Hi there,
I got these days an Self-Contained Hydraulic actuator with own hydraulic system and options to be actuated or itself, or via a electrical actuation on the existing option for the solenoid. First, I did assessed the electrical actuation option - the solenoid been powered just triggers the hydraulic system and that depressurizing release the spring and the actuator get closed. So far, so good. The solenoid was SIL certified, the ball valve the same. At the end I got a full SIF considering the PT in upstream and a control relay - all SIL rated.
Now, I have the same assembly installed in a remote location where there is no power, and the ESDV came as pilot activated upon the pipeline pressure and triggers as above the system. Well - no electricity, but the same valve and the pilots are SIL certified, because they also have an option for the NO/NC contact on if comes to H or L pressure. At this time the my SIF is just limited with the the final element itself and been rated accordingly - using the PFDs of the ball valves and the pilots. Meet the RRF target, all done. Question came - why I did such since the assembly has no E (electricity). My clarification was that there is the way to be implemented via those NO/NC contacts on pilots, so it complies with EN61508 "The risk is reduced to a tolerable level by applying safety functions which may consist of E/E/PES, associated mechanical devices, or other technologies."
And that was the right interpretation, isn't it?
Thanks