7.5 Certification of coefficient of discharge The certified de-rated coefficient of discharge Kdr of the safety valve shall be not greater than 90 % of the coefficient of discharge Kd determined by Formula (2): dr = 0,9 d (2) Neither the coefficient of discharge nor the certified de-rated coefficient of discharge can be used to calculate the capacity at a lower relieving pressure than that at which the tests to determine the flow characteristics (see 7.3) were carried out, although they can be used to calculate the capacity at any higher relieving pressure.