Patent ID: 8020574

Claim:
A method for closing a fluid passage with a nearly constant internal pressure in the passage, by using an actuator operated-type valve installed in the passage, wherein the method comprises the steps of: (a) detecting a vibration detecting signal Pr from vibration of the fluid passage caused by a change of internal pressure of the fluid passage; (b) first, moving a valve body from a fully opened state and in a valve closing direction to a partially opened state by increasing a driving input to an actuator to a predetermined value, wherein the driving input is increased to a first prescribed set value sufficient to prevent a water hammer in the fluid passage, wherein the first prescribed set value is a step pressure setting signal Ps wherein the vibration detecting signal Pr does not exceed a permissible upper limit vibration setting signal Prm; (c) maintaining the driving input to the actuator at the predetermined value for a short time; and then (d) further increasing the driving input so the valve body is brought from the partially opened state to a fully closed state to close the fluid passage without causing a water hammer, wherein the valve body is moved from the fully opened state to the fully closed state in a stepwise manner involving movement of the valve body from the fully opened state to the partially opened state and then from the partially opened state to the fully closed state, wherein the stepwise manner involves moving the valve body from the fully opened state to the fully closed state using only two, three, or four movements of the valve body.