When an ammonia compressor has been pumped down below atmospheric pressure, what care must be exercised?

When an ammonia compressor has been pumped down below atmospheric pressure, it is critical to ensure that no air is drawn into the system. This is important for several reasons.

Firstly, the presence of air in the refrigeration system can lead to a decrease in efficiency. Air is non-condensable, which means that it does not change its state under refrigeration conditions, leading to increased head pressure and reduced cooling capacity. This can cause the compressor to work harder, potentially leading to overheating and mechanical failure.

Secondly, air can react with ammonia, leading to the formation of corrosive acids which can damage components of the refrigeration system over time. This further emphasizes the need to maintain a vacuum to prevent air ingress.

By ensuring that no air enters the system, the integrity of the ammonia refrigeration cycle is maintained, which is crucial for optimal performance and longevity of the equipment.