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Pressure Relief Device: Standards and Specifications

Pressure-relieving valves and devices shall conform to the requirements specified standards and specifications. Additional requirements for certification and marking requirements such as PED (CE marking) and ASME BPVC (Designation stamp) should be apply.

Below is a list of the most important standards and specifications:

Standard/
Specification
Title
Description
Remark
API STD 520 Part 1Sizing, Selection, and Installation of Pressure-Relieving Devices in RefineriesThis standard applies to the sizing and selection of pressure relief devices used in refineries and related industries for equipment that has a maximum allowable working pressure of 15 psig (103 kPag) or greater. The pressure relief devices covered in this standard are intended to protect unfired pressure vessels and related equipment against overpressure from operating and fire contingencies. This standard includes basic definitions and information about the operational characteristics and applications of various pressure relief devices. It also includes sizing procedures and methods based on steady state flow of Newtonian fluids. Atmospheric and low-pressure storage tanks covered in API 2000 and pressure vessels used for the transportation of products in bulk or shipping containers are not within the scope of this standard. See API 521 for information about appropriate ways of reducing pressure and restricting heat input.
API STD 520 Part 2Sizing, Selection, and Installation of Pressure-relieving Devices. Part II – InThis standard covers methods of installation for pressure-relief devices (PRDs) for equipment that has a maximum allowable working pressure (MAWP) of 15 psig (1.03 barg or 103 kPAg) or greater. Pressure-relief valves (PRVs) or rupture disks (RDs) may be used independently or in combination with each other to provide the required protection against excessive pressure accumulation. As used in this standard, the term pressure-relief valve includes safety-relief valves used in either compressible or incompressible fluid service, and relief valves used in incompressible fluid service. This standard covers gas, vapor, steam, two-phase, and incompressible fluid service; it does not cover special applications that require unusual installation considerations.
API STD 521Guide for Pressure-relieving and Depressuring SystemsThis Standard is applicable to pressure relieving and vapor depressuring systems. Although intended for use primarily in oil refineries, it is also applicable to petrochemical facilities, gas plants, liquefied natural gas (LNG) facilities and oil and gas production facilities. The information provided is designed to aid in the selection of the system that is most appropriate for the risks and circumstances involved in various installations. This Standard specifies requirements and gives guidelines for the following: – examining the principal causes of overpressure; – determining individual relieving rates; – selecting and designing disposal systems, including such component parts as piping, vessels, flares, and vent stacks. This Standard does not apply to direct-fired steam boilers.
API STD 522Pressure Relief Systems CalculationsThis technical report provides equations and examples for performing relief system calculations. Users are responsible for performing their own calculations and using appropriate references for equations. This report contains a variety of calculation examples for equations and methods found in API publications on pressure-relief systems.
API STD 526Flanged Steel Pressure-relief ValvesThis standard is a purchase specification for flanged steel pressure-relief valves. Basic requirements are given for direct spring-loaded pressure-relief valves and pilot-operated pressure-relief valves as follows: -orifice designation and area; -valve size and pressure rating, inlet and outlet; -materials; -pressure-temperature limits; -center-to-face dimensions, inlet and outlet. Nameplate nomenclature and requirements for stamping are detailed in Annex A
API STD 527Seat Tightness of Pressure Relief ValvesThis standard describes methods of determining the seat tightness of metal- and soft-seated pressure relief valves, including those of conventional, bellows, and pilot-operated designs. The maximum acceptable leakage rates are defined for pressure relief valves with set pressures from 103 kPa gauge (15 psig) to 41,379 kPa gauge (6,000 psig). If greater seat tightness is required, the purchaser shall specify it in the purchase order. The test medium for determining the seat tightness—air, steam, or water—shall be the same as that used for determining the set pressure of the valve. For dual-service valves, the test medium—air, steam, or water—shall be the same as the primary relieving medium. To ensure safety, the procedures outlined in this standard shall be performed by persons experienced in the use and functions of pressure relief valves.
