0106// Vacuum System Troubleshooting 101 Rev A

22 Aug 2017 | Guan Boon, Wong 

In this post, I will share some of my experiences in troubleshooting a vacuum system. The vacuum system I referring to is the vacuum main chamber which can reach 10^-3 torr 10^-9 torr. Your vacuum system may consist multiple subsystem or gas lines. But, the causes of leakage may be similar. I may not be able to cover all types of error conditions which can cause those failure modes, but I will try to adding more information into this post in future. 

Failure mode 1: Major Leak (Helium Leak Detector cannot reach fine test at all) 

Error condition 1.1: foreign particles sit on O-ring or sealing surface 

Corrective action 1.1.1: wipe O-ring with isopropyl alcohol 

Corrective action 1.1.2: remove particles on sealing surface with kapton tape 

Error condition 1.2: scratches on sealing surface

Corrective action 1.2.1: polish sealing surface 

Corrective action 1.2.2: machined off scratched  surface if possible 

Corrective action 1.2.3: when installing O - ring, ensure thicker O-ring 'section located on scratched area. This can achieve by pushing O-ring to scratched area. This may not work sometimes. 

Error conditions 1.3: missing tubing or parts 

Corrective action 1.3.1: install back missing part or tubing 

Error condition 1.4: fastener for sealing parts not tighten to desired torque value after system pumped down (Note: fastener will losen due to compression on O-ring after system pump down ) 

Corrective action 1.4.1: use torque wrench or torque driver tighten fastener to desired torque 

Corrective action 1.4.2: redefine torque specifications 

Corrective action 1.4.3: screw thread may damage, repair for thread by tapping or change fastener may needed 

Failure mode 2: Minor Leak (Helium Leak Detector can reach fine test but can detect helium leaking into system more than given specification when spraying helium over potential leaking area) 

Error condition 2.1: foreign particles sit on O-ring or sealing surface Corrective action 2.1.1: wipe O-ring with isopropyl alcohol Corrective action 2.1.2: remove particles on sealing surface with kapton tape Error condition 2.2: scratches on sealing surface Corrective action 2.2.1: polish sealing surface Corrective action 2.2.2: machined off scratched surface if possible Corrective action 2.2.3: when installing O - ring, ensure thicker O-ring 'section located on scratched area. This can achieve by pushing O-ring to scratched area. This may not work sometimes.  

Error condition 2.3: desired leakage area larger than specified area 

Corrective action 2.3.1: replace that parts if possible 

Error condition 2.4: epoxy which use at electrical feedthru leakage 

Corrective action 2.4.1: replace that parts if possible 

Error condition 2.5: O-ring crack or damaged 

Corrective action 2.5.1: replace O-ring if possible 

Error condition 2.6: O-ring diameter undersize cause it seated entirely in groove 

Corrective action 2.6.1: replace O-ring if possible 

Error condition 2.7: O-ring diameter oversized cause it seated in groove without touching sealing surface 

Corrective action 2.7.1: replace O-ring if possible 

Error condition 2.8: Swagelok leakage 

Corrective actions 2.8.1 :slightly tighten Swagelok because Swagelok may not tighten per Swagelok guidelines at first place 

Corrective action 2.8.2 : change Swagelok (sometimes with tubing if removal of Swagelok is impossible) if nut cannot rotate freely or stuck on its ferrule or leakage still present at Swagelok after retighten per guideline 

Failure mode 3: leak detector reading unstable (assume leak detector function well) 

Error condition 3.1: Gas trap in vacuum systems 

Corrective action 3.1.1: continue pump down overnight, to remove moisture or gas which trap in parts mating surface 

Corrective action 3.1.2: purge vacuum system with Nitrogen gas 

Failure mode 4: prolonged pump down time 

Error condition 4.1: Virtual leak, air trap in the system 

Corrective action 4.1.1: poor design or workmanship, change design or rework 

Error condition 4.2: moisture attack when system expose in atmosphere 

Corrective action 4.2.1: baking the instrument to remove moisture if possible 

Corrective action 4.2.2: purge vacuum system with nitrogen gas

I hope this list can help you speed up your time for your Troubleshooting. Feel free to drop me an email if you have any other Troubleshooting experience can share with us. My email is gbwonggbwong@gmail.com. Thanks. 

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