Joe,

We have a back up air system in our lab that has a switch over valve. 
It's a common enough piece, ours is a Festo. We have a cheap oil-less 
compressor hooked up to it: we tried a cylinder, but were amazed at 
how quickly it would be consumed.

I think that with most of the solenoid valves being normally open, 
they require a constant flow of compressed air to keep them closed. A 
large cylinder of compressed air only lasted a few hours.... If you 
don't know that the house air has gone off (some sort of alarm?) then 
you won't know that you've been drawing from your tank until it runs dry.

With the compressor, it normally comes on every few days to charge 
it's tank. When it supplies the lab, it comes on every 15 minutes, so 
we know something has happened.

Paul Eby
University of Victoria

At 02:07 PM 20/07/2006, you wrote:
>Hello all,
>
>       For the past several years our Delta Plus has been fed by compressed
>air from a building compressed air system.  This has been very stable until
>the past few weeks.  We are trying to design a back up system that may at
>least give us enough time to finish a run or shut down the machine, etc.  We
>are looking into using a N2 or compressed air tank plumbed into the line
>along with "check valves" to act as an automatic backup supply of ~60 PSI
>air pressure (see attachment).  Basically, when the building PSI gets too
>low, the valve to the backup tank will open.  Has anyone set up such a
>system?  If so, I'm assuming Swagelok makes valves that will work for this?
>  What type of tank is used...N2, compressed air cylinder, a ballast tank?
>How long has this setup kept the machine operational.
>
>Any thoughts would be appreciated.
>
>Joe Lambert
>
>Alabama Stable Isotope Laboratory
>The University of Alabama
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