Application Limits; Design Verification - Fisher ED Safety Manual

ED, ES, ET, EZ, HP, HPA Valves w/ 657/667 Actuator
November 2011
Designing a SIF Using Fisher ED, ES, ET, EZ, HP, or HPA Valve
Safety Function
When the valve's actuator is de­energized, the actuator and valve shall move to its fail­safe position. Depending on
which configuration is specified fail—closed or fail­open, the actuator will move the valve plug to close off the flow path
through the valve body or open the flow path through the valve body.
The ED, ES, ET, EZ, HP, or HPA valve is intended to be part of final element subsystem as defined per IEC 61508 and the
achieved SIL level of the designed function must be verified by the designer.
Pressure and Temperature limits
The designer of a SIF must check that the product is rated for use within the expected pressure and temperature limits.
Refer to the ED, ES, ET, EZ, or HP and HPA valve product bulletin for pressure and temperature limits.

Application limits

The materials of construction of ED, ES, ET, EZ, HP, or HPA valves are specified in the product bulletins. A range of
materials are available for various applications. The serial card will indicate what the materials of construction are for a
given valve. It is especially important that the designer check for material compatibility considering on­site chemical
contaminants and environmental conditions. If the ED, ES, ET, EZ, HP, or HPA valve is used outside of the application
limits or with incompatible materials, the reliability data provided becomes invalid.
Diagnostic Response Time
The ED, ES, ET, EZ, HP, or HPA valve does not perform any automatic diagnostic functions by itself and therefore it has
no diagnostic response time of its own. However, automatic diagnostics of the final control subsystem may be
performed such as Partial Valve Stroke Testing (PVST). This typically will exercise the valve over a small percentage of
its normal travel without adversely affecting the flow through the valve. If any failures of this PVST are automatically
detected and annunciated, the diagnostic response time will be the PVST interval time. The PVST must be performed
10 times more often than an expected demand in order for credit to be given for this test.

Design Verification

A detailed FMEDA report is available from Emerson Process Management. This report details all failure rates and failure
modes as well as the expected lifetime.
The achieved SIL of an entire SIF design must be verified by the designer via a calculation of PFD
architecture, proof test interval, proof test effectiveness, any automatic diagnostics, average repair time and the
specific failure rates of all products included in the SIF. Each subsystem must be checked to assure compliance with
minimum HFT requirements.
When using an ED, ES, ET, EZ, HP, or HPA valve in a redundant configuration, a common cause factor of at least 5%
should be included in the Safety Integrity calculations.
The failure rate data listed in the FMEDA report is only valid for the useful lifetime of an ED, ES, ET, EZ, HP, or HPA valve.
The failure rates will increase after this time period. Reliability calculations based on the data listed in the FMEDA
report for mission times beyond the useful lifetime may yield results that are too optimistic, i.e. the calculated Safety
Integrity Level will not be achieved.
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SIL Safety Manual
D103401X012
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