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Re: CO2 regulation.

> Date: Mon, 11 Sep 2000 07:26:09 +1000
> From: "Neil Travis" <travisn at gravity_net.au>
> Subject: Re CO2 regulation.
> It Appear that Gomberg  is on a sell my product line at the moment. As a
> regular contributor to this list all I seem to do is get knocked by him with
> his commercial interests.
> In Australia "Dave states full of bull shit"
> a good regulator costs around $80.00. Say $50.00 US. Not as expensive as his
> dump when the tank gets low type.
> Could you imagine going into a Bar for a beer and as soon as the gas gets
> low the tap explodes?

This provocative way of stating untruths has a tendency to get the more
knowledgeable on this list a bit hot under the collar. I'm going to chime
in, but try to avoid the emotion and get a bit of the air clear. When we
know misinformation is being archived, we have some obligation to respond.

Neil's beer-tap regulators and the ones sold by Dave do not differ in any
functional way, only in the application.

> Not me. I like my beer too much. That is the type of regulator that will do
> the job properly.
> I would suggest that a bit more research is done into gas systems for
> quality and keep away from the rubbish.

The rubbish is entirely Neil's utter failure to understand the operation of
the normal single-stage gas pressure regulator. It *will* have a modest
increase in output pressure as the tank approaches empty. The increase is a
tiny fraction of the initial 900 psi, and can have no serious effect on
pressurized beer that can tolerate the slight increase. You wouldn't even
notice a 40psi to 60 psi change in the foam in your glass.

The high-pressure gauge for most beer regulators has a red zone down around
300-400 psi with a warning to refill the tank. Observing it totally
eliminates the problem, anyway.

> As it so happens I have a reply from Dave on this subject and he openly
> states that for a price he is quite willing to sell rubbish as he says it is
> economically enviable to sell quality as his customers are unwilling to pay
> the price so he sells crap.

I sincerely doubt if you are using Dave's words correctly or in context.
Don't bother to send them to me, tho, for I don't really care.

> Any one wanting a copy is welcome to it.

Why? I know Dave is a retired academic/consultant who pursues the business
as a hobby and not a way to make anything significant, so I may have an
advantage over Neil. I also know that Dave is wise enough to realize that
all the hobby will stand is the price of single-stage regulators. I won't
try to apologize for his astringent way of replying to foolish posts. 

I'm an engineer, and Dave is not. Sometimes I wish he consulted with me on
these things, but he has properly learned to be cautious about my
off-the-cuff responses, too. {Free advice worth every penny, phenomenon.

Where Dave, I, and others have been stung is by the apparent simplicity of
directly driving the Eheim diffuser assembly out of a regulator set to
*very* low pressure. We are adjusting the pressure to set the bubble-count
rate. If it changes with pressure, why are we surprised if it changes a lot
when the tank empties and the regulation fails?

Most of the typical 13 psi drop is not across the glass-frit diffuser, but
in holding barely open the heavily spring-loaded check valve that prevents
reverse flow from siphoning water out of your tank. Unfortunately, it
doesn't perform well either as a non-linear flow-regulator, or as a
second-stage pressure regulator. A few psi of increase to it causes a rather
impressive increase in bubble rate. Result? A more-or-less dumped tank, near
the end, with too much CO2 in the aquarium, but not likely to be nearly
enough to cause an atmospheric problem in a normal room.

We are generally trying to reduce the liquified tank pressure to a
manageable and safe level, and then we desire a constant volume/unit time
(number of bubbles/sec). That's best done with a *flow* regulator, and not a
pressure regulator. One time-honored way to get that flow regulation is with
a good needle valve and a constant-pressure source.

Turbulence in the flow through an orfice has long been used to control fluid
flow rate, somewhat independent of input pressure. The non-linearity of the
turbulence means the input pressure can change quite a lot for only a little
change in the flow volume. The needle valve does that rather well, if the
shape of the aperture is such as to be highly turbulent at the terribly low
flow rates we demand. It helps to have sufficient pressure drop across the
needle valve to be in that turbulent condition at all times. That is, run
the input pressure up around 20 psi or more. It's easy to see why it can be
quite thermally sensitive, too.

A number of folks here have reported particular valves they have found to
work well in this application. Modest changes in tank terminal-stage
pressure are not reflected in huge differences in bubble rate, as they have
been when running systems without the needle valve.

Single stage regulators can be used all the way to empty, if the needle
valve acts as an adequate flow restrictor over the modest range of pressures
encountered. OTOH, the Ehiem system also works quite well, as long as the
tank high-pressure gauge is monitored and the tank is refilled when the
liquid is all evaporated (about 500 psi remains). The Eheim system just
isn't tolerant of inlet pressure changes to any significant extent.

The expense of buying multi-stage regulators simply is ridiculous under
those conditions. Who needs them? They do nothing particularly useful for
most aquarists who have to feed the fish and plants a few times during the
month (and can see the gauge).

Neil, I have regulators that came from Liquid Carbonic (our local
beer-vendor supplier) and from Dave. The only significant difference is that
Dave provides some clever fittings that are brutally difficult to find
elsewhere. IMHO, his are, as a result, a huge bargain.

I hope this clears the air without increasing the confusion level.


PS. I think a good needle valve (and higher regulated pressure) in front of
the Eheim system could be a useful thing to do. I haven't tried it yet, but
will report if it does a good job.

Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

"People constantly speak of 'the government' doing this or that, as they
might speak of God doing it. But the government is really nothing but a 
group of men, and usually they are very inferior men." --H. L. Mencken

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