David, I'm not involved with vacuum systems, but you already gave half the response for the acceptable leak rate, stating the required pressure limits and holding time. If you tell the total chamber volume then the leak rate can be determined. Isaac Em 02/11/2015 06:22, David VanHorn escreveu: > 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), usi= ng >> 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 wrot= e: >> >>> 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 .