CNG Study Guide 2026

Everything you need to pass the CNG exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.

📋 CNG Exam Format at a Glance

Questions

75 min

Time Limit

70%

Passing Score

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📚 CNG Topics to Study (69)

Systems · 11 cards Engines and Fuels · 11 cards Codes, Standards, and Compliance · 7 cards Codes, Standards, and Compliance · 7 cards Codes, Standards, and Compliance · 7 cards Codes, Standards, and Compliance · 7 cards Compression Technology and Equipment · 7 cards Compression Technology and Equipment · 7 cards Compression Technology and Equipment · 7 cards Cylinder Inspection and Regulations · 7 cards Cylinder Inspection and Regulations · 7 cards Cylinder Inspection and Regulations · 7 cards Cylinder Inspection and Regulations · 7 cards Emergency Procedures and Response · 7 cards Emergency Procedures and Response · 7 cards Emergency Procedures and Response · 7 cards Emergency Procedures and Response · 7 cards Engines and Fuels · 7 cards Engines and Fuels · 7 cards Engines and Fuels · 7 cards Engines and Fuels · 7 cards Facility and Ventilation Requirements · 7 cards Facility and Ventilation Requirements · 7 cards Facility and Ventilation Requirements · 7 cards Facility and Ventilation Requirements · 7 cards Fueling Station Operations · 7 cards Fueling Station Operations · 7 cards Fueling Station Operations · 7 cards Fueling Station Operations · 7 cards Fuel System Components · 7 cards

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✍️ Sample CNG Questions & Answers

1. What type of portable fire extinguisher is most appropriate for use at a CNG fueling station?

✓ Dry chemical ABC-rated extinguisher

ABC dry chemical extinguishers are appropriate at CNG stations because they handle ordinary combustibles, flammable gases/liquids, and energized electrical equipment.

2. What material are piston rings and seals in oil-free CNG compressors commonly made from?

✓ PTFE (polytetrafluoroethylene) and carbon composites

PTFE and carbon-filled composite seals are used in oil-free CNG compressors because they are chemically resistant, maintain integrity at high pressures, and require no lubrication.

3. During a post-maintenance pressure test, a technician pressurizes the system and leaves it for 10 minutes. Pressure drops 20 psi. What does this indicate?

✓ A leak exists in the system that must be located and repaired before returning to service

Any pressure drop during a static pressure hold test indicates a leak; the system must not be returned to service until the leak is located and corrected.

4. When using a manometer to check CNG low-pressure regulator output, the reading fluctuates widely with engine speed changes. This indicates:

✓ The regulator diaphragm is damaged or the spring is fatigued, causing inconsistent pressure regulation

A healthy regulator maintains steady output pressure across engine speed ranges; wide fluctuations indicate a diaphragm or spring failure inside the regulator.

5. A Type 4 CNG cylinder is constructed from:

✓ Plastic liner fully wrapped with carbon fiber composite

Type 4 cylinders use a high-density polyethylene (HDPE) or nylon plastic liner that is completely overwrapped with carbon fiber composite for maximum strength at minimum weight.

6. What is the primary chemical component of compressed natural gas?

✓ Methane (CH4)

Natural gas is composed primarily of methane (CH4), typically 90% or more by volume, with small amounts of ethane, propane, and other gases.

🎯 Free CNG Practice Tests

Engines and Fuels · 11 questions Systems · 11 questions Compression Technology and Equipment · 7 questions Properties and Safety · 7 questions Properties and Safety · 7 questions Properties and Safety · 7 questions Emergency Procedures and Response · 7 questions Properties and Safety · 7 questions Emergency Procedures and Response · 7 questions Compression Technology and Equipment · 7 questions

📖 CNG Guides & Articles

Your CNG Study Path

1. Learn with Flashcards → 2. Drill Practice Tests → 3. Take the Full Exam Simulation

🃏 Flashcards (475)🏆 Exam Simulation