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Re:O2 at night

>Second, some folks have used solenoids, but in reverse.
>When the solenoid valve closes, there is a "T" with the solenoid attached to
>one of the ends. This causes the gas to go the other way, in this case into
>the tank. When the valve opens, the gas is dissipated into the air. It takes
>about 15 minutes for the gas to re pressurize and start bubbling into the
>tank so this is not any good for Controller type systems but is fine for
>timer set ups. Solenoids run about 40-70$ generally. Not really a good
>option IMO but I used one since I have a few laying around.

Ahh, solenoid pricing can be very cheap when one knows where to look (and 
at the right moment with the surplus places ;-). For anyone interested in 
trying this method of diverting the CO2 at night, there is a perfect little 
solenoid valve for it at Mendelson's here: 

It is the last solenoid on the page, item #530-0055. It has an input port 
(and they are all hose-barb type), and a normally open output port 
(normally open = not active when the unit is not energized) that are both 
5/16" OD. While that's bigger than the usual 3/16" airline tubing 
connections, regular airline tubing could be easily taped on (airline 
tubing is about the same overall diameter as that connector), or slightly 
larger tubing could be had at the local hardware. The normally closed 
(normally closed = active when not energized) is 5/8" OD, which is not a 
problem since this would be the "nighttime vent" and wouldn't need to be 
connected to anything.

The unit runs on 26 volts DC, and should be able to be powered by a cheap 
24 volt wall-wart from your light timer. The two small ports will be 
connected together when the device is "on", and the big port will be 
connected to the input port when off. The valve is only $6.95, and with a 
wall wart the total cost is probably around $10-12. A cheap experiment for 
anyone who wants to try.

Waveform Technology
UNIX Systems Administrator