Needle
valve vs. Flow meter: I’m going with the flow…
by
MIKE KIRDA
Sponsored in part by:
A
couple of years back, lured by the prospect of not needing to
mix up kalkwasser on a nightly basis, I purchased a used calcium
reactor from someone getting out of the hobby.It was a Knop unit with a regulator, needle valve and
solenoid. Coupled with a 15 lb. CO2 cylinder and a
peristaltic pump, I was pretty sure the Knop unit would handle
the calcium load in my 75 gallon hard coral tank, and the CO2
cylinder should only need to be filled every 6-12 months.
It
took me a while to get around to actually setting it up, but I
figured I was in for a treat. I was wrong. I finally understood
the frustration that drives people to leave this obsession…err, hobby. It was nearly impossible to get the CO2
flow rate stable for more than a day.
I
think I got lucky with my first CO2 cylinder. Although the
needle valve was difficult to adjust, I got it set to 20-30
bubbles/minute and it stayed there. My initial cylinder lasted about two
months; then seemed to go from full to empty in one day. After getting
the cylinder re-filled, I had a much harder time with the adjustment.
Although I hadn’t touched the needle valve since the first time, it
suddenlyturned ‘digital’. It either seemed to be off or “full
stream”
on, with no middle point of adjustment.
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I
consulted a few reefkeepers and asked for help. One offered the
following advice: Turn the screw to adjust the pressure on the low
pressure gauge from 10 lbs. to something in the 1-2 lbs range.
That helped. The needle valve seemed to gain some sensitivity, and
now had a point where a quarter turn could change the flow from
off to full bore. I set the flow, checked it several times over
the course of the next few hours. Satisfied it was ok I left it
alone.
Next
morning, of course, it was streaming. Major readjustment…got
the flow right again. I blew through that 15 lb. cylinder in about
two-three weeks.
The
next cylinder was worse. Set the flow at 20 ‘bubbles’ per
minute, checked it every hour for the next six hours (6 PM to
midnight), got up the next morning at 6 am only to discover that
the cylinder was completely empty. The needle valve had vented the
entire tank - 15 pounds of CO2 - in six hours.
At
this point, I was ready to toss the regulator and buy a new one.
Based
on Brian’s recommendation, I called Dwyer the next week, ordered the
recommended RMA-151-SSV part and waited. It arrived later the same week.
Not bad, but Chicago is close to Michigan City, Indiana.
So
what is the difference between a needle valve and a flow meter? In many
aspectsnot much. Both have needle
valves. The visible difference is that the flow meter has a gauge for
measuring flow of gas through the meter.
I
removed the Norgren needle valve and installed the Dwyer replacement. It
was relatively simple to replace, although I needed to bring the unit
into Home Depot in order to purchase a small connector and some Teflon
pipe thread tape.
Armed
once again with a full cylinder of CO2, I set the Knop
reactor back up, started the peristaltic feed pump, turned on the
regulator and solenoid, and slowly began to turn the needle valve on the
flow meter…
The
difference in feel was immediately evident. Dwyer’s needle
valve was much easier to adjust, and had a nice ‘feel’ to
it. I was able to set the flow to the bubble counter within a
minute to 20-30 bubbles/minute. Minor adjustments to the needle
valve now reflected in small adjustments in the bubble count as
well. Once set, I waited for the flow rate to change, but it
remained steady. I remember thinking, “This is too easy.”
Over the next few months, I’ve learned that you can pretty
much set and forget it. I’ve had to touch it only when I’ve
wanted to adjust the flow rates slightly.
There
is one down side to the unit: I’ve discovered that the gauge
isn’t all that useful for me. The unit measures from 0-50
cc/min (with 5cc gradations) and I am probably feeding my
calcium reactor something on the order of 2-4 cc/min. I wish
Dwyer made a unit with a range of 0-10 cc/min or 0-20 cc/min
instead. The meter would be much easier to read and consequently
far more useful. Possibly others feeding more CO2
into their reactors will not find this a limitation.
All in all, I’ve
found this to be one of the better investments I’ve made on my reef
tank. The needle valve on the Dwyer unit is much easier to adjust mainly
due to the fact that the needle has a larger range. While turning the
Norgren valve 10 or 20 degrees would take you from full stop to full
stream, the RMA-151-SSV’s flow rate is proportional to the amount
turned. You can easily dial it in, set it and be certain that the amount
won’t drastically change afterwards. After losing $30 of CO2
in less than a month, I can say that the Dwyer unit has paid for itself
since then.
Conclusion:
For anyone who is having any problems with their
needle valves, trying to adjust the flow of CO2
into their reactors, I wouldn’t hesitate to
recommend this Dwyer unit as a replacement. It is easy
to set and stays set.
Can
I interest anyone in a lightly used Norgren needle
valve?
