Interesting!
Brought me to look up the definition.
'IEC 61508 is an international standard of rules applied in industry. It is titled Functional Safety of
Electrical/Electronic/Programmable
Electronic Safety-related Systems (E/E/PE, or E/E/PES)' (Underlining by me).
The below is my personal opinion.
It seems that Wikipedia (if reliable!?) has a thorough and relatively simple overview in this case, which, as I thought, excludes your checkvalve, as it is a single mechanical component.
If your single valve includes other components, as for instance electronic limit switches (also including the electrical signal system), or is a part of a larger system,( including electrical operational signal components ), the system as such (including your valve) could fall under a category where SIL certification of the whole integrated system might be done (but not of separate, purely mechanical components alone).
In my opinion SIL is (among other things?) intends to ensure and lengthen a 'non failure operation time' of a 'system'.
This is different from including 'safety devices' alone. 'Safety component's for a system will include all components to ensure a safe and controlled operation, within the limits given by the process, eg. all controlling and regulating devices.
For instance could a solenoid valve (mechanical device operated by an electrical actuated coil and magnetic core) have a SIL certificate, and as such be defined as a system. The certified solenoid alone, however, says nothing of the SIL level of the system it is integrated and used in. The total system, with all components, must be analyzed.
I must confess I have a very limited experience with SIL, but SIL evaluations includes dependability statistics and failure probability. If your (mechanical) checkvalve has operational records (number of operations without failure), failure statistics or good expected lifelength figures or statistics, this will probably be a positive contribution in a discussion.
Good luck!
