switch shaft seal

12:57 Apr 17, 2015 

or is a proximity switch attached to the valve stem?

08:01 Apr 16, 2015 

Asker, not only does your question term seem a little odd, but also in the sentence you have provided.

Could you confirm for us that this is indeed reliable EN written by a native-speaker? I have an inkling that it may well be either an already-translated document from some other language, or at least written by a non-native speaker.
The reason I ask is specifically the 'switch shaft' in your question term — unless there is something in the rest of your context to suggest there is also some kind of '(electrical?) switch', I suspect this may be rferreing to the actual valve operating stem itself which (AFAIK) isn't ever called 'switch'. There is also the rather curious expression "...activation should be taken...".

So it might help to get the provenance and reliability of the EN sorted out first, before trying to translate what may possibly not be the right term in the first place.