CARO Compressor Operations and Maintenance 4

Question 1

Before opening a compressor for maintenance on an ammonia system, which step must be completed first?

Accepted Answer

Isolate, lock out/tag out, and pump down or evacuate the compressor to a safe pressure

Answer

Lockout/tagout plus isolation and pump-down ensure no energy or refrigerant is present before opening the compressor.

Question 2

Worn or broken suction valves on a reciprocating compressor most commonly produce which symptom?

Accepted Answer

Higher than normal suction pressure with reduced capacity

Answer

Leaking suction valves let gas flow back to suction, raising suction pressure and lowering pumping capacity.

Question 3

What is a typical sign of a leaking discharge valve on a reciprocating compressor?

Accepted Answer

Unusually hot cylinder head and reduced capacity as hot gas re-expands into the cylinder

Answer

Hot discharge gas leaking back into the cylinder is recompressed repeatedly, overheating the head and cutting capacity.

Question 4

When adding oil to an operating ammonia compressor, why must the oil be the type specified by the manufacturer?

Accepted Answer

Incorrect oil can have improper viscosity or compatibility, causing poor lubrication, carbon, or sludge

Answer

Using the wrong oil can cause poor lubrication, varnish, or incompatibility with the refrigerant, damaging the compressor.

Question 5

Why is oil drained from low points such as the bottom of ammonia evaporators and receivers, rather than returned automatically like in halocarbon systems?

Accepted Answer

Mineral oil is heavier than and not miscible with liquid ammonia, so it settles at low points

Answer

Common mineral oils are denser than and largely immiscible with ammonia, so they collect at low points and must be drained.

CARO - Certified Assistant Refrigeration Operator Practice Test

CARO - Certified Assistant Refrigeration Operator Practice Test

CARO Compressor Operations and Maintenance 4