ASME B31.1Power PipingArticle 107.8 Pressure-Relieving Valves and Devices
ASME BPVC Section I Power BoilersGenerale Overpressure Protection: PG-67 to PG-73;
Additional requirements:
PL-54 Pressure Relief Valves – Locomotiv Boilers
PMB-15 Pressure Relief Valves – Miniatur Boilers
PEB-15 Pressure Relief Valves – Electric Boilers
PVG-12 Pressure Relief Valves – Organic Fluid Vaporizer
PFE-3 Pressure Relief -Feedwater Economizer
PTFH-12 Overpressure Protection – Thermal Fluid Heaters
ASME BPVC Section VIII Div. 1 Unfired Pressure vesselOverpress Protection:
UG-150 General requirments
UG-151 Responsibilities
UG-152 Determination of pressure relieving requirements
UG-153 Overpress limits
UG-154 Permitted pressure relief devices and methode
UG-155 Pressure settings and performance requirements
UG-156 Installation
Appendix M: Installation and Operation
ASME BPVC Section VIII Div. 3 Unfired Pressure vessel – Alternative RulesOverpressure Protection:
KOP-1 General Requirements
KOP-2 Power-Actuated Pressure Relief Systems
KOP-3 Overpressure Protection for Impulsively Loaded Vessels
ASME BPVC Section XIIIRules for Overpressure ProtectionThis Section provides rules for the overpressure protection of pressurized equipment such as boilers, pressure vessels, and piping systems. This standard provides requirements for topics such as design, material, inspection, assembly, testing, and marking for pressure relief valves, rupture disk devices, pin devices, spring-actuated non-reclosing devices, and temperature and pressure relief valves. This standard also covers devices in combination, capacity and flow resistance certification, authorisation to use the ASME Certification Mark, installation, and overpressure protection by system design.
ASME – PTC 25Pressure Relief
Devices – Performance Test Codes
The object of this PTC test is to determine the performance of pressure relief devices. Procedures for conducting the tests, calculating the results, and making corrections are defined. This Code provides instructions for flow capacity testing and for in-service and bench testing. Testing of reclosing and nonreclosing pressure relief devices is conducted under various inlet and outlet conditions using steam, gases, and liquids for which valid physical properties are known.
EN 334Gas pressure regulators for inlet pressure up to 10 MPa (100 bar)This European Standard specifies constructional, functional, testing, marking, sizing and documentation requirements of gas pressure regulators: – for inlet pressures up to 100 bar and nominal diameters up to DN 400; – for an operating temperature range from – 20 °C to +60 °C, which operate with fuel gases of the 1st and 2nd family as defined in EN 437, used in the pressure regulating stations in accordance with EN 12186 or EN 12279, in transmission and distribution networks and also in commercial and industrial installations.
EN ISO 4126-1Safety devices for protection against excessive pressure –Part 1: Safety devices for protection against excessive pressureSpecifies general requirements for safety valves irrespective of the fluid for which they are designed.
It is applicable to safety valves having a flow diameter of 4 mm and above which are for use at set pressures of 0,1 bar gauge and above. No limitation is placed on temperature.
ISO 4126-1 is a product standard and is not applicable to applications of safety valves
EN ISO 4126-2Safety devices for protection against excessive pressure – Part 2: Bursting disc safety devicesSpecifies the requirements for bursting disc safety devices.
It includes the requirements for the design, manufacture, inspection, testing, certification, marking, and packaging.
EN ISO 4126-3Safety devices for protection against excessive pressure – Part 3: Safety valves and bursting disc safety devices in combinationThis document specifies only the requirements for a product assembled from the in-series combination of safety valves or CSPRS (controlled safety pressure relief systems) according to ISO 4126‑1, ISO 4126‑4 and ISO 4126‑5, and bursting disc safety devices, according to ISO 4126‑2, installed upstream of the valve within five pipe diameters of the valve inlet. It specifies the design, application and marking requirements for such products, composed of the bursting disc safety device, a safety valve or CSPRS and, where applicable, a connecting pipe or spool piece. In addition, it gives a method for establishing the combination discharge factor used in sizing combinations.
EN ISO 4126-4Safety devices for protection against excessive pressure –Part 4: Pilot operated safety valvesSpecifies general requirements for pilot operated safety valves, irrespective of the fluid for which they are designed. In all cases, the operation is carried out by the fluid in the system to be protected.
It is applicable to pilot operated safety valves having a valve flow diameter of 4 mm and above which are for use at set pressures of 0,1 bar gauge and above. No limitation is placed on temperature.
ISO 4126-4 is a product standard and it is not applicable to applications of pilot operated safety valves.
EN ISO 4126-5Safety devices for protection against excessive pressure –Part 5: Controlled safety pressure relief systems (CSPRS)Specifies the requirements for controlled safety pressure relief systems (CSPRS) irrespective of the fluid for which they are designed.
