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**To**:**Aquatic-Plants at actwin_com****Subject**:**Re: more high low pressure dabate****From**:**Dennis8425 at aol_com**- Date: Wed, 12 May 1999 09:59:28 EDT

Okay folks lts really look at the facts here. The big end result is that we are 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 CO2 per day. Than we need to determine what type of equipment we need to determine this. So let us pull out the formula for flow which is: Flow = ([inlet pressure -- outlet pressure)/ (an equasion with density and temperature variables)) Cv. 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 lower. 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 the height of the water column (a 14 inch high tank will have 1/3 the pressure as a 42 inch high tank) the barometric pressure, the length and diameter of the tubing, and finally the diffuse on the end if any. Most of these factors we can keep vary constant with 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 and in 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 outlet pressure since pressure differential is inlet pressure minus outlet pressure. In simple terms the outlet pressure is what we have set the regulator to. So if want a differential of .2 psi. For a low pressure system we need to set our regulator at 1.4 and for a high pressure system at 20.2 psi. Now we get the deciding factor to me and that is most regulators are rated as stable within X percentage of there setting. If this is within 1% than let us look at the variable pressure difference we get. In a low pressure system with the regulator set at 1.4 psi the inlet pressure will range from 1.386 to 1.414 while the outlet outlet pressure will range from 1.15 to 1.25. The final pressure difference for a low pressure system is 0.136 to 0.264 or about 32% swing from the ideal 0.2 psi. In a high pressure system with the regulator set at 20.2 psi the actual pressure will range from 19.98 to 20.402 psi. With the outlet pressure of the system now ranging from 19.95 to 20.05 we can recalculate the worst case of the pressure differential and find the final outlet pressure will be between -0.07 and 0.452 psi. This creates a swing of about 226% plus or minus. To me this make the lower pressure system with a small orifice valve extremely more stable. Yet neither system in this range is really acceptable. The smaller the orifice of the valve the larger the pressure difference you can work with therefore stabilizing the system. 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 larger differential pressure making things more stable but still there would be considerable variance. As I see it the only real solution is the constant monitoring of the pH allowing the automation of the system to assure a constant level of CO2. Dennis

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