Read the following technical maintenance passage:
Before technicians store an idle shipboard reverse osmosis desalination unit, they must execute a sequential preservation protocol. First, operators flush the high-pressure membrane housings with unchlorinated permeate to displace residual brine. Once the effluent conductivity drops below the baseline threshold, technicians inject the sodium metabisulfite solution into the circulation loop. Immediately following chemical distribution throughout the pressure vessels, technicians isolate the inlet and discharge valves to prevent air ingress. Finally, personnel seal the membrane housing sampling ports to maintain storage stability.
Based on the passage, match each procedural phase on the left with the correct operational action on the right.
- Initial procedural actionFlushing high-pressure membrane housings with unchlorinated permeate
- Action taken once conductivity drops below thresholdInjecting sodium metabisulfite solution into the circulation loop
- Action performed immediately following chemical distributionIsolating inlet and discharge valves to prevent air ingress
- Terminal step of the protocolSealing the membrane housing sampling ports