ISO 4126-1-2013 pdf free download.Safety devices for protection against excessive pressure – Part 1: Safety valves.
This part of ISO 4126 specifies 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.
This is a product standard and is not applicable to applications of safety valves.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4126-7:2013, Safety devices for protection against excessive pressure — Part 7. Common data
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 safety valve
valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored
Note 1 to entry: The valve can be characterized either by pop action (rapid opening) or by opening in proportion (not necessarily linear) to the increase in pressure over the set pressure.
3.2 direct loaded safety valve
safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by
a direct mechanical loading device such as a weight. lever and weight, or spring
3.3 assisted safety valve
safety valve which, by means of a powered assistance mechanism, may additionally be lifted at a pressure lower than the set pressure and will, even in the event of failure of the assistance mechanism, comply with all the requirements for safety valves given in ISO 4126
5 Design
5.1 General
5.1.1 The design shall incorporate guiding arrangements necessary to ensure consistent operation and seat tightness.
5.1.2 The seat of a safety valve, other than when it is an integral part of the valve shell, shall be fastened securely to prevent the seat becoming loose in service.
5.1.3 In the case of valves where the lift can be reduced to conform to the required discharge capacity restriction of the lift shall not interfere with the operation of the valve. The lift restricting device shall he designed so that, if adjustable, the adjustable feature can be mechanically locked and access sealed. The lift restricting device shall be installed and sealed in accordance with the design of the manufacturer.
Valve lift shall not be restricted to a value less than 30% of unrestricted liftor 1 mm, whichever is the greater.
5.1.4 Means shall be provided to lock and/or to seal all external adjustments in such a manner so as to prevent or reveal unauthorized adjustments of the safety valve.
5.1.5 Safety valves for toxic or flammable fluids shall be of the closed bonnet type to prevent leakage to atmosphere, or if vented, it shall be disposed of in a safe place.
5.1.6 Provision shall be made to prevent liquid collecting on the discharge side of the safety valve shell.
5.1.7 The design stress of pressure-retaining shells shall not exceed that specified in the appropriate standards.
NOTE For example, EN 12516 or ANSI/ASME B 16.34 may be used as reference.
5.1.8 The materials for adjacent sliding surfaces such as guide(s) and disc/disc holder/spindle shall be selected to ensure corrosion resistance and to minimize wear and avoid galling.
5.1.9 The materials for the seat and disc of safety valves shall be selected to ensure resistance to metallic bonding between these two surfaces in order to prevent an increase of set pressure, e.g. sticking or cold working.
5.1.10 Sealing elements which may adversely affect the operating characteristics by frictional forces are not permitted.
5.1.11 Easing gear shall be provided when specified.
5.1.12 Safety valves shall be constructed so that breakage of any part, or failure of any device, will not obstruct free and full discharge through the valve.ISO 4126-1 pdf free download.