On 2013-12-20, Bruce L. Bergman (munged human readable) wrote:
On Fri, 06 Dec 2013 19:47:58 -0600, Ignoramus5722
wrote:

I have a strange sounding idea. I want to have an extra compressed air
tank in my system. I have a bunch of tanks at this moment to choose
from. This way, I could run air hungry tools like breakers, etc,
intermittently but longer.

So far, so good, and nothing complicated. I have a whole bunch of
tanks right now, and thought to do something nice for my shop and have
an extra tank.

Examples of tanks I have a

http://igor.chudov.com/misc/ebay/tmp/Marengo/186.jpg
http://goo.gl/PdkzbM (Tank with "QT-15" lettering on left)

However, I also realize that with a big extra tank, it will take so
much longer for the air system to come up to pressure. This will be my
wasted money, as people will be waiting longer to use compressed air.

So, I thought, can I have a valve, that would not fill the tank, until
system pressure reached 120 PSI. And then it would shut off again if
the pressure ever falls to below 90 PSI.

Google Backpressure Regulator - Fisher makes them, and probably
others. Holds off flow till the feed side is above a minimum.

Thanks.I will check them out.

They have them in air braked trucks too for the secondary system
(wipers etc).

Interesting.

i

We used them at Ye Olde GTE so that the underground cables always had
~9 PSI on them even if someone opened the aerial to work on it, rather
than let the whole pipeline see a 'zero leak'.

Which is important if one of the manholes in the underground is full
of water and also has a tiny leak on a case, you want to maintain
pressure going out than have water coming in - if it's paper insulated
cable, just a few drops of water and you're in huge trouble.

Even with Plastic insulated cables it can be real bad - Call it in if
you ever see a flooded street with a little string of bubbles coming
out of the phone manhole. If someone lets the pressure off somewhere
else on that lead to work on a cable...