01 Operational parameters & standard limits
Target operating windows for a direct-to-chip CDU secondary (technology) loop. Use these as the acceptance band during commissioning and the alarm band during operation. Site values may differ per vendor data sheet and chip TDP — always confirm against the unit's manual and the IT hardware spec. To compute these targets (flow, ΔT, velocity, dP, approach, NPSH, dew-point) for your own load, use the CDU Calculator.
| Parameter | Typical target / limit | Notes & standard |
|---|---|---|
| Secondary supply temp (TCS supply) | ~17–45 °C | ASHRAE TC 9.9 W17–W45 classes; lower for high-TDP GPUs. Number = max supply °C. |
| Secondary ΔT (supply→return) | ~8–12 °C | Sized with flow to the rack heat load (Q = 4.186 × L/s × ΔT). |
| Coolant flow rate | ~1.0–1.5 LPM / kW | OCP guidance ~1.5 LPM/kW at a 10 °C rise; per-cold-plate min flow per chip vendor. |
| Differential pressure (CDU/manifold) | ~0.5–3.0 bar | Within the cold-plate's min/max dP window; watch for filter-clog rise. |
| System (loop) pressure | ~2–6 bar | Below component PN rating; maintain with expansion/make-up control. |
| Coolant / fluid | 25–30% PG (or DI / dielectric) | Propylene-glycol mix for freeze/biocide; DI water (ASTM Type II) for some TCS; dielectric for immersion. Per vendor wetted-material list. |
| Water quality | ASHRAE W1–W4 | Conductivity, pH, hardness, particulate per ASHRAE liquid-cooling guidelines. |
| Filtration rating | ~50 micron (integrated) | e.g. Vertiv CoolChip integrated 50-micron filter; supplement with side-stream if specified. |
| Pump redundancy | N+1 | Dual/redundant pumps + dual power feeds (e.g. CoolIT CHx N+1 pumps + N+1 PSUs). |
| Leak detection | 0 leaks · rope/zone | Leak-detection rope/sensors at CDU base, manifolds, QDs; alarm → isolate. |
| Approach temp (ATD, L2L) | ~3–5 °C | Heat-exchanger approach (e.g. Boyd 3 °C, CoolIT 5 °C ATD). Higher ATD = fouling. |
| Supply vs room dew point | ≥ +2–3 °C above dew point | Dew-point-aware reset prevents condensation on plates/pipe. Critical safety interlock. |
| Pipe velocity (sizing) | ~1.5–3 m/s | Too slow → fouling/air; too fast → erosion + high dP. Sets pipe DN for the flow. |
| Corrosion inhibitor reserve | > 100 ppm azole | No nitrites; depletes over time. Cu < 0.2 ppm / Fe < 0.1 ppm = corrosion indicators. |
| Pump NPSH margin | ≥ 10–20% | Below margin → cavitation + impeller erosion. Maintain system pressure + de-air. |
| Footprint / clearance / weight | per model (e.g. 2400×1200×1200 mm · ~1793 kg wet) | Service clearance front/rear per manual; floor loading checked for filled weight. |
02 Water quality — acceptance criteria & standard limits
The single biggest driver of cold-plate reliability is fluid chemistry. Two loops have different limits — the secondary Technology Cooling System (TCS) that touches the chips, and the primary Facility Water System (FWS) — because the fluids differ (inhibited PG25 glycol vs treated facility water). Use the table that matches your loop as the commissioning acceptance criteria and the operational monitoring band.
