What does the wet leg compensating line contain to prevent vapor condensation?

The wet leg compensating line is designed to maintain a constant level of liquid in level measurement applications, particularly for differential pressure transmitters. The function of this line is to prevent vapor condensation that can lead to inaccurate level readings and measurement errors.

Glycol is chosen for this application because of its properties as a low-temperature fluid that can remain in a liquid state over a wide range of temperatures and can prevent the formation of vapor bubbles in the line. Its ability to inhibit freezing and condensation makes it suitable for maintaining reliable pressure readings and ensuring the effective operation of the measurement system.

While dry air, water, and carbon dioxide each have their own uses in various applications, they do not provide the same level of protection against condensation in this specific context. Dry air could lead to moisture problems if not properly managed, while water can freeze or vaporize, and carbon dioxide does not have the necessary physical properties to act as an effective buffer in this situation. Thus, glycol is the most appropriate choice for a wet leg compensating line to prevent vapor condensation.