1
Is base pressure achieved?
Yes
System OK — proceed
System is performing within specification. Continue normal operations.
No
Fault detected
System cannot reach expected ultimate pressure. Proceed to Q2.
2
Rate-of-rise test: linear or decaying?
Linear
Real leak
Constant pressure rise = atmosphere entering through a fixed orifice. Check fittings, seals, and welds.
Decaying
Internal gas source
Pressure rise slows over time — gas is being released from inside the system. Proceed to Q3.
3
Did pressure improve after bakeout?
Yes
Outgassing
Adsorbed water and hydrocarbons on surfaces. Extend bakeout duration or improve materials selection.
No
Not simple outgassing
Bakeout did not resolve the issue. Another gas source is present. Proceed to Q4.
4
Is there a pressure spike when isolating the foreline?
Yes
Backstreaming
Oil vapour or gas migrating backward from the pump. Check the foreline trap, oil level, and pump condition.
No
Source is elsewhere
No pump-related backflow detected. Proceed to Q5.
5
Was the system recently opened or serviced?
Yes
Virtual leak
Trapped gas in blind holes, under washers, or in dead volumes from reassembly. Check all trapped volumes.
No
Systematic leak hunt
No obvious cause identified. Perform section isolation test — systematically seal off sections to locate the source.