STANDARD published code / spec figure · TYPICAL/VENDOR typical or vendor range, not a fixed standard
ASHRAE facility-water (W) classes — max supply temperature
ASHRAE TC 9.9 liquid-cooling classes. The number is the max facility supply temperature in °C; all classes share a 2 °C lower limit. Higher class → more free-cooling / chiller-less operation. STANDARD ASHRAE TC 9.9 (2021)
| Class (new) | Old | Max supply temp | Typical plant |
|---|---|---|---|
| W17 | W1 | ≤ 17 °C (62.6 °F) | Chiller + tower, water-side economizer |
| W27 | W2 | ≤ 27 °C (80.6 °F) | Chiller + tower, more economizer hours |
| W32 | W3 | ≤ 32 °C (89.6 °F) | Chiller-less in most climates |
| W40 | — | ≤ 40 °C (104 °F) | Chiller-less (added 2021) |
| W45 | W4 | ≤ 45 °C (113 °F) | Chiller-less for capex/efficiency |
| W+ | W5 | > 45 °C | Warmest-water designs |
TCS (secondary / cold-plate loop) — fluid acceptance criteria
For single-phase water-based cold-plate racks. STANDARD OCP, Guidelines for Using Water-Based Transfer Fluids in Single-Phase Cold-Plate Racks, Rev 1.0, Table 1
| Parameter | Acceptance limit | Notes |
|---|---|---|
| pH | 8.0 – 10.5 | Inhibited/glycol TCS runs alkaline; >9.5 may reduce biocide need. (Don't apply the older generic "7–8.5" water figure here.) |
| Conductivity | < 1,500 µS/cm @25 °C | After treatment, then monitor rate-of-rise. Inhibited fluid is intentionally conductive — the <5–10 µS/cm target is for DI-water loops only. |
| TDS (total dissolved solids) | < 1,000 ppm | — |
| TSS (suspended solids) | < 5 ppm op · < 1 ppm fill | Tighter at initial fill. |
| Total hardness (CaCO₃) | < 30 ppm · < 2 ppm fill | Scale prevention. |
| Chloride | < 50 ppm (304SS) · < 500 ppm (316SS) | Pitting risk — limit depends on wetted stainless grade. |
| Turbidity | < 5 NTU | — |
| Bacteria | < 1 CFU/mL fill · < 100 CFU/mL op | Biofilm clogs microchannels. |
| Corrosion inhibitor (azoles/TTA) | > 100 ppm | No nitrites. Depletes over time — dose per sample. |
| Cu / Fe ions | < 0.2 ppm / < 0.1 ppm | Corrosion indicators — rising = active attack. |
| Side-stream filtration | down to < 5 µm | Polishing loop keeps particulate low. |
TCS vs FWS — side-by-side limits
STANDARD ASHRAE TC 9.9, reproduced in Dell "Liquid Coolants Guidance for TCS and FWS", Table 2
| Parameter | TCS (PG25 secondary) | FWS (facility primary) |
|---|---|---|
| pH | 8.0 – 10.5 | 7.0 – 9.0 |
| Total hardness (CaCO₃) | < 50 ppm | < 200 ppm |
| Chloride | < 25 ppm | < 50 ppm |
| Sulfate | < 25 ppm | < 100 ppm |
| Sulfide | — | < 10 ppm |
| Cu / Fe | < 2 ppm each | — |
Make-up / top-off water (OCP sub-spec). STANDARD chloride < 25 ppm · sulfate < 25 ppm · Ca < 25 ppm · Mg < 25 ppm · total hardness < 50 ppm CaCO₃ · < 1 CFU/mL. Blend/dilution water benchmark: ASTM D1193 Type II (resistivity > 1 MΩ·cm, ≈ < 1 µS/cm). Not over-stated: TOC has no published numeric cold-plate limit (treat as TYPICAL/VENDOR); the biostatic glycol % is a freeze/viscosity choice, not a fixed biocide standard.
03 Installation & commissioning — numeric procedure
The numbers behind the §04 checklist ticks. Where a value is a published code/spec it is tagged STANDARD; where it is common engineering practice it is tagged TYPICAL/VENDOR so you don't over-cite it in a design package.
