We have found that silicone made tubes work better than PVC ones, They are more flexible and can be glued with Silicone, which makes them more air tight.
We have used two different tube sizes:
5mm Outer Diameter ⇒ 3mm Inner Diameter - These were the most wildly used tubes. They would connect to the actuators, valves and pumps.
4mm Outer Diameter ⇒ 2mm Inner Diameter - Those are used when a thinner tubing is necessary, for example in small actuators.
6mm Outer Diameter ⇒ 4mm Inner Diameter - Those can be used when a larger throughput of air is required.