From which part of an ammonia system can oil be drained?

The ability to drain oil from various components of an ammonia refrigeration system is crucial for maintaining optimal performance and ensuring system efficiency. The correct choice indicates that oil can be drained from multiple locations: the high-pressure receiver, low-pressure receiver, oil pots, and some evaporators.

The high-pressure receiver serves as a storage vessel for the condensed refrigerant and also acts as a location where oil can accumulate. In systems utilizing oil pots, these components are specifically designed to collect excess oil that may circulate with the refrigerant and need to be removed periodically to prevent issues such as reduced cooling efficiency or compressor damage.

Draining oil from the low-pressure receiver is also necessary as it can collect oil due to the refrigerant's phase changes. Furthermore, certain evaporators are designed to allow for oil drainage, particularly those where oil may become trapped during operation.

This comprehensive approach to oil drainage is essential for maintaining the balance of lubrication within the refrigeration system, preventing excessive oil build-up that could impact not just the compressor but the system's overall performance. Other responses that limit oil drainage to only one component overlook these critical functions throughout the entire ammonia refrigeration system.