Pressure test (hydrostatic)
- Hydrostatic test pressure = 1.5 × design pressure, temperature-corrected PT = 1.5 × PD × (ST/SD).STANDARD — ASME B31.3 / B31.1
- Hold ≥ 10 min at test pressure before/while examining joints, then for the full inspection duration.STANDARD — ASME B31.x minimum (a 4-hr hold is a TYPICAL/VENDOR DC practice)
- Acceptance = no leakage / no visible decay. ASME does not set a "% drop over N hours" — any such figure is project/vendor.pneumatic alt: B31.3 1.1× · B31.1 1.2×
Flush & cleanliness
- Turbulent flush — sustain Re > 4,000 (≈ 2–3 m/s) to scour debris before connecting cold plates.STANDARD flushing convention · velocity TYPICAL
- Cleanliness target by ISO 4406 (>4/>6/>14 µm code) or NAS 1638; sensitive loops aim ~16/14/11 or better.STANDARD frameworks · target TYPICAL
- Flush until clean — common gate: conductivity stabilises < ~5 µS/cm (DI loops); TCS in-loop turbidity < 5 NTU (OCP fluid spec).VENDOR gate · OCP turbidity STANDARD
Filtration sizing
| Loop | Filter rating | Source |
|---|---|---|
| FWS / primary | 150 – 500 µm | TYPICAL/VENDOR |
| TCS / secondary (main) | 25 – 50 µm | 50 µm ≈ 288 mesh VENDOR (Lenovo Neptune citing ASHRAE) |
| Cold-plate side-stream | < 5 – 10 µm | OCP (< 5 µm) |
| Polishing (fine side-stream) | down to 0.2 µm | VENDOR (Boyd/Eaton) |
Coolant & flow
- PG25 (25 vol% propylene glycol) is the de-facto DTC grade (freeze ≈ −10 °C); practical band 20–35%.PG25 STANDARD (OCP-listed) · band TYPICAL
- Design flow ≈ 1.5 LPM/kW at ~10 °C rise; published band 1.25–2.0 LPM/kW (7.5–12 °C ΔT). Physics: Q = ṁ·cp·ΔT, cp(PG25) ≈ 3.9–4.0 kJ/kg·K.STANDARD — OCP cold-plate design point
- 2-phase / refrigerant DLC fluids: R-1233zd(E) (GWP 1, A1, boil ≈ 18 °C) · R-515B (GWP ≈ 293, A1) · R-1336mzz(Z).vendor datasheet figures
Quick-disconnects (QD) — OCP UQD / UQDB
- Match the QD standard across the loop — no mixed couplers. UQD = hand-mate, drip-free, hot-pluggable; UQDB = blind-mate with ±1 mm radial tolerance for rack/manifold insertion.STANDARD — OCP UQD/UQDB
- Sizes UQD02/04/06/08 · max working 100 psi (6.9 bar) · min burst 300 psi (20.7 bar) · op 17–65 °C · ≥ 5,000 mating cycles · dripless spillage ~0.02–0.07 mL/connect.cross-checked vs Parker/CPC datasheets
- No standardised coupler torque (push-to-connect). Torque applies only to threaded fitting/manifold ports — per vendor.TYPICAL/VENDOR
Leak detection & response
- Two sensing types: rope/cable zone sensing (area coverage under floor / along runs) + point/spot sensors (CDU drains, QD manifolds, headers).industry practice
- Response sequence: detect → alarm to BMS/DCIM → isolate / auto-shutoff valves → contain. Guidance: OCP OAI Liquid Cooling Guidelines + ASHRAE TC 9.9 5th ed.STANDARD guidance · timing figures TYPICAL
04 Installation checklist
Phased from delivery to handover. Tick each item; the printable form (§06) captures readings + sign-off.
Site preparation
- Floor loading verified for the CDU's filled, operating weight + service access.confirm point load vs raised-floor / slab rating
- Service clearances front/rear/sides per the unit manual.e.g. ≥1 m service aisle; door swing + tube routing
- Facility water available (L2L) with isolation valves, strainer, flow/temp at design point — or confirm L2A room-air budget.CDW supply/return temp + flow per data sheet
- Dual power feeds available (A/B), correct breaker rating + earthing.N+1 PSU; verify voltage/phase
- BMS / leak-detection integration points identified (Modbus/BACnet/SNMP).
Mechanical install
- CDU set + levelled, anti-vibration mounts seated.
- Primary & secondary piping connected; pipe spec/insulation per design; supports fitted.no strain on CDU ports; correct DN size
- Manifolds + quick-disconnects installed; QD standard matched (no mixed couplers).verify drip-less QD type per vendor
- Leak-detection rope/sensors routed at base, manifolds, QDs.
Fill, flush & commission
- Pressure test primary + secondary to spec; hold + record (no decay).test pressure + hold time per manual
- Flush secondary loop to remove debris before connecting cold plates.flush until clean / target turbidity
- Fill with correct coolant (PG% / DI / dielectric) and de-air the loop.record fluid type + concentration
- Set flow + dP + supply temp to design; verify against rack heat load.
- Leak-detection + alarm test; confirm auto-isolation behaviour.
- Redundancy test — fail one pump / one PSU, confirm N+1 hold.
- BMS points verified (flow, temps, dP, pressure, alarms reading correctly).
- Handover pack — as-built, fill record, commissioning sheet, O&M manual filed.
05 Routine inspection checklist
Walk-down checks. Anything outside the §01 band → log + see the symptom table (§05).
