Functional Safety 2016
November, 2016 - London
Page 12 of 17
Equipment
Proof Test Method (brief description)
C
PT
(%)
2. Inspect the Solenoid for dirty or clogged ports and other
physical damages.
3. De-energize the solenoid coil and observe movement of the
actuator and the valve. Energize the solenoid after a small
movement of the valve.
4. Inspect the solenoid for dirt, corrosion or excessive moisture.
Clean if necessary and take corrective actions to properly clean
the air supply. This is done to avoid incipient failures due to dirty
air.
5. Record any failures in your company’s SIF inspection database.
Restore the loop to full operation.
6. Remove the bypass from the safety PLC or otherwise restore
normal operation
Actuator / Ball
Valve
Assembly
A proof test must be performed on the FE at regular intervals. The
actual inspection interval is defined by the reliability report (SIL
calculation) for the specific application. Typically for applications
requiring a SIL3 protection level a yearly proof test interval is used.
To carry out the proof test, proceed as follows.
1. Ensure that all flow through the valve is stopped or verify that
stopping the flow during the test will not cause operational
problems.
2. Perform the actions as per the Monthly inspection.
3. a) Solenoids: De-energise solenoid (one at the time) thus
initiating the valve to go to the fail safe position. Verify during
closure whether all parts of the sub-system function properly
(like the quick exhausts, did they all respond?). Assure that the
time between de-energising and full closure (or opening) is
measured. Repeat 3 times. Repeat for each solenoid. Verify
whether these timings falls within the maximum permissible
time. Compare with previous measurements and in case of big
differences contact Mokveld.
b) Mechanical initiators: As above however the trigger is not de-
energising the solenoid but creating a high pressure (above
~95%