Safety Valves

Safety valves include pressure safety valves (PSVs) and pressure relief valves (PRVs), which are installed in all pressurized equipment such as pipelines, pumps, compressors, turbines, and boilers where overpressurization may occur. This chapter contains an overview of essential design considerations and calculations for PSVs and PRVs, including relief of pressure and capacity as well as the generation of reaction forces. The chapter explains some terminology related to valve design and operation, such as set pressure, backpressure, and overpressure scenarios. Additionally, methods are presented for calculating these parameters. The principles of PSV operation and their associated loads and pressure values are described. Finally, we discuss the reaction forces resulting from valve operation and several methods for calculating them. When the pressure inside the apparatus exceeds the set or permissible pressure level, the PSV opens, the excess pressure is released from the flare lines, and the extremely high pressure returns to a normal, safe level. As the safety valve is open and blowing, reaction forces are produced by a combination of backpressure and sudden impulses. The last section of this chapter describes how to convert the relief capacity of safety valves from different services, such as gas, steam, air, and vapor, to another service.