# CSH2 Cryogenic Pump — Operational Context Knowledge # Practical knowledge that operators have but specifications don't document. # Derived from maintenance_log.xlsx, Technical PDF, and data analysis. sensor_trustworthiness: TT110: notes: > TT110 reads pipe wall temperature, not fluid temperature. After cooldown, it needs 10-15 minutes to equilibrate with the flowing cryogen. During transients (pump start/stop, flow changes), TT110 lags the actual fluid temperature by 5-30 seconds depending on flow rate. workaround: > For precise inlet temperature, use virtual T_inlet back-calculated from discharge state via ThermoProps (physics/thermo.py). The virtual sensor uses PT110 + TT130 + isentropic relations to infer inlet conditions. known_faults: - "Jul 16, 2025: 0-32K readings are sensor fault, not real cryo temps" - "Filter out readings during known warm periods where TT110 < 50K" FT140: notes: > FT140 is a Coriolis mass flow meter calibrated for LN2. When running LH2, the density difference (LN2: 808 kg/m³ vs LH2: 70.8 kg/m³) causes the raw reading to be 100-200x too high. The FT140Calibrator applies a density correction factor of approximately 11.4x. workaround: > Always apply FT140Calibrator (physics/ft140_calibration.py) density correction before interpreting flow readings. Near-zero flow at low pump speeds is expected and not a fault — the meter has a low-flow cutoff. known_faults: - "Raw FT140 reads ~100-200x too high for LH2 — apply correction" - "Near-zero flow at idle is expected, not a sensor fault" PT100: notes: > PT100 is stuck at -14.86 bar in the current dataset. This is not a physical pressure — it's a sensor fault. workaround: > Use default_when_invalid=2.0 barg for any calculations requiring PT100 (e.g., Psat estimation). This is the saturation pressure approximation. known_faults: - "Stuck at -14.86 bar — use 2.0 barg default" CalcMass: notes: > CalcMass is stuck at 0.18 kg in the current dataset. The PLC calculation is not updating. workaround: > Use FT140 integration (corrected) for actual dispensed mass calculation. Integrate corrected FT140 over the fill duration. known_faults: - "Stuck at 0.18 kg — use FT140 integration instead" M130_Speed_vs_MC130: notes: > Tag 68 (M130_Speed) replaces tag 13 (MC130_VFD_Speed) after May 28, 2025. Both map to motor speed percentage but are different register addresses. TAG_ALIASES in config.py handles this mapping. workaround: > Check TAG_ALIASES. Use tag 68 for post-May data, tag 13 for pre-May. Both are valid speed readings. post_maintenance_expectations: hp_seal_replacement: description: "After HP seal replacement or energizer work" expected_behavior: - "Initial friction: 7-9 kgf (from Jul 18 maintenance entry)" - "Break-in period: ~1000 cycles to reach 4-5 kgf steady state" - "Motor current will be higher initially — this is normal" - "Volumetric efficiency may be slightly higher initially (tighter seal)" timeline: "1000 cycles (~2-3 days at normal testing rate)" ref: "2025-07-18 maintenance event" icv_replacement: description: "After ICV replacement or reseating" expected_behavior: - "Immediate improvement in pressure build if ICV was the issue" - "New valve may need seating-in (initial performance varies)" - "Jul 22: orientation fix restored 700 bar immediately" - "Jul 14: polished ICV helped but didn't fully fix — surface not flat" timeline: "Immediate improvement expected" ref: "2025-07-01, 2025-07-14, 2025-07-22 events" dcv_polishing: description: "After DCV sealing surface polishing" expected_behavior: - "Immediate improvement in leak test results" - "Run PT130 decay test before and after to quantify improvement" - "Jul 1: polishing improved seal but some residual leakage" timeline: "Immediate improvement" ref: "2025-07-01 maintenance event" regime_caveats: ln2_vs_lh2: description: "LN2 and LH2 data are not directly comparable" details: > LN2 (77K, 808 kg/m³) and LH2 (20K, 70.8 kg/m³) have very different fluid properties that shift all performance curves. Compression ratios, volumetric efficiencies, heat transfer rates, and valve dynamics all change significantly between fluids. The SPEED_SCALE_FACTOR in config.py was calibrated for LN2 and needs adjustment for LH2. impact: - "Flow rate scales with density ratio" - "Pressure build rate changes with bulk modulus" - "Thermal effects are very different (77K vs 20K)" pressure_drift: description: "Discharge pressure drifts down during extended fills" details: > Documented in Technical PDF p.22. The pump operates at approximately fixed pressure ratio. As the small test cryotank depletes, inlet pressure (PT110) drops, and PT130 follows. This is NOT a fault — it's an expected consequence of the small tank size. impact: - "PT130 and flow rate decline over extended fills" - "Production tanks will be sized to maintain pressure" subcooling_sensitivity: description: "Pump performance is very sensitive to inlet subcooling" details: > From Technical PDF p.17: the pump is 169x more efficient with subcooled liquid than with gas. Even small amounts of flash gas at the inlet significantly reduce volumetric efficiency. Ensure adequate subcooling margin (>5K) before starting fills. impact: - "Inlet quality > 0 = reduced efficiency" - "Subcooling margin < 2K = risk zone" system_personality: recurring_issues: - priority: 1 description: "ICV sealing is the #1 recurring issue" details: "3 occurrences in July 2025. Check ICV first for any pressure build problem." refs: ["2025-07-01", "2025-07-14", "2025-07-22"] - priority: 2 description: "DCV sealing is the #2 issue" details: "1 occurrence. DCV polishing was effective but residual leakage remained." refs: ["2025-07-01"] - priority: 3 description: "Safety loop tuning needs attention at high pressures" details: "AOV141 hunting observed. PID tuning required." refs: ["2025-07-22"] strengths: - "HP seal life is excellent (8.2M cycle lower bound = 3+ months at 20 fills/day)" - "Phase 1B achieved 100% uptime across 6 fills" - "Specific energy of 0.26 kWh/kg matches target" - "Back-to-back fill capability demonstrated (4 consecutive fills)" known_limitations: - "Pump gas ratio 14.4% vs 2.7% target — efficiency gap exists" - "Peak pressure 370 bar vs 700 bar H70 target — further testing needed" - "Small test tank causes pressure drift during extended fills" - "FT140 requires density correction for LH2 — raw readings are wrong"