What is the minimum size of blow-off pipe and valve required on a cast iron heating boiler with a safety valve relieving capacity of 3000 pounds per hour?

The minimum size of the blow-off pipe and valve for a cast iron heating boiler that has a safety valve relieving capacity of 3000 pounds per hour is determined by the need to adequately handle the discharge from the safety valve without causing excessive pressure or flow restriction.

For safety valves on boilers, the National Board of Boiler and Pressure Vessel Inspectors provides guidelines to ensure that blow-off piping is appropriately sized based on the safety valve's capacity. A boiler with a safety valve that relieves 3000 pounds per hour typically requires a minimum blow-off pipe size of 1 inch to allow for effective drainage and to prevent cavitation or other flow issues during operation.

Choosing a smaller diameter pipe could lead to potential hazards, including the risk of the pipe becoming blocked or the discharge pressure exceeding safe levels. By using the correct minimum size of 1 inch, the system ensures that steam and water can be discharged efficiently, thereby maintaining safety and functionality within the boiler system.