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Re: Aquatic Plants Digest V4 #642

With all the CO2 discussions:
     at 70 F, saturated liquid CO2 has a vapor pressure of 851.68 psia 
and a density of 47.57 lb/ft3
     the saturated vapor at the above conditions has a density of 12.56 
lb/ft3 ( if you know your flow rate and the volume of your cylinder you 
can calculate how long your cylinder will last when the last drop of 
liquid is gone )
     at 70 F and 14.7 psia, CO2 has a vapor density of 0.1144 lb/ft3

Some single stage regulators utilize the cylinder pressure to balance the 
spring force and diaphram forces generated by the pressurized gas.  When 
the cylinder pressure drops it can unbalance the opposing forces, 
resulting in the force that is trying to open the regulators valve being 
greater than the force that is trying to close the regulators valve. This 
results in the "venting" that is being described.  If this condition 
where monitored what you would see is the discharge pressure of the 
regulator increasing as the cylinder pressure decreases.  

     Putting a second regulator after the cylinder regulator is one way 
of minimizing this effect, but it is also a dangerous one if the wrong 
regulator is used.  Any component downstream of the cylinder regulator 
should be rate for cylinder pressure unless you have a pressure relief 
device or something that will fail in a safe manner , like airline tubing 
on a hose barb.  If the downstream regulator is not designed for the 800+ 
psig of the CO2 cylinder and the upstream ( cylinder regulator ) fails or 
"vents", the downstream regulator could fail with tremendous energy and 
generate shrapnel.