It is applicable for main valves having a flow diameter of 4 mm and above which are for use at pressures of 0,1 bar gauge and above. No limitation is placed on temperature.
ISO 4126-5 is a product standard and is not applicable to applications.
EN ISO 4126-6Safety devices for protection against excessive pressure –Part 6: Safety devices for protection against excessive pressure –Application, selection and installation of bursting disc safety devicesISO 4126-6 gives guidance on the application, selection and installation of bursting disc safety devices used to protect pressure equipment from excessive pressure and/or excessive vacuum.
EN ISO 4126-7Safety devices for protection against excessive pressure –Part 7: Common dataISO 4126-7specifies requirements for safety valves. It contains information which is common to ISO 4126-1 to ISO 4126-6 to avoid unnecessary repetition.
EN ISO 4126-9Safety devices for protection against excessive pressure –Part 9: Application and installation of safety devices excluding stand-alone bursting disc safety deviceISO 4126-9 covers the application and installations of safety devices such as safety valves, safety valves and bursting disc safety devices in combination, pilot-operated safety valves and controlled safety pressure-relief systems for the protection of pressure equipment. ISO 4126-6 covers the selection, application and installation of bursting disc safety devices.
ISO 4126-9 describes the normative requirements for applications and installations of safety devices to protect static pressure equipment. The information contained in ISO 4126-9 assumes single-phase flow of the fluid discharged from the safety device. ISO 4126-10 provides guidance specific to two-phase flow conditions.
Equipment connected together in a system by piping of adequate capacity, which is free from potential blockages and does not contain any valve that can isolate any part, can be considered to be a safety system for the application of pressure relief.
ISO 4126-9 does not deal with other safety devices, such as safety related monitoring, control and regulation devices and other limiting devices allowed by some national regulations.
EN ISO 4126-10Safety devices for protection against excessive pressure –Part 10: Sizing of safety valves and bursting discs for gas/liquid two-phase flowISO 4126-10 specifies the sizing of safety valves for gas/liquid two-phase flow in pressurized systems such as: reactors, storage tanks, columns, heat exchangers, piping systems or transportation tanks/containers.
ISO/AWI 4126-11Safety devices for protection against excessive pressure –Part 11: Performance TestingThe purpose of the International Standard is to define specifically all requirements on tests and laboratory personal, test parameter and its precision and to give options for the testing procedures to be applied for carrying out performance tests on closing, non-reclosing and combined safety devices for protection against excessive pressure as specified in ISO 4126 Parts 1, to 10, with particular reference to type testing. Function and capacity tests of the valve shall be considered and inlet and outlet conditions shall be included. Back-pressure influence shall be considered, if necessary. Alternative test rig configurations measurement techniques as well as to testing procedures should be given as informative examples. Further topics to be considered must be low and high pressure applications.
EN 13648-1Cryogenic vessels – Safety devices for protection against excessive pressure – Part 1: Safety valves for cryogenic serviceThis European Standard specifies the requirements for the design, manufacture and testing of safety valves for cryogenic service, that is to say for operation with cryogenic fluids (as defined in EN 1251-1) below – 10 °C in addition to operation at ambient temperature. It is a requirement of this European Standard that the valves comply with EN ISO 4126 1 or EN ISO 4126-4. 
This European Standard is restricted to valves not exceeding a size of DN 100 for category B. The valves of category A are limited to DN 25 and set pressures up to 40 bars. 
EN 13953LPG equipment and accessories – Pressure relief valves for transportable refillable cylinders for Liquefied Petroleum Gas (LPG)This document specifies the design, testing and marking requirements for spring loaded pressure relief valves (PRV), for use in liquefied petroleum gas (LPG) cylinders of water capacity of 0,5 l up to and including 150 l. These PRVs can be either an integral part of a cylinder valve (see EN ISO 14245 and EN ISO 15995 or a separate device.
EN 14071LPG equipment and accessories – Pressure relief valves for LPG pressure vessels – Ancillary equipmentThis European Standard specifies the design, testing and inspection requirements for pressure relief valve isolating devices, valve manifolds, vent pipes and system assemblies which are, where necessary, used with pressure relief valves for use in static pressure vessels for Liquefied Petroleum Gas (LPG) service. This European Standard addresses both prototype testing and production testing of isolating devices and PRV manifolds. Pressure relief valves for LPG pressure vessels are specified in EN 14129.
