RSES Compressor Systems 5

Question 1

Which parameter is used to express the overall efficiency of a compressor by comparing actual work input to ideal isentropic compression work?

Accepted Answer

Isentropic (adiabatic) efficiency

Answer

Isentropic efficiency compares the actual work input to the theoretical minimum work of reversible adiabatic compression, quantifying how well the compressor converts power into refrigerant compression.

Question 2

A scroll compressor will not start and the motor draws locked rotor amperage. After ruling out electrical faults, what mechanical condition should be investigated?

Accepted Answer

Liquid refrigerant locked in the compression chamber preventing rotation

Answer

Liquid refrigerant trapped in the scroll compression chambers is incompressible and can hydraulically lock the compressor, preventing the motor from turning and drawing locked rotor current.

Question 3

What does the term 'compression ratio' mean for a refrigeration compressor?

Accepted Answer

The ratio of absolute discharge pressure to absolute suction pressure

Answer

Compression ratio is the absolute discharge pressure divided by the absolute suction pressure, and it directly affects compressor efficiency, discharge temperature, and valve reliability.

Question 4

What causes 'oil pumping' in a reciprocating compressor, and what symptom would a technician observe?

Accepted Answer

Worn piston rings allowing oil past the piston; indicated by oil carryover into the system

Answer

Worn piston rings allow crankcase oil to bypass into the compression chamber and be discharged into the system, resulting in oil carryover and oil-fouled heat exchangers.

Question 5

Why is it important to equalize oil levels between compressors in a parallel rack system?

Accepted Answer

To ensure each compressor has adequate lubrication and prevent bearing failure from oil starvation

Answer

Without oil equalization, one compressor may accumulate excess oil while another runs low, leading to bearing failure in the oil-starved compressor.

(RSES) Refrigeration Service Engineers Society Certification Practice Test

(RSES) Refrigeration Service Engineers Society Certification Practice Test

RSES Compressor Systems 5