Ammonia Refrigeration System Oil Draining Requirements

Ammonia refrigeration systems must be equipped with a means of draining oil from the system. Over time, small amounts of oil are carried out of the compressors and mix with the ammonia vapor. The ideal place to collect and drain this oil is on the low pressure side of the refrigeration system. The cold temperatures encourage the oil to thicken so it can collect in a low point like a vessel drop leg or oil pot. 

Oil removal must be accomplished by one or more of the following options according to ANSI/IIAR 9-2020 §7.2.5.3 and ANSI/IIAR 2-2021 §5.9.3:

1. A rigid-piped oil return or transfer system.
2. A vessel equipped with a shut-off valve in series with a self-closing shut-off valve.
3. A valve and piping assembly at the drain point where oil is removed from the system. At a minimum, a shut-off valve in series with a self-closing shut-off valve is required.

Option 1 can be accomplished by using piping to re-route the collected oil and send it back to the compressors. This option is not a common practice in ammonia refrigeration systems.

Option 2 can be accomplished by using an oil pot like the one shown above. The oil pot is equipped with a shut-off valve in series with a spring return (deadman) valve as required.

Option 3 can be accomplished by installing a shut-off valve and spring return valve in series at a vessel drop leg. This is a common practice for accumulators installed in a bunker, or smaller accumulators/recirculators that can easily be isolated.

IIAR 2 and 9 also state that if oil draining requires the use of temporarily attached rigid piping, that piping must be supported and have tight connections. (ANSI/IIAR 2-2021 §5.9.4, ANSI/IIAR 9-2020 §7.2.5.4)

The oil collection in oil pots or drop legs should be monitored to ensure oil draining is performed when needed. The oil level can be determined based on the frost line visible on the oil pot or drop leg. Since oil is heavier than ammonia, it will collect at the bottom of the oil pot/drop leg and no frost will form where the oil is present. For example, the picture below shows an oil pot that is approximately 50% full of oil. 

Oil draining should only be performed by qualified individuals who are knowledgeable in the facility’s oil draining operating procedures. Ensure proper safety measures are taken and PPE is worn as necessary.