What should an operator always ensure to avoid overfilling the cylinder?

To avoid overfilling a cylinder, an operator should always ensure the proper level of the liquid inside the cylinder. This involves knowing the safe fill level and adhering to it rigorously during the filling process. Each cylinder is designed to hold a specific amount of gas, and exceeding this limit can lead to dangerous situations, such as increased pressure from the gas and potential rupture.

Proper level refers to the liquid's gauge reading inside the cylinder, and operators must frequently check this measure to ensure it remains within the manufacturer's specifications. Recognizing the correct fill level contributes critically to safety practices within LP-gas operations. It helps maintain the cylinder's structural integrity and prevents hazardous leaks or explosions related to overpressure.

The other choices, while important for various aspects of safety and functionality, do not directly relate to the prevention of overfilling. Proper connections and valve adjustments pertain more to ensuring safe operation rather than the management of liquid levels, while temperature considerations are relevant to pressure behavior but do not directly dictate safe filling practices regarding liquid levels within the cylinder.