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By: DavidR@Fast.net  Date: Friday, May 20, 2011 Time: 6:48:47 AM
Sir - In my view, if your tank has vents then it will be at atmospheric pressure inside and the vapor pressure can be ignored. If you are designing an Appendix F tank then you should add the vapor pressure to the liquid pressure. If you are pressurizing the Appendic F tank by some other means - nitrogen blanket for instance - then you only need to add your vapor pressure to the applied pressure to the extent that your vapor pressure exceeds the blanket pressure. My opinion only - independent verification is suggested!