737 Isolation Valve?

An insulation Valve isolates systems that operate independently of one another, whether fuel, hydraulic or Pneumatic, but also allows cross-operation in case of failure of a system.

Example Pneumatic supply of the B737: There are two Bleed Air systems, each supplied by the left and right engines.

In normal condition, the insulation Valve is closed (switching position AUTO) and each Bleed system supplies its Air Conditioning Pack for air supply to the cabin.

If a Bleed Air System or one of the Air Conditioning Packs fails, the Valve insulation moves into the OPEN position and thus allows the supply of the other side.

Of course, as in any aircraft, manual control of the Valves by the cockpit crew is also possible.