RE: Cv for your micro-metering valve

["Ashcraft, Bob" <BAshcraft at medrad_com>]

> At 03:48 PM 5/9/99 -0400, Steve Pushak wrote:
> >The less expensive valves such as the ARO NO1 (part # 104104-NO1) have a
> >full open valve coefficient Cv of about 0.04 whereas the Nupro S series
> >has a Cv of about 0.004
> 
	And then, some time afterwards, Dave Gomberg wrote:

> Here is the sad part.   If your input pressure is 5psi (go below this and
> you risk serious instability problems) and your output is 1.5 psi (36" of
> water) and your temperature is 70F, then the Cv you need is .000007 for
> one
> liter per day.   If you want one 2mm bubble of CO2 per second, that is
> about 4mm3/sec or 15cm3/hour or .4L/day or a Cv of about .000003
> 
> That is a long way from .004, or the Hoke value of .0008 which still
> doesn't hack it.
> 
> This is why I advocate high pressure systems, they work.
> 
> Dave Gomberg, San Francisco 
> 
	Dave,

	If all this is true, then please explain to me why my system works
so well.  I have 2 regulators in series.  The first one is set at 50psi and
the second at 10psi which feeds a 1psi check valve, then a Nupro valve which
I can set all the way down to 1 bubble every 30 seconds.  I currently have
it set at 2 bubbles/sec. during the day.  At night it is switched through a
secondary circuit, as per Dave Gombergs' suggestion (thanks again Dave, pH
is rock steady), with another Nupro valve set at 1 bubble every 2 seconds.
It hasn't varied at all in the last 4 months.  Even when I refilled the
bottle, I didn't have to touch the adjustment, it stayed exactly the same.

	Bob Ashcraft
	Pittsburgh

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