Data Centers
Guide
Data Center Filtration: Micron Ratings by Cooling Loop
- Quotes within one business day
- Case and bulk pricing on request
- Blind shipping available
- Cross-referencing from any part number or spec
- Call (657) 500-0938
- Email sales@filterbridgesupply.com
Short answer
A data center liquid-cooling (TCS / CDU secondary) loop is typically filtered at about 25 µm inline, with ≤50 µm acceptable and a finer side-stream under 5 µm. Facility water into the CDU is strained at about 100–500 µm, with OCP listing a primary filter at ≤200 µm, and OCP asks for makeup water filtered to 1 µm where possible. The equipment maker's spec always governs.
Quick reference
| Loop | Published micron guidance | Source |
|---|---|---|
| TCS / CDU secondary (cold plates) | ≤25 µm for microchannel cold plates; 25/50 µm inline; side-stream <5 µm | OCP Modular TCS Rev 1; OCP L2L CDU methodology |
| CDU secondary loop filter (example datasheet) | 25 µm standard, 50 µm optional, with ΔP clog detection | Rittal CDU In-Rack datasheet |
| Endpoint filtration without CDU | ≤100 µm | ASHRAE TC9.9 white paper |
| Facility water system (FWS) | Primary ≤200 µm (OCP); 100–500 µm strainers (Eaton) | OCP; Eaton |
| Cooling tower side-stream | Cartridges 5–50 µm, bags 5–75 µm | Fil-Trek; DOE FEMP |
| Makeup water | 1 µm where possible | OCP Modular TCS Rev 1 |
| Flush / commissioning | 5–50 µm cartridges or bags | Fil-Trek |
Questions and answers
What micron filter does a CDU secondary loop need?
OCP documents describe 25–50 µm as typical for the TCS loop. Microchannel cold plates call for ≤25 µm, plus side-stream polishing below 5 µm. The cold-plate or CDU maker's spec is the deciding requirement.
What's the difference between nominal and absolute ratings?
A nominal rating means the filter captures a share of particles at that size. An absolute or beta-ratio rating (ISO 16889, cited by ASHRAE TC9.9) is a tested capture efficiency. Liquid cooling specs often call for absolute or beta ratings. Each FilterBridge product page gives the rating type the manufacturer publishes.
Do you sell filters rated for CDU coolant loops?
Send us your filter spec (micron rating and rating basis, cartridge size, media, fluid, temperature and flow) and we'll quote to it, usually within one business day.
What filtration is used on the facility water side?
Strainers, typically 100–500 µm. OCP lists a primary filter at ≤200 µm.
What micron for cooling tower side-stream?
Cartridges about 5–50 µm (bags about 5–75 µm), on 3–10% of flow (up to 20%) per DOE FEMP. See the side-stream guide.
How fine should makeup water be filtered?
OCP's Modular TCS document says 1 µm where possible. Many sites also use RO for makeup or humidification. See commercial RO pretreatment.
What micron is used for flushing new loops?
Typically 5–50 µm cartridges or bags, stepping finer as the system cleans up. See the system flush guide.
When should filters be changed?
At the differential pressure limit your system specifies. One published cold-plate example sets a side-stream alarm around 1.5 psi (DLB Associates, 2025). Follow your own system's limit.
Who sets the final spec?
The cooling equipment maker and the engineer of record. This guide summarizes public guidance and doesn't replace either.
Get a quote
Send your spec and we'll quote within one business day. See also the filtration RFQ checklist and how to compare filter specifications.
Sources
- OCP, Modular TCS for Cloud Scale Rev 1 (2025)
- OCP, Liquid-to-Liquid CDU Test Methodology
- Rittal, CDU In-Rack SK 3343.230 technical datasheet
- ASHRAE TC9.9, Water-Cooled Servers white paper
- Eaton, Data center filtration (2026)
- DLB Associates, Liquid Cold Plates Part 3 (Dec 2025)
- US DOE FEMP, Side Stream Filtration for Cooling Towers (2013)
- Fil-Trek, Data center filtration solutions
Send us one part number. We'll take it from there.
No account, no minimum, no sales call required to get a number. Tell us what you buy today and we'll come back with available options and case pricing on what we can supply.