A gate valve used in drainage work having a 102 mm diameter or larger shall have _____ bodies.

The correct choice is that a gate valve used in drainage work with a diameter of 102 mm or larger should have cast iron bodies. Cast iron is highly favored for such applications due to its strength, durability, and resistance to corrosion, which makes it suitable for handling wastewater and other aggressive media typically found in drainage systems. Its robust nature allows it to withstand high pressure and thermal fluctuations, ensuring a reliable and long-lasting performance in various environmental conditions.

While other materials may be used in specific applications, cast brass, bronze, and galvanized iron do not offer the same balance of structural integrity and corrosion resistance as cast iron for larger gate valves in drainage scenarios. Cast brass and bronze valves are typically utilized in smaller, low-pressure applications or where aesthetics are a priority. Galvanized iron, while durable, may suffer from corrosion issues over time, particularly if exposed to certain chemicals or moisture levels found in drainage systems. Hence, the use of cast iron is a standard practice in this context.