Final answer:
Recovery or reclaim cylinders are large refrigerant cylinders positioned upside-down with valves at the bottom, facilitating the transfer of liquid refrigerant for refrigeration systems.
Step-by-step explanation:
Large refrigerant cylinders are often positioned upside-down with their valves at the bottom; these are specifically known as recovery or reclaim cylinders. This positioning is important because it allows for the liquid refrigerant to be easily withdrawn, which is essential in both the recovery and charging processes of refrigeration and air conditioning systems. By having the valve at the bottom, gravity helps in the transfer of liquid refrigerant without the risk of dispensing vapor, which can happen if the cylinder is upright, and the refrigerant is drawn from the top.