Before any flange bolts are tightened, valves should be centered within the flanges and then carefully opened to assure free, unobstructed disc movement.

• 在紧固阀门螺栓之前，阀门应该处于法兰之间的中心位置，然后小心打开，以确保阀瓣能够灵活、无障碍的运动。