Guide
Flushing and cleaning a TCS loop before commissioning
A technology cooling loop is only as clean as its commissioning. This guide summarises the Open Compute Project's pre-commissioning guidance for TCS row manifolds and shows where flanges come into it.
A TCS loop is hydro tested at 1.3 to 1.5 times working pressure, recirculated and cleaned until clear, flushed at 3 to 5 ft/s until conductivity is close to the procedure water value, filtered down to about 5 microns, then filled with coolant or dried and blanketed with nitrogen.
Before you start
Cleaning cannot fix the wrong material. Confirm that pipe, fittings, flanges and valves are stainless or another approved wetted material, that stainless items arrived treated to ASTM A380, and that welds were made with an inert gas purge. Positive material identification on incoming flanges and fittings catches mix-ups before they are welded in.
Step by step
| Stage | What happens | Targets |
|---|---|---|
| Hydrostatic test | Fill slowly from a low point, vent at high points, hold test pressure | 1.3 to 1.5 times working pressure; do not break joints that passed |
| Initial recirculation | Circulate through temporary filters until clear | Turbidity under 20 NTU; at least 3 system volumes |
| Cleaning | Circulate a caustic cleaner | At least 4 hours; no rise in filter pressure drop for 1 hour |
| Flushing | Drain and refill with procedure water, recirculate | At least 8 system volumes per cycle; 3 to 5 ft/s |
| End point | Repeat flushing until clean | Conductivity within 10 to 20 µS/cm of procedure water, or 60 µS/cm max; turbidity under 5 NTU |
| Lay-up or fill | Fill with glycol coolant, or drain, dry and blanket | Dry nitrogen blanket; compressed air only to ISO 8573-1 Class 2 |
| Parameter | Value |
|---|---|
| Procedure water conductivity | 50 µS/cm max |
| Procedure water pH | 6 min |
| Total aerobic bacteria | 1,000 CFU/ml max |
| First stage filtration | 50 to 100 µm |
| Final filtration | 5 µm recommended (1 to 25 µm industry range) |
| Filter change | At about 10 psi pressure drop |
Flush immediately after cleaning, and do not leave water stagnant in the loop for more than 24 hours without chemical treatment. Bacteria grow quickly in warm, untreated water.
Where flanges help
- Flushing connections: 316L blind flanges on header ends become connection points for temporary pumps and filter skids.
- Bypasses: flanged spools let installers take cold plates, manifolds and heat exchangers out of the cleaning circuit and replace them with jumpers.
- Crevice-free joints: weld neck and stub end joints flush out more easily than slip-ons with internal fillet welds.
Frequently asked questions
Should the cold plates be in the loop during flushing?
Keep equipment with fine passages, such as cold plates, rack manifolds and plate heat exchangers, out of the initial cleaning and flushing circuit, using bypasses or jumpers, so debris is not driven into them. Follow the equipment and coolant suppliers' procedures.
How fine should the final filtration be?
The OCP guide recommends 5 microns final filtration, noting an industry range of 1 to 25 microns, with a first stage of 50 to 100 microns.
Can the flushed loop be left full of water?
Not for long. The guide warns against leaving water stagnant for more than 24 hours without chemical treatment. Fill with coolant promptly, or drain, dry and blanket the loop with dry nitrogen.
Source
Open Compute Project, guidelines for pre-commission preparation of technology cooling system (TCS) row manifolds in liquid-cooled data centers. Always follow the version adopted by your project and the coolant supplier's instructions.