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Re: [APD] Re: Bubbles? -- or - Backin' up is hard to do

Stab # 3 at the first question:

If there are no other devices inbetween the irrigatin tap
and the reactor, the pressure should be the same at the
current location and at the reactor.

If the tap extends into a length of the water tube/pipe
coming off the pump utput, and is *not* angled (even
slightly) so that it is pointed towards the water flow,
then it should act more like a venturi and tend to suck gas
in from the CO2 tube rather than push water up the CO2
tube. If you can't get a venturi effect, close off the tap
and move the CO2 connection to the reactor where the
increase in the water line diameter should reduce the water
line pressure relative to the CO2 line pressure.


If you increase the CO2 out put pressure, that should
prevent water going up the CO2 line. The water pressure is
likely not very high; few aquarium pumps develop more than
a few psi unless you have the output constricted (for
example with a ball valve) and the CO2 is between the
constriction and the pump. Even constricted, most aquarium
pumps develop only a few psi.

Question # 2:

The bubbles *will* trap and tend to collect at the top but
only up to point. The water will flow through the CO2 at
the top of the reactor and down and out the reactor. If the
water flow is too strong, then it might carry out small CO2
bubbles with it -- in which case put the reactor on a
Teed-off line from the main line so that it gets a lower
flow or use a larger diameter reactor. 

If the water flow is too low or the CO2 rate too high, the
CO2 will collect in the reactor faster than it can be
absorbed, eventually filling the reactor with gas and
leaking out the bottom opening of the reactor, which is a
waste.  In that case, increase the water flow or decrease
the CO2 output. If decreasing the CO2 doesn't yield a high
enough CO2 level in the aquarium water or a higher flow
blows out CO2 bubbles, then use a larger diameter reactor
to support the higher water flow.

You might need to go back and forth a bit to get a useful
balance, but the set shouldn't be very sensitive to the
amount of water flow and you'll be able to control CO2
levels by adjusting the CO2 flow rate. If the set up is
very sensitive to the water flow rate, and you have to keep
fidling with the CO2 rate and water flow rate to get a
stable reactor and CO2 levels, then use a larger diameter
NOte that these suggestions are "IF/thens".  I think you
can probably get where you want to go with the reactor you
have, inverted so water enters the top, with a few
adjustments to flow rates.

2 examples on hand:

I have a 3" x about 12" reactor on a 1/2" water line
flowing about 200 gph. That can maintain 15-30 ppm in a 150
g aquarium.

I have a 2" reactor, about 12" on 3/8" water line flowing
about 50 gph -- that works on a 30g. It might even work on
the 150g, with higher flow rates but I never tried it.

Scott H.
--- David Terrell <Dave at terrellclan_com> wrote:
> Actually, let me rephrase to clear this up, this being
> the third time
> someone misunderstood my problem I guess it was just
> clearer in my head.
> The airline from my CO2 tank comes out of the needle
> valve, through a
> check valve then down the line to the intake for the
> reactor (but not
> _at_ the reactor).  Now, I didn't drill a hole in the
> reactor
> specifically for the airline.  I had an irrigation tap in
> the output
> line from the pump (nylon return tube).  I put the
> airline on that
> tap...so when the pump is on water is forced up the
> airline.  There is a
> check valve after the needle valve (you can see it on the
> left in the
> reactor picture) so I wasn't nervous about it returning
> to the tank and
> causing problems.  However, it seems I won't get a
> regular flow when the
> airline has to build pressure to go back to the pump
> return.
> The question is/was:  How can I reduce the backpressure
> of water on the
> airline from the pump return to the CO2 tank?
> My next question is, if I turn over the flow through the
> reactor (so it's
> closer to the proper design ;-) are the bubbles really
> going to flow
> upwards/trap?  I have a 750g/hr. pump, rated at this head
> it flows
> ~500g/hr.  I don't know fluid dynamics so this is a big
> problem!  The
> pump return is a 3/4" nylon tub that goes to some
> adapting fittings of
> PVC pipe, which eventually reaches 1-1/2" PVC, so a 2x
> growth in volume.
>  Will the flow be slow enough to allow the bubbles to
> rise/trap in the
> ractor chamber?

S. Hieber

-  -   -   -   -   -   -   -
Amano Returns
to the AGA Annual Convention
Nov 2004 -- Baltimore

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