Quick-closing valves (QCV) are used, among other functions, to prevent fires by isolating the oil in tankers and preventing oil in the system being distributed and maintaining a fire. The valves can be operated locally but also from other places onboard. It is important that their function is intact. Maintenance must be carried out and spare parts must be avail-able. Despite such measures, it happens that valves become locked in the open position after having closed spontaneously due to vibrations or wear and tear of components. Sometimes the valves are incorrectly installed at the shipyard or after repairs. Be sure to service the valves properly and to carry out functional tests.