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Re: CO2 pressure head

Scott said:
> 
> If the pump is in the tank and pumps through the tubing/reactor from
> the tank and back to the tank -- and the tank is "closed off" from the
> atmosphere -- then doesn't the gravity pulling the water down towards
> the reactor exactly compensate for the head preasure from gravity that
> works against the water going back up.  I.e, when pumping out of and
> then back into a tank, isn't the head pressure always 0" regardless of
> how high or low the tube goes?

You still have to push the water through a long tube and you have losses
from turbulent flows and the turbulence inside the chamber and a slight
pressure from the gas bubble inside that. The longer the tube, the worse
this is. An open hole at the bottom removes the pressure inside the tube and
allows a larger but less dense bubble but at a higher flow rate.
You can try this your self if you wish but you will lose a fair amount of
flow when using a smaller pump. Larger HP pumps are fine for this
application though. This is why I suggested a maxi jet 900 etc over the
stock Rio 180 for a larger 92 gallon tank.

>  You gain from the siphon on the
> downward side but lose all the gain on the upward side, so to speak.
> Of course, tube length and other factors add resistance too.

Yes, you got it. Generally, having a shorter "out" tube and a longer "in"
tube is better. That's the design I use on a sump model which is about as
good as it gets for CO2 reactor designs. It allows high flow and low
pressure drop. Not a big deal for most folks but I'm not quite normal about
certain things:)
Regards, 
Tom Barr
> 
> Scott H.