The Logic Behind The Magic. “Shut Down Valve".

The isolation of sections of plant will typically be an engineering judgement based on:
1. The purpose for the isolation; either maintenance/operation or shutdown
2. The design condition of the section, particularly pressure
3. The nature of the fluid in the section, e.g. flammability, toxicity etc

Isolation of a section for shutdown purpose will always consist of a single, actuated valves on the perimeter, which will respond to a shutdown signal(s) from ESD systems. Single shutdown valves are normally sufficient for the event initiating the shutdown and associated risk


Shutdown valve is a block valve that is actuated through the PSD and ESD system and used to isolate sections of plant

Shutdown valves will typically be actuated (but occasionally motor driven) ball valves located on the perimeter of the isolated section.

These type of valves usually have 3 signals output and 8 input status that are shown in the control room,
Input:

1. Group Reset
2. keyswitch SDV
3. close command
4. Logic command not trip
5. open limit sw
6. close limit sw (not close)
7. Timer SP

Output:

1. Valve Command "Open"
2. Logic status "Trip"
3. Discrepancy alarm

The logic are:

1. If the  logic command trip, logic status trip will be activated
2. The valve cannot be opened until SDV switch, close command and Logic command trip deactivated and Group reset command becomes active.
3. If valve is in open condition but limit switch closed active, Discrepancy alarm shall be activated
4. If valve is in close condition but limit switch open active, Discrepancy alarm shall be activated

Sample of the logic is shown below: