17:04 Sep 30, 2011 

a bunch for the feedback. Glad we could help. Best.

16:46 Sep 30, 2011 

I have received a response from the client and in actual fact "pressurised" is the correct interpretation. With regard to "vorgespannte Stillstand", it means that the compressor is in the fully charged state even when stationary - at least that is what I am told. Thanks to Opolt and Hazmatgerman for their contribution. I will close this now.

14:15 Sep 30, 2011 

the source excerpt it could be argued that some gas is kept pressurized in ready use bottles/tanks to avoid starting compressors / pressurizers. In effect that would make this gas a storage gas or supply gas. Another possibility, and more likely I think: to reduce loss of pressurized gas (which will be compressed further in the next stage) an additional shaft packing is provided for.
Vorgespannter Stillstand: turbocompressor not running but still containing pressurized gas in the various stages. I.e., not safe to open, but ready to restart with working pressure available quickly.

07:15 Sep 30, 2011 

I had thought of "pressurized" or "charged" but I am not sure so have referred this back to the client for clarification.

21:32 Sep 29, 2011 

... is about the gas being "pressurized" -- that's (almost) all.

The translation of the "vor-" part will depend on the context (which is somewhat lacking here); in some cases, it might refer to some reservoir-like storage where the gas is being kept. Or you might translat it as "being kept/maintained at pressure" -- along those lines. In still other cases, it might be sufficient to just write "pressurized" and leave it at that. Because normally, "vorgespannt" should refer to some other substance being pressurized by the gas.

I'm at a loss wrt the "Stillstand" thing -- more context needed.