Where is the purge unit located in a low-pressure system?

In a low-pressure refrigeration system, the purge unit plays a crucial role in maintaining system efficiency by removing non-condensable gases that accumulate within the refrigerant circuit. The correct location for the purge unit is at the top of the condenser.

This is because non-condensables, such as air, tend to rise and collect at the highest points in the refrigeration system. The condenser, being one of the upper components in the system design, allows for the collection of these gases where they can be effectively removed. Additionally, placing the purge unit here ensures that any air or other non-condensable gases can be vented out safely, preventing inefficiencies in the refrigeration cycle that can occur if these gases remain in the system.

The other potential locations—such as the bottom of the evaporator, midway in the compressor, or at the expansion valve—are not ideal for the purge unit since they do not facilitate the effective collection and removal of non-condensables. The bottom of the evaporator is where refrigerant evaporates, making it unsuitable for gas collection. Midway in the compressor and at the expansion valve would not capture rising gases adequately, ultimately reducing system performance. Thus, the top of the condenser is strategically the best position for