Isolations for Shutdown Valves and Blowdown Valves
ESD and Blowdown valves are NOT meant to be isolated, because of the inherent danger that the isolation valve is accidentally left closed or its gate drops and shuts off flow, thereby endangering the safety of the Plant. Your Insurance Policy may not be valid if you introduce isolation valves for ESD and Blowdown valves. These are ultimate safety devices, to be treated with respect.
You have to shut down and overhaul the defective vavles, I am afraid.