What fluid is most commonly used in pneumatics?

Air is the most commonly used fluid in pneumatics due to its availability, safety, and effectiveness in transmitting power. Pneumatic systems rely on the compressibility of air, which allows it to be easily compressed and expanded to generate force and motion. Using air also means that systems can be operated in a wide range of environments without concerns about contamination or leakage that might be presented by other fluids. Additionally, since air is abundant and does not pose significant health risks, it is the preferred choice for applications across various industries, including automation, manufacturing, and construction.

While other fluids like oxygen, water, and oil can be used in specific applications, they come with limitations. Oxygen, while a gas, is not typically used in standard pneumatic systems due to its reactive nature, which can lead to safety hazards. Water can be used in some specialized pneumatic systems, but it poses issues like freezing and corrosion. Oil is generally utilized in hydraulic systems rather than pneumatic systems, as hydraulic systems require incompressible fluids to transmit power effectively. Thus, air remains the primary and most practical fluid for pneumatic applications.