Hi Steamer
The vessel had a scrubber system installed sometime after 2019. Given that they re-purposed the original main engine exhaust, guessing that it is one common scrubber for the main engine, aux boiler and at least 2 DGs. I think the intent is to utilize the system in special environmental zones and at sea, the scrubber would be by-passed. So then you would need a damper (flap butterfly type valve) on the original exhaust as well as the new exhaust line leading to the scrubber. On the DG for example to utilize the scrubber, you would open the damper leading to the scrubber and close the damper on the original straight through exhaust.
Doubt these are equipped with limit switches and alarmed. Possibly a locking mechanism in the closed and open position.