Instruction Manual Supplement
D103546X012
A41 Valve
June 2017
5
SIL Capability
Systematic Integrity
Figure 2. exida SIL 3 Capable
The product has met manufacturer design process requirements of IEC 61508 Safety Integrity Level 3. These are
intended to achieve sufficient integrity against systematic errors of design by the manufacturer. A Safety
Instrumented Function (SIF) designed with this product must not be used at a SIL level higher than stated without
“prior use” justification by the end user or diverse technology redundancy in the design.
Random Integrity
A41 valves are classified as a Type A device according to IEC 61508, having a hardware fault tolerance of 0. The
complete final element subsystem, with a Fisher butterfly valve as the final control element, will need to be evaluated
to determine the Safe Failure Fraction of the subsystem. If the SFF for the entire final element subsystem is between
60% and 90%, a design can meet SIL 2 @ HFT=0.
Safety Parameters
For detailed failure rate information refer to the Failure Modes, Effects and Diagnostic Analysis Report for the A41
valve.
Connection of the Fisher A41 Valve to the SIS Logic-solver
The final element subsystem (consisting of a positioner, actuator, and A41 valve) is connected to the safety rated logic
solver which is actively performing the Safety Function as well as any automatic diagnostics designed to diagnose
potentially dangerous failures within the A41 valve , actuator and any other final element components, (i.e. Partial
Valve Stroke Test).
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