Which medium is typically used to inflate the main shaft seal under normal conditions?

The medium typically used to inflate the main shaft seal under normal conditions is nitrogen. Nitrogen is favored because it is inert, non-flammable, and does not support combustion, making it safe for use in mechanical systems. Its stable properties help maintain the necessary pressure within the seal without introducing any reactivity that could lead to deterioration of the materials used in the seal.

Other gases like carbon dioxide, while potentially useful in various applications, can have limitations such as being corrosive in certain environments or reacting with moisture. Helium, although it has some unique properties, is generally not used for this purpose due to its higher cost and lower density compared to nitrogen. Air might be used in some applications, but it contains moisture and oxygen, which can lead to corrosion and other issues in mechanical seals. Therefore, nitrogen is the best choice for ensuring the integrity and longevity of the main shaft seal.