- Cartridge (replaceable filter element) = the industrial "frame + replaceable tire" — a metal or plastic housing lasts 10 years, you just swap cartridges on schedule
- Capsule (integrated capsule filter) = the biotech lab's "single-serve coffee pod" — disposable, gamma-sterilized at the factory, zero cross-contamination
- Cartridge standard lengths are 10 / 20 / 30 / 40 inch, with 222 / 226 / DOE end-cap codes — pick the wrong one and it won't fit
- Capsules look 5x more expensive per piece, but once you factor in CIP labor, validation costs, and stainless housing depreciation, capsules are actually cheaper for small-batch biotech applications
- This article gives you a sizing reference table + decision cards to pick the right format in 10 seconds
- Why does the same membrane cost 5x more in capsule form than in cartridge form?
- Cartridge filter: the industry's "frame + replaceable tire"
- Capsule filter: the biotech lab's "single-serve coffee pod"
- Sizing and standards quick reference (10 / 20 / 30 / 40 inch + end cap codes)
- Which one to pick when? Decision cards
- Cost comparison: purchase price vs Total Cost of Ownership
- Sterility validation: the hidden advantage of capsules
- Installation orientation: vertical vs horizontal
- Common pitfalls
- FAQ
- References
Why does the same membrane cost 5x more in capsule form than in cartridge form?
Many customers are shocked the first time they see a quote: the same brand, the same 0.22 µm PES membrane, made into a 10-inch cartridge costs NT$5,000, but the equivalent filtration-area capsule costs NT$25,000. Same membrane, same pore size — how can the price be 5x different?
The answer isn't in the membrane — it's in everything around it. A cartridge is a bare replaceable element: just membrane + end caps + center core. It needs a metal or plastic housing to operate. A capsule, on the other hand, has the housing injection-molded as one piece with the membrane inside, complete with vent, drain, and inlet/outlet ports — plug-and-play, then dispose.
So before comparing prices, answer this fundamental question: does your facility already have a housing? How often do you change membranes? How long does one CIP cycle take? These three questions decide whether cartridge or capsule is cheaper — not the unit price, but the Total Cost of Ownership.
Cartridge filter: the industry's "frame + replaceable tire"
Think of a cartridge like a bicycle tire: the housing is the frame (a one-time purchase that lasts 10 years), the cartridge is the tire (a consumable replaced on schedule). This architecture supports 90% of the world's industrial fluid filtration systems — water treatment, chemicals, semiconductor UPW, food and beverage lines, pharmaceutical WFI pretreatment, and more. As long as flow rates are large and uptime is long, cartridge + housing is always the most economical answer.
Anatomy
- Outer cage: PP or 304 / 316L SS, protects the pleated membrane from being deformed by flow
- Pleated membrane: several square meters of membrane folded into 28–60 pleats, packing 0.6–0.8 m² of filtration area into a 10-inch volume
- Support layers: two layers of PP nonwoven on either side, supporting the membrane against compression
- Core: the central flow outlet, withstands radial compression
- End caps: heat-welded seal — the most critical leak point, and what determines which housing accepts the cartridge
Core advantages
Typical applications
High-flow turbidity removal in municipal water, prefilter / final filter on semiconductor UPW systems, sterile pretreatment for pharmaceutical WFI, clarification of chemical reactor feeds, wine clarification. Common features: high flow, long uptime, an existing formal housing and piping.
Capsule filter: the biotech lab's "single-serve coffee pod"
If a cartridge is the hardcore industrial type — bolts, O-rings, torqued caps — then a capsule is the convenience-store type: the entire coffee is sealed in a pod; you tear open the bag, snap on the connector, hit the pump — and start filtering.
Structural features
- One-piece injection-molded plastic shell: usually PP, sometimes PFA / glass-fiber reinforced PP, with the complete pleated membrane inside
- Built-in vent + drain: top air vent, bottom drain port, for easy wetting and emptying
- Multiple connector options: sanitary tri-clamp, hose barb, stepped barb, Luer lock (small format)
- Pre-sterilized at the factory: 25–40 kGy gamma irradiation, double-bagged for cleanroom entry
- Single-use: discarded after one use, no cleaning validation required
Size range
Capsules range from palm-sized to 30-inch equivalents:
- Mini capsule (≤10 mL/min): lab sampling, syringe prefiltration, membrane area 8–80 cm²
- Small capsule (0.1–2 LPM): small process applications, cart-mounted skids, membrane area 200–1,000 cm²
- Mid capsule (5–15 LPM): cell therapy, small-batch monoclonal antibody purification, membrane area 0.1–0.4 m²
- Large capsule (20–60+ LPM): equivalent to a 20-inch cartridge, membrane area 0.8–1.5 m²
Typical applications
Sterile filtration in mAb / vaccine / mRNA processes, sterile sampling of culture media, in-line buffer filtration, cell harvest prefiltration, lab HPLC mobile phase, sterile small-batch fill-finish for clinical trials, in-line filtration of IVD reagents. Common features: small batches, frequent changeovers, high sterility level, no cleaning validation desired.
