Which types of valves are preferred for use in fire service mains according to NFPA 24?

Gate valves are preferred for use in fire service mains primarily due to their design and functionality, which make them ideal for applications requiring a full flow of water. With a gate valve, the flow is unobstructed when the valve is fully open, allowing for minimal resistance and efficient operation. This feature is crucial in fire service systems where maximizing water flow during a fire emergency can be life-saving.

Additionally, gate valves provide a clear indication of whether they are fully open or closed, which is important during emergencies when quick decisions must be made. Their durability and ability to withstand high pressure also make them suitable for underground installations, which is common in fire service mains.

While other valve types, such as check valves or ball valves, have their respective applications and advantages, they may not fulfill the specific requirements of fire service mains as effectively as gate valves. Check valves are typically used to prevent backflow and aren't designed for throttling or flow control. Ball valves, while they offer rapid operation, tend to create turbulence when partially opened. Butterfly valves can be useful in certain scenarios but may not provide the same level of flow efficiency as gate valves when fully open.