On Tue, 11 Feb 2003 10:30:53 -0800, Dave Millman
wrote:

However, about 3 weeks ago my dual gage regulator-needle valve system ran out of
gas. It did an end of tank dump. pH dropped from about 6.4 to a bit under 6
before I noticed fish behavior and turned it off.

So a needle valve does not prevent an empty tank pressure dump.


Yes it does.
You had some other funky thing happening in this system, eg the check
valve etc.
I've run my tanks down over the years many times.
I've watched the pH carefully with a pH monitor.
I never got any variation till the tank was compleley out and then the
pH went up.

I use clippard needle valves and have done this same experiment at
least 6 times on my own system and have heard the same thing from at
least a dozen others.

I have a German check valve on the hose from the regulator to the reactor.
The whole system came from M3 about 15 months ago.

Not sure what they sold you.

I've seen cases where the regulator pressure was set VERY low (2psi)
and the resulting increase when the "tank dump" happened caused in a
CO2 overdose. But if the regulator pressure is set higher, the
needle-valve needs to be closer tighter, and when the output pressure
rises, the needle-valve still limits the CO2 and prevents problems.

Ditto here.

Additionally, if there is a check-valve located after the
needle-valve, the needle-valve often has to be set at a higher rate in
order to overcome the resistance of the check-valve. Some
check-valves cause problems, others don't.

Ditto.
I don't use check valves, nahnannahnah! But I don't need them the way
I design my CO2 system.

This is really interesting. In between my last post and this, I was up at a fish
store that told me about a fish die-off they attributed to not turning off the CO2 at
night. I looked at their tank: needle valve, no cover, lights suspended 8 inches
above the tank, no chance of CO2 being trapped above the water and displacing O2.

That would not occur anyway.

I don't like check valves. Unless you are adding the CO2 under
pressure in line etc, there's no call for them. By feeding the CO2
into a suction side of a pump, only positive suction pressure is
applied. No negative backpressure will ever occur even if the tank
runs out of gas, it's only neutral 0 pressure then.

No check valve to stick or get clogged and blow out at the last second
etc.

Like I said, I've watch carefully the effects of a tank going all the
way down to zero pressure many times. I've never had anything remotely
like a dump in any way.

I can therefore attest to the neelde valve's ability without any check
valve, solenoids, diffusers etc to muddle anything and my measurement
were accurate using a well calibrated pH monitor.

Regards,
Tom Barr