CNG Fueling Station Operations 2 — Questions and Answers
Question 1: What is the primary purpose of a breakaway coupling on a CNG fueling hose?
- To increase fuel flow rate
- To automatically disconnect if a vehicle drives away with the nozzle attached (Correct answer)
- To regulate dispenser pressure
- To measure the volume of fuel dispensed
Correct answer: To automatically disconnect if a vehicle drives away with the nozzle attached
A breakaway coupling automatically separates the hose if a vehicle drives off without disconnecting the nozzle, preventing hose damage and uncontrolled gas release.
Question 2: In a CNG cascaded storage system, which bank is drawn from FIRST to fill a vehicle?
- The high-pressure bank
- The medium-pressure bank
- The low-pressure bank (Correct answer)
- All banks simultaneously through a manifold
Correct answer: The low-pressure bank
Cascade systems draw from the low-pressure bank first to maximize storage efficiency, then switch to higher-pressure banks as the differential decreases.
Question 3: What is the standard CNG fueling pressure for most light-duty vehicles in the United States?
- 1,800 PSI
- 2,400 PSI
- 3,000 PSI
- 3,600 PSI (Correct answer)
Correct answer: 3,600 PSI
The US standard CNG service pressure is 3,600 PSI (248 bar), established by SAE and ANSI/CSA NGV standards for light-duty and most heavy-duty applications.
Question 4: What does a priority panel control in a CNG fueling station?
- Employee access to restricted areas
- Which storage bank is used to fill a vehicle at each stage of fueling (Correct answer)
- Recording of daily transaction data
- The odorization level of dispensed gas
Correct answer: Which storage bank is used to fill a vehicle at each stage of fueling
A priority panel directs gas flow from the lowest-pressure storage bank first, then automatically switches to higher banks as pressure differentials decrease.
Question 5: What does frost or ice forming on the exterior of a CNG storage cylinder most likely indicate?
- Normal condensation from humidity — no action needed
- A gas leak causing rapid expansion and temperature drop (Correct answer)
- The cylinders are performing at peak efficiency
- The cylinders need repainting to improve insulation
Correct answer: A gas leak causing rapid expansion and temperature drop
Frost on a CNG cylinder indicates rapid gas escape causing Joule-Thomson cooling; this is a leak warning that requires immediate shutdown and inspection.
Question 6: How does a significant rise in gas temperature affect the amount of CNG energy delivered during a fill?
- More energy is delivered because the gas expands
- Less energy (mass) is delivered for the same dispensed volume (Correct answer)
- Temperature has no effect on energy content delivered
- The dispenser automatically compensates with higher pressure
Correct answer: Less energy (mass) is delivered for the same dispensed volume
Warmer gas is less dense, so at the same pressure and volume, fewer molecules (and therefore less energy) are dispensed.
Question 7: Which standard governs the nozzle-to-receptacle interface for CNG vehicle fueling in the United States?
- SAE J2601
- ANSI/CSA NGV1 (Correct answer)
- NFPA 52
- API RP 1115
Correct answer: ANSI/CSA NGV1
ANSI/CSA NGV1 specifies the design and performance requirements for CNG fueling nozzles and vehicle receptacles to ensure compatibility.
CNG Fueling Station Operations 2
What is the primary purpose of a breakaway coupling on a CNG fueling hose?