- No leak alarm; visually dry at base, manifolds, QDs, HX, pump seals.0 leaks · check for glycol residue / drips
- Flow within band.~1.0–1.5 LPM/kW
- Differential pressure stable (no clog rise).~0.5–3.0 bar
- Supply / return temps + ΔT at target.supply ~17–45 °C · ΔT ~8–12 °C
- System pressure in band; expansion / make-up healthy.~2–6 bar
- Pump status — duty running, standby ready (N+1); no noise/vibration.
- Filter dP within clean range; no clog warning.
- No alarms on HMI; data quality live (not stale).
06 Preventive-maintenance (PM) checklist
PM tasks by cadence. DAILY WEEKLY MONTHLY QUARTERLY ANNUAL. Intervals are a baseline — follow the vendor PM schedule and adjust to fluid-sample results. The Parts / consumable column points to the line in §07 — Spare-parts register with part reference, critical-spare class and cost band.
| Task | Frequency | Acceptance / action | Parts / consumable |
|---|---|---|---|
| Read & log flow / dP / temps / pressure; check alarms | DAILY | All within §01 band; trend for drift. | none |
| Visual leak walk-down (base, QDs, manifolds, seals) | DAILY | Dry; any glycol residue → investigate. | none |
| Verify N+1 (standby pump/PSU healthy) | WEEKLY | Standby ready; exercise per vendor. | none |
| Check make-up rate & expansion-tank level/pressure | WEEKLY | Make-up minimal; level/pressure in band — rising make-up = slow leak. | PG25 top-up · bladder |
| Verify dew-point reset active (supply ≥ room dew point +2–3 °C) | WEEKLY | No condensation risk; RH sensor reading true. | RH sensor |
| Leak-detection function test | MONTHLY | Alarm + isolation confirmed. | leak rope/controller |
| Filter / strainer dP check — replace element if clogged | MONTHLY | Replace when filter dP > vendor threshold (typ. >+0.3–0.5 bar above clean); record. | filter element |
| Coolant sample — pH, conductivity, glycol%, biology, particulate | QUARTERLY | Within ASHRAE W-quality; dose/replace per result. | PG25 · inhibitor/biocide |
| Flow & dP sensor calibration check | QUARTERLY | Within sensor tolerance; re-cal if drift. | flow · dP xmtr |
| Pump seal / bearing inspection (vibration, noise) | QUARTERLY | Service per runtime hours / vendor; weep or rising vibration → reseal. | seal kit · pump |
| Control-valve stroke / actuator demand-vs-feedback test | QUARTERLY | Deviation <10%; fail-safe (bypass) confirmed. | TCV actuator |
| BMS/DCIM telemetry & alarm-point verification | QUARTERLY | All points live + correct; no stale data; alarms route. | none |
| Corrosion-inhibitor reserve + Cu/Fe ion test | QUARTERLY | Inhibitor >100 ppm; Cu <0.2 / Fe <0.1 ppm (rising = active corrosion). | inhibitor |
| QD / gasket / O-ring seal inspection (glycol-compatible EPDM) | QUARTERLY | No weep; replace any seal showing compression-set or leak. | QD · EPDM kit |
| Pressure-relief valve (PSV/PRV) test | ANNUAL | Relieves at set pressure < component PN; reseats. Replace if passing/stuck. | PSV |
| Heat-exchanger approach (ATD) check / clean | ANNUAL | Rising ATD = fouling → clean / CIP the fouled side. | HX gaskets (if opened) |
| Coolant replacement (or per sample) | ANNUAL | Replace full charge if chemistry out of band. | PG25 full charge |
| Air-side coil & filter service (L2A only) | ANNUAL | Clean coil; replace air filter at dP threshold — restores room-reject capacity. | air filter |
| Full redundancy + failover drill; firmware/controls review | ANNUAL | N+1 holds under fault; backups current. | none |
07 Spare-parts & consumables register
Every PM line that consumes a part maps to a row here: what to replace, the acceptance / replace-when trigger, the interval, a part reference / spec (commodity manufacturer family or OEM service-part class — exact OEM part numbers are proprietary and obtained from the unit's IPB, see §08), a critical-spare class, and an estimated unit-cost band. CRITICAL = hold on site (failure stops cooling). RECOMMENDED = short-lead consumable. ON-DEMAND = order when condition-flagged.
