pressure relief valves in buried tank

huangyhg

pressure relief valves in buried tank
i have a partially buried tank that needs to have the size and number of pressure relief valves specified.  does anyone know the procedure for making this determination?  i notice that the manufacturers do not seem to be calling out anything on their cut sheets.  thanks in advance for any input.
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you'll be amazed how quickly everyone disappears when you ask this question.  it's kind of a gut feel call. let's say you can drain the tank at some rate, say 200 gpm.  provide enough pressure relief valves to fill the tank at that rate, assuming groundwater at its highest level.  you can figure out the rate per valve by doing an orifice calculation.
if anyone has any other suggestions, feel free to contribute.  they're probably just as valid.
i'll suggest an approach- not that this is the kind of thing i normally use:
assume or find a maximum rainfall rate.  assume the rainwater goes into the ground.  assume or determine the amount of void space that can be filled.  that should give you the maximum rate of rise of the ground water, and assume the water inside the tank must be filled at the same rate.  that gives you a flow rate of water into the tank.  determine the maximum differential water pressure you can have in the tank shell or tank floor.  that gives you the driving pressure for that flow rate.  then it's a matter of sizing flow in the ground and piping for thos conditions.
thank you both for your responses.  you're right jedclampett, it is not the type of question that i imagined people would be rushing to help me with and yet i got two great responses.  i'll probably check both scenarios and see which controls.  thanks again!