Is there a valves wall of each air sac in the lung?

There is no valves wall of each air sac in the lung.

The air sacs in the lungs, known as alveoli, do not have valves that control airflow. Instead, they have a unique structure that allows for efficient gas exchange between the air and the bloodstream. The alveoli are tiny, balloon-shaped structures that form the functional units of the lungs and are responsible for the exchange of oxygen and carbon dioxide. Gas exchange occurs through the process of diffusion, where oxygen from the inhaled air moves into the bloodstream, and carbon dioxide from the bloodstream moves into the air to be exhaled. The movement of gases is driven by pressure gradients and concentration differences, and there is no need for valves to control this process.