SIS Requirements for valve assemblies

How does emerson define SIS requirements for valves? From what I have seen the general consensus is that the "final element" is rated to IEC 61508 standard. Where the "final element" notation stops is where I am having the issue. We have pneumatic shut off valves going back to the SIS system. The solenoid valve that controls air to the actuator has an IEC 61508 certification but I cannot find the same certification on any valve or actuator. Is there a comparable ISO standard that the mechanical elements follow or am I not looking hard enough for IEC 61508 valves and actuators? 

  • Emerson have Valves & Actuators, which meets SIL suitability requirements in line with IEC61508. If you can send me your email, will guide within Emerson team to furnish copy of certs.
    Unlike electrical / electronics components, Mechanical items have more deterministic failure rate, depending upon applications, process fluid, fluid physical properties, operational history, maintenance records, environmental conditions, test philosophy, etc. Though mechanical items, on its own do not have self diagnostics, like Microprocessor based Digital Valve Controller, Final Element may be dominate SIL budget during PFDavg calculation. Certainly, diagnostics coverage can be improved (to provide better PFDavg) by utilizing Smart Microprocessor based intelligent device, which can replace existing SOV or can be added pneumatically in series with existing SOV. There are microprocess based devices, which also have the capabilities to diagnose accessories like SOV etc., mounted between smart device and actuator.