EN 14129LPG Equipment and accessories – Pressure relief valves for LPG pressure vesselsThis European Standard specifies the requirements for the design and testing of spring loaded pressure relief valves and thermal expansion valves for use in: – static LPG pressure vessels, NOTE The pressure vessels can be situated above ground, underground or mounded. – LPG pressure vessels on road tankers, rail tankers, tank-containers or demountable tanks. This document does not address production testing. Normative Annex B prescribes testing with conditioning at – 40 °C for valves for use under extreme low temperature conditions. The requirements for pressure relief valve accessories such as isolating devices, changeover manifolds and vent pipes are specified in EN 14071. EN 14570 identifies the requirements for the pressure relief valve capacities for static pressure vessels. EN 12252 identifies the requirements for the pressure relief valve capacities for road tankers. Valves designed in accordance with this standard are specifically for use in LPG applications. Valves manufactured in accordance with EN ISO 4126 1 may also be used in certain LPG applications. Terms used with LPG pressure relief valves are described graphically in Annex A.
EN 14596Tanks for transport of dangerous goods – Service equipment for tanks – Emergency pressure relief valveThis document covers the emergency pressure relief valve. It specifies the performance requirements and the critical dimensions of the emergency pressure relief valve. It also specifies the tests necessary to verify the compliance of the equipment with this document. The service equipment specified by this document is suitable for use with liquid petroleum products and other dangerous substances of Class 3 of ADR which have a vapour pressure not exceeding 110 kPa at 50 °C and petrol, and which have no sub-classification as toxic or corrosive.
EN 16631LPG equipment and accessories – Pressure relief valves for LPG pressure vessels – Reconditioning requirementsThis European Standard specifies the requirements for the reconditioning, retesting and certification of Pressure Relief Valves (PRVs) for LPG pressure vessels covered under the scope of EN 14129. This European Standard applies to retesting and reconditioning of PRVs that are carried out in a workshop and does not apply to site adjustment of installed PRVs. Annex A is an informative Annex detailing a sampling approach for PRV requalification which should only be used in case of on-site requalification of series produced pressure vessels fitted with series produced PRVs.
EN 17955Industrial valves – Functional safety of safety-related automated valvesThis standard defines procedures and methods with which all relevant mechanical components of automated industrial valve packages that are used as final elements in a safety instrumented system can be evaluated according to the rules of EN 61508 Parts 1, 2, 4, 6 and 7 in order to integrate them into a safety instrumented system (SIS).
ISO 12614-7Liquefied natural gas (LNG) fuel system components – Part 7: Pressure relief valve (PRV)This document specifies tests and requirements for the pressure relief valve (PRV), a liquefied natural gas fuel system component intended for use on the types of motor vehicles defined in ISO 3833. This document is not applicable to the following:
a) fuel containers;
b) stationary gas engines;
c) container mounting hardware;
d) electronic fuel management;
e) refuelling receptacles.
It is recognized that miscellaneous components not specifically covered herein can be examined to meet the criteria of this document and tested according to the appropriate functional tests.
All references to pressure in this document are to be considered gauge pressures unless otherwise specified.
This document is based upon a working pressure for natural gas as a fuel of 1,6 MPa [16 bar]. Other working pressures can be accommodated by adjusting the pressure by the appropriate factor (ratio). For example, 2 MPa (20 bar) working pressure system will require pressures to be multiplied by 1,25.
ISO 21013-1Cryogenic vessels – Pressure-relief accessories for cryogenic service – Part 1: Re-closable pressure-relief valvesThis document specifies the requirements for the design, manufacture and testing of pressure relief valves for cryogenic service, i.e. for operation with cryogenic fluids below −10 °C in addition to operation at ambient temperatures from ambient to cryogenic.
This document is applicable to valves not exceeding a size of DN 150 designed to relieve
single-phase vapours or gases. A valve can be specified, constructed and tested such that it is suitable for use with more than one gas or with mixtures of gases.
NOTE       This document does not provide methods for determining the capacity of relief valve(s) for a particular cryogenic vessel. Such methods are provided in ISO 21013-3.
ISO 21013-2Cryogenic vessels – Pressure-relief accessories for cryogenic service – Part 2: Non-reclosable pressure-relief devicesISO 21013-2 specifies the requirements for the design, manufacture and testing of non‑reclosable pressure‑relief devices for cryogenic service, i.e. for operation with cryogenic fluids in addition to operation at temperatures from ambient to cryogenic. 
