Cryorefrigerator Pump Leak Hunting & Fault Diagnostics Protocol

Document Metadata & Equipment Scope

Document ID: TS-CRYO-2022-012 (Rev 2.0)
Author: Kadeem Manning (Tier II Facility Technician)
Target Systems: Leybold COOLVAC 1500 / COOLPOWER Cold Heads & COOLPAK 2000i / 5000i Compressors
Official PDF: Download Official Diagnostic Protocol PDF

1. Diagnostic Decision Tree for Pressure & Thermal Stalls

[Cryopump Stalls Above 15K on 2nd Stage]
                 │
      ┌──────────┴──────────┐
      ▼                     ▼
[Cold Head Power Stalled] [Helium Mass 4 Signal High]
      │                     │
      ├─ Adsorber Saturated ├─ Check Aeroquip Coupling O-rings
      └─ Low He Gas Charge  └─ Displacer Dynamic Seal Leak

2. Root Cause & Fault Isolation Matrix

Symptom / Observed Fault	Probable Root Cause	Diagnostic Verification Check	Corrective Action & Protocol
High Helium Background (Mass 4 Signal)	1. Cold head displacer seal leak. 2. Aeroquip coupling poppet leaking into vessel.	Mass 4 signal increases directly when static helium pressure is raised from 16 to 18 bar(g) on COOLPAK compressor.	Overhaul cold head displacer drive and dynamic seals. Replace leaking Aeroquip flexline couplings.
Second Stage Fails to Reach $< 15\text{ K}$	1. Charcoal array saturated with hydrogen/neon. 2. High radiative thermal load.	Perform pressure rise rate test ($dP/dt$) with gate valve closed. If rate $> 1.0 \times 10^{-3}\text{ mbar}\cdot\text{L/s}$, thermal load is excessive.	Execute full thermal regeneration with dry $N_2$ purge at $65^\circ\text{C}$ for 4 hours.
Relief Valve Continuous Venting	1. Particulate debris on Viton seal seat. 2. Weakened ISO 4126 relief spring.	Inspect exhaust line with acoustic ultrasonic probe and leak detector sniffer.	Vent cryopump safely to ambient atmospheric pressure; clean valve seat and replace spring assembly.

3. Standard Cool-Down & Regeneration Verification

Temperature (Kelvin)
  300K ──┐
         │ (1st Stage Cool-down: ~65K in 45 min)
   80K ──┼───────────┐
         │           │ (2nd Stage Cool-down: <12K in 75 min)
   15K ──┼───────────┼───────────┐ (Operational Base: ~10K)
    0K ──┴───────────┴───────────┴────── Time (Minutes)

Roughing Cross-Over: Never open cryopump gate valve to chamber until roughing pressure is $< 5.0 \times 10^{-2}\text{ mbar}$ to avoid oil backstreaming and rapid cryo-array icing.
Purge Regeneration: Backfill with ultra-high purity dry Nitrogen ($99.999%$) heated to $65^\circ\text{C}$ to release condensed water, hydrocarbons, and cryogenic gases.