25 years ago we were working on a project for holding parts with vacuum.=20 our boss who owned the company new a engineering professor at the local=20 university. while talking to him he stated that " if you have a vacuum=20 then there is nothing there to measure a flow rate of." He then said=20 good day and left. When we talked to our boss the next morning he said=20 he would be in later that it was just the old professors idea of humor. On 11/2/2015 9:00 AM, David wrote: > The total volume would be maybe as much as 6 cu in. Not less than 2 cu i= n. > On Nov 2, 2015 3:18 AM, "Isaac Marino Bavaresco" < > isaacbavaresco@yahoo.com.br> wrote: > >> 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 vacuu= m >>>> world but previously I have had a chamber at a low vacuum (30 torr), >> using >>>> ball valves from McMaster, remain under 60 torr for a month, if I reca= ll >>>> 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 sour= ce >>>> 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 micro= ns >>>> 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 >> controlling >>>>> 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 >>>> >> -- >> 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 .