How do you calculate and verify SIL capability for control valves in safety systems?

SIL capability verification: obtain certified failure rate data from valve/actuator manufacturer (PFD, SFF, lambda values per IEC 61508), calculate subsystem PFDavg including valve, actuator, solenoid, and positioner contributions, verify hardware fault tolerance meets requirements (single valve typically HFT=0, requires SFF>60% for SIL 2), determine proof test interval and dangerous failure coverage. SIL 2/3 may require: redundant solenoids, partial stroke testing to reduce PFD, position feedback separate from positioner, and diagnostic coverage credit. Document calculations in SIS datasheet, maintain proof test records, and verify assumptions during periodic testing.