3.14 balanced bellows device which

3.14 balanced bellows device which minimizes the effect of back pressure on the set pressure and/or the operation of a safety valve 3.15 blowdown difference between set and reseating pressures Note 1 to entry: Blowdown is normally stated as a percentage of set pressure except for pressures of less than 3 bar when the blowdown is expressed in bar. 3.16 lift actual travel of the valve disc away from the closed position 3.17 flow area minimum cross-sectional flow area (but not the smallest area between disc and seat) between inlet and seat which is used to calculate the theoretical flow capacity, with no deduction for any obstruction 3.18 flow diameter diameter corresponding to the flow area 3.19 theoretical discharge capacity calculated capacity expressed in mass or volumetric units of a theoretically perfect nozzle having a cross-sectional flow area equal to the flow area of a safety valve 3.20 coefficient of discharge value of actual flowing capacity (from tests) divided by the theoretical flowing capacity (from calculation) 3.21 certified (discharge) capacity that portion of the measured capacity permitted to be used as a basis for the application of a safety valve Note 1 to entry: It may, for example, equal the: a) measured flow rate times the derating factor; or b) theoretical flow rate times the coefficient of discharge times the derating factor; or c) theoretical flow rate times the certified de-rated coefficient of discharge. 3.22 DN (nominal size) alphanumeric designation of size that is common for components used in a piping system, used for reference purposes, comprising the letters DN followed by a dimensionless number having an indirect correspondence to the physical size of the bore or outside diameter of the component end connection