ASME Section IV Pressure Relief Valves and Devices

Safety Valves and Safety Relief Valves

• A safety valve for a steam boiler should discharge at a maximum pressure of 3% above the allowable working pressure, according to HG-400.1 (a).
• The minimum size of a safety valve for a steam boiler is 1/2 inch, according to HG-400.1 (b).
• The safety valve capacity for each steam boiler should prevent a maximum pressure 3% above the allowable working pressure, according to HG-400.1 (e).
• The purpose of the body drain provided by the Manufacturer for all safety valves and safety relief valves is to prevent dirt and moisture from accumulating, according to HG-401.1 (h).
• ASME-section I safety valves are required for steam boilers, according to HG-400.1 (a).
• There is no maximum size limit for safety valves for steam boilers, according to HG-400.1 (b).
• Safety valves and safety relief valves must be located on the boiler, according to ASME BPVC IV, Part HG-700.
• A welded or threaded connection is required between the boiler and any safety valve or safety relief valve, according to ASME BPVC IV, Part HG-700.
• Discharge pipes of safety valves must be full-size and not smaller than the valve outlet, according to ASME BPVC IV, Part HG-700.

Low-Pressure Steam Heating Boilers

• The maximum allowable operating pressure for low-pressure steam heating boilers is 15 psi, according to the text.
• Low-pressure safety valves do not have a manual reset feature, unlike high-pressure safety valves.

Hot Water Heating or Supply Boilers

• Safety relief valves are required for hot water heating or supply boilers, according to ASME BPVC IV, Part HG-400.2.
• It is advised against tampering with safety relief valves during normal plant operation.
• Water conditions, poor maintenance, and improper installation can cause frequent operation or water leakage from safety relief valves in hot water heating systems, according to the text.
• Safety relief valves are used for low-pressure boilers, while safety valves are used for high-pressure boilers.