Intercept the fluid medium upstream of the valve to be inspected with a shut-off valve and ensure that the subject valve is not under pressure (vent downstream, if necessary).

• 截取阀门上游的流体介质,用一个关闭阀门来进行检测,确保相关的阀门不处在压力下(如果必要的话,排除下游的流体介质)。