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ISO 4126-4:2013 pdf free

ISO 4126-4:2013 pdf free.Safety devices for protection against excessive pressure
The design shall incorporate guiding arrangements necessary to ensure consistent operation and seat tightness.
The seat of the main 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.
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 pilot operated safety valve.
In the case of main valves with restricted lift, the lift restricting device shall limit the main valve lift but shall not otherwise interfere with the operation of the main valve. The lift restricting device shall be designed so that, if adjustable, the adjustable feature can be mechanically locked and sealed. The lift restricting device shall be installed and sealed in accordance with the design of the manufacturer.The valve lift shall not be restricted to a value less than 1 mm.
Pilot operated safety valves for toxic or flammable fluids shall have the pilot vented to a safe place.
The main valve shall be provided with a drain connection at the lowest point where liquid can collect unless other provisions for draining are provided.
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.
The materials for adjacent sliding surfaces such as guides and disc/disc holder/spindle shall be selected to ensure corrosion resistance and to minimize wear and avoid galling.
In the case of reasonably foreseeable damage to connections between the various components,the resulting flow areas shall be such that the pilot operated safety valve will discharge its certified capacity at not more than 1,1 times the maximum allowable pressure.
When the superimposed back pressure can be higher than the inlet pressure, means shall be provided so that the main valve does not open.
Easing gear shall be provided when specified or alternatively means for connecting and applying pressure to the pilot adequate to verify that the moving parts critical to proper operation are free to move.ISO 4126-4 pdf download.

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