How does the pounds per hour rating of a relief valve relate to the BTU of the boiler?

The pounds per hour rating of a relief valve is a critical safety parameter that must be carefully evaluated in conjunction with the BTU (British Thermal Unit) rating of the boiler or pressure vessel. The rationale behind the correct choice is based on the fundamental principles of thermal energy and the need for appropriate steam release to prevent overpressure scenarios.

When the BTU capacity of a boiler is known, it indicates the energy expenditure of the boiler; thus, to safely manage the steam produced, the relief valve must have a specified capacity to discharge enough steam. The choice indicating that the relief valve's rating must be equal to the BTU rating divided by 1,000 reflects this relationship, ensuring that the valve can adequately vent steam under emergency conditions—thus preventing potentially hazardous situations such as overpressure that could lead to equipment failure or safety incidents.

Understanding this correlation helps technicians size relief valves correctly in relation to the boilers they serve, ensuring that safety standards are met and maintained effectively. The other choices do not align with the necessary safety practices regarding valve sizing and could lead to significant operational issues if not properly addressed.