Re: [APD] Aro valve or - My Aro flew into the air and fell to earthin the waste basket

["Eric Wahlig" <ewahlig at earthlink_net>]

> The other value of a metering valve is to impede the flow
> if the regulator dumps. I doubt the Aro would do that.
>
> If they won't work without a solenoid, then they probalby
> aren't doing much good with a solenoid.
 
I'm saying that any type of needle valve, even these rather rough ones, is
better than relying on only the regulator to set the delivery rate. If you
run only a single stage regulator and connect its output to your aquarium
without any other valve after it then you are going to have problems. You
need the minimum of some kind of flow restricting device (needle valve)
after the regulator. If you can get one of these ARO No. 1 valves to at
least slow down the gas dump then you are improving your odds against
suffocating your fish.
 
While this particular valve is very hard to adjust for a continuous,
stabilized, and reliable rate of delivery at the extremely slow flow rates
we require, its adjustment ability is accurate enough to restrict the
increased flow caused by the "dump" of a single stage regulator when the
pressure differential becomes too small for the regulator to distinguish.
Although its far better than having nothing, it still doesn't solve the
problem of accurately and reliably regulating (metering) the flow rate. For
this reason master control of the delivery should be given to either a
solenoid/ light timer setup or a pH controller.
 
The light timer/solenoid setup is still a bit risky but at least you have
cut off the delivery at night when the plants don't need it and when you do
allow the system to deliver CO2 it is during the photo period and you're
depending on the plants to utilize much of it. The potential for
over-delivery, and consequences to your fish, is only possible during the
delivery period set by the timer so the duration of over-gassing is
limited. You'd have to set it up and periodically check on the condition of
your fish during the delivery time to see if you are over-doing it and if
the valve you are using can be adjusted adequately to prevent this. I
believe, from my experience with five copies of this valve, is that its
going to work sufficiently in this application. Personally, I'm more
concerned with large pH swings in relatively soft water (3-4 dKH) using
this method. I haven't tested this yet so if anyone has any input on this
I'd appreciate it.
 
Of course the most accurate control would be by pH controlled delivery. Now
I must say I have never used a pH controller but I have seen it used on
George & Karla Booths tank(s) with this valve and in this case the valve
functions adiquatly. Maybe George could offer his experience on this setup.
Since pH range is the function which controlls the delivery of CO2, the
valve is only needed to adjust the relatively rough delivery rate. The gas
delivery rate and the plant utalization both contribute to the rate of
change of the water's pH and this determines how quickly the set points are
reached and how often the unit cycles on and off. The valve is just there
to slow down and smooth out the abrupt changes that would happen if you ran
the controller directly off of the regulator. 

---Eric



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