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Re: End-of-Tank Dump with Tap-Rite #742 regulator

 Bob Alston quoted Tap-rite who said their regulator:

>    The Tap-Rite regulator ( 742 ) which you have & are
>    using, will have minimal drift ( less than 2 lbs. )
> from
>    full to empty CO2 tank.
>    Other regs. on the market have a much greater drift
>    up to 5 to 7 lbs. 
>    You have the best CO2 regulator available, and should
>    not have any problems with pressure drift.

I doubt this for a single stage regulator.  As long as the
tank's  high side pressure is high, sure; but not when it
gets low.

The regulated pressure is maintained by a spring (and
low-pressure gas) pressing one side of a diaphragm and the
hi-pressure gas pressing the other side.  Depending on how
forcefully the spring is pressing, you can change what that
balance of pressures is, change the regulated pressure. 
But when the gas pressure is low enough that it can't press
the spring at all, then the spring wins out and the tank
dumps what pressurized gas is left.  That's why dumps occur
-- the hisgh-side gas pressure is insufficient to close the
diaphragm.  In fact, for many regulators, the low-side
pressure climbs when the high-side pressure drops jsut
because the balance is affected by the pressure on both
sides of the diaphragm.  You can keep fiddling with the
spring pressure (the knob) for a while to keep
compensating, or just buy more CO2, which doesn't cost much
in most places.

As long there there is liquid CO2 in the CO2 tank, the
high-side pressure remains constant (if room temp is also
constant).  It doesn't start to drop until the liquid is
gone and just gaseous CO2 is in the tank.

Scott H.

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