Contamination Diagnostic Decision Tree
Module 02 — Contamination & Gas Loads | VacTech, Selkirk College
Pumpdown slower than expected?
Q1
Rate-of-rise test result:
Linear or decaying pressure rise?
LINEAR
⚠
Real leak detected
Check all seals, fittings, and welds.
Use helium leak detection to locate.
DECAYING
Q2
Was the system recently
opened or vented?
YES
✅
Outgassing
Extended pump time or
mild bakeout (60–120 °C)
NO
Q3
Hydrocarbon
contamination visible?
YES
🧴
Clean
IPA wipe, replace
O-rings if swollen
NO
Q4
H₂O dominant
on RGA?
YES
Moisture
Bakeout required
NO
Virtual leak
Check trapped volumes