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

Rebuild the compressor's piston rings immediately

Answer

Replace the inlet gas filter cartridge

Answer

Manually pressurize the inlet line to force the startup sequence

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

Excessive lubricating oil accumulation in the crankcase

Answer

Excessively low inlet gas supply pressure

Answer

Moisture contamination in the incoming gas stream

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

Prevent backflow from storage banks into the compressor

Answer

Release excess gas automatically if the system exceeds maximum allowable working pressure

Answer

Control gas distribution between individual cascade storage banks

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

Ambient humidity level outside the compressor building

Answer

Crankcase oil level in the compressor only

Answer

Inlet gas odorant (mercaptan) concentration levels

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

Add oil and continue operation at reduced output capacity

Answer

Switch the unit to manual bypass control mode

Answer

Increase compressor speed to restore oil pressure through pump centrifugal action

Question 6

What does an increasing pressure differential across a CNG compressor inlet filter indicate?

Accepted Answer

The filter is becoming clogged with contaminants and requires cleaning or replacement

Answer

Normal wear that requires no operator action until the next scheduled service

Answer

A change in the Btu content or composition of the supply gas

Answer

Compressor valve clearance needs adjustment

Question 7

How frequently should compressor valve inspections typically be performed in a CNG fueling station?

Accepted Answer

Per manufacturer specifications, typically every 1,000 to 4,000 operating hours

Answer

Only when a valve failure is suspected based on performance degradation

Answer

Once every five years as part of a major equipment overhaul schedule

Answer

Daily external visual checks are sufficient for valve maintenance requirements