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Re:CO2 Issues

From: krombhol at teclink_net (Paul Krombholz) 
Date: Thu, 2 Nov 2000 06:33:35 -0600 
> Jeff's CO2 dumping disaster prompts me to again bring up an idea I have
> suggested two or three times previously---the use of capillary tubing as a
> "valve" to control flow.  I am thinking of the kind of glass capillary
> tubing that has very thick walls with a narrow capillary running down the
> center as in a glass thermometer.  At a given pressure, the flow should be
> inversely proportional to the length of capillary tubing....

I have also brought up the subject of using capillary tubing to meter
the CO2 several times, and the subject is resoundingly ignored --
probably too unorthodox. My current CO2 system uses a copper capillary
tube of sorts (1/4" soft copper tubing hammered flat in the middle) to
restrict the flow.  I adjust the flow rate with the pressure regulator. 
The flow rate is nonlinear.  As the pressure increases dramatically, the
flow rate increases slightly.  I'm not sure if this is due to turbulance
in the restrictor, or the speed of sound in CO2 as the gas tries to pass
through the smallest areas of the tube (this might be two ways of saying
the same thing).  I usually operate the system at about 4 psig, but if I
crank it up to 40 psig, the flow rate only about doubles.