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Dumping on CO2 Dumps -- or $Buck ing the CO2 System in Stages

When the pressure on the high-pressure side of the pressure regulator
lowers, the pressure on the low-pressure side rises.  This is a
function of how adjustable pressure regulators are concocted.  Thus, as
you CO2 tank empties, the pressure coming out of the regulator climbs. 
As this change in pressures continues, at some point you get a sudden
dump of the remaining CO2 or a very rapid release.  

Alternative 1) You can keep adjusting the regulator or the needle valve
(the name of which has taken on new meaning lately so I prefer
"metering valve").  Of course, if you forget to reset these things back
to their normal position when you put on a refilled CO2 tank, you can
get a sudden dump before the CO2 tank is even near empty.

Alternative 2) If you're really worried about CO2 dumps, you can refill
you CO2 tank as soon as the liquid CO2 is gone.  Once the pressure on
the high side is dropping, there is just gaseous CO2 left in the tank,
roughly about $1 worth.  So don't wait for the CO2 tank to drop to 400
or 200 psi; just take the not yet empty tank and get a refill for $10 -
$15.  BTW, the price of CO2 just recently dropped from $11 to $9 for 5
pounds of CO2 where I live -- who says things don't keep getting

When the liquid CO2 is gone the CO2-tank pressure drops until all the
pressurized CO2 is gone or the regulator diaphragm unseats -- and it
takes a few days, probably a few weeks in many cases before the CO2
tank pressure drops so low that the regulator stops seating and dumps
the remaining CO2.  So if you use Alternative 2, you don't wait but you
don't have to rush either -- I could do it today but don't feel like
it; I think I'll put it off until tomorrow.

Alternative 3) Can't be sure you'll be at home when the pressure drops
(on the high side)?  Going on a two week vacation and don't know if
your CO2 tank will reach empty while you're gone -- and you don't have
a spare full tank to use?  And you don't want to refill the CO2 tank
just to be sure it will last?  Get a 2-stage regulator.  The purpose of
a 2-stage regulator is to maintain the low side pressure when the
high-side pressure changes.  Yes, they are made for just this kind of
situation.  It doesn't eliminate the problem but severely reduces it. 
I.e., it would buy you lots more time until the threat of a rapid
release or a dump was upon you after the liquid CO2 was gone.

2-stage regulators are very roughly twice as expensive as single stage
regulators, other things being equal.

Alternative 3 seems pretty extreme to me compared to Alternative 2; I
can throw away a lot of "remaining gaseous CO2" for less than the
"upgrade" cost of a 2-stage regulator.

Alternative 1 seems too fussy to me.  I'd be willing to pay someone a
mere buck to do that repeated daily adjustments for me.  Besides, I
dumped a new tank of CO2 that way because I forgot to reset everything
just right -- oops  :-o  

Using a metering valve (i.e., a you-know-what valve) you can help
restrict the flow which can buy you even more time to use that last
dollar or two of CO2.  Well I have the valve in place anyway just to
regulate CO2 levels under normal pressure conditions.

Alternative 4)  Put a solenoid on your system.  What?  You  don't want
to control you normal CO2 levels with a solenoid?  Or you are already
using a solenoid on a timer to let your CO2 run only in the daytime? 
No problem -- put a (normally open) solenoid and pH monitor/controller
on your system that is triggered for a slightly higher CO2 level than
you normally want -- even if this is a second solenoid.  Then it will
only "kick in" if CO2 starts coming out of the regulator too fast.  Now
if you just get that Un-interruptible power supply for the solenoid,
you will have few worries about CO2 dumping on you.

Alternative 4 uses the most parts and probably costs the most money,
but might be the most effective way to use that last dollar or so of

Scott H.

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