Why must carbon dioxide cylinders be used in a vertical position?

Using carbon dioxide cylinders in a vertical position is important primarily to prevent drawing off liquid CO2. Unlike many gases that remain in the gaseous state within a cylinder, carbon dioxide can exist both as a gas and as a liquid at certain pressures. When a CO2 cylinder is in a horizontal position, it's possible for liquid CO2 to be drawn into the delivery system instead of just gas. This can lead to improper operation of the equipment, inconsistent flow, and potential damage. By maintaining the cylinder in an upright position, only the gaseous phase of CO2 is drawn, ensuring a stable and reliable supply.

Other options may touch on aspects of gas flow and pressure, but they do not address the critical issue of liquid CO2 presence that vertical positioning directly prevents.