Using the Zahm-Nagel carbonation chart, determine what the temperature of the beer is. Cross reference this with the beer's CO2 volume level and this will give you the pressure required to acquire what is called equilibrium. The gas in the beer stays put and the gas head pressure will not impart itself into the beer. Their site is down at this time so a link is not available.
Since when the faucet is opened there is a pressure drop, you will require up to two additional PSI referred to as "push pressure" above what the chart called out. This compensates for the pressure drop reducing gas breakout from the beer while dispensing. This can result in slight over carbonation but not enough that you, I or anyone else could detect as a flavor issue.
The key to success in utilizing 100% CO2 is to know exactly what temperature your beer is and maintain this 24/7 all of the way to the faucet. Not easy! This is why gas blends are much more effective than 100% CO2 for dispensing. It allows you to use much higher pressure compensating for temperature issues and long runs while maintaining carbonation level of the beer. Although, you must use the correct ratio of CO2 to nitrogen for ales and lagers. 60% CO2 / 40% N will take care of the range CO2 volumes found in this group.
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