Sizing and standards quick reference
Cartridge standard lengths
| Standard length | Actual length (mm) | Membrane area per element (PES 0.22 µm) | Typical flow (water, 30 kPa) |
|---|---|---|---|
| 10 inch | ~250 mm | 0.6–0.8 m² | 10–20 LPM |
| 20 inch | ~500 mm | 1.2–1.6 m² | 20–40 LPM |
| 30 inch | ~750 mm | 1.8–2.4 m² | 30–60 LPM |
| 40 inch | ~1,000 mm | 2.4–3.2 m² | 40–80 LPM |
OD is roughly standardized at 2.5–2.7 inch (about 64–69 mm), so a 10-inch housing accepts a 10-inch cartridge — but 20 / 30 / 40 inch require correspondingly sized housings. ODs vary slightly across brands (Pall / Sartorius / Cytiva / Cobetter / 3M / Parker), so always measure OD and end-cap specs before mixing brands.
End cap standard codes
| End cap type | Description | Common applications |
|---|---|---|
| DOE (Double Open End) | Both ends open, each with O-rings sealing against the housing inner wall | Water treatment, prefiltration, industrial OEM — the cheapest option |
| SOE (Single Open End) | One end open, the other end closed; the bottom is positioned by O-ring + locking tabs | Pharmaceutical / food / semiconductor high-cleanliness applications |
| 222 bayonet | SOE, two protruding O-rings forming flat-face seal | Pharmaceutical liquid sterile filtration — most common |
| 226 bayonet | SOE, two protruding O-rings + side locking tabs (bayonet lock) | High-vibration / high-pressure applications where dislodgement must be prevented |
| Flat / Fin top | Flat = flat surface; Fin = top fins (increase fluid turbulence) | Fin suits venting / steam, flat suits general liquids |
| Code 213 / 215 | Newer European specs integrating 222/226 + locking mechanism | Adopted by new European GMP lines |
Which one to pick when? Decision cards
Cost comparison: purchase price vs Total Cost of Ownership
Just looking at sticker price, capsules are indeed expensive. But once you factor in housing, CIP chemicals, cleaning labor, cleaning validation, and downtime losses, you'll often find: capsule TCO is actually lower than cartridge TCO, especially for small-batch applications.
| Cost item | Cartridge + Housing | Capsule (single-use) |
|---|---|---|
| Element / capsule unit price (10-inch equivalent) | NT$3,000–6,000 | NT$15,000–30,000 |
| SS Housing (10-inch) one-time investment | NT$80,000–150,000 | 0 |
| CIP labor per batch | 2–4 hours × technician wage | 0 (just remove and discard) |
| CIP chemicals + WFI | NT$500–2,000 per batch | 0 |
| Cleaning validation documentation | NT$500K–3M one-time per product / process | None (single-use documentation) |
| Cross-batch contamination risk | Must demonstrate cleaning effectiveness | Structurally eliminated |
| Per-batch integrity test | WIT (water) or IPA WIT | WIT, handheld instrument is sufficient |
Sterility validation: the hidden advantage of capsules
Sterility validation is the most overlooked yet most cost-impacting difference between cartridges and capsules.
Cartridge route: full CIP / SIP suite
- SIP (Sterilization In Place): 121–134 °C steam for 30+ minutes before each batch, requires validation that every dead leg reaches F0 ≥ 15
- CIP (Cleaning In Place): hot caustic (1% NaOH at 80 °C) + hot acid + WFI rinse, with TOC, bioburden, and conductivity verification after each batch
- Cleaning validation: each product / process requires three consecutive successful cleaning validations, with documentation costing NT$500K–3M
- Sanitization cycles: cartridge specs typically allow ≤25 cycles; beyond that, residue must be validated
Capsule route: gamma-sterilized at factory
- Pre-sterilized: 25–40 kGy gamma irradiation before shipment, double PE bag packaging
- SAL ≤ 10⁻⁶: sterility assurance level meeting USP <1207> / EU GMP Annex 1
- Bioburden certificate + extractables / leachables report: vendor provides full BPOG test reports
- Single-use: discarded after use, zero cross-contamination risk, zero cleaning validation
Installation orientation: vertical vs horizontal
Cartridges and capsules can both be installed vertically or horizontally, but the details matter:
Vertical installation (most common)
- Feed enters from below, exits at top: bubbles naturally rise to the vent, never trapping against the membrane to cause air lock
- Drain at the bottom: residual liquid drains completely at shutdown, preventing microbial growth
- Suits most single-use bioprocessing: capsule top/bottom connectors are aligned for vertical install logic
Horizontal installation (limited use)
- For space-constrained sites: e.g. piping is already horizontal, no vertical space available
- Vent must be at the highest point: if the vent is on the side, rotate the unit so it points up during install
- Watch for air pockets: bubbles trap easily against the membrane in horizontal orientation, leaving local filtration area idle
- Cartridge SOE OK horizontally, DOE not recommended: DOE relies on O-rings at both ends, and gravity sag in horizontal orientation can cause leaks
Common pitfalls
FAQ
For the same sterile filtration step, why do major pharma plants use cartridges while biotech startups use capsules?
