Recommendation | Rationale |
|---|---|---|
| Pre-filtration ahead of RO and EDI | CHT depth cartridge | High dirt-holding capacity; 5 micron recommended immediately upstream of EDI |
| Pharmaceutical pre-filtration, pre-sterile protection | POLYFIL PP | Pharmaceutical-grade polypropylene; 121°C autoclave |
| Sterile liquid filtration | POLYFIL PES 0.20 µm + TLSH housing | Integrity testable, 130°C steam, low protein binding |
| Compressed air, gas, tank vent | TEFPOR GF + LSH/TLSH | Hydrophobic, 121°C autoclave, 0.01 µm rating |
| Hot gas, steam, aggressive chemicals | CHTM metal cartridge | Up to 480°C, washable and reusable |
| High-flow process water | Megapleat, MP-CHT, bag filter | Large filtration area, low pressure drop, compact housing |
| Paint, coatings, chemicals, wastewater | Felt or microfiber bag | High dirt load, easy changeout |
For selection, share your line flow rate, operating pressure and temperature, target particle size, fluid chemistry and existing housing details.
Frequently Asked Questions on Cartridge and Bag Filter Selection
Micron rating, filter media, changeout differential pressure, bag vs cartridge and housing compatibility.
How do you select a cartridge filter?
Five questions determine the selection: the particle size to be retained and micron rating (absolute or nominal), the fluid chemistry and temperature (material), construction (depth, pleated, membrane, metal), the existing housing and end-cap standard (222, 226, DOE, Big Blue; 10–40 inch) and whether the line requires sterilization or sanitization. Looking at the micron value alone is not sufficient.
What is the difference between absolute and nominal micron rating?
An absolute rating means that particles of the specified size are retained with a defined efficiency (99.98% for ChemTech CHT) and that this efficiency has been measured: multipass testing and a laser particle counter are used on CHT and Megapleat cartridges, while ACFTD particles are measured with a multichannel laser counter on POLYFIL PP. A nominal rating is a value whose retention efficiency and test method vary by manufacturer; unless efficiency and test method are stated, the nominal ratings of two products cannot be compared.
Polypropylene, PES, PTFE or metal?
Polypropylene (CHT, POLYFIL PP, Megapleat) for general water and acid/base/aliphatic solutions. 0.20 micron PES membrane (POLYFIL PES) for sterile liquid filtration, offering low protein binding and use across the entire pH range. Hydrophobic PTFE-impregnated glass microfiber (TEFPOR GF) for air and gas. Washable, reusable stainless steel (CHTM, 316L and 304; max 480°C for SS 304 and 316L) for high temperatures, steam and aggressive chemicals.
When should a cartridge filter be replaced?
Based on differential pressure. ChemTech catalogs specify the recommended changeout pressure drop: 1 bar for CHT, 2 bar (20°C) for POLYFIL PP, and 2 bar for Megapleat. Maximum differential pressure is 4 bar (40°C) for CHT, 4 bar (20°C) for POLYFIL PP, 5 bar (20°C) for POLYFIL PES, and 3.5 bar for Megapleat. Flow reduction or quality deviation occurring below these limits is also a reason for replacement.
What is the difference between a cartridge filter and a bag filter?
A cartridge filter is designed for fine particle retention and sterile/critical lines (0.01–120 micron); a bag filter is used in high-flow, dirty or coarse lines (1–1500 micron) and installs into a side-entry bag housing (HDB plus XL). A bag holds a large dirt load in a single pass and is easy to change; a cartridge provides finer ratings and higher efficiency. In many lines both are used in series: bag first, cartridge second.
Which cartridge fits my existing filter housing?
End-cap style and length compatibility determine the fit. ChemTech CHT cartridges are manufactured from 5 to 60 inches and ordered with DOE (double open end), 222 and 226 O-ring, flat or fin, M (double open end) and Big Blue end caps; O-ring material can be NBR, EPDM, silicone, Viton or PFA/Viton. Megapleat conforms to the HFU standard. Share your housing standard and existing cartridge code and we will verify compatibility.
Send the make and model of your current instrument to [email protected] — our engineers will propose the equivalent with the same connection and measuring range.
Planning a project? Send us your flow rate, feed water source and target water quality to [email protected] — our engineers will reply with a technical proposal.