ASME PTC 25-2008 pdf download
ASME PTC 25-2008 pdf download.Pressure Relief Devices .
2-1 PURPOSE The purpose of this Section is to define pressure-relief devices and their functional and operational characteris- tics and standardize the terminology covering such devices, their characteristics, and testing methods. It also incudes a description of terms and symbols used in this Code. These definitions and terms shall take precedence should there be any discrepancy with the referenced material. 2-2 GENERAL bench testing: testing of a pressure relief device on a test stand using an external pressure source with or without an auxiliary lift device to determine some or all of its operating characteristics. field testing: testing of a pressure relief device installed on a system to determine some or all of its operating characteristics. It may be either of the following methods: (a) in-place testing: testing of a pressure relief device installed on but not protecting a system, using an exter- nal pressure source, with or without an auxiliary lift device to determine some or all of its operating characteristics. (b) in-service testing: testing of a pressure relief device installed on and protecting a system, using system pres- sure or an external pressure source, with or without an auxiliary lift device to determine some or all of its operating characteristics. flow capacity testing: testing of a pressure relief device to determine its operating characteristics, including mea- sured relieving capacity. pressure relief device: a device designed to prevent pres- sure or vacuum from exceeding a predetermined value in a pressure vessel by the transfer of fluid during emer- gency or abnormal conditions. 2-3 TYPES OF DEVICES 2-3.1 Reclosing Pressure-Relieving Devices pressure relief valve (PRV): a pressure relief device designed to actuate on inlet static pressure and reclose after normal conditions have been restored. It may be one of the following types and have one or more of the following design features: (a) low-lift PRV: a pressure relief valve in which the actual discharge area is the curtain area.
(b) fllit PRV: a pressure relief valve in which the actual discharge area is the bore area. (c) reduced bore PRV: a pressure relief valve in which the flow path area below the seat is less than the flow area at the inlet to the valve. (d) full-bore PRV: a pressure relief valve in which the bore area is equal to the flow area at the inlet to the valve, and there are no protrusions in the bore. (e) direct spring-londed PRV: a pressure relief valve in which the disk is held closed by a spring. (f) pilot-operated PRV: a pressure relief valve in which the disk is held closed by system pressure, and the hold- ing pressure is controlled by a pilot valve actuated by system pressure. (g) conuentional direct spring-londed PRV: a direct spring-loaded pressure relief valve whose operational characteristics are directly affected by changes in the back pressure. (h) balanced direct spring-loaded PRV: a direct spring- loaded pressure relief valve that incorporates means of minimizing the effect of back pressure on the operational characteristics (opening pressure, closing pressure, and relieving capacity). (i) internal spring PRV: a direct spring-loaded pres- sure relief valve whose spring and all or part of the operating mechanism is exposed to the system pressure when the valve is in the closed position. (j) temperature and pressure relief valve: a pressure relief valve that may be actuated by pressure at the valve inlet or by temperature at the valve inlet. (k) power-actuated PRV: a pressure relief valve actu- ated by an externally powered control device. relief valve: a pressure relief valve characterized by grad- ual opening that is generally proportional to the increase in pressure. It is normally used for incompressible fluids. safety relief valve: a pressure relief valve characterized by rapid opening or by gradual opening that is generally proportional to the increase in pressure. It can be used for compressible or incompressible fluids. safety valve: a pressure relief valve characterized by rapid opening and normally used to relieve compressible fluids. 2-3.2 Nonreclosing Pressure Relief Device A pressure relief device designed to actuate and remain open after operation. A manual resetting means may be provided.
