Abstract: In the cooling water system of water circulating pump of a 600 MW units, the threads of many valves were stripped, and this influenced on safety operation of units. Therefore, the valves must be replaced. Before replacement of the valves, the cooling water of the water circulating pump must be switched over to a temporary system, and the measures for the switching over and the matters needing attention were introduced. Some experiences and lessons were summarized, providing a reference for persons of same occupation.

Key words: water circulating pump, motor, cooling water, valve, isolation, replace