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Re: needle valve! (Aquatic Plants Digest V4 #1710

> Date: Thu, 21 Mar 2002 16:20:33 -0600
> From: "Matt Wassenhove" <Wass29 at qconline_com>
> Subject: needle valve!
> Does anybody have a needle valve they are not using and would like to give
> to a good person who just ran into some bad luck.  I was using DIY co2
> until
> a week ago I saved enough nickels and pennies to afford to by a used co2
> tank and regulator but not a needle valve.  Being anxious I put them in
> place instead of waiting till I had the money for the needle valve.  At
> first it seemed as if I could regulate the co2 just fine without it...
> Until last night.....
> [sad story snipped]
> It will be a while till I can afford a needle valve now so I just thought
> I would check and see if someone might have a spare sitting around they
> might part with.

I don't use a needle valve with my pressurized CO2 set-up.  I made a flow
restrictor very much like the cappilairy tubes in a refrigeration system. 
I took a short piece of 1/4" copper tubing and hammered it shut in the
middle until it would just barely pass enough 15 psi CO2 (actually, I used
O2 for testing because it was handy) to bubble about once per second in a
glass of water.  It works beautifully like a needle valve that is stuck in
approximately the right position.  I make fine adjustments in the flow rate
by making gross adjustments in the regulator pressure -- this thing is
extremely non-linear and it takes a large change in input pressure to get a
small change in the flow rate.

It took several attempts to get a tube that sufficiently restricted the
flow without being closed totally shut, so don't give up if the first try
doesn't work.

Hope this helps :-)