STD published standard / spec
VENDOR typical vendor part family
EST illustrative cost band — representative market range, not a quote
| Item | Function / where | Replace-when (acceptance trigger) | Interval | Part reference / spec | Critical | Est. unit cost | Src |
|---|---|---|---|---|---|---|---|
| Secondary-loop filter / strainer element | Y-strainer or cartridge on the TCS loop — protects cold-plate micro-channels. | Filter dP > clean +0.3–0.5 bar, or monthly. | MONTHLY | 50 µm SS mesh (Y-strainer) / 25–50 µm pleated cartridge e.g. Parker, 3M, Eaton families | CRITICAL | $25–120 | VENDOR EST |
| Heat-transfer fluid — inhibited PG25 | Secondary coolant (25 % inhibited propylene glycol) touching the cold plates. | Chemistry out of band (pH/conductivity/glycol %/biology) or annual. | QUARTERLY top-up · ANNUAL charge | 25 % inhibited PG, low-conductivity e.g. Dynalene PG, DOWFROST, ClearTech 25-PG; charge ≈ 60–200 L/unit | RECOMMENDED | $8–25 / L (charge $1k–4k) | VENDOR EST |
| Quick-disconnect coupling (dry-break) | Rack-manifold & CDU service connections — no-spill on de-mate. | Seal weep, drip on de-mate, or compression-set on inspection. | QUARTERLY inspect | Dripless / dry-break QD e.g. Stäubli CGO/SPT, CPC LQ, Parker Non-Spill; EPDM seals | CRITICAL | $40–180 | VENDOR EST |
| EPDM gasket / O-ring kit | Manifold, HX ports, flange & QD seals — must be glycol-compatible EPDM, not NBR. | Any weep; replace whenever a joint is broken for service. | QUARTERLY inspect | EPDM O-ring / gasket set per unit seal schedule (peroxide-cured EPDM) | CRITICAL | $40–150 / kit | VENDOR EST |
| Pump mechanical / cartridge seal kit | Circulation pump shaft seal (duty & standby). | Weep at seal, rising vibration/noise, or per runtime-hour limit. | QUARTERLY inspect | Mechanical seal kit per pump model e.g. Grundfos / Wilo / canned-rotor service kit | RECOMMENDED | $80–400 | VENDOR EST |
| Spare circulation pump (N+1) | Duty/standby secondary pump — the unit holds N+1 with auto-changeover. | Bearing/seal failure, persistent low flow after reseal. | condition | EC/wet-rotor or canned pump per CDU e.g. Grundfos CRE / Wilo-Stratos class | RECOMMENDED (1/fleet) | $600–3,500 | VENDOR EST |
| Expansion-tank bladder / diaphragm | Holds loop pressure & absorbs thermal expansion. | Waterlogged tank, pressure won't hold, air on bladder side. | condition | EPDM bladder per tank model | ON-DEMAND | $60–300 | VENDOR EST |
| Leak-detection rope + controller | Sensing cable at base/manifolds/QDs feeding the leak alarm & isolation. | Fails monthly function test, contamination, or physical damage. | MONTHLY test | Water/glycol-sensing rope + zone controller e.g. TTK, RLE SeaHawk, nVent Raychem | CRITICAL | rope $15–40/m · ctrl $300–900 | VENDOR EST |
| Flow sensor (turbine / vortex / ultrasonic) | Secondary flow measurement — the primary cooling-delivery proof. | Drift beyond sensor tolerance vs reference; signal loss. | QUARTERLY cal | Inline flow sensor e.g. ifm SM-series, Grundfos VFS | RECOMMENDED | $150–600 | VENDOR EST |
| Pressure / differential-pressure transmitter | Loop & filter dP, system pressure (drives VFD & filter alarm). | Drift vs gauge, signal loss, out-of-range. | QUARTERLY cal | 4–20 mA P / ΔP transmitter e.g. ifm PN/PT, Danfoss MBS | RECOMMENDED | $120–450 | VENDOR EST |
| Temperature / RH sensor (+ thermowell) | Supply/return temp & room dew-point reset reference. | Drift vs reference; dew-point reset depends on a true RH reading. | QUARTERLY cal | PT100/PT1000 + thermowell; RH probe | ON-DEMAND | $25–120 | VENDOR EST |
| Control-valve actuator (TCV / PICV) | Modulates supply temp / bypass — fail-safe to a safe (cooling) position. | Demand-vs-feedback >10 %, stiction, signal loss. | QUARTERLY test | Modulating actuator per valve e.g. Belimo class | ON-DEMAND | $200–900 | VENDOR EST |
