The Logic Behind The Magic. “Blow Down Valve"

Blowdown valve (BDV) is a block valve that is actuated through the ESD system which is situated in the system requiring pressure depressurisation during plant emergeny or shutdown. BDV is not used in process control.

BDV is typically with shutdown valve but in the reverse condition.(BDV is Fail Open valve, SDV is Fail Closed valve)


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 BDV
3. open command
4. Logic command not trip
5. close limit sw
6. not open limit sw (not close)
7. Timer SP

Output:

1. Valve Command "Close"
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 closed until SDV switch, open 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: