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 500
> > microns more or less and the breeze is killing my backfill.
> > On Nov 2, 2015 1:08 AM, "Sean Breheny" <shb7@cornell.edu> 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 <microbrix@gmail.com>
> 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.
> >>> --
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