| Corrosion inhibitor / biocide dosing | Maintains inhibitor reserve & controls biology in the loop. | Inhibitor <100 ppm; biology positive; Cu/Fe rising. | QUARTERLY | Glycol-compatible inhibitor + isothiazolinone biocide e.g. Dynalene inhibitor pack | RECOMMENDED | $20–60 / L | VENDOR EST |
| Pressure-relief valve (PSV / PRV) | Over-pressure protection below component pressure rating (PN). | Fails annual lift test, passes/weeps, or stuck. | ANNUAL test | Set-pressure relief valve < loop PN | ON-DEMAND | $80–300 | STD EST |
| Air-side coil filter (L2A only) | Protects the liquid-to-air reject coil; L2A rejects to room air. | Air-side dP at threshold; reduced room-reject capacity. | ANNUAL | Panel / pleated air filter per unit | ON-DEMAND | $15–60 | VENDOR EST |
Stocking logic. Hold every CRITICAL item on site (a clogged filter, failed QD, weeping seal or dead leak-rope can stop cooling or trip the rack). Keep a charge-fraction of PG25, one seal kit and one spare pump per fleet as RECOMMENDED. Cost bands are EST illustrative market ranges for budgeting — confirm against your OEM service-parts quote and the unit's IPB before purchase.
Spares planning — stock levels, service life & annual budget
The register turned into a stocking plan: min stock to hold on site, typical service life (how often the part actually needs replacing, not just inspecting), lead time (which is what really forces you to stock a critical item), and an estimated annual spend per CDU. Quantities assume one CDU; RECOMMENDED/fleet items are shared across the fleet.
| Item | Min stock (per CDU) | Typical service life | Lead time | Annual spend / CDU (EST) |
|---|---|---|---|---|
| Filter / strainer element CRIT | 2 | ~1 month (replace at dP) | 1–2 wk | $300–1,440 |
| PG25 fluid REC | 10–20 % of charge | top-up quarterly · full charge 1–3 yr | 1–3 wk | $350–2,000 amortised |
| Dry-break QD CRIT | 2 | 5+ yr / on failure | 2–6 wk | in kit |
| EPDM gasket / O-ring kit CRIT | 1 kit | 2–5 yr / on each joint break | 2–4 wk | $100–400 |
| Pump seal kit REC | 1 | 1–3 yr (runtime) | 2–4 wk | $100–300 amortised |
| Spare pump REC | 1 / fleet | 5–10 yr | 4–12 wk | capex $600–3,500/fleet |
| Inhibitor / biocide REC | 1 dose pack | per quarterly sample | 1–3 wk | $100–400 |
| Flow / dP / temp sensors REC | 1 of each | 5–10 yr | 2–6 wk | $100–500 amortised |
| Leak rope + controller CRIT | 1 rope spare | 7–10 yr / on failure | 2–6 wk | on failure |
Budget roll-up (EST, per CDU) — recurring consumables (filters, fluid top-up, dosing, amortised seals/sensors) sum to roughly $1,000–4,000 / yr. A one-time on-site critical-spare kit (2× filter, 2× QD, 1× gasket kit, 1× seal kit, 1× leak-rope spare) runs roughly $1,500–6,000, plus a shared fleet spare pump at $600–3,500. These are EST planning bands rolled up from the register above — not a quote; size to your fleet count, runtime hours and OEM service-parts pricing. The dominant driver is usually filter elements (frequency) and fluid (charge volume × $/L).
08 Exploded-view & IPB resources — per CDU type
Exact service-part numbers live in each unit's Illustrated Parts Breakdown (IPB) / service manual — request it from the OEM for your model (it is not public for most CDUs). Below, per CDU type, are the representative manufacturers and where to obtain the exploded-view / parts documentation. Match your unit to a row in the CDU comparison to find its OEM, then pull that OEM's manual.
In-Rack
L2L · in-cabinet 3U–4UCompact in-rack CDU. Exploded views cover the pump module, plate-HX, filter and QD manifold. Request the model's service manual / IPB.
In-Row
L2L · between-rack cabinetThe density workhorse. IPB covers dual-pump skid, expansion tank, dual-stage filtration, instrumentation & control valve.
