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RE: High Pressure vs Low Pressure CO2 systems

Dave Gomberg recently (and very kindly) answered a question I had. As luck
would have it, that only leads to more questions...

>And why, if this is the
>proper way to set up a "low pressure" system, does EVERY commercial
>manufacturer who sells purpose designed CO2 devices recommend the
>regulator-needle-valve combination?

[Because they are trying to push their own appliance.   The only company
[that sells a complete system (that I know of) and uses a high-pressure
[appliance is ADA.  So his design is fine.   Everyone is trying to use a
[needle valve when they really need a second regulator.   They do this
[because it is cheaper and simpler.  But it is also unstable unless you use
[a very very expensive needle valve (the Hoke, made in England, would be my
[choice if I insisted on low pressure via a needle valve).  A Hoke costs
[about $100 tho.

I've located Hoke's website and they do list a number of needle valves, but
they all seem to be rated of extremely high pressures - which Hoke Needle
Valve would you recommend?

[To summarize, low pressure systems seem to make more sense until you look
[at the details of how you are going to build your system.   But they are
[hard to build so they are stable.   If you like a stable system, high
[pressure systems are so much easier to build that is worth restricting
[yourself to the four or so high pressure appliances available (Dupla, ADA,
[Eheim, Point Four).  Of these the Eheim is the clear preference for

Christopher Coleman ran some comparison tests on th Eheim diffuser vs. the
ADA Pollen Glass diffuser and posted the results a while ago. He seemed to
agree that the Eheim won out on price/performance but did note that the ADA
unit was more efficient. I have an Eheim diffuser and a Dupla Atomizer and
the biggest difference I can see (other than the fact that the Eheim forces
you to use "micro tubing") is that in the Eheim unit, the diffusion plate is
held within the rubber "O-ring" gasket, while in the Dupla Atomizer the
actual disk is larger and there are "O-ring" gaskets both above it and below
it. Another poster mentioned that he has possibly experienced some leakage
of CO2 between the disk and the gasket (it's only a friction fit), producing
larger bubbles than if all of the CO2 was being forced through the ceramic
disk. I haven't had the opportunity to actually get these things wet yet, so
I can't say for certain if this is the case, but I suspect that the physical
design of the Dupla unit is superior to the Eheim (due to the dual "O-rings"
and the decreased likely hood of leakage). And that has nothing whatsoever
to do with any bias on my part for "Dulpa" equipment.

I checked out Point Four's website (yeah! another Canadian firm!!!) and
their devices look interesting (http://www.pointfour.com/diffuser.htm). One
of the things which people complain about using diffusion devices as well as
power heads to break up CO2, is the fine mist of bubbles which "clouds" the
water column in the tank. The Point Four diffuser looks like it could be a
major offender in this regard (due to it's large size and obvious
efficiency, if the photo on the website is accurate) but I could imagine
constructing an in-tank reactor for one of these where water was introduced
at the top and the diffuser was located close to the bottom, where the water
would exit (counter-current design). The fine mist of CO2 would rise against
the downward flow of water and pick up CO2 on its way.

Gosh, it seems like there is no end to the gadgets...

James Purchase