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Re: More CO2 Injection Stuff

Peter G. Aitken wrote:

> I have been looking into the Swagelock needle valves. The "S series metering
> valves" is indeed the lowest flow rate valve style they make. The maximum Cv
> is 0.004 (valve fully open) but according to the flow data graph I have you
> can get a Cv as low as 0.00025 with the valve open 2 of its 10 turns. I
> think this will be fine for a low pressure system - if not someone please
> enlighten me before I order one!

Peter, I don't know how useful the Cv numbers are with gasses, but most
people who have used the Nupro S valve say it's very nice. My recent
attempts to find this valve locally were not successful, but in the process
I stumbled upon a Parker HR series valve for slightly more (about $52) than
the Nupro S valve. I bought it and am so far very pleased with it.

The HR stands for "High Resolution" and the series comes in seven different
valve stem tapers (HR-0 through 6) that offer various flow coefficients. The
one I got was the HR-1, although from the spec sheets the HR-0, 2, 3, and 4
models appear to be at least as precise as the Nupro S valve. Here are the
Cv figures for the Parker HR-0 through 4 valves:

HR-0:   .00034
HR-1:   .00080
HR-2:   .00140
HR-3:   .00310
HR-4:   .00770

Here are some of the manufacturers' specs for the Nupro S and Parker HR-1
                           Nupro S Series        Parker HR-1

Max pressure:                2000 psig            250 psig
Max flow coefficient (Cv):    .004                .0008
Turns to open:               10 (+/-2)           15 (+/-1)
Shutoff:                    not intended        bubble-tight
Cv at turns open (approximate*):
        1 turn                .00010               .00005
        2                     .00025               .00007
        3                     .00050               .00008
        4                     .00080               .00010
        6                     .00180               .00015
        8                     .00280               .00025
       10                     .00400               .00035
       12                       ---                .00050
       15                       ---                .00080

(* I derived these numbers from somewhat lo-rez graphs, so they could be off

To make sense of these numbers, I had to learn what "Cv" meant. The flow Cv
(Coefficient of volume) is defined as the number of gallons per minute of
room temperature water that will flow through the valve with a pressure drop
of 1 psi across the valve. However, since we are metering CO2 and not water,
all sorts of variables factor into the equation because gases are
compressible and the flow rates are affected by temperature and pressure.
The math to calculate flow rates for CO2 through these valves is available,
but it's beyond my time/interests/brainpower/etc. Here it is for those so


In a nutshell, the Cv numbers are relative, I think.

Since most folks who use the Nupro are apparently quite satisfied with its
control resolution, the Parker HR-1 is possibly a bit more resolution than
is needed. For people who find that they only use the lower range of the
Nupro (1 turn or less), the extra resolution of the HR valves might be

Another nice feature is the shut-off capability. Unlike the Nupro S valves,
the Parker HR valves are *designed* to be shut off. Factor in the cost of a
ball valve and the extra expense is a bit easier to swallow.

The only downside was that the Parker came with 1/8" connectors because
that's all the dealer had. Adapting this my Cornelius regulator (aka "beer
keg guage") was problematic; 1/4" connectors would have been a lot less
hassle to hook up.

As soon as I've had more time to play with the Parker HR-1 I will post my
experiences, but so far it appears to be a very nice valve. Right now I'm
running about 20 psi into it and I open it up about 3 turns to achieve 1

BTW, I think I saw 3 or 4 more on the shelf of this dealer, so if anyone
else is interested, email me off list and I'll send dealer info. The person
who helped me said they've been collecting dust for 4 or 5 years, so they
just want to move them out. I think Parker redesigned the valve, because
their current picture on the web site differs slightly from the valve I

I also learned that it doesn't hurt to poke around locally first before
buying mail order. I was about to order the Nupro from an out-of-town dealer
when I stumbled onto the Parker deal. There may be other high resolution
metering valves out there made by other manufacturers besides Swagelok and
Parker. If you happen upon a dealer of other brands of metering valves, ask
the dealer to cross-reference thiers to a Nupro S and see what they come up
with. You never know what you may discover.

Good luck!

Dan Dixon