Sidecar
L2L · rack-side slim unitSlim rack-mounted unit. Exploded views focus on the side-mounted HX/pump pack and rack-manifold QDs.
L2L · End-of-Row
L2L · facility-scaleLarge facility-coupled CDU (e.g. ≈2.3 MW). IPB covers large plate-HX, N+1 pump bank, facility-water interface & PSV.
L2A · Air-cooled
L2A · room-air rejectLiquid-to-air unit — no facility water. Exploded views add the air-side reject coil, fans & air filter to the standard liquid pack.
External links open the manufacturer's site — navigate to Support / Documentation and request the service manual or IPB for your exact model. These pages may block automated access but open normally in a browser.
09 Symptom → cause → action
Troubleshooting reference. On any active symptom: protect the IT load first (the CDU's N+1 / isolation logic), then diagnose.
| Symptom | Likely cause | Immediate action | Corrective action |
|---|---|---|---|
| High differential pressure | Filter clogging; valve throttled; air pocket | Check filter dP; confirm valves open; bleed air | Replace filter; re-balance; full de-air |
| Low / no flow | Pump fault; closed valve; QD not seated; airlock | Confirm standby pump took over (N+1); check valves/QD | Service/replace pump; reseat QD; purge air |
| Leak alarm | Loose QD; failed seal/gasket; manifold/HX leak | Acknowledge → isolate affected zone; locate via rope/zone | Tighten/replace QD or seal; pressure-test; refill + de-air |
| High coolant supply temp | Facility water warm/low flow (L2L); HX fouling; high ATD | Check primary supply temp/flow; check ATD | Restore CDW; clean HX; verify control setpoint |
| High room temp (L2A) | Room CRAH can't absorb rejected heat; coil dirty | Check CRAH capacity/airflow; clean coil | Add room cooling / move to L2L; coil service |
| Rising ATD (approach) | Heat-exchanger fouling; reduced flow one side | Compare primary/secondary ΔT; check flows | Clean/flush HX; restore flow |
| Pump fault / vibration | Bearing/seal wear; cavitation (low pressure/air) | Switch to standby; raise system pressure; de-air | Replace pump/seal; correct expansion control |
| Coolant chemistry out of band | Biology growth; glycol degradation; contamination | Sample; dose biocide / inhibitor | Partial/full coolant replacement; side-stream filtration |
| Air in loop (gurgling, unstable dP) | Incomplete de-air; make-up drawing air; leak | Bleed at high points; check make-up | Find/seal air ingress; re-fill correctly |
| Stale / lost telemetry | Sensor fault; comms loss to BMS | Treat values as suspect; local gauge check | Replace sensor; restore comms; re-cal |
| Condensation / sweating on plates & pipe | Supply temp driven below room dew point; dew-point reset disabled / RH sensor fault | Raise supply setpoint above room dew point; check RH sensor | Enable dew-point-aware reset (≥2–3 °C above dew point); fix humidity sensor; insulate |
| GPU throttling / hot sleds | Flow maldistribution across the manifold; under-provisioned flow vs chip TDP | Compare per-branch flow; verify total flow ≥ design L/min/kW | Balance manifold (balancing valves / flow restrictors); raise flow setpoint |
| Two-phase cold-plate dry-out (2-phase) | Vapour quality too high in hot sleds; uneven 2-phase distribution | Check refrigerant charge / sub-cooling; inspect distribution | Re-balance flow restrictors; restore charge; correct manifold geometry |
| Frequent make-up / falling level | Slow leak; air being purged; expansion bladder fault | Trend make-up rate + level (LT); leak walk-down | Find/seal leak; recharge / replace expansion bladder; re-pressurise |
| Control valve fault (TCV) | Actuator demand vs feedback >10%; signal loss → fail to bypass = no cooling | Switch to manual / verify fail-safe position; protect IT load | Re-stroke / replace actuator; re-tune PID (Ziegler-Nichols) |
| System over-pressure | Thermal expansion with closed expansion path; PSV not relieving | Verify expansion/relief path open; check PT vs component PN | Restore expansion control; test/replace PSV; re-set fill pressure |
10 FMECA fault reference — liquid cooling (F11.x)
The five direct-to-chip liquid-cooling fault modes from the site's FMECA knowledge graph, ordered by RPN (Risk Priority Number = Severity × Occurrence × Detectability, per IEC 60812). These are the same faults the Mini-BMS injects and the §07 register stocks against. Higher RPN → act first — but RPN can understate a high-severity, rarely-occurring fault: F11.2 (pump failure) scores S=10 yet RPN=60 because it's detectable and infrequent. Expand a card for component, mechanism, effect chain, detection, and corrective/preventive actions.
