I need to pump down to 20 micron or so and then backfill to 0.5 to 2 torr. Hold time of tens of minutes. Current system leak rate keeps me to 500 microns more or less and the breeze is killing my backfill. On Nov 2, 2015 1:08 AM, "Sean Breheny" wrote: > David, > > What is an acceptable leak rate? I am just getting into the high vacuum > world but previously I have had a chamber at a low vacuum (30 torr), usin= g > ball valves from McMaster, remain under 60 torr for a month, if I recall > correctly. > > It seems that high vacuum stuff I've seen often uses butterfly valves. > > Sean > > > On Sun, Nov 1, 2015 at 1:07 PM, David VanHorn wrote= : > > > I have a vacuum project in the works, and I've just isolated one source > of > > leaks. > > The system needs three shutoff valves. I used ball valves, and I'm > finding > > that they are leaking. Probably designed for positive pressure I'm > > guessing. > > > > Is there someone on the list with vac experience down around 20 microns > who > > could suggest relatively inexpensive valves that I could use? The > system > > is now built with 1/8 NPT but I could switch if I need to. > > > > These valves just need to be on or off, and they are used for controlli= ng > > the flow of air and other gases. No liquids, nothing harsh. > > > > Thanks. > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .