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
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  ----- 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]>