On a hot water boiler, the highest value on the graduated scale of the pressure gauge shall not be less than ______ times the pressure at which the pressure relief valve is set.

The requirement that the highest value on the graduated scale of the pressure gauge should not be less than 1.5 times the pressure at which the pressure relief valve is set is based on safety and operational efficiency principles in boiler design.

The pressure relief valve is a critical safety device designed to prevent the boiler from exceeding safe operating pressures. By setting the graduated scale on the pressure gauge to at least 1.5 times the relief valve setting, it ensures that operators have a clear and accurate visual reference of the operating pressure under all conditions. This provides a margin that accounts for pressure fluctuations and helps prevent overpressure situations which could lead to dangerous failures or accidents.

Moreover, this standardization aids operators in managing the system effectively, ensuring that they can monitor and react to changes in pressure that occur during operation. The enhanced gauge range beyond the relief valve setting contributes to the overall reliability and safety of the boiler system, allowing for a clear understanding of operating parameters while maintaining an adequate safety buffer.