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Re: Regulator & Needle Valve Specs & Selection

On Mon, 11 Sep 2000, George Booth wrote:
> > From: "James Purchase" <jpurch at interlog_com>

> > C. Needle Valve Specs & Selection:

> > Model        Max Working    Cv    Stem Taper   Capable of Cutoff
> > Service?        Pressure
> > Nupro 31       5000 psig   0.04
> > Series Union Bonnet
> > Nupro BMG       350 psig   0.019     3 degrees  metering
> > Nupro BMRG      350 psig   0.30     20 degrees  regulating
> > Nupro BMW       700 psig   0.019     3 degrees  metering
> > Nupro BMRW      700 psig   0.30     20 degrees  regulating
> > Nupro L        1000 psig   0.15      5 degrees  can be used for cutoff service
> > Nupro M        1000 psig   0.03      3 degrees  not designed for cutoff 
> service
> > Nupro S        2000 psig   0.004     1 degree   not designed for cutoff 
> service


Been away all weekend, just read through the 100 postings, a majority of
which were on this whole CO2 dumping regulator problem.  Wright and one
other person had the insight that perhaps explains why people are fighting
here:

THE INCREASE IN PRESSURE AT THE END OF THE TANK IS ONLY A NOTICABLE
PROBLEM FOR PEOPLE USING THE EHEIM OR AMANO SINTERED GLASS DIFFUSERS!

Neil Travis, George Booth, myself and others don't use sintered glass
diffusers.  We use the old needle valve approach.  The needle valve acts
as a flow restrictor.  Some of these valvues (like the Nupro series'
above) can even be run straight from the tank at 800 PSI input pressure!  
I remember someone in this forum speculating about removing the regulator
(essentially a first stage of a two stage system with the needle valve as
the second) entirely.

So what happens?  Let's try some arbitrary numbers -- perhaps someone will
chime in with more realistic ones --- say we set the needle valve to
provide a nominal 1 bubble per second when driven at 20 PSI.  Near the end
of the life of the cylinder, we hit a bump in pressure where it goes up to
200 PSI downside of the regulator.  This then causes the needle valve to
increase its flow by at most a factor of 10 as, aka 10 bubbles per second.  
Annoying, but not catastrophic.  And it happens slowly.

In a sintered glass diffuser, though, that pressure of 200 PSI is going to
"pop" the diffuser and cause the CO2 to vent into the tank as quickly as
it can, which is almost certain to kill the fish.  I've seen a diffuser
pop and spew an entire bottle of CO2 into a tank.
It's not pretty.

My question is, if the only way to avoid this effect is to add a flow
restricter between the regulator and the diffuser, is it really any better
than just going with the traditional reg-needle combination to begin with?

    - Erik

PS: http://showcase.aquatic-gardeners.org (19 days left... blah blah..
great prizes... blah blah... entries starting to pile in... why not finish
YOURS now instead of the absolute last minute!)

-- 
Erik Olson
erik at thekrib dot com