can anyone explain to me the difference between vent and fast vent?

Hi

https://community.agilent.com/knowledge/gcms-portal/w/gcms-knowledgebase/6928/how-to-vent-shut-down-the-gc-msd---ei---masshunter

Check above link...

But what is the difference between vent and fast vent?

Actually, if u will see above notes then you will find it that it depends on configuration that need to use pump down or fast vent..More detail, you can find in help section of software...

ok if we have a method to do this then it can speed the process of preparation to shut off gcms