Because their batch sizes and validation budgets differ. Traditional big pharma runs 5,000–20,000 L per batch with stable products for 20 years — cleaning validation amortizes cheaply, and cartridge + SS housing is the most economical answer. Biotech startups run 50–500 L per batch and reformulate every two years — a single cleaning validation costs millions of NTD, so single-use capsules zero out that cost line and end up cheaper.
Why must a fit test be performed when changing cartridge brands within a housing?
Because cartridge OD, O-ring groove depth, and total end-cap length specifications vary between brands — even though they're "close." Putting Brand A's cartridge in Brand B's housing may physically fit but leave the O-ring under-compressed — the moment pressure rises, you get leaks and downstream contamination. The fit test sequence: disassemble housing, install new cartridge, run WIT integrity test + pressure-hold test; only deploy after all pass.
Can capsules really not be regenerated and reused?
Structurally impossible. Capsules are injection-molded as one piece, with no way to disassemble and clean the membrane, nor are they designed for high-temperature steam sterilization (most PP shells tolerate only 80–95 °C). Even if you tried, you couldn't perform meaningful cleaning validation, and the FDA / EMA wouldn't accept it. Single-use means single-use — that's the design philosophy and the selling point.
How do I choose between 10-inch, 20-inch, and 30-inch cartridges?
Look at flow rate + change frequency. Estimate total daily filtration volume, divide by single 10-inch capacity (about 200–500 L depending on feed dirtiness), and see how many you'd swap per day. If 4+ per day, step up to 20-inch; 8+, go to 30-inch; 12+, go to 40-inch. Fewer elements means fewer downtime swaps and higher overall efficiency. Just confirm housing and piping clearance for longer sizes.
Do capsule vent and drain ports really need to be used?
Strongly recommended — otherwise the capsule may use less than 60% of its filtration area. The vent expels bubbles trapped during wetting; the drain empties residual liquid at shutdown to prevent microbial growth. Standard SOP: open the vent for 30 seconds before feeding, close once liquid flows steadily; close the feed at shutdown, then open the drain to empty.
Who actually defined the Code 7 / Code 8 codes?
Mostly Pall Corporation's early internal numbering, which became the industry de facto standard. Code 7 = 222 + flat top, Code 8 = 226 + fin top, etc. ASTM / ISO never officially adopted this scheme, but global pharma and Sartorius / Cytiva / Cobetter all follow it. The newer Code 213 / 215 are integrated bayonet designs from European vendors (Sartorius / Pall Europe), used mainly on new GMP lines.
Can SIP (steam sterilization) be applied to capsules?
Most standard PP capsules — no. PP shells have a long-term temperature limit of 80–95 °C, and 121 °C SIP will deform them. But certain brands (Sartorius Sartopore Platinum capsule, Pall Kleenpak Nova) offer reinforced versions rated for 121 °C × 30 min × multiple cycles. If your process requires SIP, only specify versions explicitly labeled "steam sterilizable in line" — generic capsules will fail.
References
- Pall — Sterile Filtration Products (cartridge + capsule specification manual)
- Sartorius — Sterile Filtration Cartridges and Capsules
- Cytiva — Bioprocess Filtration Solutions (ULTA + Supor capsule)
- Cobetter Filtration — Cartridge & Capsule Product Line
- FDA — Sterile Drug Products Produced by Aseptic Processing (cGMP requirements for sterile filtration)
- EU GMP Annex 1 — Manufacture of Sterile Medicinal Products (2022 revision)
- USP <1207> — Sterile Product Packaging — Integrity Evaluation
- Parker Hannifin — Process Filtration (DOE / SOE / 222 / 226 end cap reference)
- 3M Purification — LifeASSURE Sterile Cartridges & Capsules
- BioProcess International — Single-Use Equipment Disposability Considerations