Can anyone out there point me in the direction of a critical review of devices designed to allow changing a column in a GC/MS without venting the MS? So far I've seen three such devices advertised--Restek's EZ-vent, Agilent's No-vent, and Alltech's GC/MS switching valve. I'm looking for opinions of real users, not sales literature!

I'm a user of NoVent but from SGE which is the real manufacturer of this device (at least is that they told me). I saw it in the Agilent's catalog and it is the same device which is not cotrolled by the electronic of the GC.
I've installed it in a Shimadzu QP5050. It's really easy to install an to use but forget of setting flow-rates from the either GC panel or software, the device increase the back-column pressure (excuse my English I'm trying to study it with no very much success!!)and the actual carrier flow is quite different from the value you have set. I've got to determine the real flow-rate (or linear velocity) by using a non-retained compound such as methane (well, natural gas). Once you have set the new assay conditions is reletively reproducible. Therefore you'll need some extra work in order to transfer your methods. So, if you do not require very ("between-days") reproducible retention times you'll find it useful, because you will be able to change the column in less than 5 minutes (that it's true, sale literature!) without any lose of vacuum, and you'll be ready in 20-30 min to inject new samples.
Ferrules for NoVent were difficult to obtain in my country (Argentina, we're used to it) and it was due to a problem with SGE's people in Australia. Check if the supplying is appropiate in your country.
Summarizing, it's good for both qualitative and quantitative analysis of different samples. For long series (several days or even weeks) of the same method and analite I simply switch off the NoVent.
Hope this help

We installed the MS NoVent supplied by Agilent on our Agilent 6890/5973. I know it is the device made by SGE, but we preferred to get it from Agilent for support reasons.
In our case, it is controlled by the GC's electronics and the software/EPC compensates for the backpressure change.

Thanks Marcelo Befumo and Beppe! Any users of the other devices (Alltech and Restek) out there?

Hi Beppe

How does the epc control compensates for the backpressure change.
Where do you see in the software that a ms novent is installed?

See you