A pressure relief valve for packages in which the valve element comprises a liquid impregnated porous element covering outlet openings in the package, with the liquid layer in the porous element being torn open by package contents pressures in {HEAD ~ excess} of {TAIL ~ a predetermined value} to permit gas outflow from the package 
A pressure relief valve for packages in which the valve element comprises a liquid impregnated porous element covering outlet openings in the package , with the liquid layer in the porous element being torn open by package contents pressures in { HEAD ~ excess } of { TAIL ~ a predetermined value } to permit gas outflow from the package
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