He was dead right. Unfortunately my vacuum sucks. Very frustrating not knowing how to frame the question in their terms. I dont want to overly constrain the solution. Spent a while at mendelsons surplus today but they only had huge stuff with no specs. On Nov 3, 2015 3:40 PM, "BOB" wrote: > 25 years ago we were working on a project for holding parts with vacuum. > our boss who owned the company new a engineering professor at the local > university. while talking to him he stated that " if you have a vacuum > then there is nothing there to measure a flow rate of." He then said > good day and left. When we talked to our boss the next morning he said > 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 > in. > > 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 5= 00 > >>> 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), > >> using > >>>> 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 valve= s. > >>>> > >>>> 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 > >> 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 > >> > > -- > 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 .