What is the purpose of a sounding tube in a tank?

The purpose of a sounding tube in a tank is primarily to measure liquid levels. Sounding tubes provide a means for operators to determine how much liquid is present within the tank by allowing for manual measurement. This device typically consists of a tube that extends into the tank liquid; by inserting a graduated measuring stick or a weight, the operator can ascertain the depth of the liquid in the tank.

In the context of tank operations, knowing the liquid level is crucial for various reasons, including ensuring safety, supporting calculations for cargo loading and unloading, and maintaining operational efficiency. Since the correct answer focuses on measuring the liquid levels, it highlights a fundamental function of inventory management in storage and transport operations, particularly in tanker environments.

Monitoring temperature, facilitating venting, and controlling pressure are important operational considerations but do not fall under the primary function of the sounding tube, which is specifically designed for level measurement.