ISO 4126-1:2013 pdf download.Safety devices for protection against excessive pressure一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
3.4
supplementary loaded safety valve
safety valve which has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional force which increases the sealing force
Note 1 to entry: This additional force (supplementary load), which may be provided by means of an extraneous power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge capacity at a pressure not greater than 1,1 times the maximum allowable pressure of the equipment to be protected.
Note 2 to entry: Other types of supplementary loaded safety devices are dealt with in ISO 4126-5.
3.5
set pressure
predetermined pressure at which a safety valve under operating conditions commences to open
Note 1 to entry: It is the gauge pressure measured at the valve inlet at which the pressure forces tending to open the valve for the specific service conditions are in equilibrium with the forces retaining the valve disc on its seat.ISO 4126-1 pdf download.