Mode of operation for BDV with Interlocks

The mode of operation for BDVs will also be the same (pneumatic),when they operate with interlocks? Also,could you please make a clear definition from interlock?

Yes, during interlocks also, they operate based on pneumatic mode. The “cause & effect” diagrams are interlock diagrams.

For example, consider a pump having suction vessel in upstream. A Low-Low level in vessel (a cause) will shut down (effect) the pump in order to prevent damage of a pump. Similarly, there are detailed interlocks for entire plant.

BDVs are sometimes provided based on “de-pressurization philosophy” and study in details. During safety interlock, a particular section of process would be entirely isolated by means of ESDV and then, BDV in that section will open to de-pressurize that section.