STD published code / standard (ASME · OCP)
VENDOR vendor data (Vertiv · 3M)
F11.1Coolant chemistry driftRPN 140ASME · HIGH
ComponentCDU coolant / dielectric fluid (C-LQC-005)
MechanismCoolant pH / conductivity drift (M-CHM-005)
EffectpH / conductivity drift → long-term cold-plate corrosion → reduced asset life
DetectionConductivity · pH · TDS · ORP
CorrectiveCoolant change + flush (on detection)
PreventiveInline chemistry monitoring (continuous)
S 7O 5D 4RPN 140
F11.4Dielectric fluid degradationRPN 1203M · THIN
ComponentDielectric fluid (single-phase) (C-LQC-005)
MechanismDielectric fluid oxidation (M-CHM-006)
EffectViscosity rise · dielectric-strength fall → heat-transfer loss
DetectionFluid sample analysis
CorrectiveFluid replacement (on detection)
PreventiveQuarterly fluid sample
S 6O 4D 5RPN 120
F11.3Manifold / hose leakRPN 108OCP · MEDIUM
ComponentIn-rack manifold (C-LQC-003)
MechanismHose / fitting leak (M-MEC-009)
EffectCoolant spill → electrical-short risk · rack damage → IT loss + cleanup (24–168 h)
DetectionLeak rope · drip-pan · pressure decay
CorrectiveReplace QD or hose (on detection)
PreventivePressure-decay test (quarterly)
S 9O 4D 3RPN 108
F11.2CDU pump failure · S=10 catastrophicRPN 60Vertiv · THIN
ComponentCDU canned-rotor pump (C-LQC-001 · ~50,000 h MTBF)
MechanismPump bearing wear (M-WER-007)
EffectFlow loss to cold plates → CPU thermal trip in <10 s → server reboot / damage (0–4 h)
DetectionFlow meter · ΔP · pump vibration
CorrectiveReplace CDU pump (on detection)
PreventiveN+1 pump + vibration test (monthly)
S 10O 3D 2RPN 60
F11.5Filter cloggingRPN 60OCP · MEDIUM
ComponentFilter (5–50 µm) (C-LQC-007)
MechanismCDU filter loading (M-FOU-005)
EffectΔP across filter rises → secondary-loop flow loss → ΔT / approach creep
DetectionFilter ΔP
CorrectiveReplace filter (on detection)
PreventiveMonitor filter ΔP (monthly)
S 5O 6D 2RPN 60
Source. FMECA-KG seed (Lin & Ompusunggu 2026 synthesis; per-fault: ASME J.Electron.Packag. 140 020902 · Vertiv · OCP · 3M) at
docs/research/csv/. S·O·D + RPN per IEC 60812; confidence tiers (HIGH / MEDIUM / THIN) reflect data provenance — vendor MTBF is often confidential. Full knowledge base + ML advisory concept: AI Engineering Maintenance.11 CDU service record — printable form
Fill on-screen and Print / Save as PDF. Captures site identity, readings against the §01 band, checklist pass/fail, and sign-off. Stored on the RZ site as the standard CDU service-record form.
Readings vs target band
| Parameter | Target band | Reading | Pass / Fail |
|---|---|---|---|
| Supply temp (°C) | ~17–45 | ||
| ΔT (°C) | ~8–12 | ||
| Flow (LPM/kW) | ~1.0–1.5 | ||
| Differential pressure (bar) | ~0.5–3.0 | ||
| System pressure (bar) | ~2–6 | ||
| Coolant pH / cond. / glycol% | ASHRAE W1–W4 | ||
| Filter dP / status | clean range | ||
| Leak detection | 0 leaks | ||
| Pump N+1 (duty/standby) | both healthy |
Disclaimer. Independent educational reference built from publicly available vendor pages and ASHRAE TC 9.9 / OCP guidance. Parameter bands are generic baselines — confirm exact limits, fluid spec, torque/pressure values and PM intervals against the specific CDU's manufacturer manual and your IT hardware spec. Not procurement, safety, or engineering advice; validate with the vendor and a qualified mechanical engineer.