Final answer:
Recovery cylinders must have a liquid withdrawal valve and a vapor withdrawal valve for the safe and efficient recovery of refrigerants in HVAC systems.
Step-by-step explanation:
Recovery cylinders used in HVAC (Heating, Ventilation, and Air Conditioning) systems must have two ports, which are essential for the recovery of refrigerants. The first port is a liquid withdrawal valve, which is used to remove refrigerant in its liquid state. The second is a vapor withdrawal valve, which is designed for removing refrigerant in its gaseous state. Having both ports allows for efficient and safe recovery, ensuring that the system is not damaged during the process. It's crucial for HVAC technicians to understand the function of these ports for proper maintenance and adherence to environmental regulations concerning refrigerant recovery.