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Re: more high low pressure dabate
Okay folks lts really look at the facts here. The big end result is that we
looking a set amount of flow of CO2 into the tank. This amount of CO2 can
vary considerably from one individual tank size, density of plants absorbing
the CO2, light being applied, and even fish load. Therefore instead of simply
saying that one needs an 0.4 liters of CO2 per day is a real vague statement.
Individual daily need here could be anywhere from probably 0.1 liters to a
full liter. The only way of really telling our exact needs is the measure
what we have.
If we could guestimate the daily need say we put this need at 0.2 liters of
per day. Than we need to determine what type of equipment we need to
So let us pull out the formula for flow which is:
Flow = ([inlet pressure -- outlet pressure)/ (an equasion with
density and temperature
Breaking this down further we can determine that the Cv required will
be an indirect
proportion to the pressure difference between inlet and outlet pressure. Or
if the Cv
is small the pressure difference needs to larger than if the the pressure is
Next let us look at determines the pressure difference. Outlet
pressure is basically the
total of how much resistance to flow is in the system. This is determined by
of the water column (a 14 inch high tank will have 1/3 the pressure as a 42
tank) the barometric pressure, the length and diameter of the tubing, and
the diffuse on the end if any. Most of these factors we can keep vary
the exception of barometric pressure. Therefore lets say that this totals to
be 1.2 psi
of total outlet pressure with a variance of .05 psi in a low pressure system
a high pressure system it is 20psi with a similar variance of .05 psi.
Moving onward to inlet pressure we need a value slightly larger than the
pressure since pressure differential is inlet pressure minus outlet pressure.
simple terms the outlet pressure is what we have set the regulator to. So if
a differential of .2 psi. For a low pressure system we need to set our
at 1.4 and for a high pressure system at 20.2 psi. Now we get the deciding
to me and that is most regulators are rated as stable within X percentage of
setting. If this is within 1% than let us look at the variable pressure
In a low pressure system with the regulator set at 1.4 psi the inlet pressure
from 1.386 to 1.414 while the outlet outlet pressure will range from 1.15 to
The final pressure difference for a low pressure system is 0.136 to 0.264
32% swing from the ideal 0.2 psi.
In a high pressure system with the regulator set at 20.2 psi the actual
will range from 19.98 to 20.402 psi. With the outlet pressure of the system
from 19.95 to 20.05 we can recalculate the worst case of the pressure
and find the final outlet pressure will be between -0.07 and 0.452 psi. This
swing of about 226% plus or minus.
To me this make the lower pressure system with a small orifice valve
stable. Yet neither system in this range is really acceptable. The smaller
of the valve the larger the pressure difference you can work with therefore
However, in reality for a free flowing unmonitored system neither method in
itself is really acceptable. The Cv of the valve being reduced would allow a
pressure making things more stable but still there would be considerable
As I see it the only real solution is the constant monitoring of the pH
automation of the system to assure a constant level of CO2.