ISO 21013-2 is restricted to bursting‑disc and buckling‑pin devices not exceeding a size of DN 200 designed to relieve single‑phase vapours or gases. A bursting‑disc or buckling‑pin assembly may be specified, constructed and tested such that it is suitable for use with more than one gas or with mixtures of gases.
ISO 21013-2 does not provide methods for determining the capacity of bursting disc or buckling pin devices for a particular cryogenic vessel. Such methods are provided in ISO 21013-3.
EN ISO 21013-3Cryogenic vessels – Pressure-relief accessories for cryogenic service – Part 3: Sizing and capacity determination ISO 21013-3 provides separate calculation methods for determining the required mass flow to be relieved for each of the following specified conditions:
– vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal vacuum, outer jacket at ambient temperature, inner vessel at temperature of the contents at the specified relieving pressure;
– vacuum-insulated vessels with insulation system (outer jacket + insulating material) intact under normal vacuum, outer jacket at ambient temperature, inner vessel at temperature of the contents at the specified relieving pressure, pressure regulator of the pressure build-up system functioning at full potential;
– vacuum or non-vacuum-insulated vessels with insulation system remaining in place, but with loss of vacuum in the case of vacuum-insulated vessels, outer jacket at ambient temperature, inner vessel at temperature of the contents at the specified relieving pressure or vacuum or non-vacuum-insulated vessels with insulation system remaining fully or partially in place, but with loss of vacuum in the case of vacuum-insulated vessels, fire engulfment, inner vessel at temperature of the contents at the specified relieving pressure;
– vacuum-insulated vessels containing fluids with saturation temperature below 75 K at 1 bar with insulation system remaining in place, but with loss of vacuum with air or nitrogen in the vacuum space;
– vacuum insulated vessels containing fluids with saturation temperature below 75 K at 1 bar with insulation system remaining in place, but with loss of vacuum with air or nitrogen in the vacuum space with fire engulfment;
– vessels with insulation system totally lost and fire engulfment.
Good engineering practice based on well-established theoretical physical science needs to be adopted to determine the required mass flow where an appropriate calculation method is not provided for an applicable condition.
Recommendations for pressure relief devices for cryostats are given in Annex A.
ISO 21013-4Cryogenic vessels – Pilot operated pressure relief devices – Pressure-relief accessories for cryogenic serviceISO 21013-4 specifies the requirements for the design, manufacture and testing of pilot operated pressure relief valves for cryogenic service, i.e. for operation with cryogenic fluids in addition to operation at temperatures from ambient to cryogenic. It is restricted to valves not exceeding a size of DN 300 designed to relieve single phase vapours, gases, or mixtures of gases and/or vapours.
EN ISO 21922Refrigerating systems and heat pumps – Valves – Requirements, testing and markingThis document specifies safety requirements, certain functional requirements, and marking of valves and other components with similar bodies, hereinafter called valves, for use in refrigerating systems including heat pumps. This document includes requirements for valves with extension pipes. This document describes the procedure to be followed when designing valve parts subjected to pressure as well as the criteria to be used in the selection of materials. This document describes methods by which reduced impact values at low temperatures may be taken into account in a safe manner. This document applies to the design of bodies and bonnets for pressure relief devices, including bursting disc devices, with respect to pressure containment but it does not apply to any other aspects of the design or application of pressure relief devices. In addition, this document is applicable to valves with a maximum operating temperature not exceeding 200 °C and a maximum allowable pressure not exceeding 160 bar[1].   [1] 1 bar = 0,1 MPa.
ISO 23551-12Safety and control devices for gas burners and gas-burning appliances – Part 12: Multifunctional controls with integral overpressure protection safety function (OPSF) for use with butane gas cartridges used in portable gas appliancesThis document specifies safety, construction, performance and testing requirements for multifunctional controls with integral overpressure protection safety function (OPSF) intended for use with portable gas appliances.
This document is applicable to:
—     multifunctional controls which consist of a pressure-limiting device and at least one or more controls, including but not limited to a manual gas valve, a pressure regulator and a thermoelectric flame supervision device; and
—     multifunctional controls with declared maximum operating pressures in normal use, up to and including 500 kPa for use with a butane gas cartridge specified by ISO/TS 21985.
This document does not apply to multifunctional controls with OPSF having thread connections for mounting butane gas cartridges.
This document covers type testing only.
