Hi Michael, We regularly use valco valves for exactly the application you refer to and have had no problems what so ever. The only thing you have to make sure is that you use the correct ferrules. When sealing metal on metal I would advise using the gold plated ferrules (part number ZF1GP-10), but make sure your sample gas is relatively inert. If you are attaching fused silica to the valve I would suggest using an external reducing adapter, this prevent ferrules sticking in the valve and results in a significantly better seal (part number FS.4-5, check the catalogue if you are using fused silica with an OD greater than 0.5mm). Hope this helps Cheers Simon p.s. the part numbers above are for 16" valve fittings ______________________________________ Simon Davis PhD. Mass Spec Solutions Technical Director Tel. 01612867890 Fax: 01619029624 Mobile: 07811367751 Email: [log in to unmask]<mailto:[log in to unmask]> http://www.massspecsolutions.co.uk<http://www.massspecsolutions.co.uk/> ----- Original Message ----- From: Michael Bock<mailto:[log in to unmask]> To: [log in to unmask]<mailto:[log in to unmask]> Sent: 09 May 2006 10:09 Subject: [ISOGEOCHEM] Valco valves in vacuum Dear all, I go about building a preconcentration system for methane in small air samples. Did anyone use Valco switching valves (6port, 1/8 or 1/4'', type 6UWE or 6MWE2) under vacuum conditions? What leak rate did you observe at which pressures? Any recommendations concerning the switching between vacuum conditions in one postion and non-vacuum in the other? Any infomation will be very much appreciated... Regards Michael -- Michael Bock Alfred Wegener Institute for Polar and Marine Research Am Alten Hafen 26 27568 Bremerhaven Germany tel: +49-471-4831-1967 lab: +49-471-4831-1026 fax: +49-471-4831-1926 email: [log in to unmask]<mailto:[log in to unmask]>