The calculation of the minimum relief area on the basis of the iterative procedure, as reported in EN ISO 4126-4 and by adopting an explicit method as carried out in the industrial practice, leads to the same valve size. This applies to valves with a high and low value of the related lift, respectively, with a valve nozzle orifice according to API RP 526. However, under extraordinary conditions it may be possible that the discharge areas differ due to the graduation of the valve sizes within a suppliers' production program. Indeed, neither method gives systematically larger relief areas than the other, the procedures are equivalent. (c) 2005 Elsevier Ltd. All rights reserved.