Which type of blowdown valve must be slow opening for safety in a boiler?

In a boiler system, a slow opening blowdown valve is essential for safety because it allows for a controlled release of pressure and temperature from the boiler. When blowdown occurs, the sudden loss of water and pressure can lead to rapid fluctuations that may cause stress and potential damage to the boiler structure or associated components.

The slow opening feature of this type of valve helps to mitigate these risks by gradually reducing the pressure, allowing the system to adjust without causing thermal shock or mechanical failure. This is particularly important in high-pressure boiler operations, where the rapid expansion or contraction of materials could create dangerous conditions.

On the other hand, a quick opening valve, although useful in specific scenarios, does not provide the necessary safety controls during blowdown operations. It can lead to sudden changes in system dynamics, which are undesirable in a boiler environment. Therefore, the slow-opening blowdown valve is the correct choice for ensuring safe operations in a boiler system.