CARO System Lubrication and Purging 2

Question 1

In an ammonia refrigeration system, where does carried-over compressor oil tend to collect?

Accepted Answer

At low points of vessels and evaporators, below the liquid ammonia

Answer

Mineral oil is denser than liquid ammonia and does not mix with it, so it settles at the low points of vessels and coils.

Question 2

Why is mineral oil considered essentially immiscible with ammonia?

Accepted Answer

It does not mix with ammonia and separates into a distinct layer

Answer

Ammonia and mineral oil stay largely separate, which is why oil must be drained from low points rather than returned with the refrigerant.

Question 3

What is the main job of the oil separator in an ammonia compressor discharge line?

Accepted Answer

To separate oil from the discharge gas and return it to the compressor

Answer

The oil separator captures oil carried out of the compressor with the hot gas and returns it to the crankcase or oil system.

Question 4

Before draining oil from an ammonia vessel, what should the operator do first?

Accepted Answer

Isolate the oil pot and let its pressure drop so ammonia boils off from the oil

Answer

Isolating the oil pot and lowering its pressure lets the trapped ammonia boil off so less ammonia comes out with the oil.

Question 5

Which valve is recommended on the final drain point of an ammonia oil drain?

Accepted Answer

A spring-loaded self-closing (dead-man) valve

Answer

A self-closing valve shuts automatically if the operator lets go, which limits ammonia release during draining.

CARO - Certified Assistant Refrigeration Operator Practice Test