60. Which of the following listed valves would require «blow down» to insure proper operation and prevent damage due to repeated and rapid opening and closing?

Safety valves require blowdown to prevent rapid opening and closing, which can damage the valve. Blowdown is the pressure difference between the set pressure and reseating pressure, ensuring the valve remains open until sufficient pressure is relieved. This prevents chattering and protects the valve's internal components; pressure-reducing, pressure-relief, and pressure-regulating relief valves do not utilize this feature.