Answer / sebastian

ESD valve or EIV(Emergency Isolation valves) are only used
(operates)for Emergency conditions only, usually theses
valves are reamins open till incase any Emergency occures
that is fire .some times it remains open till plant next
turnaround@3-4 years).so valve trim or actuator may stuck
due to some reason and valve never clos when real
Emergency, to avoid this situation , goverment athority or
insurance company guidlines are given to plant operation
section to check availablity and functionality of ESD
valves periodically, may be each 3 month, 6 month etc.
Partial stroke: Valve start to move from its open position
to close postion only @20-25% of its total traval(to avoid
process upest)and return back.there is a Function logic
built in the ESD logic with Protection timer(incase valve
limit switch not moved from open postion at set time the
logic will re set for valve its open condition and
indicate failed.(partial stroke test failed) .
if valve moved from open position (by means of limt switch
leves its contact)logic will re set and remais for open
position and indicate succes test.
if any details requred with logic contact me
sebalukose@gmail.com

Answer / syed abdul mateen

ESD's are checked anually by applying partial signal from
DCS to ESD's.They are made to open partial and checked.

Answer / robert

Esd valves are required by gov. safety standards to be
checked periodically to be able to stroke i.e. (move to a
determined position, usually 90 % and back to original
position.) If the valve does as required, it passes
function test and can remain in service. In some
applications valves tend to stay in one position for long
periods of time. This often has an effect on the
bearings "freezing" up, and in an emergency situation the
valve may not close when required.

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A PLC is programmed to drive three motors A, B and C as follows : After running motor A for an hour, motor B should get ON and motor A should get OFF. And after running motor B for an hour, motor C should get ON and motor B should get OFF. And after running motor C for an hour, motor A should get ON and motor C should get OFF. (That is, a cyclic repetition with time period one hour) Now, the second condition is: If any motor gone faulty and is tripped, the consecutive motor should get ON and the faulty (tripped) motor should be eliminated from cyclic repetition. The remaining two motors should bear the cyclic repetition of one hour each. (For healthy motor take logic as high and for tripped motor take logic as low) Now, the third condition is: When motor A load(Amps) exceeds 60% of its rated load, motor B should get ON in parallel to motor A. And when both motors A & B are running in parallel, and if their load exceeds 60% of their rated load, motor C should also start in parallel to A & B. [Here the cyclic repetition is eliminated, until their loads become normal(40%)] [Take logic high(1) for load at 60% and logic low(0) for load at 40%] Now draw a flow chart or a ladder diagram to fulfill the above condition.

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