Re: End-of-tank-dump comment

["Eric Wahlig" <ewahlig at earthlink_net>]

One of my CO2 systems happened to run out of gas lately. I noticed the tank
pressure starting to fall on Tuesday or Wednesday of last week. Perfect
timing for observing the "gas dump".

This system is completely manual and involves only a 10 pound cylinder, a
Cornelius beer regulator set at 25 PSI line pressure, brass manifold with
four Swagelok/Nupro SS-2MG metering valves, and 3/32" ID silicone fuel line
tubing. This system delivers CO2 to two 25 gallon tanks and two 15 gallon
tanks continuously. The gas is delivered to the four "hang-on-the-back"
style filters by connecting the delivery tubing to the filter intake
strainer by drilling a small hole in the bottom of the strainer (or
enlarging one that may already be present as part of the design) and using
the small plastic airline connectors (union connection and 90 degree elbow)
that are commonly available.
For those of you wondering what the valves are, they are straight pattern
1/8" stainless steel precise metering valves. These would normally cost
around $110 each but I found a place that had several used ones and I got
them for $25 each. I should say that one of them had the needle broken off
and another had a damaged needle, so, a word to the wary about buying used
valves. The broken one was replaced and I'm still using the damaged one; it
seems to be OK for this application. For more information on these valves
go to:
http://www.swagelock.com/ProductDetails_cat.asp?Cat=724&CATDESC=Fine+Meterin
g+%2D+Angle&TYPE=&TYPEDESC=Valves+%2D+Regulating&Series=69&bigp=NPH634CROPan
gle%2DS%2EJPG&nump=3 and click on "Catalog Information (PDF)".

It took four days to use the remaining unliquified gas in the cylinder. The
line pressure increased 1 or 2 PSI when the tank pressure dropped to
something pretty low; I think it was around 100 to 150 PSI. The delivery
rate (bubble rate) seemed to increase slightly at this time also. I
measured the pH of the tanks and it dropped an average of approximately 0.2
units from the normal reading. I think I can say that I had no "end of tank
dump" but a small increase in the amount of CO2 being injected and a very
minor fluctuation in the pH even though I run the tanks at a low KH;
between 4.5 degrees and 0.5 degree (80 mg/L and 10 mg/L). It was
interesting to note the regulator held the line pressure at about 27 PSI
until the tank pressure decreased to equal this. The line pressure then
started to drop and I exchanged the cylinder for a new one.

--- Eric