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RE: CO2 (yet again!)

Hi James,

I hope I could add to the confusion.

First of all, lets get a few things straight.

Pressure Regulator is for regulating / controlling /stabilising
the pressure.

Flow Regulator / Metering Valve / Flow Valve /Fine Metering Valve
is for regulating / controlling the amount of flow.

Check Valve / One Way Valve is for controlling the direction of the

I am using both Kare's and Eheim CO2-reactor (diffusors with ceramic
/glass porous disc). I am using a Dennerle PROFI 2000 CO2 pressure
regulator running at 0.5 bar. The main CO2 distribution line is connected
after the pressure regulator, followed by a T-connector. The two lines
from the T-connector are each connected to a Neupro S series Metering
Valve. The CO2-reactors are then connected to the respective Metering
valve (output side).

What ever amount of CO2 released would be dependent on the pressure
and the flow. You may choose to fix one of them (either the pressure
or flow) and adjust the other.

If you use the same hose and keep the same length and same
temperature (not running one of the hose near to your light source
for example), the same make/model of reactor and placing the reactor
at the same depth in the tank. You should be getting fairly
accurate dosing of CO2 from the bubble count. You can minimise
the error of the bubble count by timing the time required for
100 bubbles for example and adjust the metering valve.

You can also get the Nupro Metering Valve with Calibrated Vernier
Handle which should allow you to set all the Metering valves to the
same flow. Provided that the pressure is the same, the amount of
CO2 should be the same. If you use Calibrated metering valve or
fixed orific device. You don't need to count the bubbles.  

If you want to improve on the pressure regulation, you can
increase the pressure from the regulator attached to your tank
to a higher level 3 bar for example and install individual precision
pressure regulator to step down from 3 bar or whatever to 1 bar
or 0.5 bar. The precision pressure regulator could be something
like Manoset Precision Pressure Regulators type 10B from Matronair
/ Watson Smith (under Control Instrumentation Products). Or IR2000
series Precision Regulator from SMC with setting pressure range
from 0.05 to 2.0kgf/cm2. Sensitivity of 0.2% F.S. Max., 
Repeatability +-0.5% F.S. Max., Only thing is you would need to
sacrifice CO2 as they are air (CO2) consumption type of device.
You can also work with a fixed orific (Metering Valve
with Calibrated Vernier Handle or other precision fixed orifice
device) and regulate the pressure to get the amount of CO2. If you
orific is very small, precise and the pressure is precisely regulated
you should get very accurate CO2 dosing.

If you want even higher precision in pressure regulation, you can use
SMC series ITV2000 Electro-Pneumatic Regulator with Digital display
for set pressure with the additional advantage of near zero air (CO2)
consumption. You can have additonal pressure sensors installed to
monitor / control the pressure as a closed loop system.

So it is up to you to which level of accuracy you wish to have.

As for the check valve, you just need one after the pressure regulator
intalled on the cylinder because in any case CO2 is soluble in water
and the water will creep up the hose with or without the check valve.
As long as the metering valve is placed high up or you run the hose
from top down you are ok.

For the working pressure, the lowest you can go without introducing
instability into the system you are ok. Like I said, I am running mine
at 0.5 bar.

For the hose material, FEP, PTFE are the best if you don't mind the
price. Otherwise, Polyethylene hose which are commonly available would
be just as good for your application. Only use silicone hose at the
shortest possible length under water to connect to the reactors
(diffusors) because of flexibility needed for the bending. Silicone
hose are highly permeable for CO2 compared to Polyethylene (ref. Cole-
Parmer catalogue).

Casey Huang 

Date: Tue, 15 Dec 1998 02:03:10 -0500
>From: "James Purchase" <jpurch at interlog_com>
>Subject: RE: CO2 (yet again!)
>Just when I think I'm beginning to understand something, I find out I know
>squat. <grin>
>I needen't go over my reasons for wanting an equal input of CO2 into each of
>the 4 tanks I wish to set up (I can hear your cheers from here).
>But I see several well respected people, advocating different methodologies,
>and I don't know enough except to be dangerous (to myself and my fish), so
>I'm requesting clarification from all sources.