Fire pump pressure gauges with a dial less than how many inches in diameter require a nominal 1/4" gauge valve?

The correct answer indicates that fire pump pressure gauges with a dial less than 3.5 inches in diameter require a nominal 1/4" gauge valve. This requirement is based on the design and functionality of pressure gauges in fire protection systems.

Smaller diameter gauges can have limitations in terms of readability and overall robustness due to their size. A gauge valve of nominal 1/4" is appropriate for these smaller gauges as it allows for adequate flow and pressure measurement without compromising the interface needed for accurate readings.

Using a gauge valve that corresponds to the size of the gauge ensures proper installation, allows for easy maintenance, and maintains safety standards within the fire protection system. Larger gauges are typically better supported with larger valve sizes, but for gauges below this specific size threshold, the 1/4" valve is specified to ensure efficiency and effectiveness in the system.