ISO 23555-1Gas pressure safety and control devices for use in gas transmission, distribution and installations for inlet pressures up to and including 10 MPa – Part 1: General requirementsThis document specifies generic safety, constructional, performance, testing and documentation requirements for high pressure controls for use in gas transmission, distribution and installations (hereafter referred to as controls).
This document is applicable to controls with operating pressures greater than 500 kPa (5 bar) and up to and including 10 MPa (100 bar) and nominal size up to DN 400 for use with fuel gases as natural gas, manufactured gas, biomethane or liquefied petroleum gas (LPG) in commercial, industrial installations, including fuel gas infrastructures.
The test methods given in this document are intended for product type test, routine tests and batch surveillance tests.
This document is not applicable to:
—    controls upstream from/on/in domestic gas-consuming appliances which are installed downstream of domestic gas meters;
—    controls designed with declared maximum capacity ≤200 m3/h (normal conditions) and declared maximum inlet pressure ≤500 kPa (5 bar), to be incorporated into pressure control systems used in service lines (pipework from the main pipework in a gas infrastructure to the point of delivery of the gas);
—    industrial process control valves, such as IEC 60534;
—    controls used in aggressive/sour gas environments (gas environments containing water and H2S are considered sour) or severely corrosive conditions;
—    controls in service conditions with renewables (e.g. H2NG with hydrogen more than 10 %) and/or waste gases (e.g. biogas, etc.), if additional information is not provided (e.g. contaminant, liquid, etc.)
ISO 23555-2Gas pressure safety and control devices for use in gas transmission, distribution and installations for inlet pressures up to and including 10 MPa – Part 2: Gas pressure regulatorThis document specifies safety, constructional, performance, testing and documentation requirements for gas pressure regulators for use in gas transmission and distribution installations (hereafter referred to as regulators).
This document is applicable to regulators with operating pressures greater than 500 kPa and up to and including 10 MPa (100 bar) and nominal diameters up to DN 400 for use with fuel gases as natural gas, manufactured gas, biomethane or liquefied petroleum gas (LPG).
This document is applicable to:
—    test methods which are intended for product type test, routine tests and product surveillance tests;
—    regulators which use the pipeline gas as a source of control energy unassisted by any external power source;
—    regulators integrating on the same body a second regulator, used as monitor, complying with the requirements in this document;
—    regulators integrating a safety shut off device (SSD) according to ISO 23555-3;
—    regulators incorporating a creep (venting) relief device and/or a vent limiter complying with the requirements in this document.
This document does not apply to:
—    regulators upstream from/on/in domestic gas‑consuming appliances which are installed downstream of domestic gas meters;
—    regulators designed to be incorporated into pressure control systems used in service lines (pipework from the main pipework in a gas infrastructure to the point of delivery of the gas) with declared volumetric flow rate ≤ 200 m3/h at normal conditions and declared inlet pressure ≤ 500 kPa (5 bar);
—    industrial process control valves, such as IEC 60534 (all parts);
—    regulators used in aggressive/sour gas environments (gas environments containing water and H2S are considered sour) or severely corrosive conditions;
—    regulators in service conditions with renewables (e.g. H2NG with hydrogen more than 10 %) and/or waste gases (e.g. biogas etc.), if additional information is not provided (e. g. contaminant, liquid, etc.).
ISO 23555-3Gas pressure safety and control devices for use in gas transmission, distribution and installations for inlet pressures up to and including 10 MPa –  Part 3: Safety shut-off devices
EN ISO 24664Refrigerating systems and heat pumps – Pressure relief devices and their associated piping – Methods for calculation1.1 This Standard describes the calculation of mass flow for sizing pressure relief devices for components of refrigerating systems. NOTE The term “refrigerating system” used in this Standard includes heat pumps. 1.2 This Standard describes the calculation of discharge capacities for pressure relief valves and other pressure relief devices in refrigerating systems including the necessary data for sizing these when relieving to atmosphere or to components within the system at lower pressure. 1.3 This Standard specifies the requirements for selection of pressure relief devices to prevent excessive pressure due to internal and external heat sources, the sources of increasing pressure (e.g. compressor, heaters, etc.) and thermal expansion of trapped liquid. 1.4 This Standard describes the calculation of the pressure loss in the upstream and downstream line of pressure relief valves and other pressure relief devices and includes the necessary data. 1.5 This Standard refers to other relevant standards in Clause 5.

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Difference of Pressure Safety Valve & Pressure Relief Valve

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