ISO 4126-5:2013 pdf free
ISO 4126-5:2013 pdf free.Safety devices for protection against excessive pressure
The material of guiding surfaces shall be corrosion resistant and shall be selected to minimize the possibility of galling or seizure.
Seat and disc of CSPRS shall be made of suitable material in order to avoid increasing set pressure,e.g. cold welding or sticking.
The main valve opens without the assistance of any energy other than that of the fluid to be relieved under the principle of 3.3 or 3.4 (see Figure 2). The design of the main valve shall not be of gate or rotating disc valve type.
Operating forces other than those created by the fluid itself can only be used for closing the main valve. They can be mechanical, e.g. springs or weight, hydraulic, pneumatic or electrical [see Figure 2a].
For main valves and valves used as control module where the system pressure or control medium acts on the valve disc in the direction of closing, the opening force shall be rated such that the valve opens completely with twice the system pressure.
The internal functional reserve of safety-related components in the control paths shall be ensured by rating operating forces to be at least twice the force necessary for opening the main valve. The opening forces of main valves not in accordance with ISO 4126-1 shall be rated at least twice the necessary forces.
Each individual control path shall be so designed that the relevant main valve will operate reliably in case of failure of the other individual control paths. At least three control paths, each independent of each other, shall be in operation. At least two control paths shall be in accordance with the closed circuit principle.
NOTE Installations with two main valves each covering the required capacity, two installed control pathsper main valve comply with this part of ISO 4126-5.
It is permissible to operate more than one main valve from a single control unit subject to its application. Redundancy of individual control systems shall be in accordance with this part ofISO 4126. If one control path has to be made inactive for performance testing during operation, two shall stay active.ISO 4126-5 pdf download.
