How should the overpressure value of a breather valve be selected?
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First question: Typically, the overpressure values for breathing valves are 100%, 40%, and 10%. But how should this overpressure value be chosen? Second question: I just read a book that contained a case study involving a cylindrical storage tank with a diameter of 36 meters and a height of 19.5 meters, without any insulation. I calculated the volume of fluid that could be released in an emergency fire situation. Using API 2000, the wetted area I determined was the same as that given in the book. However, the values for the discharge volume obtained from the tables and formulas used in the book differed significantly from those in the book, which indicated 19,000 cubic meters per hour. I’m seeking advice from the experts on these two questions~~~
:Q: Where are the Q:Q:Q:Q:Q people? Why isn’t anyone answering?
This post was last edited by zhengxue on 2016-3-19 22:48. First, let’s answer your first question. 10% overpressure of 40% and 100% are like this. Assuming the design pressure of your tank is a positive pressure of 2 kPa, choose a breathing valve with a 10% overpressure setting; in this case, the setting pressure for the breathing valve can be set at 1.8 kPa of positive pressure (in the absence of an emergency relief valve or other discharge devices). When the valve pressure exceeds 10% to reach 2 kPa, it reaches its rated discharge capacity and is in a fully open state. The set pressures of 40% and 100% should be fixed at 1.2 kPa and 1 kPa respectively. From this, we can draw a common insight: the greater the set pressure of the valve is close to the design pressure of the tank or container, the smaller the overpressure within a fixed period, and thus the greater the amount of steam that can be saved by such a valve. I hope the above examples can be helpful to you. If you have any questions, feel free to call Finekay® – our professional engineers are available to assist you. Thank you
Thank you for your reply. The first question was answered very well; I now understand it. Thank you again. It would be great if you could also answer the second question
Regarding the second question, the table data in API2000 is all calculated based on n-hexane; I’m not sure if your calculations are also based on n-hexane as the medium.
Use a table for wetting areas less than 260㎡； For areas greater than 260㎡, with a design pressure greater than 7 KPa and less than 103.4 kPa, use the formula