CNG Compression Technology and Equipment 2

Question 1

What should an operator check FIRST if a CNG compressor fails to start?

Accepted Answer

Check electrical power supply, control circuit status, and any fault indicators on the control panel

Answer

Electrical and control system faults are the most common and easily corrected causes of compressor startup failures, making power supply and control panel diagnostics the logical first step.

Question 2

What condition is most likely indicated by an abnormally high final-stage discharge temperature on a CNG compressor?

Accepted Answer

Failed or worn compressor valves, or inadequate intercooling between stages

Answer

Faulty or worn compressor valves that allow gas blow-by, or inadequate intercooling between stages, are the primary causes of excessive final discharge temperatures.

Question 3

What is the purpose of an unloader valve on a CNG reciprocating compressor?

Accepted Answer

Allow the compressor motor to start without compression load before gradually applying load

Answer

Unloader valves allow the compressor motor to start without compression resistance, reducing starting current and mechanical stress, with compression load applied gradually as the motor reaches operating speed.

Question 4

Which parameter is most critical to monitor continuously during CNG compressor operation to detect developing problems early?

Accepted Answer

Stage discharge pressures and temperatures at each compression stage

Answer

Monitoring stage discharge pressures and temperatures reveals compressor valve condition, intercooler effectiveness, and compression efficiency, providing early warning of developing mechanical failures.

Question 5

What action should an operator take IMMEDIATELY if a CNG compressor's lubricating oil pressure drops below the minimum safe operating level?

Accepted Answer

Immediately shut down the compressor to prevent bearing and mechanical damage

Answer

Low oil pressure causes rapid bearing and crankshaft wear; immediate shutdown is mandatory to prevent catastrophic mechanical damage and potential gas release from seal failure.

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG Compression Technology and Equipment 2